Cellulose-Based Daytime Radiative Cooling Materials

Xiushuang Jiang; Junming Wang; Hongzhi Liu

doi:10.7536/PC240612

Progress in Chemistry >

2025 , Vol. 37 >Issue 5: 724 - 742

DOI: https://doi.org/10.7536/PC240612

Review

Cellulose-Based Daytime Radiative Cooling Materials

Xiushuang Jiang ¹^,² ,
Junming Wang ³ ,
Hongzhi Liu ^,¹^,^*

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¹ School of Materials Science and Engineering，NingboTech University，Ningbo 315100，China
² College of Chemical and Biological Engineering，Zhejiang University，Hangzhou 310027，China
³ Ningbo Asia Pulp & Paper Co.，Ltd.，Ningbo 315803，China

^* hzliu@iccas.ac.cn or hongzhil@nbt.edu.cn

Received date: 2024-06-21

Revised date: 2024-12-02

Online published: 2025-04-30

Supported by

Ningbo Key R&D Projects(2022Z101)

Ningbo Key R&D Projects(2023Z188)

Ningbo “3315 Innovative Team” Project

Scientific Research Foundation of NingboTech University(20200323Z0018)

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Abstract

With the improvement of living standard and heightened awareness of environmental protection，renewable and environmentally friendly cellulose materials have attracted much attention in the field of daytime radiative cooling due to their high mid-infrared emissivity and the advantages of tunability of hierarchical structure. In this review，the classification，advantages/disadvantages of radiative cooling materials，the principles of radiative cooling，and the factors influencing their performance are introduced. The classification，state of the art as well as radiative cooling properties of cellulose-based daytime radiative cooling materials are elaborated. The recent progress in the four main application areas including building thermal management，personal thermal management，photovoltaics and low-temperature storage/transportation are summarized. Finally，the existing challenges in the current research are discussed and the future development in this field is also envisaged.

Contents

1 Introduction

2 Radiative cooling

2.1 Principles

2.2 Influencing factors

3 Cellulose-based daytime radiative cooling materials and classification

3.1 Natural cellulose-based materials

3.2 Cellulose derivatives-based materials

3.3 Bacterial cellulose-based materials

4 Application fields

4.1 Building thermal management

4.2 Personal thermal management

4.3 Photovoltaics

4.4 Low-temperature storage/transportation

5 Conclusion and outlook

Key words： daytime radiative cooling; cellulose; cellulose derivatives; nanocellulose

Cite this article

Xiushuang Jiang , Junming Wang , Hongzhi Liu . Cellulose-Based Daytime Radiative Cooling Materials[J]. Progress in Chemistry, 2025 , 37(5) : 724 -742 . DOI: 10.7536/PC240612

1 Introduction

In recent years, with the improvement of living standards, people have become increasingly dependent on cooling technologies (e.g., air conditioning). However, the extensive application of cooling technologies has intensified global energy consumption, while environmental issues such as ozone layer depletion, air pollution, and global warming have also become increasingly severe^[1-3]. Statistics show that energy consumption in buildings accounts for more than 30% of the total global energy consumption, and the greenhouse gas emissions from this sector account for 10% of the total global greenhouse gas emissions^[4]; approximately 40% of global food requires cold-chain storage and transportation, which consumes 11% of the world's electricity and produces about 2.5% of global greenhouse gas emissions^[5]. Therefore, it is urgently necessary to explore a new cooling technology with zero energy consumption and zero emissions to meet the needs of national economic development and daily life.

Passive radiative cooling is a strategy that reduces temperature by radiating excess heat to the cold universe through the atmospheric transparent window (8–13 μm) without requiring any energy consumption.^[6-7] In recent years, passive radiative cooling materials have shown great application prospects in fields such as energy-efficient buildings,^[8] personal thermal management,^[11-17] farm cooling systems,^[18] photovoltaic cooling,^[19] thermophotovoltaic systems,^[20] and food preservation.^[21-23] Although significant progress has been made in enhancing mid-infrared emissivity and improving cooling capacity of passive radiative cooling materials, the development and application of daytime radiative cooling materials still face tremendous challenges due to the absorption of solar radiation during the day, which can offset the cooling effect from infrared radiation.^[24-25]

Daytime radiative cooling materials can both emit heat to the cold universe through the atmospheric transparency window and reflect sunlight in the wavelength range of 0.3~2.5 μm, making them a new class of functional materials capable of achieving all-weather spontaneous cooling^[26]. These materials reduce the offsetting effect caused by traditional passive radiative cooling materials absorbing solar radiation during the day, thereby offering broader application prospects in the field of radiative cooling and becoming one of the current research hotspots both domestically and internationally^[27-30].

At present, scholars both domestically and internationally have developed various types of materials with daytime radiative cooling capabilities, such as inorganic non-metallic materials^[26,31-32], porous polymer materials^{[15,18,33-35]}, polymer-inorganic non-metallic composite materials^[36-37], polymer-metal composite materials^[38], and polymer-inorganic non-metallic-metal ternary composite materials^[39-40]. Table 1 summarizes the radiative cooling performance, advantages, and disadvantages of the aforementioned typical daytime radiative cooling materials.

表1 各类辐射制冷材料辐射制冷性能和优缺点归纳表

Table 1 Comparison of radiative cooling performance，advantages and disadvantages of various radiative cooling materials

Classification	Example	Solar power intensity（W/m²）	Daytime radiative cooling power（W/m²）	Sub-ambient temperature drop（℃）	Advantages	Disadvantages
Inorganic materials	TiO₂/SiO₂/SiC^[31]	860	40.1±4.1	5.0	（1）High solar reflectivity and mid-infrared emissivity；（2）Precise regulation in the internal structure；（3）Excellent radiative cooling performance	（1）Complicated material design；（2）Unfavorable mechanical flexibility
	HfO₂/SiO₂^[26]	850	40.1	4.9
	Al₂O₃/Glass^[32]	790	60	3.5
Porous polymers	[P（VDF-HFP）_HP]^[33]	890/750	96	6.0	（1）Low cost；（2）High solar reflectivity；	（1）Unstable porous morphology；（2）Environmental unfriendliness of preparation process；（3）Poor degradability
	Nano PE^[15]	n.a.	n.a.	2.7（a）
	PTFE^[18]	n.a.	n.a.	10
	PMMA^[34]	900	85	6.0~8.9
	PMMM^[35]	n.a.	97	6.0
Polymer-inorganic composites	PVDF/TEOS/SiO₂^[36]	1000	61	6.0	Good and stable radiative cooling performance	（1）Complex preparation process；（2）Unfavorable degradability
Polymer-inorganic composites	ZrO₂/PVDF^[37]	1000	139.35	4.0	Good and stable radiative cooling performance
Polymer-metal composites（Polymer-inorganic-metal ternary composites）	PVF/Ag^[38]	950	<300	2.0	Good radiative cooling performance through the combination with precious metals	（1）The use of precious metal；（2）Unfavorable degradability
	PDMS/SiO₂/Ag^[39]	1000	127	8.2
	Nano PE/SiN/Ag^[40]	920	114	2.5±0.7（b）

[P（VDF-HFP）_HP]： poly（vinylidene fluoride-co-hexafluoro propene）； Nano PE： nanoporous polyethylene； PTFE： polytetrafluoroethylene； PMMA： polymethyl methacrylate； PMMM： polymer-based micro-photonic multi-functional metamaterial； PVDF： polyvinylidene fluoride； TEOS： tetraethyl orthosilicate； PDMS： polydimethylsiloxane； PVF： polyvinyl fluoride； n.a.： not available； a： compare with cotton； b： vertical surfaces.

Although the aforementioned materials exhibit good cooling performance, they also have disadvantages such as high raw material costs and difficulty in degradation after use. Cellulose, as the most abundant natural polymer material in nature, has advantages including wide availability of raw materials, renewability, biodegradability, and ease of structural regulation across multiple scales. Moreover, its molecular structure can vibrate within the atmospheric transparency window wavelength range, endowing it with certain potential for radiative cooling^[41-42]. Considering its economic and environmental benefits, developing cellulose-based daytime radiative cooling materials is of great significance for implementing sustainable development strategies and achieving the "dual carbon" goals.

In recent years, cellulose-based daytime radiative cooling materials have developed rapidly[43,44,45-46]. Currently, some scholars have elaborated and summarized the research progress of cellulose-based radiative cooling materials[47-48]. However, a review that reasonably classifies cellulose-based daytime radiative cooling materials according to their material sources and systematically summarizes the effects of their chemical structures and micro/nano-scale structures on radiative cooling performance has not yet been reported. Therefore, this paper first introduces the principle of radiative cooling and the environmental and material factors influencing its performance. Then, it focuses on the classification of cellulose-based daytime radiative cooling materials from the perspective of their material sources, as well as the research progress regarding how these materials' properties affect radiative cooling performance. Furthermore, the current research status in major application fields is summarized. Finally, the existing challenges and future development directions of cellulose-based daytime radiative cooling materials are discussed and prospected.

2 Radiative Cooling

2.1 Principle

Thermal radiation is a phenomenon that universally exists in nature, where any object with a temperature above absolute zero continuously emits heat outward. The sun, with its high temperature of 6000 K, serves as the most important heat source, while outer space, at around 3 K, represents the ultimate heat sink. The radiation process on Earth's surface is illustrated in Fig. 1a ^[49-50]. At an average ambient temperature of 300 K, while the Earth's surface and atmosphere absorb solar radiation, they also dissipate excess heat into the cold outer space through thermal radiation to maintain thermal equilibrium; the balance between these two processes determines the planet's average temperature ^[7,24].

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图1 辐射制冷原理及多孔材料制备示意图：（a）发生在地球表面的辐射热流示意图^[3]；（b）太阳光谱及地面辐射光谱示意图^[7]；（c）相分离法示意图^[51]；（d）冰模板法示意图^[52]；（e）静电纺丝法示意图^[53]；（f）球磨法示意图^[54]

Fig.1 Schematic diagram of the principle of radiative cooling and the preparation of porous materials：（a）Schematic diagram of radiant heat flow occurring on the Earth's surface^[3]. Copyright 2020 American Association for the Advancement of Science.（b）Solar spectrum and ground radiation spectrum diagram^[7]. Copyright 2019 Optica.（c）Diagram of phase separation method^[51]. Copyright 2021 Elsevier BV.（d）Ice-templating method diagram^[52]. Copyright 2022 American Chemical Society.（e）Diagram of electrospinning^[53]. Copyright 2022 Science China Press.（f）Diagram of ball milling^[54]. Copyright 2024 Wiley-VCH Verlag

The Earth's atmosphere is a semi-transparent medium composed of a mixture of several gases (mainly N₂, O₂, CO₂, and water vapor), which can absorb, emit, and scatter thermal radiation^[55]. Due to the scattering and absorption effects of atmospheric gases, solar radiation and surface infrared radiation are mostly absorbed and scattered when passing through the atmosphere. However, these gases almost do not absorb long-wave thermal radiation within the wavelength range of 8–13 μm. Therefore, thermal radiation in this band can directly pass through the atmosphere into outer space, known as the atmospheric transparent window band (also called the first atmospheric window). The atmospheric transparent window is highly transparent and exhibits significant spectral selectivity, resulting from the combined effects of various gases^[55]. At an ambient temperature of approximately 300 K, the atmospheric transparent window aligns with the peak wavelength of blackbody radiation spectrum (9.7 μm) and overlaps significantly with the blackbody radiation spectrum, enabling maximized radiative heat transfer. Consequently, any object on Earth facing the sky can radiate heat into space through the atmospheric transparent window, thereby reducing its own temperature^[56].

Radiative cooling is a thermal equilibrium process, in which the net cooling power of the radiator at a given temperature is obtained by subtracting the power reabsorbed from incident solar radiation and atmospheric thermal radiation, as well as the power lost through local thermal conduction and convection, from the thermal radiation power generated at the surface of the radiator[26]. Considering all thermal exchange processes, the net cooling power of the radiative cooler during the day (Pnet-day) and at night (Pnet-night) can be calculated using equations (1) and (2), respectively:

（1）

P n e t - d a y = P r a d - P a m b - P s u n - P c o n d + c o n v

（2）

P n e t - n i g h t = P r a d - P a m b - P c o n d + c o n v

here,

P r a d

is the power radiated by the radiative cooler,

P a m b

is the power reabsorbed in atmospheric thermal radiation,

P s u n

is the solar power absorbed by the radiative cooler, and

P c o n d + c o n v

is the non-radiative power loss due to convection and conduction. Their calculation expressions are given by equations (3) to (6), respectively^[50]:

（3）

P r a d = ∫ d Ω c o s θ ∫ 0 ∞ d λ I B B (λ, T r) ε (λ, Ω)

（4）

P a m b = ∫ d Ω c o s θ ∫ 0 ∞ d λ I B B (λ, T a) ε (λ, Ω) ε a m b (λ, Ω)

（5）

P s u n = ∫ 0 ∞ d λ I A M 1.5 (λ) ε (λ, 0)

（6）

P c o n d + c o n v = q (T a - T r)

among them,

∫ d Ω = 2 π ∫ 0 π / 2 d θ s i n θ

is the hemispherical integral, and

ε (λ, Ω)

represents the emissivity of the radiative cooler, which can be replaced by the absorptivity of the radiative cooler according to Kirchhoff's radiation law.

