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Journal of Inorganic Materials

Abbreviation (ISO4): J Inorg Mat      Editor in chief: Lidong CHEN

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Journal of Inorganic Materials >

2024 , Vol. 39 >Issue 4: 383 - 389

DOI: https://doi.org/10.15541/jim20230457

RESEARCH ARTICLE

Sandwich Structured Ru@TiO2 Composite for Efficient Photocatalytic Tetracycline Degradation

  • Zhaoyang WANG , 1 ,
  • Peng QIN 2 ,
  • Yin JIANG 1 ,
  • Xiaobo FENG 1 ,
  • Peizhi YANG , 1 ,
  • Fuqiang HUANG , 3
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  • 1. Key Laboratory of Advanced Technique & Preparation for Renewable Energy Materials, Ministry of Education, Yunnan Normal University, Kunming 650500, China
  • 2. State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
  • 3. State Key Lab of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
YANG Peizhi, professor. E-mail: ;
HUANG Fuqiang, professor. E-mail:

Received date: 2023-10-07

  Revised date: 2023-12-13

  Online published: 2024-04-25

Supported by

National Natural Science Foundation of China(U1802257)

National Natural Science Foundation of China(12264057)

Key Foundation of Basic Research of Yunnan Province(202201AS070023)

“Yunnan Revitalization Talent Support Program” and “Spring City Plan” Introduction and Training Project of High-level Talent(2022SCP005)

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Abstract

TiO2 nanomaterials are widely used photocatalysts due to high photocatalytic activity, good chemical stability, low cost, and nontoxicity. However, its lower photon utilization efficiency is still limited by larger bandgap width and higher recombination rate between photon and hole. In this study, two-dimensional TiO2 nanosheets were synthesized via microetching, which were then inserted by ruthenium atoms to form an efficient photocatalyst Ru@TiO2 with sandwich structure. The surface morphology, electronic structure, photoelectric properties, and photocatalytic degradation performance of tetracycline hydrochloride of Ru@TiO2 sandwich structure were investigated using different measurements. Results indicated that the material’s photoresponse range extended from UV to visible- near-infrared regions, improving photon absorption and carrier separation efficiency while enhancing photocatalytic activity. Under simulated sunlight irradiation (AM 1.5 G, 100 mW·cm-2) for 80 min, sandwich structured Ru@TiO2 efficient photocatalyst exhibited superior degradation performance on tetracycline hydrochloride with a degradation efficiency up to 91.91%. This work offers an effective way for the construction of efficient TiO2 based photocatalysts.

Key words： layered titanium dioxide; ruthenium intercalation; photocatalysis; tetracycline hydrochloride

Cite this article

Zhaoyang WANG , Peng QIN , Yin JIANG , Xiaobo FENG , Peizhi YANG , Fuqiang HUANG . Sandwich Structured Ru@TiO2 Composite for Efficient Photocatalytic Tetracycline Degradation[J]. Journal of Inorganic Materials, 2024 , 39(4) : 383 -389 . DOI: 10.15541/jim20230457

抗生素在临床医学、农业以及牲畜业中发挥着重要作用。据统计, 从2000年到2015年全球抗生素使用量增加了约65%[1]。抗生素在生物体内代谢率极低, 大部分未经吸收就直接通过生活、生产废水排入生态系统, 进入地表水和地下水中, 对生命健康与环境资源构成严重危害[2-3]。但是常规污水处理技术对四环素类抗生素的去除率低于80%[4]。因此, 开发高效、低成本去除水中四环素类抗生素的新方法十分必要。
目前去除水中四环素类抗生素的主要方法包括物理吸附、膜分离、厌氧生物处理、电化学氧化和臭氧氧化等, 但这些方法均受到环境二次污染与高成本的制约[5]。近年来, 光催化降解凭借操作简单、成本低、绿色环保、降解效率高、反应速率快等优势, 成为降解水中四环素类抗生素污染物的有效手段, 其核心是设计与制备高效光催化剂[6]。金属氧化物, 比如g-C3N4/MnCo2O4[7]、ZnFe2O4[8]、CuO/Bi2O3[9]、TiO2[10-11], 已被用于光催化降解盐酸四环素(TC)。其中TiO2凭借高催化活性、高化学稳定性、低成本和环境友好等优势, 成为最受关注的光催化材料之一。进一步提高TiO2的光子利用率与光催化活性, 是该材料未来发展面临的主要问题[12]。Wu等[13]通过氮掺杂实现了TiO2的宽光子吸收, 在120 min内TC降解效率达到94.8%; Yu等[14]在Ti3+-TiO2介晶中引入等离子体Ag/AgCl纳米粒子, 改善了光谱响应区, 对TC的可见光催化降解性能提升3.52倍。
目前TiO2光催化剂的研究主要聚焦于三维纳米颗粒的结构掺杂与异质结构建。相比于传统纳米颗粒, 二维TiO2纳米片有望调控表面晶相与活性位点, 进一步提升光催化活性。以此为基础, 在TiO2纳米片表面沉积贵金属纳米颗粒, 二者在界面处易发生诱导界面电荷转移, 促进光生电子空穴分离；同时贵金属区域表面的等离子体共振效应有助于提升光激发半导体的光响应, 实现高光子利用。以层状钛酸盐为前驱体, 在酸性环境下刻蚀制备的层状TiO2具有比表面积大、层间距大、易于发生离子交换与嵌入的特点[15]。该结构有助于在TiO2层间引入贵金属纳米颗粒, 形成三明治结构光催化剂, 得到的纳米片结构可有效抑制金属颗粒的团聚[16]。
基于此, 本研究以商用二氧化钛和碳酸钾为原料, 室温下固相球磨生成层状四钛酸钾, 再利用水杨酸刻蚀溶出层间K+离子, 经Ar气氛退火后获得层状TiO2纳米晶片(L-TiO2)[17-18]。采用浸泡插层法将Ru3+吸附在TiO2层间, 退火得到Ru纳米颗粒插层于TiO2层间的三明治结构催化剂(L-Ru@TiO2)。在AM 1.5G, 100 mW·cm-2 光照条件下, 对比L-TiO2和L-Ru@TiO2样品光催化去除TC的性能。通过对样品结构组成表征、光电特性和活性物质捕捉实验, 探讨L-Ru@TiO2的光催化机理。

1 实验方法

1.1 主要试剂

K2CO3、TiO2 (平均粒径400 nm)、RuCl3(Ru 45%~55% (质量分数))、水杨酸(99.0%)和TC(96%)均购于阿拉丁生化科技股份有限公司, 乙醇(分析纯AR)购于科隆化学品有限公司。

1.2 材料制备

前驱体K2Ti4O9 将K2CO3、TiO2和乙醇以物质的量比1 : 2 : 15均匀混合, 经高能球磨机(FRITSCH Pulverisette 7)球磨24 h (转速分别为300、400 r/min, 碾磨球尺寸为1、3 mm, K2Ti4O9样品分别记为Rs300-1, Rs300-3, Rs400-1, Rs400-3)后放入烘箱中干燥, 用研钵磨成细粉。将制备好的粉体在管式炉850 ℃下煅烧10 h, 自然冷却后取出, 并用乙醇和去离子水各洗涤3次, 获得K2Ti4O9。
层状TiO2(L-TiO2) 将0.2 g Rs400-3和0.8 g水杨酸放入10 mL乙醇和10 mL水的混合溶剂中, 搅拌5 min后转移至配有钢套管的密封聚四氟乙烯高压反应釜(总体积50 mL)中, 120 ℃下反应3 h。自然冷却后, 采用去离子水和乙醇多次洗涤, 并在70 ℃真空干燥箱内干燥10 h。烘干后的粉体在400 ℃ Ar气氛下退火2 h, 获得层状L-TiO2。
三明治结构Ru插层TiO2(L-Ru@TiO2) 与层状L-TiO2合成类似, 首先合成前驱体K2Ti4O9, 继而加水杨酸在高压反应釜(总体积50 mL)中进行刻蚀, 自然冷却后将其与RuCl3混合并搅拌(nRu : nRu+Ti=5 : 100), 确保材料充分吸附Ru3+。经离心、烘干后, 于500 ℃ Ar气氛下退火2 h, 获得三明治结构L-Ru@TiO2。