The emissivity of the atmosphere is given by

ε a m b (λ, Ω) = 1 - t (λ) 1 / c o s θ

. Here,

t (λ)

represents the atmospheric transmittance in the zenith direction. The solar irradiance in Equation (5) is expressed as

λ I A M 1.5 (λ)

. Assuming the cooler faces the sun (

θ = 0

), the

P s u n

term does not involve angular integration, and the emissivity of the cooler is represented by its value in the zenith direction.

T r

denotes the surface temperature of the radiative cooler,

T a

is the ambient air temperature, and

q = q c o n d + q c o n v

represents the non-radiative heat transfer coefficient due to thermal conduction and convection. Some reports on radiative cooling indicate that to effectively suppress non-radiative heat transfer, the

q

value should range between 2 and 6.9 W/m²·K^[50].

2.2 Factors Affecting Radiative Cooling Performance

2.2.1 Environmental Factors

First, solar radiation is a key factor affecting the cooling efficiency of materials. The heat brought by solar radiation cannot be ignored; only when the heat radiated outward by the radiator exceeds the heat gained from absorbing sunlight and atmospheric thermal radiation can the radiator achieve daytime radiative cooling.

Secondly, objects primarily radiate heat to outer space through the atmospheric window; therefore, the transmittance of the atmospheric window directly affects the efficiency of radiative cooling. The transmittance of the atmospheric window is influenced by various environmental factors (such as air humidity, geographical location, and cloud cover). Among these, air humidity is a significant factor affecting daytime radiative cooling performance. In dry environments, the atmospheric window not only opens at λ=8~13 μm but also opens at λ=16~25 μm (this wavelength band is called the "second atmospheric window"), thereby enabling effective thermal radiation. However, in humid environments, water vapor's infrared absorption reduces the atmospheric window's transparency, leading to a decline in the cooling performance of materials^[57].

2.2.2 Material Factors

According to the Stefan-Boltzmann law, the total energy emitted per unit time per unit area by a black body is given by Equation (7):

（7）

P = ɛ A σ T 4

here, P is the total emission power, A is the surface area of the emitter, σ is the Stefan-Boltzmann constant, T is the temperature of the emitter's surface, and ε is the average emissivity of the emitter. For an ideal emitter, ε should equal 1 (see Fig. 1b).

When light passes through an object (λ), the interaction of light with the object can be categorized into three types: reflection, transmission, and absorption. The relationship between reflectivity (

ρ λ

), transmissivity (

τ λ

), and absorptivity (

α λ

) is given by equation (8):

（8）

ρ λ + τ λ + α λ = 1

according to Kirchhoff's law, under certain conditions, the emissivity value (ε_λ) of any material is equal to its absorptivity value (

α λ

), as shown in equations (9) and (10):

（9）

α λ = ε λ

（10）

ε λ = 1 - ρ λ - τ λ

based on the aforementioned theory, under the same environmental conditions, a material's radiative cooling performance depends on its surface radiative properties. For daytime radiative cooling, to effectively release heat through the atmospheric transparency window into outer space, the material must not only generate strong thermal radiation within the atmospheric transparency window wavelength range but also maintain near-zero absorption across the entire solar spectrum to counteract the heating effect of sunlight^[7]. To achieve effective daytime radiative cooling, the radiator should typically reflect at least 90% of the incident sunlight^[26]. Currently, matrix materials used in the field of daytime radiative cooling mainly include inorganic nanomaterials with characteristics such as high refractive index and high infrared emissivity (e.g., titanium dioxide, vanadium dioxide, calcium carbonate, hafnium dioxide, silicides, etc.), as well as polymeric materials containing functional groups with high absorption in the mid-infrared wavelength range. Figure 2 summarizes common functional groups with high absorption in the infrared wavelength range.

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图2 中红外波段常见高吸收官能团示意图

Fig.2 Schematic diagram of common high-absorption functional groups in the mid-infrared band

Research has found^[58] that hollow structured nanoparticles are more favorable for multiple reflection and scattering of sunlight, and nanoparticles with a broad size distribution can scatter sunlight over a wider wavelength range, thereby producing higher reflectivity.

For polymers containing functional groups with high absorption in the mid-infrared band, their solar reflectance largely depends on their microstructure (i.e., the aggregated or supramolecular structure of the polymer). To design polymeric daytime radiative cooling materials with both high solar reflectance and mid-infrared emissivity, three main strategies have been primarily adopted in the literature: (1) incorporating inorganic nanoparticles with high refractive index and high infrared emissivity into the polymer matrix; (2) designing polymer-metal composite materials with a bilayer structure; and (3) constructing porous polymeric materials. Among these, the pore size and porosity significantly influence the radiative cooling properties of porous materials. Finite-difference time-domain (FDTD) simulations^[58] have confirmed that numerous micropores with sizes ranging from 2 to 5 μm can effectively reflect sunlight, and hierarchical pore structures at both micro- and nanoscales can scatter sunlight across a broader wavelength range, thereby achieving higher solar reflectance compared to single-pore structures under the same material thickness.

At present, the main methods reported in the literature for preparing porous cellulose-based daytime radiative cooling materials include phase separation (Figure 1c), ice templating (Figure 1d), electrospinning (Figure 1e), and ball milling (Figure 1f). Among these, the phase separation method is currently the most commonly used approach for preparing porous cellulose-based daytime radiative cooling materials. Table 2 compares the advantages and disadvantages of various preparation methods for porous cellulose-based daytime radiative cooling materials.

表2 多孔纤维素基辐射制冷材料不同制备方法的优缺点对比表

Table 2 Comparison of preparation methods of porous cellulose based radiative cooling materials

Preparation method	Advantages	Disadvantages
Phase separation^[51]	（1）Simple and fast preparation process （2）Tunable pore size	Environmentally unfriendly production process due to the common use of organic solvents
Ice-templating^[52]	（1）Macro-porous materials with ordered architecture （2）Environmentally friendly production process	（1）Complex fabrication process （2）Difficulty in the large-scale manufacture
Electrospinning^[53]	（1）Large specific surface area （2）Adjustable pore size （3）Easy surface modification	（1）Relatively high preparation cost （2）Environmentally unfriendly production process due to the common use of organic solvents
Ball milling^[54]	（1）Simple and fast preparation process （2）High yield	High energy consumption

3 Cellulose-Based Daytime Radiative Cooling Materials and Their Classification

Cellulose is a polysaccharide composed of glucose units connected via β-1,4-glycosidic bonds. It is widely present in plant cell walls and represents the most abundant natural polymer in nature. Compared to synthetic polymers, cellulose offers advantages such as broad availability of raw materials, renewability, biodegradability, and ease of modification. Furthermore, cellulose molecules can exhibit group vibrations within the wavelength range of 770–1250 cm^-1, including C—O—H bond bending, C—O bond stretching, —OH association, and —CH₂ rocking motions, which enable strong emission within the atmospheric transparent window band. Therefore, cellulose is considered a highly promising environmentally friendly radiative cooling material^[59-60]. Currently, researchers both domestically and internationally have mainly focused on enhancing the mid-infrared emissivity and reducing solar heat absorption of cellulose-based substrates through strategies such as designing multi-level structures of cellulose-based materials and combining them with other inorganic materials, thereby achieving all-weather radiative cooling performance^[61].

According to the source of matrix materials, cellulose-based daytime radiative cooling materials reported in current literature can be divided into three categories: natural cellulose-based radiative cooling materials, chemically synthesized cellulose derivative-based radiative cooling materials, and bacterial-synthesized cellulose-based daytime radiative cooling materials.

3.1 Natural Cellulose-Based Daytime Radiative Cooling Materials

According to the differences in the size of natural cellulose fibers, the matrix materials used for natural cellulose-based daytime radiative cooling materials are mainly divided into two categories: bulk natural cellulose materials (such as delignified wood, bamboo, agricultural and forestry residues, and pulp) and nanostructured natural cellulose.

3.1.1 Cellulose-Based Radiative Cooling Materials

As is well known, wood consists of lignin, cellulose, and hemicellulose. Among these components, cellulose and hemicellulose are colorless, while lignin, which contains a large number of aromatic structures, is typically dark in color and thus causes certain thermal radiation absorption. To address this issue, Li et al.^[60] fabricated dense wood with radiative cooling functionality by hot-pressing fully delignified wood. Due to the multi-level structure of cellulose and micro/nano-scale pores formed between fibers in this wood acting as disordered scattering units, strong broadband reflection can be generated in the visible light wavelength range. Moreover, molecular vibrations and extensions of cellulose contribute to strong mid-infrared emission, endowing the wood with excellent daytime radiative cooling capability. Additionally, the radiative cooling power of this wood is directly proportional to the ambient temperature (i.e., the higher the material's outer surface temperature, the higher the radiative cooling power), with nighttime and daytime cooling powers of 63 W/m² and 16 W/m², respectively, and average temperature reductions exceeding 9.0 ·C and 4.0 ·C, respectively. Furthermore, following lignin removal, the increased hydrogen bonding area between hydroxyl groups exposed on the growth direction of cellulose nanofibers provides this cooled wood with excellent mechanical strength and toughness, reaching 8.7 and 10.1 times the tensile strength and toughness of natural wood, respectively.

In order to investigate in detail the influence of lignin content in wood on its thermal radiation properties, She et al.^[62] immersed poplar wood slices longitudinally cut into a NaOH/Na₂SO₃ mixed solution for pretreatment, followed by immersion in boiling H₂O₂ solution to adjust the lignin content within the wood samples. The study found that longer immersion time in H₂O₂ solution resulted in lower lignin content. As the amorphous lignin components were removed and the cellulose microfibers realigned directionally, both the average solar reflectance and daytime radiative cooling power density increased with decreasing lignin content, while no significant changes were observed in mid-infrared emissivity or nighttime radiative cooling performance (as shown in Figure 3a). When the lignin content was reduced to 0.94 wt%, the cooling power of the delignified wood sample reached 20.39 W/m², achieving average temperature reductions of 2.60 °C during the day and 3.81 °C at night, thereby realizing all-weather radiative cooling performance (as shown in Figure 3b).

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图3 木质素含量与去木质化木材热辐射性能关系示意图^[62] ：（a）不同木质素含量去木质化木材的光谱特性；（b）不同木质素含量去木质化木材的辐射制冷功率密度

Fig.3 Relationship between lignin content and thermal radiative properties of delignified wood^[62].（a）Spectral properties of delignified wood with different lignin contents；（b）Radiative cooling power density of delignified wood with different lignin contents. Copyright 2023 Elsevier

To meet diverse aesthetic demands, Chen et al.^[63] stained delignified wood fibers with CoCl₂·6H₂O, NiCl₂·6H₂O, and CuCl₂ solutions to obtain ionically colored cellulose. Based on this material, they prepared ionically colored cooling cellulose bulk materials using a gel-assisted and hot-pressing method. These materials exhibited unstable and relatively low solar reflectance due to additional absorption in the visible and near-infrared ranges. However, the high emissivity (~90%) of the ionically colored cooling cellulose bulk materials within the atmospheric transparency window partially offset the disadvantages caused by the coloring structure, enabling temperature reductions of 2.2~3.9 °C under sunlight for three different colored samples. Additionally, their flexural strength and impact toughness reached 111 MPa and 79.8 kJ·m^-2, respectively.

Compared with wood, bamboo exhibits characteristics such as rapid growth and strong regeneration ability, making it a promising biomass material. Piao et al.^[64] assembled bamboo fibers obtained from delignified and densified bamboo materials with nano-SiO₂ modified by sodium dodecyl sulfate and a silane coupling agent (KH570) to form a three-dimensional network block, preparing an organic-inorganic hybrid material capable of all-weather radiation cooling. Due to the unique phonon vibration mode of SiO₂ and the optical scattering properties of cellulose, the prepared hybrid material demonstrates high solar reflectance and mid-infrared emissivity; the material's mechanical strength reaches 270.1 MPa, exhibiting higher specific strength compared with most structural materials, achieving average subambient temperature reductions of 3 degrees Celsius during the day and 2 degrees Celsius at night.

Cheap and abundant agricultural and forestry residues possess a multi-level structure similar to wood. Utilizing these agricultural and forestry residues as raw materials to replace wood for preparing radiative cooling materials not only reduces the raw material cost of cellulose-based daytime radiative cooling materials, but also promises to open up new avenues for their high-value utilization. Chen et al.^[65]mixed SiO₂powder with a wood fiber suspension extracted from agricultural and forestry residues at a certain mass ratio, followed by grinding and delignification treatment using boiled H₂O₂solution, finally obtaining a cost-effective structural material with radiative cooling functionality through hot pressing (Figure 4). The mechanical strength and toughness of this material are 8.7 times and 10.1 times higher than those of pure wood fiber blocks, respectively, and its sub-ambient temperature drops during the day and night can reach up to 6 °C and 8 °C, respectively.

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图4 使用农业残渣构建辐射制冷材料的过程及材料结构示意图^[65]：（a）制备过程示意图；（b）材料表面辐射制冷机理示意图；（c）材料辐射制冷能力示意图

Fig.4 Process and structure diagram of radiative cooling materials constructed with agricultural residues^[65].（a）Preparation process diagram；（b）Schematic diagram of material surface radiative cooling mechanism；（c）Schematic diagram of material radiative cooling capacity. Copyright 2021 American Chemical Society

In addition, Zhang et al.^[66] first utilized the endothermic property of lignin to process cellulose and lignin derived from wood waste into a gel, which was then laminated to produce a structural material with dual-mode thermal management. The cellulose surface (cooling side) of the material can backscatter solar radiation and emit infrared radiation, while the lignin surface (heating side) absorbs visible and near-infrared light primarily through non-radiative transitions to release energy. Therefore, by simply flipping the material during daytime, it achieves a cooling effect of 6 °C below ambient temperature and a heating effect of 27.5 °C above ambient temperature. Notably, this dual-mode thermal management material also exhibits excellent mechanical strength, with a flexural strength reaching 102 MPa.

The above-mentioned "bottom-up" preparation methods for natural cellulose-based daytime radiative cooling materials have disadvantages such as low production efficiency and difficulty in large-scale manufacturing. If industrial papermaking technology could be applied to the fabrication of cellulose cooling paper, it would potentially significantly reduce the production cost of cellulose cooling paper. Zhu et al.^[67] obtained cooling paper by further air-drying wood chips softened with steam after sequential treatments of mechanical pulping, screening/washing, and spray bleaching. The cooling paper produced through this process achieved an average cooling power of 33.2 W/m², with a solar reflectance of 89.8%, demonstrating excellent daytime radiative cooling performance.

Sun et al.^[68] fabricated a cooling paper composed of cellulose fibers and nano-hydroxyapatite (HA) using mature pulping and papermaking techniques. Due to the chemical and structural properties of cellulose fibers and nano-HA, this cooling paper exhibits a high solar reflectance of ~94% and a mid-infrared emissivity of ~95% within the atmospheric transparency window, achieving a cooling effect of 5.4·C below ambient temperature under direct sunlight. Additionally, interactions between cellulose fibers and nano-HA, including hydrogen bonding, adsorption, and entanglement, endow the material with reprocessing capabilities. This cooling paper can be recycled and reused, with the recycled material yielding cooling paper that demonstrates radiative cooling performance comparable to the original.

Due to its ultra-high refractive index (close to 2), nano-ZnO is often used to enhance the solar reflectance of cellulose-based materials. Zhao et al.^[69] first prepared a superhydrophobic ZnO nanorod@cellulose composite membrane via an in-situ growth method, and subsequently obtained a cellulose-based daytime radiative cooling material with self-cleaning functionality after hydrophobic modification with sodium laurate. The ZnO nanorods were uniformly deposited on qualitative filter paper, improving its mid-infrared emissivity. The porous grass-like cluster structure composed of ZnO nanorods contained numerous micropores, with diameters close to the average wavelength of the visible spectrum, thereby further enhancing visible light reflectance. The visible reflectance and mid-infrared emissivity reached 93.6% and 84.1%, respectively. A model house covered with this membrane achieved a cooling effect of approximately 5 °C below ambient temperature in a simulated experiment (using direct infrared light irradiation).

Zhang et al.^[70] modified the fiber network of dust-free paper using nano-ZnO particles, resulting in a flexible nanocomposite paper (ZnO-DF) that combines daytime radiative cooling, superhydrophilicity, and superoleophobicity. The wet ZnO-DF paper achieves a cooling effect of approximately 5.6 °C through the synergistic effects of radiative cooling and water evaporation, with an oil contact angle as high as 159° and a water contact angle <0°, showing promise for wearable applications integrating passive radiative cooling and phase-change cooling (e.g., sweat evaporation).

3.1.2 Nano-cellulose-based Radiative Cooling Materials

Compared with native cellulose-based radiative cooling materials, nanocellulose not only retains the inherent characteristics of native cellulose but also possesses a longer fiber aspect ratio, larger specific surface area, excellent mechanical properties, and unique optical properties, showing broader application potential in the field of radiative cooling. Depending on the preparation methods and microfibril morphologies, nanocellulose can be further classified into two categories^[71-74].

(1) Cellulose nanocrystals (CNC), also known as cellulose nanowhiskers (CNW) or nanocrystalline cellulose (NCC), are rigid, rod-like nanocrystals typically obtained by acid hydrolysis to remove the amorphous regions while retaining the crystalline regions from plant or animal cellulose sources. Their diameters range between 3∼50 nm and their lengths range between 100∼250 nm (plant-derived cellulose) or 100 nm to several micrometers (tunicate cellulose). CNC exhibits characteristics such as high crystallinity, high Young's modulus, low coefficient of thermal expansion, and liquid crystalline behavior.

(2) Cellulose nanofibers (CNF), also known as microfibrillated cellulose (MFC) or nanofibrillated cellulose (NFC), are high aspect ratio nanofibrils with diameters ranging from 3 to 100 nm and lengths reaching several micrometers. These nanofibers are obtained through mechanical disintegration of cellulose pulp. During the mechanical separation process, both the amorphous and crystalline regions of the cellulose, which are alternately arranged, are preserved, resulting in a network-like morphology characterized by randomly entangled fibrils. Compared to CNC, CNF exhibits lower crystallinity but superior mechanical toughness, making it more suitable for preparing flexible film materials or aerogels. The differences in properties between CNC and CNF are summarized in Table 3.

表3 CNC与CNF特性差异表

Table 3 Comparative characteristics between CNC and CNF

Name	Preparation method	Morphological characteristics			Feature
CNC	Direct mechanical treatment or pretreatment（e.g. enzymatic hydrolysis，chemical pretreatment）+mechanical treatment	Rigid and rod-like shape；			（1）High crystallinity；（2）High Young's modulus；（3）Low coefficient of thermal expansion；（4）Liquid crystalline properties；（5）High cost & Low yields
		Diameter	3~50 nm
		Length	100~250 nm	Plant-derived cellulose
		Length	100 nm to a few microns	Tunicin
CNF	Acid hydrolysis	Flexible and entangled network consisting of many long cellulose nanofibrils；			（1）Lower crystallinity compared with CNC；（2）Superior mechanical toughness；（3）Low cost & High yields
		Diameter	3~100 nm
		Length	>100 nm，up to several microns

CNC： Cellulose nanocrystals，also known as nanocrystalline cellulose（NCC）or cellulose nanocrystalline whiskers（CNW）； CNF： Cellulose nanofibers，also known as microfibrillated cellulose（MFC）or nanofibrillated cellulose（NFC）.

3.1.2.1 CNC-based Radiative Cooling Materials

Inspired by the "brick-mortar" structure, Sun et al.^[75] developed a nanocellulose-based daytime radiative cooling material with ultra-high mechanical strength and excellent mechanical flexibility through the incorporation of CNC and nano-zirconia (ZrO). In this material, CNC forms an interwoven framework (acting as the brick structure), while inorganic nanoparticles are uniformly distributed within the skeleton (serving as the mortar structure). Sufficient chemical functional groups (such as C—O—C and C—O) exposed during mechanical pulping, along with the introduction of numerous Zr—O single bonds, enhanced broadband spectral emission in the mid-infrared wavelength range, endowing the material with high solar reflectance (>96%) and mid-infrared emissivity (>90%). During outdoor testing, the surface temperature was 8.8 °C lower than the ambient temperature, and even under a noon solar irradiance of 640 W/m², a temperature reduction of 6.6 °C was still achieved.

Most existing materials have white or silver-white surfaces, which cannot satisfy people's diverse aesthetic needs. If traditional colorants (such as dyes and pigments) are added to daytime radiative cooling materials, the heat absorbed by these additives would offset the radiative cooling effect of the material itself^[76]. CNC is a nanorod material with natural chirality that can spontaneously assemble into left-handed cholesteric liquid crystals, thereby producing radiative cooling materials with structural colors^[77]. Ravi et al.^[76] utilized the ability of CNC to self-assemble into helical structures to prepare highly emissive and low-absorption films with structural colors, and adjusted the color of the self-assembled films by adding different amounts of glucose. The films in three colors all exhibited low solar absorption (<5%) and enabled silicon substrates to achieve a cooling effect up to 9 °C below ambient temperature.

Zhu et al.^[78] prepared CNC-EC composite films by coating CNC films onto a porous EC substrate, which exhibited structural color and achieved highly reflective properties under sunlight (Figure 5). This composite film not only maintains a low solar absorption rate (≈3%) and a high mid-infrared emissivity (>90%), but can also be manufactured at scale via roll-to-roll processes^[83].

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图5 CNC-EC膜的结构与辐射制冷性能示意图^[78]

Traditional CNC-based radiative cooling materials are susceptible to contamination from external dust, leading to reduced daytime cooling efficiency. To overcome the adverse effects of environmental factors on the daytime cooling performance of materials, Cai et al.^[79] developed CNWs/ZnO composite aerogel films using a freeze-casting and hot-pressing process. The Si-O-C bonds formed by chemical cross-linking between cellulose and MTMS can simultaneously enhance the hydrophobic properties and mid-infrared emissivity of the film surface. Moreover, the uniformly dispersed ZnO nanoparticles and the porous structure of the material enable high broadband solar reflectance. Therefore, the film exhibits excellent solar reflectance (97%) and mid-infrared emissivity (92.5%). Under direct sunlight during hot weather conditions, the tested surface temperature reduction reaches 6.9·°C. Additionally, the rough surface of the film provides it with good hydrophobicity (water contact angle: 133°).

Although the structural color of CNC films can be regulated by adjusting the glucose content, both glucose and hydrophilic CNC are highly sensitive to environmental humidity. High humidity can alter the helical structure and pitch of CNC, leading to failure of CNC-based radiative cooling materials; therefore, structural color changes under different environmental conditions must be avoided. Inspired by the epicuticular wax layer of plant leaves, Anusuyadevi et al.^[80] found that coating a synthetic wax layer (a copolymer of hydroxyhexadecanoic acid and glycerol) onto the surface of CNC/glucose (CNC/GLU) films reduced the water vapor permeability of the CNC/GLU film from 2.1×10⁷ g·μm·m^-2·day^-1·atm^-1 to 12.3×10⁴ g·μm·m^-2·day^-1·atm^-1, significantly extending its operational lifespan in high-humidity environments.

Similar to other synthetic polymer materials, prolonged ultraviolet exposure can also cause aging of CNC-based radiative cooling materials, leading to a deterioration in their cooling performance after long-term use. To address this issue, Cai et al.^[81] prepared a CNC aerogel grating (CAG) with ultra-high solar reflectance (97.4%) and mid-infrared emissivity (94%), combining excellent radiative cooling properties and anti-aging performance. Benefiting from the controllable micro/nanostructured metasurface with efficient scattering, CAG exhibits ultra-broadband solar reflection. Meanwhile, the intrinsic phonon vibration of SiO₂ particles anchored on the cellulose nanocrystal framework and the molecular vibrational modes of the cross-linked network contribute to the high infrared emissivity of CAG. In outdoor tests, CAG achieved a cooling effect of up to 10.5 °C under direct sunlight and still maintained a cooling performance of approximately 9.4 °C after being exposed to hot weather conditions for six months.

3.1.2.2 CNF-based Radiative Cooling Materials

Gamage et al.^[59] fabricated a metamaterial with tunable transparency, low visible light absorption (<5%), and high mid-infrared emissivity (>90%) by combining CNF with micrometer-sized SiO₂ particles, achieving a cooling effect of 2∼3 ·C below ambient temperature under noon sunlight.