1.3 表征方法

采用UitimaTV型X射线衍射仪(XRD，Cu Kα源)分析样品的结晶性。采用KAlpha X型射线光电子能谱仪(XPS)分析样品的元素价态。采用Bruker A300型电子顺磁共振波谱仪在室温下测量电子顺磁共振谱(EPR)。采用SKP5050开尔文探针系统(KP)测试样品的功函数。采用JEM-2100型透射电子显微镜(TEM)测试样品的晶粒尺寸。采用Agilent 700型电感耦合等离子体原子发射光谱仪(ICP-AES)测定样品的元素组成及比例。采用贝士德仪器科技有限公司的3H-2000PS2型比表面和孔隙度分析仪(BET)测试样品的比表面积和孔径。采用UV-3600型紫外-可见分光光度计(UV-Vis)、电化学工作站(CHI)和F-4500型荧光光谱仪(PL)测试样品的光电性能。

2 结果与讨论

2.1 结构与组成

图1为三明治结构L-Ru@TiO2的合成示意图。以碳酸钾和商用二氧化钛为原料, 利用球磨过程的机械作用诱发化学反应, 生成层状结构前驱体K2Ti4O9。采用有机酸水杨酸作为刻蚀剂, 层状结构K2Ti4O9在酸性介质中与质子发生离子交换形成Hx[Ti4O9], 同时K+从层间脱出[19]。Hx[Ti4O9]浸入RuCl3溶液后, 通过浸泡插层在层间引入Ru3+离子形成Ruy[Ti4O9]。随后在Ar气氛退火过程中, Ti/O层脱水重构形成层状锐钛矿型L-TiO2, Ru3+被还原成Ru纳米颗粒插入层间, 最终获得三明治结构L-Ru@TiO2[20]。
图1 三明治结构L-Ru@TiO2的合成示意图

Fig. 1 Schematic diagram of preparation of sandwich structured L-Ru@TiO2

图2为前驱体K2Ti4O9的XRD图谱, 与标准K2Ti4O9特征峰吻合, 四组样品的主相均为K2Ti4O9(PDF#32-0861)[21]。其中衍射角2θ=12°处的杂质峰为六钛酸钾。伴随碾磨球尺寸、转速增大, 六钛酸钾杂质减少, K2Ti4O9特征峰增强。其中, Rs400-3中K2Ti4O9的结晶性最好、纯度最高, 表明高转速和大尺寸碾磨球能提供更大的机械能, 在一定条件下有利于晶体形核生长, 因此选择该条件进行后续实验[22]。
图2 不同条件制备的前驱体K2Ti4O9的XRD图谱

Fig. 2 XRD patterns of precursor K2Ti4O9 prepared under different conditions

将该前驱体K2Ti4O9进行水杨酸刻蚀、Ru插层以及退火处理。在不添加RuCl3的情况下, K2Ti4O9中Ti/O层发生脱水重构形成层状锐钛矿型L-TiO2。加入RuCl3后, Ru3+离子进入层间, 退火后还原形成纳米颗粒。ICP-AES检测到在L-Ru@TiO2结构中, Ru/Ru+Ti的摩尔比为4%, 与初始投料比相近。图3(a)为锐钛矿型L-TiO2和L-Ru@TiO2的XRD谱图。与L-TiO2相比, L-Ru@TiO2的TiO2(101)晶面衍射角(2θ=25.3°)向低角度偏移, 说明Ru插层后TiO2的层间距增大[23-24]。2θ=11°, 30°处的衍射峰属于未完全刻蚀的K2Ti4O9。在2θ=44.01°处检测到Ru(101)晶面的衍射峰, 表明Ru以纳米粒子的形式分散于TiO2层间[25⇓-27]。
图3 L-TiO2和L-Ru@TiO2的XRD、XPS、EPR和BET表征