To further enhance the radiative cooling performance of CNF-based radiative cooling materials, Geng et al.^[82] utilized trimethoxysilane (TMS) as a silane coupling agent to crosslink CNF and polyvinyl alcohol (PVA) during the freeze-drying process, and incorporated zinc oxide nanoparticles (ZnO) and metal-organic frameworks (MOFs) to improve the mechanical properties and solar reflectance of the foam, fabricating a dual-network hybrid cellulose foam. Benefiting from the synergistic effects of ZnO and MOFs, the resulting hybrid cellulose foam achieved a high solar reflectance of up to 96.5% and an infrared emissivity of 94%, yielding a cooling effect of 7.5 ·C under direct sunlight. Additionally, Chen et al.^[83] developed a mechanically stable and biodegradable CNF aerogel-based radiative cooler through LiCl crosslinking. The design of its nested porous structure enhanced internal reflection and Mie scattering, endowing the material with high solar reflectance. Moreover, the introduction of Li created gap orbitals in the electronic transition bands, thereby reducing the energy required for electronic transitions and achieving high infrared emissivity. Studies showed that this CNF aerogel-based radiative cooler exhibited an ultra-high solar reflectance of 97% and a mid-infrared emissivity of 91%, realizing a cooling effect of 9.3 ·C in hot environments.

Jaiswal et al.^[84] utilized thermochromic materials (TC) combined with CNF to achieve temperature-driven adaptability in CNF-based cooling films. TC particles, changing color from black to white, were doped into the CNF membrane, and a thin layer of silver was selectively coated on one side of the membrane. The optical properties of the film rapidly transformed at 22 ℃, becoming transparent above the transition temperature. This composite material achieved a cooling peak of 12 ℃ during bright sunlight. Table 4 summarizes the radiative cooling performance of the aforementioned natural cellulose-based daytime radiative cooling materials.

表4 天然纤维素基辐射制冷材料的辐射制冷性能对比表

Table 4 Comparison of radiative cooling performance of natural cellulose based radiative cooling materials

Natural cellulose base	Example	Solar reflectivity（%）	Mid-infrared emissivity（%）	Solar power intensity （W/m²）	Daytime radiative cooling power （W/m²）	Sub-ambient temperature drop（℃）
Wood fibers	Cooling wood^[60]	n.a.	>90	n.a.	16	>4
	Delignified wood（0.94 wt%）^[62]	92	90.68	n.a.	20.39	2.60
	Ion-dyed cooling cellulose bulk^[63]	n.a.	~90	n.a.	27.6 ~43.3	2.2~3.9
Bamboo fibers	Cooling bamboo^[64]	n.a.	>90	n.a.	n.a.	3
Biomass fibers	Cooling lignocellulosic bulk^[65]	∼94	>90	900	65.3	6
Biomass fibers	Dual-mode TMS material^[66]	∼95	>90	n.a.	52.5	6
Cellulose pulps	Cooling pulp^[67]	89.8	93.6	1000	33.2	1~2
	Cooling paper^[68]	94	95	970	n.a.	5.4
	ZnO nanorods @cellulose^[69]	93.6	84.1	n.a.	n.a.	5
	ZnO-DF^[70]	81	93	1000	n.a.	5.6
CNC	Cellulose cooler^[75]	>96	>90	640	n.a.	6.6
	CNC/GLU^[76]	>95	>80	n.a.	n.a.	9
	CNC-EC^[78]	97	>90	900	<120	1.4
	CNWs/ZnO^[79]	97	92.5	1000	n.a.	6.9
	CAG^[81]	97.4	94	640	n.a.	10.5
CNF	CNF-SiO₂^[59]	>95	>90	n.a.	n.a.	23
	Cellulosic foam^[82]	96.5	94	n.a.	n.a.	7.5
	CNF/SA@LiCl ^[83]	97	91	n.a.	n.a.	9.3

n.a.： not available

3.2 Cellulose Derivative-based Radiative Cooling Materials via Chemical Synthesis

Micro-nano multi-scale pore structures not only help improve the total scattering efficiency of sunlight, but also increase the probability of sunlight achieving infrared radiation through multiple diffuse reflections. Previous studies have confirmed that micropores and nanopores in polymer films play an important role in enhancing solar reflectivity and mid-infrared emissivity^[34]. Compared with natural cellulose, which is difficult to dissolve and melt, cellulose derivatives offer better processability, making it easier to fabricate porous films, thus showing great potential as radiative cooling materials. Currently, the cellulose derivatives reported for application in radiative cooling are mainly ethyl cellulose (EC) and cellulose acetate (CA).

EC is a cellulose ethyl ether derivative with excellent thermal stability, chemical stability, solubility, and mechanical strength. Liu et al.^[85] used ethanol/water (volume ratio 1:1) as a mixed solvent to prepare porous EC-based super-white coatings filled with nano BaSO₄ particles via a phase separation method. Due to the use of porous EC as the matrix and the incorporation of nano BaSO₄ with high reflectivity, the coating exhibited a solar reflectance of up to 98.6% and a mid-infrared emissivity of 98.1%, resulting in a surface temperature reduction of at least 2.5 Â°C compared to the ambient temperature under a solar irradiance of approximately 920 W/m².

CA is a cellulose derivative prepared by acetylation of cellulose, featuring good biodegradability, hydrophobicity and film-forming properties^[23,86]. Moreover, due to the introduction of some new chemical bonds (such as C

̿

O bonds), CA exhibits higher mid-infrared emissivity than natural cellulose, making it a promising substrate for daytime radiative cooling. Wei et al.^[87] fabricated an alumina-cellulose acetate coating (Al₂O₃-CA) on the surface of fabric (commercial name: Soalon) via a dip-coating process. The addition of Al₂O₃ enhanced heat conduction between the textile and skin; with the incorporation of both Al₂O₃ and CA, the solar reflectance of this textile increased from 62.6% to 80.1%; in actual human body cooling experiments, the inner surface temperature of the fabric could be reduced by 1.9-3.3 °C. To enable the fabric to possess both cooling and heating capabilities, Xue et al.^[88] coated both sides of the fabric with coatings exhibiting cooling (CA@Al₂O₃) and heating (multi-walled carbon nanotubes) characteristics respectively, to prepare multimodal thermal management materials with multilayer structures. The porous CA@Al₂O₃ coating (cooling side) exhibited a high solar reflectance of 92.12% and a mid-infrared emissivity of 83.22%, achieving a net cooling power of 55.85 WDIANm^-2, while the multi-walled carbon nanotubes (heating side) showed high solar absorption (88.4%); compared with the original fabric, this textile achieved additional cooling of 4.58 °C and extra heating of 38.02 °C.

Zeng et al.^[89] designed a recyclable dual-mode thin film material. This film utilizes porous cellulose acetate (CA) as the substrate for the cooling side, achieving a cooling effect of 8.5 °C in hot environments due to its high solar reflectance (96.3%) and mid-infrared emissivity (95.4%). The heating side coated with carbon black (CB) achieves a heating effect of 20.9 °C, allowing easy switching between cooling and heating by simply flipping the film. Additionally, the components can be separated and extracted based on their solubility differences, and the reassembled material shows almost no visible change in appearance compared to the original material.

Because pores have a higher refractive index, constructing porous structures can effectively enhance solar reflectivity^[90]. To investigate the influence of film thickness on the radiative cooling performance of materials, Jaramillo-Fernandez et al.^[56] prepared two types of three-dimensional disordered network structured CA films with different thicknesses using the phase separation method. Thicker films facilitate strong emissivity in the infrared range and provide thermal insulation to minimize conductive heat loss; therefore, thick films (300.0 μm) exhibit superior radiative cooling performance compared to thin films (30.0 μm) (see Table 5).

表5 两种厚度的CA膜在太阳光谱和中红外光谱范围内的吸收率对比表

Table 5 Comparison of absorption rates of CA films of two thicknesses in the solar spectrum and mid-infrared spectrum

Name	Thickness（μm）	Solar absorptivity（%）	Mid-infrared emissivity（%）
CA thin film	30.0	5.2	87.9
CA thick film	300.0	5.0	93.6

To further enhance the solar reflectance of CA materials, incorporating inorganic nanoparticles with high refractive index and high infrared emissivity into the CA matrix is also an effective strategy (Fig. 6a). Xiang et al.^[51] fabricated a CA-based film (3DPCA) with one side rich in SiO₂ microspheres via a phase separation method. Unlike traditional organic-inorganic hybrid materials that aim for uniform dispersion of optical resonators within a polymer matrix, the SiO₂-rich side of this 3DPCA film efficiently radiates heat to the cold universe through the atmospheric transparency window, while the three-dimensional porous structure formed by CA effectively scatters sunlight. With its 3D porous structure, this film exhibits a high solar reflectance (∼96%) and mid-infrared emissivity (∼95%), achieving cooling effects of ∼6.2 °C during the day and ∼8.6 °C at night.

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图6 无机粒子-3DPCA薄膜举例示意图：（a）薄膜的结构特征和其在白天和夜间的PRC机理^[51]；（b）相分离法制备3DPCA/TiO₂膜示意图；（c）TiO₂掺杂量与3DPCA/TiO₂膜辐射制冷性能关系图^[91]

Fig.6 Schematic illustration of inorganic particle-3DPCA film：（a）Structural characteristics of thin films and their PRC mechanism during day and night^[51]. Copyright 2021 Elsevier BV；（b）Schematic diagram of preparation of 3DPCA/TiO₂ films by phase separation；（c）Relationship between TiO₂ doping amount and radiative cooling performance of 3DPCA/TiO₂ film^[91]. Copyright 2021 Elsevier.

In addition, Chen et al.^[91] prepared a CA-based porous film containing nano-TiO₂ (3DPCA/TiO₂) by incorporating nano-TiO₂, which has higher refractive index and mid-infrared emissivity, into a porous CA substrate through a phase separation method (Figure 6b). The study found that the radiative cooling performance of this 3DPCA/TiO₂ film is related to the TiO₂ doping content (Figure 6c). When the TiO₂ doping level was 8.75 wt%, the composite film achieved optimal cooling effects (solar reflectance and mid-infrared emissivity reached 97% and 96%, respectively, achieving a cooling effect of approximately 10 degrees Celsius below ambient temperature under solar irradiance of 897 W/m²), due to many ~5 μm pores and uniform dispersion of TiO₂ within the CA matrix. Liu et al.^[92] utilized a phase separation method to transform CA and Si-Al inorganic polymer particles into a regular 3D network. Due to the rationally designed 3D porous structure as well as the unique chemical bonds between the inorganic polymer powders (Si—O, Si—O—Al, and Al—O—P) and CA, both the solar reflectance and mid-infrared emissivity of the film were enhanced, reaching up to 98% and 83%, respectively. The nighttime and daytime cooling effects achieved were 2.38 degrees Celsius and 6.56 degrees Celsius, respectively.

However, the constructed porous structure may increase the material's instability to some extent. In addition, the color of cellulose derivative-based radiative cooling materials changes (from white to yellow) under long-term ultraviolet irradiation, leading to failure of cellulose-based daytime radiative cooling materials. To address these issues, Cai et al.^[93] prepared a novel CA-based composite film (CCF) with micro/nano hierarchical pore structures via a phase separation method, and further improved the optical, mechanical, and UV resistance properties of the material using TiO₂@potassium titanate obtained through ball-milling technology. Due to multiple scattering at the pore/cellulose interfaces and unique chemical bonds (C—O—C, C—O, Ti—O) in the cellulose composite system, the CCF exhibited excellent daytime radiative cooling performance, achieving a solar reflectance of up to 97.6%, and maintaining stable even after 720 h of UV testing.

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图7 CA/TiO₂@PT膜的制备原理及辐射制冷性能图^[93]

Compared to doping inorganic nanoparticles and constructing porous structures, this method has a relatively high cost. To address this issue, Zhang et al.^[94] prepared a novel CA/CaSiO₃ film using inexpensive cellulose acetate (CA) and calcium silicate (CaSiO₃) as raw materials through a simple phase inversion method. This composite film exhibits a novel dendritic cell structure and excellent radiative cooling performance, with a solar reflectance and mid-infrared emissivity of up to 97.3% and 97.2%, respectively, achieving a cooling effect of 7.3 °C.

Cellulose derivative-based radiative cooling materials are typically limited to single colors such as white or silver, restricting their aesthetic applications. Wang et al.^[53] developed a scalable electrospinning/inkjet printing process to fabricate quantum dot photoluminescent-based colored radiative cooling materials, achieving sub-ambient full-color cooling. Although the color of the patterns has some influence on the radiative cooling performance, green, yellow, and red patterns can all achieve daytime cooling effects of 2.2∼5.4 °C below ambient temperature when the peak solar irradiance exceeds 740 W/m².