Fig. 3 XRD, XPS, EPR, and BET characterizations of L-TiO2 and L-Ru@TiO2

(a) XRD patterns; (b) Ru3d XPS spectrum of L-Ru@TiO2; (c) O1s, and (d) Ti2p XPS spectra; (e) EPR spectra; (f) Nitrogen adsorption and desorption isotherms and corresponding pore size distribution curves. 1 Gs=10-4 T

为了进一步研究Ru插层对TiO2表面化学性质的影响, 对两种材料进行XPS表征。在图3(b)中, L-Ru@TiO2样品中280.2和284.3 eV处的结合能峰分别对应Ru03d5/2和Ru03d3/2。281.3和285.5 eV处的峰则分别归属于结合能较高的Ruδ+3d5/2和Ruδ+3d3/2, 表明Ru纳米颗粒与TiO2层间存在强相互作用, 使电子由Ru向TiO2转移[26], 同时伴随O1s和Ti2p XPS主峰向低结合能的位置偏移0.21和0.13 eV(图3(c, d))。EPR光谱显示(图3(e)), L-TiO2和L-Ru@TiO2结构中均存在少量氧空位(g=2.003), 插入Ru后氧空位强度略有提高[28-29]。L-TiO2和L-Ru@TiO2的N2吸附-解吸等温线如图3(f)所示, 均属于IUPAC分类Ⅳ型, 具有迟滞回线, Ru插层前后材料的比表面积分别为42.64和32.63 m2/g, 平均孔径分别为9.57和7.53 nm, Ru插层后L-Ru@TiO2的比表面积和平均孔径均减小。

2.2 形貌表征

图4(a, b, d, e)的TEM照片表明L-TiO2和L-Ru@TiO2具有层状特性, 两者平均尺寸均为60 nm×500 nm, Ru插层后并未显著改变L-TiO2形貌。L-TiO2层间相对光滑, 且片层内存在明显的间隙和孔隙, 这是离子传输和吸附的重要通道[30]。在HRTEM照片(图4(c, f))中, L-TiO2和L-Ru@TiO2的晶格间距分别为0.176和0.184 nm, 对应锐钛矿型TiO2的(105)晶面, 其中L-Ru@TiO2的晶格间距略大, 表明插入Ru后TiO2层间距变大, 这与XRD分析结果一致。图4(h)为高角环形暗场像(HAADF)中Ru(101)晶面的晶格条纹, 其晶格间距为0.244 nm。插层后, Ru纳米颗粒(椭圆区域)包埋在TiO2层下, 证明Ru被夹在TiO2片层间形成三明治结构。图4(i)的元素分布图展示了L-Ru@TiO2的元素分散特性。Ti和O分散均匀, Ru则较多分散在边缘, 这是因为三明治结构使Ru更容易暴露在粒子的边缘。
图4 L-TiO2和L-Ru@TiO2的形貌表征

Fig. 4 Morphology characterization of L-TiO2 and L-Ru@TiO2

(a,b,d,e) TEM images of (a, b) L-TiO2 and (d, e) L-Ru@TiO2; (c, f) HRTEM images of (c) L-TiO2 and (f) L-Ru@TiO2 with insets showing lattice fringes of TiO2 (105); (g, h) HAADF images and (i) element distributions for L-Ru@TiO2

2.3 光电特性

图5(a)为L-TiO2和L-Ru@TiO2的紫外-可见吸收光谱图, L-TiO2在386 nm处有明显吸收边, 光响应范围主要在波长短于400 nm的紫外光区。插入Ru后, L-Ru@TiO2的吸收拓展到整个可见光区域, 显著提高了材料光子利用率。另外, L-TiO2在350~600 nm范围内存在一个强发射峰, 与已报道的锐钛矿型TiO2一致[31⇓-33]。而插入Ru后光致发光峰的强度显著降低, 并出现光谱蓝移, 说明二者间存在电荷转移(图5(b))。图5(c)为L-TiO2和L-Ru@TiO2的瞬态光电流响应曲线, 进一步表明L-Ru@TiO2的光子吸收和载流子分离效率得以提升。同时, 插入Ru后体系的功函数由4.73 eV降低到4.49 eV, 较低的功函数有助于光催化反应过程中电子转移至催化剂表面[34](图5(d))。
图5 L-TiO2和L-Ru@TiO2的光电特性

Fig. 5 Photoelectric properties of L-TiO2 and L-Ru@TiO2

(a) UV-Vis absorption spectra; (b) PL spectra; (c) Transient photocurrent responses; (d) Work functions

2.4 光催化性能

在模拟太阳光(AM 1.5G, 100 mW·cm-2)下, 研究L-TiO2和L-Ru@TiO2对TC降解的光催化性能。光照80 min后, 原料TiO2、L-TiO2和L-Ru@TiO2对TC的降解效率分别为62.81%、66.45%、91.91% (图6(a))。L-Ru@TiO2物理吸附能力较弱, 但光催化能力强。由图6(b)可知, L-Ru@TiO2的光降解动力学曲线与一级动力学模型匹配度较高, 通过高斯拟合获得降解速率常数k为(0.29890±0.00238) min-1。鉴于Ru纳米颗粒在可见-近红外光区的等离子体共振效应[35-36], 系统研究了环境介质温度对催化剂性能的影响。在环境介质温度为0, 25 ℃, 和不控制环境介质温度(55 ℃)三种条件下, 光照80 min后L-Ru@TiO2对TC的降解效率分别为82.44%、91.91%和95.61%(图6(c))。365 nm紫外和900 nm红外单色光照80 min后条件, L-Ru@TiO2对TC的降解效率分别为89.04%和50.49%(图6(d))。900 nm单色光照条件下L-Ru@TiO2的催化性能主要源于热电子的贡献。
图6 L-TiO2和L-Ru@TiO2的催化降解性能

Fig. 6 Catalytic degradation performance of L-TiO2 and L-Ru@TiO2

(a) TC degradation and (b) TC photodegradation kinetics curves of photocatalytic raw materials TiO2, L-TiO2 and L-Ru@TiO2 under simulated sunlight; (c, d) Photocatalytic degradation efficiencies of TC by L-Ru@TiO2 at different (c) temperatures and (d) wavelengths; (e, f) Photocatalytic degradation efficiencies of TC in active species trapping experiment by L-Ru@TiO2 (Initial conditions: AO 1 mmol/L, LA 0.5 mmol/L)

超氧阴离子自由基(•O2-)、羟基自由基(•OH)和空穴(h+)是TC光降解过程中的主要活性物质[37]。为了进一步揭示三者在体系中的贡献, 分别加入抗坏血酸(L-ascorbic acid, LA)、异丙醇(Isopropanol, IPA)和草酸铵(Ammonium oxalate, AO)作为清除剂来猝灭•O2-、•OH和h+。结果表明, 加入LA、IPA和AO使TC的降解效率由91.91%分别下降至27.13%、60.19%和28.77%(图6(e, f))。这说明在L-Ru@TiO2体系中•O2-和h+是光降解TC过程中的主要活性物质。

3 结论

本研究采用两步微刻蚀法制备了二维层状TiO2纳米片, 并进一步利用金属离子插层获得三明治结构Ru@TiO2光催化剂。Ru纳米颗粒的等离子体共振效应将催化剂光响应范围由紫外光区拓展至整个可见-近红外光区, Ru与TiO2间的电荷转移则进一步促进了光生电子与空穴分离, 同时功函数由4.73 eV降低至4.49 eV, 有助于电子转移至催化剂表面。该设计策略有利于构建兼具高光子利用率与高催化活性的光催化体系。三明治结构Ru@TiO2表现出较高的TC光降解活性, 模拟太阳光(AM 1.5G, 100 mW·cm-2)照射80 min后其降解效率达到91.91%; 捕捉实验结果表明, 超氧阴离子自由基和空穴是光降解TC过程中的主要活性物质。本研究为构建高效氧化钛基光催化剂提供了一种有效手段。

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