To address the shortcomings of poor toughness and inability to form complex shapes in conventional cellulose derivative-based radiative cooling materials, Cai et al.^[95] successfully fabricated a CA/TPU polymer film with excellent flexibility by incorporating thermoplastic polyurethane (TPU) and hydroxyapatite nanorods with enhanced infrared emissivity through a solution blending method. This composite film features asymmetric coral-like pores that enhance sunlight scattering within the pore sizes, exhibiting a high solar reflectance of 97.26% and a high mid-infrared emissivity of 97.22%. It not only retains the excellent optical properties of CA but also maintains the mechanical properties of TPU, achieving integration of radiative cooling performance and mechanical toughness. Table 6 summarizes the radiative cooling performance of the aforementioned cellulose derivative-based radiative cooling materials.

表6 纤维素衍生物基辐射制冷材料的辐射制冷性能对比表

Table 6 Comparison of radiative cooling performance of the radiative cooling materials based on cellulose derivatives

Cellulose derivatives base	Example	Solar reflectivity（%）	Mid-infrared emissivity（%）	Solar power intensity（W/m²）	Daytime radiative cooling power（W/m²）	Sub-ambient temperature drop （℃）
EC	EC/BaSO₄^[85]	98.6	98.1	920	≤125.8	2.5
CA	Al₂O₃-CA^[87]	80.1	97	800	n.a.	1.9∼3.3（Fabric）
	Dual-mode CA@Al₂O₃/MWCNTs^[88]	92.12	83.22	1000	83.22	83.22
	Dual-mode CA/EC/CB^[89]	96.3	95.4	873	115.4	8.5
	CA thick film^[56]	95	93.6	n.a.	n.a.	4.6
	3DPCA/SiO₂^[51]	96	95	900	n.a.	6.2
	3DPCA/TiO₂（8.75 wt%）^[91]	97	96	897	n.a.	10
	3DPCA/Si-Al^[92]	98	83	1600	n.a.	6.56
	CA/TiO₂@PT^[93]	97.6	95	n.a.	n.a.	6.5
	CA/CaSiO₃^[94]	97.3	97.2	803~885	90.7	7.3
	CA/CsPbX₃ film^[53]	82~89	95	>740	25.6~51.7	2.2∼5.4
	CA/TPU^[95]	97.26	97.22	1550	n.a.	9.2

n.a.： not available

3.3 Bacterial Synthesis of Cellulose-based Daytime Radiative Cooling Materials

Bacterial cellulose (BC), also known as bacterial nanocellulose (BNC), is a nanocellulosic material synthesized by microorganisms (such as Acetobacter, Rhizobia, and Gluconacetobacter xylinus) through fermentation using low molecular weight sugars and other organic compounds as carbon sources. It consists of randomly arranged microfibrils (diameter: 20–100 nm, length: >100 μm) that intertwine to form a network-like morphology.

Inspired by the surface structures of natural biological skins, Zhao et al.^[96] successively prepared a hydrophobic bilayer gel (BC aerogel/polyvinyl alcohol hydrogel) integrating both radiative cooling and evaporative cooling functions through solvent exchange, freeze-drying, hydrophobic modification, and dip-coating processes. This bilayer gel exhibited a high solar reflectance (98.8%) and mid-infrared emissivity (86%), achieving a remarkable cooling effect of up to 16.4 °C when applied to roof coverings.

Shi et al.^[97] prepared a BC-based radiative cooling film (Bio-RC) by utilizing the entanglement characteristics of SiO₂ microspheres and cellulose ribbon-like filaments (secreted by Gluconacetobacter xylinus) during in-situ cultivation. This film exhibited a high solar reflectance (95.3%) and mid-infrared emissivity (93.4%), achieving excellent radiative cooling performance when applied to solar cells. Additionally, Shi et al.^[98] applied BC-based radiative cooling materials for human body thermal management, reporting a dual-mode BC-based Janus material (J-BC) that combines both cooling and heating functions. This material demonstrated outstanding performance in both cooling and heating modes, achieving a cooling effect of approximately 3.8·C below ambient temperature and a heating effect of approximately 14.2·C above ambient temperature during daytime.

To address the degradation of radiative cooling performance in BC-based radiative cooling materials caused by contamination with aqueous or oily pollutants, Wang et al.^[99] successively prepared M-BC/BaSO₄ composite materials through silane modification and unidirectional freeze-casting processes. The composite exhibited an average solar reflectance of 97.75% and an average mid-infrared emissivity of 95.74%; furthermore, its surface water and oil contact angles were 154° and 145.5°, respectively, with minimal change in radiative cooling performance before and after self-cleaning. Additionally, Zhong et al.^[100] developed a BC/BaSO₄ aerogel material using BC as the structural framework, modified BaSO₄ as functional particles, and a fluoride coating as a hydrophobic modifier via a freeze-drying and spraying process. This composite aerogel not only demonstrated high average solar reflectance (95.6%) and mid-infrared emissivity (98.1%), but also exhibited excellent surface hydrophobicity and oleophobicity (water contact angle: ~151°, ethylene glycol contact angle: ~141°, n-hexadecane contact angle: ~139°). Table 7 summarizes the radiative cooling performance of the aforementioned cellulose derivative-based radiative cooling materials.

表7 细菌纤维素基日间辐射制冷材料的辐射制冷性能对比表

Table 7 Comparison of radiative cooling performance of bacterial cellulose based radiative cooling materials

Nanocellulose base	Example	Solar reflectivity （%）	Mid-infrared emissivity（%）	Solar power intensity （W/m²）	Daytime radiative cooling power （W/m²）	Sub-ambient temperature drop（℃）
BC	BC/PVA^[96]	98.8	86	1000	n.a.	16.4
	Bio-RC^[97]	95.3	93.4	647	n.a.	3.7
	J-BC^[98]	98.1	93.6	736	n.a.	3.8
	M-BC/BaSO₄^[99]	97.75	95.74	n.a.	n.a.	10.4
	M-BC/BaSO₄-14^[100]	95.6	98.1	755.4	n.a.	6.64
	M-BC/BaSO₄-14^[100]	95.6	98.1	955.35	n.a.	8.49

n.a.： not available

4 Application Areas

Cellulose-based daytime radiative cooling materials have broad application prospects due to the aforementioned advantages. This section will focus on reviewing the application progress of cellulose-based daytime radiative cooling materials in four main fields: building energy efficiency, personal thermal management, photovoltaic cooling, and low-temperature storage and transportation.

4.1 Passive Building Energy Efficiency

Cooling in buildings has a significant impact on human comfort, storage of special items, and the normal operation of high-precision instruments. Among various materials, cellulose has attracted considerable attention in the field of building energy efficiency due to its inherent advantages, such as excellent mechanical properties, high solar reflectance and infrared emissivity, environmental friendliness ("green" property), and wide availability. Therefore, the development of cellulose-based daytime radiative cooling materials is of vital significance for building energy conservation.

Natural wood has been used as a building material for thousands of years due to its low cost and abundant availability. Additionally, the multi-level structure and excellent thermal insulation properties of natural wood make it a promising energy-saving building material. However, its inferior mechanical properties limit its application. To address this issue, Song et al.^[101] found that removing part of the lignin can significantly improve the mechanical properties of wood, solving the problem of poor mechanical properties in lignocellulose-based composites. Subsequently, Chen et al.^[102] developed a composite material with ultra-high specific strength, which is 1.8 to 4.4 times greater than that of modified lignocellulosic materials, surpassing most natural structural materials and some metals and alloys, demonstrating the feasibility of cellulose-based materials for construction applications.

In addition to directly modifying natural biomass cellulose (derived from natural wood and agricultural residues) to obtain building radiative cooling materials, recently, many functional cellulose-based building materials (such as ultra-white coatings and aerogels) have emerged, all of which exhibit excellent radiative cooling capabilities. However, the stability of cellulose-based radiative cooling materials without hydrophobic modification is insufficient. Considering that building materials need to maintain stable radiative cooling performance, designing and fabricating cellulose-based radiative cooling materials with stable microstructures, self-cleaning properties, and low cost is highly significant. Tian et al. [104] embedded polytetrafluoroethylene (PTFE) particles into the micrometer-scale pores of cellulose fibers via a spray-coating process, constructing a superhydrophobic bilayer structure. This PTFE/cellulose coating demonstrated excellent radiative cooling and self-cleaning performance; under solar irradiance of 834 W/m², its surface temperature could decrease by 5 °C, and under solar irradiance of 671 W/m², its radiative cooling power reached 104 W/m². Furthermore, the material exhibited good waterproof performance during water immersion tests and maintained stable optical and self-cleaning properties under various harsh environmental conditions (such as ultraviolet irradiation, rain washing, low- and high-temperature exposure, high humidity exposure, and mechanical abrasion).

Aerogels, as ultra-lightweight materials with low thermal conductivity and porous structures, have garnered significant attention in the construction industry due to their ability to minimize parasitic absorption of solar radiation and provide insulation to reduce environmental heat gain. Cai et al.^[52] developed a novel tunable, insulating, and compressible CNC-based aerogel cooler through chemical cross-linking and unidirectional freeze-casting processes. The hierarchical and ordered nanoporous structure of this aerogel significantly enhances solar light scattering efficiency, achieving a surface temperature reduction of 9.2 °C under direct sunlight, and maintaining a cooling effect of approximately 7.4 °C even in extreme conditions characterized by high heat, humidity, and variability (relative humidity of 70%). By adjusting the compression ratio of this shape-memory aerogel, its cooling performance can be modulated. Additionally, compared to traditional building cooling energy consumption in China, it reduces cooling energy demand by 35.4%.

The low mechanical strength of cellulose aerogels poses a challenge for their application as structural materials in buildings. Inorganic materials are commonly added to improve the mechanical strength of cellulose aerogels; however, these inorganic materials cannot be completely degraded, which compromises the sustainability of the material^[105]. Zhong et al.^[106] fabricated a bio-inspired hierarchical structured cellulose aerogel (HSCA) through a high-voltage electrostatic field-assisted assembly strategy (e.g., Figure 8). Benefiting from the ordered hierarchical porous network microstructure formed by the in-situ assembly of cellulose nanofibers, HSCA exhibits excellent daytime radiative cooling performance and mechanical strength; its axial compressive strength reaches 1.9 MPa, with a maximum cooling temperature of up to 7.2 ·C. The hydrophobic modified HSCA shows no significant decline in cooling performance after being placed outdoors for three months; building energy-saving simulations demonstrate that using HSCA for building side walls and roofs can save 52.7% of the baseline cooling energy consumption in buildings (China).

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图8 日间辐射制冷技术在建筑节能中的应用^[106]：（a）HSCA示意图；（b）太阳光下疏水HSCA建筑围护结构和包装箱的光学图像和红外图像

Fig.8 Application of daytime radiative cooling technology in building energy conservation：（a）schematic of HSCA；（b）Optical and infrared images of hydrophobic HSCA building envelope and packing box under sunlight^[106]，Copyright 2023 American Chemical Society

The emerging concept of Janus materials has attracted significant interest for the integration of building heating and cooling functions. The highly asymmetric nature of both sides of Janus materials can endow them with asymmetric infrared radiation properties, thus enabling controllable thermal radiation, which holds great promise in the field of passive building energy saving.^[107]

Yang et al.^[108] prepared a Janus-type Mxene-CNF aerogel using an ice-template method. This composite aerogel possesses advantages such as low density, high porosity, and excellent mechanical strength. When used as a smart roof, it can achieve passive radiative cooling and heating by switching between different surface layers. When the CNF layer of the aerogel is exposed, it enables highly reflective solar radiation. When the MXene-CNF composite layer, characterized by high absorption and low infrared emissivity, serves as the outer layer, it efficiently converts sunlight into thermal energy, while the inner CNF layer, with its high infrared emissivity, significantly increases indoor temperatures.

4.2 Human Body Thermal Management

Developing "green," low-energy, and low-emission human body thermal management technologies is crucial for human health and sustainable development. Radiative cooling-based human body thermal management technology represents a zero-energy-consumption solution that can efficiently cool the human body in hot environments without consuming any energy or emitting greenhouse gases. It serves as a strong complement, and even an alternative, to traditional high-energy-consuming cooling devices (such as air conditioners), demonstrating significant potential for development.

The good solvent dispersibility and stronger infrared emissivity of CA make it an important base material for cooling fabrics. Wei et al.^[87] first dispersed Al₂O₃ in a solution and mixed it with CA, then coated and dip-coated the solution onto fabrics, finding that this could reduce the fabric temperature by 1.9~3.3 ·C and lower human skin temperature by 0.6~1 ·C. Feng et al.^[109] prepared a 3D porous CA/aluminum phosphate hybrid film (3DPCA/h-AlPO₄) with a biomimetic skin structure through a solvent polarity matching strategy. Benefiting from the wrinkled surface and dense h-AlPO₄ nanolayer of the film, this biomimetic material exhibited a high mid-infrared emissivity of 94.7%. Du et al.^[110] designed a radiative cooling fabric (PET-CA-MgO) with high solar reflectance (94.6%) and high mid-infrared emissivity (96.8%) by embedding magnesium oxide (MgO) nanorods into a porous CA matrix, which was subsequently dip-coated onto a polyethylene terephthalate (PET) substrate.

Similar to conventional fabrics, the aforementioned cellulose-based radiative cooling fabrics also face issues of durability and stability. Therefore, developing fabrics that integrate efficient thermal management with excellent durability holds significant research importance. Inspired by the unique "fruit-branch" structure found in fruits, Li et al.^[111] prepared a cellulose fabric with long-term stable cooling performance by in situ synthesis of nano-SiO₂ on cellulose fibers, which still exhibited good breathability and radiative cooling performance after exposure to sunlight for 100 days and undergoing 100 cycles of mechanical washing.

To further enhance the abrasion resistance of fabrics, Zhong et al.^[112] integrated natural cellulose hierarchical structures and micro-nano porous structures into a cellulose coating, fabricating a natural cellulose-based fabric (RCCF) with excellent daytime radiative cooling performance. This fabric achieved a solar reflectance of 90.2% and a mid-infrared emissivity of 98.1%. When covering the surface of a simulated skin under clear sky conditions, it provided a cooling effect of 6.5·℃ compared to conventional cotton fabric. Real human body cooling tests also demonstrated its superior cooling performance. Moreover, after 5000 cycles of abrasion testing and 20 standard washing cycles, the fabric still maintained excellent hydrophobicity and radiative cooling properties. Notably, the hydrophobic performance on the fabric's surface can be restored under heating conditions (i.e., during high-temperature weather, the fabric can simultaneously cool and recover its hydrophobic properties, thereby prolonging its stain-resistant effectiveness), offering new insights for the design and development of novel outdoor personal thermal management textiles.

To enable fabrics to possess both cooling and heating functions, Zhang et al.^[113] integrated radiative cooling, radiative heating, and active heating capabilities through electrospinning and coating techniques. This Janus film (see Figure 9) achieves a solar absorption rate of up to 88% in heating mode, while exhibiting a solar reflectance of 97% and mid-infrared emissivity of 96% in cooling mode; in cooling mode, its outdoor average temperature is 9.4 °C lower than that of commercial cotton fabric, and in heating mode, its average temperature is 40 °C higher than that of cotton fabric.

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图9 Janus膜在人体热管理领域的应用示意图^[113]：（a）Janus膜原理图；（b）制冷模式下Janus膜的太阳反射率和中红外发射率示意图和红外图像；（c）加热模式下Janus膜的太阳反射率示意图和红外图像

Fig.9 Schematic diagram of application of Janus film in the field of personal thermal management：（a）janus film schematic；（b）Schematic and infrared images of solar reflectivity and mid-infrared emissivity of Janus film in cooling mode；（c）solar reflectivity schematic and infrared image of Janus film in heating mode^[113]，Copyright 2023 Elsevier

Besides extreme temperatures, electromagnetic pollution has become a new concern due to the widespread use of electronic devices. To address the deterioration of living environments caused by extreme temperatures and excessive electromagnetic waves, Zhao et al.^[114] prepared a Janus-type MXene/cellulose/ZnO membrane for personal thermal management and electromagnetic interference shielding. This Janus membrane exhibits high visible light reflectivity (96.3%) and mid-infrared emissivity (83.7%) on the ZnO nanorod side, while the visible light absorption and average infrared reflectivity exceed 90% and 70%, respectively, on the MXene side. Additionally, its electromagnetic shielding efficiency (~30 dB) outperforms commercial shielding materials (20 dB).

4.3 Photovoltaic Cooling

Photovoltaic power generation is currently one of the best alternatives to fossil fuels. In practical applications, due to the limited conversion efficiency of solar cells, only a portion of solar radiation is converted into electrical energy, while the remaining part is absorbed by the solar cell components in the form of heat, causing the temperature of the solar cells themselves to rise above the ambient temperature. Because of the intrinsic semiconductor properties of solar cells, excessively high operating temperatures can severely affect the output performance and safety of the devices. Therefore, it is necessary to dissipate heat from the core components to keep the operating temperature of the solar cells below the ambient temperature. In recent years, some researchers have attempted to apply cellulose-based daytime radiative cooling materials to the field of photovoltaic cells.

Lv et al.^[115] prepared a transparent cellulose membrane/EVA composite material by impregnating thermally cross-linked ethylene-vinyl acetate copolymer (EVA) into a cellulose membrane. The composite exhibits solar reflectance and mid-infrared emissivity both exceeding 90%, demonstrating excellent radiative cooling performance. By utilizing this composite as the encapsulation layer for solar modules during module packaging, a temperature reduction of approximately 2 °C was achieved in outdoor exposure experiments.

In addition to reducing the temperature of photovoltaic cell components by using the aforementioned embedded cellulose membrane method, cellulose-based radiative cooling films can also be directly covered on the surface of photovoltaic cells to achieve a cooling effect. Chowdhury et al.^[116] combined CNC with PDMS to prepare a new type of CNC-modified polymer film. This film exhibits low solar absorptivity and high emissivity in the mid-infrared region. Under direct sunlight, the surface temperature reduction of samples covered with this film can reach 3.97 ·C, and its cooling power can achieve 82.66 W/m²; when placed on top of solar cells, the working temperature of the cells under direct sunlight decreases, and the cell efficiency increases from 8.217% to 8.634%.

4.4 Low-Temperature Storage and Transportation

The application of innovative preservation technologies is of great significance for extending the shelf life of agricultural products and improving their market share^[117]. Postharvest quality of agricultural products is mainly affected by three factors: intrinsic metabolic processes, external environmental conditions (such as temperature, humidity, and atmospheric gases), and surface microorganisms. Therefore, lowering temperature to slow down the metabolism of agricultural products, vacuum packaging, and using antimicrobial packaging materials are currently the three main methods for prolonging the lifespan of agricultural products.

Good solvent solubility endows CA with excellent film-forming properties, making it highly promising in the field of food preservation. Li et al.^[22] prepared a hierarchically designed CA film that can effectively protect ice of various sizes and shapes under sunlight. The CA film exhibits a solar reflectance of up to 97.4% and a mid-infrared emissivity of 92%, achieving a cooling power of up to 110 W/m² and a temperature reduction of approximately 12 ℃ under direct sunlight, which provides potential for preserving fresh products (especially frozen ones).

ZnO possesses photocatalytic properties and the ability to absorb ultraviolet light, which can prevent photosensitive oxidation of fresh food, inhibit the synthesis of mycotoxins, and suppress the proliferation of Aspergillus niger. Therefore, it can be used as an antimicrobial agent to extend the shelf life of food. Zhang et al.^[23] developed a CA/nano-ZnO composite film with hierarchical pores using a water-induced phase separation method (as shown in Figure 10), achieving passive cooling without energy input. When applied for fruit and vegetable packaging, this film reduced the temperature of mushrooms by 18·C under direct sunlight irradiation, demonstrating superior cooling performance during preservation compared to other commercially available food packaging materials, and extending the storage time of strawberries up to 9 days. In addition, the film also exhibited excellent antibacterial properties and self-cleaning capabilities.

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图10 辐射制冷技术在食品保鲜领域的应用示意图^[23]：（a）工作原理图；（b）CA/ZnO薄膜结构示意图；（c）金针菇状态对比图；（d）草莓状态对比图

Fig. 10 Schematic diagram of application of radiative cooling technology in the field of food preservation：（a）working principle diagram；（b）structure diagram of CA/ZnO film；（c）state comparison of flammulina velutipes；（d）strawberry state comparison diagram^[23]，Copyright 2023 American Chemical Society

As a natural chromatic indicator, anthocyanin changes color in response to environmental pH variations. Incorporating anthocyanin into packaging materials enables visual functionality, allowing the spoilage process of agricultural products to be directly displayed through color changes, thus achieving real-time visual freshness detection. To realize the fresh delivery of agricultural products, Chen et al.^[21] prepared a three-layer packaging material named zinc oxide-nanorods/cellulose membrane-starch membrane@blueberry anthocyanin (ZnO-NRs/CM-SM@BA). This material not only has efficient heat dissipation capability to delay the decay of agricultural products but also can monitor their freshness through real-time color changes.

5 Conclusion and Prospect

Compared with traditional daytime radiative cooling materials, cellulose-based daytime radiative cooling materials offer advantages such as abundant raw material sources, good biodegradability, and nontoxicity, and are expected to play an important role in the field of radiative cooling, holding broad development prospects. However, there is still a long way to go before they can truly replace traditional radiative cooling materials and significantly reduce cooling energy consumption on a large scale. To achieve practical applications of cellulose-based daytime radiative cooling materials, the following issues need to be addressed.

(1) Similar to other polymers, natural cellulose exhibits unsatisfactory solar reflectance under direct sunlight, resulting in poor net cooling power. Currently, most studies employ phase separation methods to construct porous structures in order to improve the solar reflectance of cellulose-based materials. However, these phase separation methods typically require the consumption of large amounts of organic solvents, leading to environmental concerns during preparation. Therefore, it is urgent to develop environmentally friendly approaches for constructing cellulose-based porous structural materials.

(2) Natural cellulose surfaces contain a large number of hydrophilic hydroxyl groups, which can cause changes in their microstructure when exposed to high humidity or water, thereby deteriorating their cooling performance and mechanical strength. Meanwhile, when exposed outdoors, natural cellulose materials are susceptible to ultraviolet radiation and pollution from airborne dust, particulate matter, and soot, further impairing the cooling performance of cellulose-based daytime radiative cooling materials. Numerous studies have already focused on improving the water resistance and weather resistance of cellulose materials through hydrophobic surface modification. However, most currently used hydrophobic modifiers are fluorine-containing compounds that are difficult to degrade or toxic, leading to significantly reduced degradability of the modified materials. Therefore, future efforts should focus on developing "green" and non-toxic modifiers to enhance the weather resistance and water resistance of cellulose-based daytime radiative cooling materials while also emphasizing their anti-ultraviolet aging properties.

(3) At present, most cellulose-based daytime radiative cooling materials still enhance solar reflectance by constructing hierarchical micro/nano-porous structures, which is not conducive to their large-scale production. Therefore, developing micro/nano-fabrication technologies suitable for mass production and balancing material and processing costs are of great significance for the further development of cellulose-based daytime radiative cooling materials.

In summary, cellulose-based daytime radiative cooling materials hold great potential to effectively address current challenges related to energy crises, environmental issues, and preservation of fruits and vegetables. We believe that a wide range of cellulose-based daytime radiative cooling materials with excellent performance, low cost, easy scalability, environmental friendliness, and multifunctionality will be developed in the future.

References

Publishing order | Descend order by publishing year | Descend order by cited within

[1]	Shankar S, Khodaei D, Lacroix M. Food Hydrocoll., 2021, 117: 106750.

[2]	Ly K C S, Liu X H, Song X K, Xiao C Y, Wang P, Zhou H, Fan T X. Adv. Funct. Mater., 2022, 32(31): 2203789.

[3]	Yin X B, Yang R G, Tan G, Fan S H. Science, 2020, 370(6518): 786.

[4]	Li X Q, Sun B W, Sui C X, Nandi A, Fang H M, Peng Y C, Tan G, Hsu P C. Nat. Commun., 2020, 11: 6101.

[5]	Gao H Y. IOP Conf. Ser. Earth Environ. Sci., 2019, 252: 032007.

[6]	Sun X S, Sun Y B, Zhou Z G, Alam M A, Bermel P. Nanophotonics, 2017, 6(5): 997.

[7]	Li W, Fan S H. Opt. Photonics News, 2019, 30(11): 32.

[8]	Li X Q, Xie W R, Sui C X, Hsu P C. ACS Mater. Lett., 2020, 2(12): 1624.

[9]	Wu X K, Li J L, Xie F, Wu X E, Zhao S M, Jiang Q Y, Zhang S L, Wang B S, Li Y R, Gao D, Li R, Wang F, Huang Y, Zhao Y L, Zhang Y Y, Li W, Zhu J, Zhang R F. Nat. Commun., 2024, 15: 815.

[10]	Zhou J W, Chen T G, Tsurimaki Y, Hajj-Ahmad A, Fan L L, Peng Y C, Xu R, Wu Y C, Assawaworrarit S, Fan S H, Cutkosky M R, Cui Y. Joule, 2023, 7(12): 2830.

[11]	Zhang X A, Yu S J, Xu B B, Li M, Peng Z W, Wang Y X, Deng S L, Wu X J, Wu Z P, Ouyang M, Wang Y H. Science, 2019, 363(6427): 619.

[12]	Peng Y C, Chen J, Song A Y, Catrysse P B, Hsu P C, Cai L L, Liu B F, Zhu Y Y, Zhou G M, Wu D S, Lee H R, Fan S H, Cui Y. Nat. Sustain., 2018, 1(2): 105.

[13]	Song Y N, Lei M Q, Lei J, Li Z M. Mater. Today Energy, 2020, 18: 100504.

[14]	Wu X K, Li J L, Jiang Q Y, Zhang W S, Wang B S, Li R, Zhao S M, Wang F, Huang Y, Lyu P, Zhao Y L, Zhu J, Zhang R F. Nat. Sustain., 2023, 6(11): 1446.

[15]	Hsu P C, Song A Y, Catrysse P B, Liu C, Peng Y C, Xie J, Fan S H, Cui Y. Science, 2016, 353(6303): 1019.

[16]	Cai L L, Song A Y, Li W, Hsu P C, Lin D C, Catrysse P B, Liu Y Y, Peng Y C, Chen J, Wang H X, Xu J W, Yang A K, Fan S H, Cui Y. Adv. Mater., 2018, 30(35): 1802152.

[17]	Zeng S N, Pian S J, Su M Y, Wang Z N, Wu M Q, Liu X H, Chen M Y, Xiang Y Z, Wu J W, Zhang M N, Cen Q Q, Tang Y W, Zhou X H, Huang Z H, Wang R, Tunuhe A, Sun X Y, Xia Z G, Tian M W, Chen M, Ma X, Yang L Y, Zhou J, Zhou H M, Yang Q, Li X, Ma Y G, Tao G M. Science, 2021, 373(6555): 692.

[18]	Wu J R, He J, Yin K, Zhu Z, Xiao S, Wu Z P, Duan J A. Nano Lett., 2021, 21(10): 4209.

[19]	Li S, Zhou Z H, Liu J W, Zhang J, Tang H J, Zhang Z F, Na Y L, Jiang C X. Renew. Energy, 2022, 198: 947.

[20]	Nakamura K. Am. J. Physiol. Regul. Integr. Comp. Physiol., 2011, 301(5): R1207.

[21]	Chen Y N, Wang Z Y, Dai Y T, Yang D Y, Qiu F X, Li Y Q, Zhang T. ACS Sustainable Chem. Eng., 2023, 11(41): 15135.

[22]	Li J L, Liang Y, Li W, Xu N, Zhu B, Wu Z, Wang X Y, Fan S H, Wang M H, Zhu J. Sci. Adv., 2022, 8(6): eabj9756.

[23]	Zhang K, Mo C Q, Tang X L, Lei X J. ACS Sustainable Chem. Eng., 2023, 11(20): 7745.

[24]	Guo C Y, Pan H D, Xu Q H, Wang J Y, Zhao D L. J. Refrig., 2022, 43(3): 1. (郭晨玥, 潘浩丹, 徐琪皓, 王佳云, 盛茗峰, 赵东亮. 制冷学报, 2022, 43(3): 1.).

[25]	Zhu L X, Raman A, Wang K X, Abou Anoma M, Fan S H. Optica, 2014, 1(1): 32.

[26]	Raman A P, Abou Anoma M, Zhu L X, Rephaeli E, Fan S H. Nature, 2014, 515(7528): 540.

[27]	Zhou L, Song H M, Liang J W, Singer M, Zhou M, Stegenburgs E, Zhang N, Xu C, Ng T, Yu Z F, Ooi B, Gan Q Q. Nat. Sustain., 2019, 2(8): 718.

[28]	Peng Y C, Fan L L, Jin W L, Ye Y S, Huang Z J, Zhai S, Luo X, Ma Y X, Tang J, Zhou J W, Greenburg L C, Majumdar A, Fan S H, Cui Y. Nat. Sustain., 2022, 5(4): 339.

[29]	Bhatia B, Leroy A, Shen Y C, Zhao L, Gianello M, Li D H, Gu T, Hu J J, Soljačić M, Wang E N. Nat. Commun., 2018, 9: 5001.

[30]	Lin K X, Chen S R, Zeng Y J, Ho T C, Zhu Y H, Wang X, Liu F Y, Huang B L, Chao C Y, Wang Z K, Tso C Y. Science, 2023, 382(6671): 691.

[31]	Bao H, Yan C, Wang B X, Fang X, Zhao C Y, Ruan X L. Sol. Energy Mater. Sol. Cells, 2017, 168: 78.

[32]	Zhao X P, Li T Y, Xie H, Liu H, Wang L Z, Qu Y R, Li S C, Liu S F, Brozena A H, Yu Z F, Srebric J, Hu L B. Science, 2023, 382(6671): 684.

[33]	Mandal J, Fu Y K, Overvig A C, Jia M X, Sun K R, Shi N N, Zhou H, Xiao X H, Yu N F, Yang Y. Science, 2018, 362(6412): 315.

[34]	Wang T, Wu Y, Shi L, Hu X H, Chen M, Wu L M. Nat. Commun., 2021, 12: 365.

[35]	Huang G, Yengannagari A R, Matsumori K, Patel P, Datla A, Trindade K, Amarsanaa E, Zhao T H, Köhler U, Busko D, Richards B S. Nat. Commun., 2024, 15: 3798.

[36]	Wang X, Liu X H, Li Z Y, Zhang H W, Yang Z W, Zhou H, Fan T X. Adv. Funct. Mater., 2020, 30(5): 1907562.

[37]	Liu H H, Kang H J, Jia X, Qiao X S, Qin W, Wu X H. Adv. Mater. Technol., 2022, 7(10): 2101583.

[38]	Meng S, Long L S, Wu Z X, Denisuk N, Yang Y, Wang L P, Cao F, Zhu Y G. Sol. Energy Mater. Sol. Cells, 2020, 208: 110393.

[39]	Kou J L, Jurado Z, Chen Z, Fan S H, Minnich A J. ACS Photonics, 2017, 4(3): 626.

[40]	Xie F, Jin W L, Nolen J R, Pan H, Yi N Q, An Y, Zhang Z Y, Kong X T, Zhu F, Jiang K, Tian S C, Liu T J, Sun X J, Li L N, Li D B, Xiao Y F, Alu A, Fan S H, Li W. Science, 2024, 386(6723): 788.

[41]	Fang Z Q, Zhu H L, Bao W Z, Preston C, Liu Z, Dai J Q, Li Y Y, Hu L B. Energy Environ. Sci., 2014, 7(10): 3313.

[42]	Lei C, Chen J Q, Robertson G P. GCB Bioenergy, 2023, 15(11): 1373.

[43]	Feng S J, Zhou Y M, Liu C H, Zhang T, Bu X H, Huang Y Z, He M. Chem. Eng. J., 2023, 452: 139377.

[44]	Li Z D, Tian Q, Chen Y, Zhao B C, Qiu F X, Zhang T. Cellulose, 2023, 30(8): 5145.

[45]	Liao M N, Banerjee D, Hallberg T, Åkerlind C, Alam M M, Zhang Q L, Kariis H, Zhao D, Jonsson M P. Adv. Sci., 2023, 10(8): 2206510.

[46]	Zhang K, Lei X J, Mo C Q, Huang J, Wang M, Kang E T, Xu L Q. Adv. Sci., 2023, 10(11): 2206925.

[47]	Cai C Y, Ding C X, Wu X D, Chen Y. Acta Mater. Compos. Sin., 2024, 41(11): 5800. (蔡晨阳, 丁春香, 武小丹, 陈溢. 复合材料学报, 2024, 41(11): 5800.).

[48]	Zhang Q, Li X D, Wang W W, Liu X. Energy Storage Sci. Technol., 2023, 12(5): 1427. (张奇, 李晓东, 王文雯, 刘晓. 储能科学与技术, 2023, 12(5): 1427.).

[49]	Fan S H. Joule, 2017, 1(2): 264.

[50]	Hossain M M, Gu M. Adv. Sci., 2016, 3(7): 1500360.

[51]	Xiang B, Zhang R, Luo Y L, Zhang S, Xu L, Min H H, Tang S C, Meng X K. Nano Energy, 2021, 81: 105600.

[52]	Cai C Y, Wei Z C, Ding C X, Sun B J, Chen W B, Gerhard C, Nimerovsky E, Fu Y, Zhang K. Nano Lett., 2022, 22(10): 4106.

[53]	Wang X Y, Zhang Q, Wang S H, Jin C Q, Zhu B, Su Y C, Dong X Y, Liang J, Lu Z D, Zhou L, Li W, Zhu S N, Zhu J. Sci. Bull., 2022, 67(18): 1874.

[54]	Cai C Y, Wu X D, Cheng F L, Ding C X, Wei Z C, Wang X, Fu Y. Adv. Funct. Mater., 2024, 34(40): 2405903.

[55]	Zeyghami M, Goswami D Y, Stefanakos E. Sol. Energy Mater. Sol. Cells, 2018, 178: 115.

[56]	Jaramillo-Fernandez J, Yang H, Schertel L, Whitworth G L, Garcia P D, Vignolini S, Sotomayor-Torres C M. Adv. Sci., 2022, 9(8): 2104758.

[57]	Suichi T, Ishikawa A, Hayashi Y, Tsuruta K. AIP Adv., 2018, 8(5): 055124.

[58]	Bijarniya J P, Sarkar J, Maiti P. Sci. Rep., 2021, 11: 893.

[59]	Gamage S, Kang E S H, Åkerlind C, Sardar S, Edberg J, Kariis H, Ederth T, Berggren M, Jonsson M P. J. Mater. Chem. C, 2020, 8(34): 11687.

[60]	Li T, Zhai Y, He S M, Gan W T, Wei Z Y, Heidarinejad M, Dalgo D, Mi R Y, Zhao X P, Song J W, Dai J Q, Chen C J, Aili A, Vellore A, Martini A, Yang R G, Srebric J, Yin X B, Hu L B. Science, 2019, 364(6442): 760.

[61]	Gamage S, Banerjee D, Alam M M, Hallberg T, Åkerlind C, Sultana A, Shanker R, Berggren M, Crispin X, Kariis H, Zhao D, Jonsson M P. Cellulose, 2021, 28(14): 9383.

[62]	She Y N, Wang J, Zhu C F, Tian F Y, Jin Y Y, Mao W, Wu Y T, Chen K, Xu X W. Ind. Crops Prod., 2023, 193: 116242.

[63]	Chen Y P, Zhang J Y, Zhuang Z R, Zhou J H, Peng Y, Dang B K, Sun Q F. Ind. Crops Prod., 2024, 220: 119094.

[64]	Piao X X, Cao Y W, Guo H X, Jin C D, Wang Z. ACS Sustainable Chem. Eng., 2022, 10(48): 15692.

[65]	Chen Y P, Dang B K, Fu J Z, Wang C, Li C C, Sun Q F, Li H Q. Nano Lett., 2021, 21(1): 397.

[66]	Zhang J Y, Yin K R, Zhuang Z R, Zhou J H, Tang Y X, Xu J Y, Chen Y P, Li Y Y, Sun Q F. Mater. Horiz., 2024, 11(15): 3633.

[67]	Zhu W K, Zhang Y, Mohammad N, Xu W H, Tunc S, Shan X W, Zhou C L, Semple K, Dai C P, Li T. Cell Rep. Phys. Sci., 2022, 3(11): 101125.

[68]	Sun H D, Tang F J, Chen Q F, Xia L M, Guo C Y, Liu H, Zhao X P, Zhao D L, Huang L L, Li J G, Chen L H. Chem. Eng. J., 2023, 455: 139786.

[69]	Zhao B C, Yue X J, Tian Q, Qiu F X, Zhang T. Cellulose, 2022, 29(3): 1981.

[70]	Zhang H Y, Yu M, Du Y, Xu L, Ma D P, Wang Q. Mater. Chem. Phys., 2022, 285: 126069.

[71]	Rahimi Kord Sofla M, Brown R J, Tsuzuki T, Rainey T J. Adv. Nat. Sci.: Nanosci. Nanotechnol., 2016, 7(3): 035004.

[72]	Liu H Z, Geng B Y, Chen Y F, Wang H Y. ACS Sustainable Chem. Eng., 2017, 5(1): 49.

[73]	Lv P F, Lu X M, Wang L, Feng W. Adv. Funct. Mater., 2021, 31(45): 2104991.

[74]	Dufresne A. Mater. Today, 2013, 16(6): 220.

[75]	Sun H D, Chen Y W, Zeng W C, Tang F J, Bi Y H, Lu Q X, Mondal A K, Huang L L, Chen L H, Li J G. Carbohydr. Polym., 2023, 314: 120948.

[76]	Shanker R, Ravi Anusuyadevi P, Gamage S, Hallberg T, Kariis H, Banerjee D, Svagan A J, Jonsson M P. ACS Nano, 2022, 16(7): 10156.

[77]	Fernandes S N, Lopes L F, Godinho M H. Curr. Opin. Solid State Mater. Sci., 2019, 23(2): 63.

[78]	Zhu W K, Droguet B, Shen Q C, Zhang Y, Parton T G, Shan X W, Parker R M, De Volder M F L, Deng T, Vignolini S, Li T. Adv. Sci., 2022, 9(26): 2202061.

[79]	Cai C Y, Sun Y B, Chen Y, Wei Z C, Wang Y B, Chen F L, Cai W Q, Ji J W, Ji Y X, Fu Y. J. Bioresour. Bioprod., 2023, 8(4): 421.

[80]	Anusuyadevi P R, Singha S, Banerjee D, Jonsson M P, Hedenqvist M S, Svagan A J. Adv. Mater. Interfaces, 2023, 10(7): 2202112.

[81]	Cai C Y, Chen W B, Wei Z C, Ding C X, Sun B J, Gerhard C, Fu Y, Zhang K. Nano Energy, 2023, 114: 108625.

[82]	Geng A B, Han Y M, Cao J Y, Cai C Y. Int. J. Biol. Macromol., 2024, 264: 130676.

[83]	Chen Y, Sun Y B, Cheng F L, Ji Y X, Cai C Y, Fu Y. ACS Sustainable Chem. Eng., 2024, 12(29): 10680.

[84]	Jaiswal A K, Hokkanen A, Khakalo S, Mäkelä T, Savolainen A, Kumar V. ACS Appl. Mater. Interfaces, 2024, 16(12): 15262.

[85]	Liu R, Zhou Z G, Mo X W, Liu P, Hu B, Duan J J, Zhou J. ACS Appl. Mater. Interfaces, 2022, 14(41): 46972.

[86]	Vatanpour V, Pasaoglu M E, Barzegar H, Teber O O, Kaya R, Bastug M, Khataee A, Koyuncu I. Chemosphere, 2022, 295: 133914.

[87]	Wei W, Zhu Y, Li Q, Cheng Z F, Yao Y J, Zhao Q, Zhang P, Liu X P, Chen Z, Xu F, Gao Y F. Sol. Energy Mater. Sol. Cells, 2020, 211: 110525.

[88]	Xue T, Chen X, Wang C X, Yin Y J. Chem. Eng. J., 2024, 500: 156713.

[89]	Zeng Z W, Tang B, Zeng F R, Chen H, Chen S Q, Liu B W, Wang Y Z, Zhao H B. Adv. Funct. Mater., 2024, 34(39): 2403061.

[90]	Ma H C, Wang L, Dou S L, Zhao H P, Huang M, Xu Z W, Zhang X Y, Xu X D, Zhang A Q, Yue H Y, Ali G, Zhang C H, Zhou W Y, Li Y, Zhan Y H, Huang C. ACS Appl. Mater. Interfaces, 2021, 13(16): 19282.

[91]	Chen X, He M, Feng S J, Xu Z J, Peng H, Shi S N, Liu C H, Zhou Y M. Opt. Mater., 2021, 120: 111431.

[92]	Liu C H, Feng S J, He M, Chen X, Shi S N, Bu X H, Zhou Y M. Mater. Today Commun., 2022, 31: 103530.

[93]	Cai C Y, Chen F L, Wei Z C, Ding C X, Chen Y, Wang Y B, Fu Y. Chem. Eng. J., 2023, 476: 146668.

[94]	Zhang S, Jing W L, Chen Z, Zhang C Y, Wu D X, Gao Y F, Zhu H T. Renew. Energy, 2022, 194: 850.

[95]	Cai H R, Feng S J, Feng M X, He X, Liu C H, He M, Bu X H, Huang J, Zhou Y M. ACS Appl. Polym. Mater., 2023, 5(12): 10053.

[96]	Zhao B C, Yue X J, Tian Q, Qiu F X, Li Y Q, Zhang T. Cellulose, 2022, 29(14): 7775.

[97]	Shi S K, Lv P F, Valenzuela C, Li B X, Liu Y, Wang L, Feng W. Small, 2023, 19(39): 2301957.

[98]	Shi S K, Valenzuela C, Yang Y Z, Liu Y, Li B X, Wang L, Feng W. Chin. J. Chem., 2023, 41(20): 2611.

[99]	Wang Q, Zhong S L, Zheng Z H, Lei H, Li S Y, Yu W. Mater. Lett., 2023, 352: 135220.

[100]

Zhong

S L

, Gou

Y C

, Huang

X W

, Zheng

Z H

, Yu

, Li

S Y

, Lei

. Opt. Mater., 2023, 142: 114068.

[101]

Song

J W

, Chen

C J

, Zhu

S Z

, Zhu

M W

, Dai

J Q

, Ray

, Li

Y J

, Kuang

Y D

, Li

Y F

, Quispe

, Yao

Y G

, Gong

, Leiste

U H

, Bruck

H A

, Zhu

J Y

, Vellore

, Li

, Minus

M L

, Jia

, Martini

, Li

, Hu

L B

. Nature, 2018, 554(7691): 224.

[102]

Chen

Y P

, Dang

B K

, Jin

C D

, Sun

Q F

. ACS Nano, 2019, 13(1): 371.

[103]

Belhadj

, Bederina

, Dheilly

R M

, Mboumba-Mamboundou

L B

, Quéneudec

. Energy Build., 2020, 225: 110348.

[104]

Tian

Y P

, Shao

, Liu

X J

, Chen

F Q

, Li

Y S

, Tang

C Y

, Zheng

. ACS Appl. Mater. Interfaces, 2021, 13(19): 22521.

[105]

Zhang

J Y

, Cheng

Y H

, Xu

C J

, Gao

M Y

, Zhu

M F

, Jiang

. Adv. Funct. Mater., 2021, 31(19): 2009349.

[106]

Zhong

S J

, Yuan

S X

, Zhang

J W

, Xu

T Q

, Zuo

, Cai

, Yi

L M

. ACS Appl. Mater. Interfaces, 2023, 15(33): 39807.

[107]

Yue

X J

, Zhang

, Yang

D Y

, Qiu

F X

, Wei

G Y

, Zhou

. Nano Energy, 2019, 63: 103808.

[108]

Yang

W Q

, Xiao

, Li

, Deng

, Ni

, Zhang

, Gu

J C

, Yang

J L

, Kuo

S W

, Geng

F X

, Chen

. Small, 2023, 19(30): 2302509.

[109]

Feng

S J

, Zhou

Y M

, Chen

, Shi

S N

, Liu

C H

, Zhang

. J. Mater. Chem. A, 2021, 9(44): 25178.

[110]

L L

, Zhou

Z G

, Li

J J

, Hu

, Wang

C L

, Zheng

J H

, Liu

, Li

R H

, Chen

W X

. Chem. Eng. J., 2023, 469: 143765.

[111]

J G

, Tang

F J

, Bi

Y H

, Sun

H D

, Huang

L L

, Chen

L H

. Nano Energy, 2023, 117: 108921.

[112]

Zhong

S J

, Song

L M

, Ren

W J

, Liu

W J

, Yuan

S X

, Xu

T Q

, Xu

, Zhang

J W

, Cai

, Yi

L M

. Chem. Eng. J., 2024, 489: 151482.

[113]

Zhang

Y X

, Wu

D S

, Liao

S Q

, Chen

D S

, Mensah

, Guo

, Lv

P F

, Wei

Q F

. Compos. Part A Appl. Sci. Manuf., 2023, 172: 107622.

[114]

Zhao

B C

, Li

C Z

, Chen

Y F

, Tian

, Yurekli

, Qiu

F X

, Zhang

. Cellulose, 2023, 30(8): 5171.

[115]

T Z

, Huang

J P

, Liu

, Zhang

. Case Stud. Therm. Eng., 2020, 18: 100596.

[116]

Chowdhury

F I

, Xu

Q W

, Sinha

, Wang

X H

. J. Quant. Spectrosc. Radiat. Transf., 2021, 272: 107824.

[117]

M X

, Shi

Z X

, He

S L

, Hu

, Cai

, Gan

, Huang

, Zhang

Y Q

. Carbohydr. Polym., 2023, 321: 121317.

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Outlines

模态框（Modal）标题

Abstract

Cite this article

1 Introduction

表1 各类辐射制冷材料辐射制冷性能和优缺点归纳表

2 Radiative Cooling

2.1 Principle

2.2 Factors Affecting Radiative Cooling Performance

2.2.1 Environmental Factors

2.2.2 Material Factors

图2 中红外波段常见高吸收官能团示意图

表2 多孔纤维素基辐射制冷材料不同制备方法的优缺点对比表

3 Cellulose-Based Daytime Radiative Cooling Materials and Their Classification

3.1 Natural Cellulose-Based Daytime Radiative Cooling Materials

3.1.1 Cellulose-Based Radiative Cooling Materials

图3 木质素含量与去木质化木材热辐射性能关系示意图[62] ：（a）不同木质素含量去木质化木材的光谱特性；（b）不同木质素含量去木质化木材的辐射制冷功率密度

图4 使用农业残渣构建辐射制冷材料的过程及材料结构示意图[65]：（a）制备过程示意图；（b）材料表面辐射制冷机理示意图；（c）材料辐射制冷能力示意图

3.1.2 Nano-cellulose-based Radiative Cooling Materials

表3 CNC与CNF特性差异表

3.1.2.1 CNC-based Radiative Cooling Materials

图5 CNC-EC膜的结构与辐射制冷性能示意图[78]

3.1.2.2 CNF-based Radiative Cooling Materials

表4 天然纤维素基辐射制冷材料的辐射制冷性能对比表

3.2 Cellulose Derivative-based Radiative Cooling Materials via Chemical Synthesis

表5 两种厚度的CA膜在太阳光谱和中红外光谱范围内的吸收率对比表

图6 无机粒子-3DPCA薄膜举例示意图：（a）薄膜的结构特征和其在白天和夜间的PRC机理[51]；（b）相分离法制备3DPCA/TiO2膜示意图；（c）TiO2掺杂量与3DPCA/TiO2膜辐射制冷性能关系图[91]

图7 CA/TiO2@PT膜的制备原理及辐射制冷性能图[93]

表6 纤维素衍生物基辐射制冷材料的辐射制冷性能对比表

3.3 Bacterial Synthesis of Cellulose-based Daytime Radiative Cooling Materials

表7 细菌纤维素基日间辐射制冷材料的辐射制冷性能对比表

4 Application Areas

4.1 Passive Building Energy Efficiency

图8 日间辐射制冷技术在建筑节能中的应用[106]：（a）HSCA示意图；（b）太阳光下疏水HSCA建筑围护结构和包装箱的光学图像和红外图像

4.2 Human Body Thermal Management

图9 Janus膜在人体热管理领域的应用示意图[113]：（a）Janus膜原理图；（b）制冷模式下Janus膜的太阳反射率和中红外发射率示意图和红外图像；（c）加热模式下Janus膜的太阳反射率示意图和红外图像

4.3 Photovoltaic Cooling

4.4 Low-Temperature Storage and Transportation

图10 辐射制冷技术在食品保鲜领域的应用示意图[23]：（a）工作原理图；（b）CA/ZnO薄膜结构示意图；（c）金针菇状态对比图；（d）草莓状态对比图

5 Conclusion and Prospect

References

图3 木质素含量与去木质化木材热辐射性能关系示意图^[62] ：（a）不同木质素含量去木质化木材的光谱特性；（b）不同木质素含量去木质化木材的辐射制冷功率密度

图4 使用农业残渣构建辐射制冷材料的过程及材料结构示意图^[65]：（a）制备过程示意图；（b）材料表面辐射制冷机理示意图；（c）材料辐射制冷能力示意图

图5 CNC-EC膜的结构与辐射制冷性能示意图^[78]

图6 无机粒子-3DPCA薄膜举例示意图：（a）薄膜的结构特征和其在白天和夜间的PRC机理^[51]；（b）相分离法制备3DPCA/TiO₂膜示意图；（c）TiO₂掺杂量与3DPCA/TiO₂膜辐射制冷性能关系图^[91]

图7 CA/TiO₂@PT膜的制备原理及辐射制冷性能图^[93]

图8 日间辐射制冷技术在建筑节能中的应用^[106]：（a）HSCA示意图；（b）太阳光下疏水HSCA建筑围护结构和包装箱的光学图像和红外图像

图9 Janus膜在人体热管理领域的应用示意图^[113]：（a）Janus膜原理图；（b）制冷模式下Janus膜的太阳反射率和中红外发射率示意图和红外图像；（c）加热模式下Janus膜的太阳反射率示意图和红外图像

图10 辐射制冷技术在食品保鲜领域的应用示意图^[23]：（a）工作原理图；（b）CA/ZnO薄膜结构示意图；（c）金针菇状态对比图；（d）草莓状态对比图