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Abbreviation (ISO4): Prog Chem      Editor in chief: Jincai ZHAO

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Degradation of Antibiotics Using ZVI/H2O2 Fenton-Like Technology

  • Baizhou Lu 1 ,
  • Zhanqiang Fang , 1, 2
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  • 1. School of Environment,South China Normal University,Guangzhou 510006,China
  • 2. Guangdong Province Environmental Remediation Industry Technology Innovation Alliance,Guangzhou 510006,China

Received date: 2024-05-11

  Revised date: 2024-06-19

  Online published: 2024-07-01

Supported by

National Natural Science Foundation of China(42277003)

Abstract

ZVI/H2O2 Fenton-like technology overcomes some problems existing in the traditional homogeneous Fenton reaction, and can effectively remove antibiotics in water, which has good application potential. However, the degradation efficiency and mineralization rate of antibiotics in water by ZVI/H2O2 technology alone need to be improved. Therefore, researchers have adopted different strengthening measures to improve the deconta mination efficiency of ZVI/H2O2 technology and its mineralization rate of pollutants. In this paper, the research of antibiotics removal in water by ZVI/H2O2 technology is statistically analyzed. The main strengthening measures of ZVI/H2O2 technology and their effects on the system are summarized. The degradation efficiency, mechanism, advantages and disadvantages of antibiotics in water by different strengthening measures combined with ZVI/H2O2 technology are described and analyzed. Finally, this paper looks forward to the future development of ZVI/H2O2 technology for the degradation of antibiotics in water, and puts forward relevant suggestions for further research work.

Contents

1 Introduction

2 Development status of ZVI/H2O2 technology for removing antibiotics in water at home and abroad

3 The main strengthening measures of ZVI/H2O2 technology and its effect on the system

3.1 Physical modification

3.2 Synthesis of n-ZVI

3.3 Biochar loading

3.4 External oxidant

3.5 Addition of non-oxidative promoter

3.6 Pickling

3.7 Metal doping

3.8 Other

3.9 combination

4 The degradation efficiency and mechanism of antibiotics in water by ZVI/H2O2 technology

5 Conclusion and outlook

Cite this article

Baizhou Lu , Zhanqiang Fang . Degradation of Antibiotics Using ZVI/H2O2 Fenton-Like Technology[J]. Progress in Chemistry, 2025 , 37(3) : 411 -424 . DOI: 10.7536/PC240509

1 Introduction

With the improvement of social and economic levels, antibiotics have been widely used worldwide1-4. Among them, the several classes of antibiotics with the largest usage can be divided into tetracyclines, sulfonamides, quinolones, macrolides, β-lactams, and lincosamides according to their chemical structures5-9. These antibiotics are widely used in antibacterial treatment for humans and animals10, 11. However, since most of the antibiotics used are difficult to be absorbed by human or animal bodies, a large portion of the antibiotics or their metabolites may be released into the environment12-14. Although the concentration of these pollutants in wastewater is extremely low (ng/L~mg/L), their mixtures are frequently detected in surface water, groundwater, and the effluents of sewage treatment plants with increasing levels, posing a threat to the ecological environment and human health15-23. Nevertheless, traditional sewage treatment plants only use physical and biological treatment methods24, which cannot completely remove residual antibiotics and their metabolites, potentially causing adverse effects on the surrounding ecological environment and residents22, 23. Therefore, there is an urgent need to study effective treatment methods that can remove antibiotics to prevent their discharge into aquatic environments and thus avoid ecological risks.
Advanced oxidation technologies are commonly used for the removal of organic pollutants in wastewater, among which the ZVI/H2O2 Fenton-like technology uses ZVI instead of ferrous salts as the donor of ferrous ions (Fe2+) in the Fenton reagent, which can effectively degrade organic pollutants in water and also better overcome the disadvantages of traditional homogeneous Fenton reactions such as high chemical consumption, large amounts of iron sludge production, and susceptibility to secondary pollution[25]. In recent years, many researchers have proposed the application of ZVI/H2O2 Fenton-like technology for the removal of antibiotics in wastewater. For example, Fornazari et al.[26] utilized the ZVI/H2O2 system to efficiently degrade Sulfamethazine (SMT) and Sulfathiazole while partially removing the antibacterial activity of sulfonamide antibiotics (E. coli). Chen Junyi et al.[27] used the ZVI/H2O2 Fenton-like system to effectively degrade Tetracycline (TC) and mineralize it to a certain extent. Furia et al.[28] found that the ZVI/H2O2 system could completely or almost completely degrade antibiotics such as cefazolin, vancomycin, and imipenem in wastewater within 1 hour, and the removal of magnetic ZVI after the reaction was much easier than the removal of iron sludge in traditional Fenton reactions. However, the ZVI/H2O2 Fenton-like technology itself still has problems such as dependency on an initially low pH value and the ease of passivation and deactivation of ZVI[29]. Therefore, researchers have proposed different enhancement measures to improve the removal efficiency of ZVI/H2O2 Fenton-like technology for pollutants in water. For instance, Wan Ling et al.[30] constructed a ZVI/H2O2/citrate system under energy-saving lamp irradiation, where the degradation rate of crystal violet reached over 90% under aerated conditions, compared to less than 50% degradation by the standalone ZVI/H2O2 system. Segura et al.[31], through short-term ultrasonic irradiation coupled with the ZVI/H2O2 system, significantly enhanced the degradation and mineralization of phenol by the ZVI/H2O2 system, achieving a phenol mineralization rate as high as 90% within 24 hours. Therefore, under the promotion of various enhancement measures, the ZVI/H2O2 Fenton-like technology is an effective method for removing organic pollutants from water.
Therefore, this paper statistically analyzes the research status of the application of ZVI/H2O2-based Fenton-like technology for removing antibiotics in water both domestically and internationally; summarizes the main enhancement measures of the current ZVI/H2O2-based Fenton-like technology and their impact on the system; expounds and analyzes the degradation efficiency, mechanisms, and pros and cons of different enhancement measures synergizing with ZVI/H2O2-based Fenton-like technology for degrading antibiotics in water. Finally, this paper provides an outlook on the future development of ZVI/H2O2-based Fenton-like technology for degrading antibiotics in water and proposes relevant suggestions for further research work.

2 Analysis of the Development Status of ZVI/H2O2-Based Fenton-Like Technology for Antibiotic Removal in Water at Home and Abroad

The Fenton method is a commonly used advanced oxidation technology that can effectively degrade organic pollutants32. The classical homogeneous Fenton reaction is composed of the Fe2+/H2O2 system, which can generate highly oxidative radicals (such as ·OH, ·O2-, etc.), thereby rapidly degrading organic pollutants in water and to some extent mineralizing the pollutants33, 34. However, the classical homogeneous Fenton reaction has significant drawbacks, such as large amounts of chemicals required, narrow pH operating range, insufficient mineralization of pollutants, high sludge production, and causing secondary pollution easily32, 35. Therefore, researchers have conducted extensive studies to find effective solutions to address the issues in the classical homogeneous Fenton reaction and have developed many Fenton-like technologies that can effectively overcome these shortcomings. As shown in Figure 1a, the number of domestic and international publications related to Fenton-like technologies has been increasing year by year over the past decade, rising from 274 papers in 2014 to 1,323 papers in 2023, showing a vigorous development trend, indicating great application potential for Fenton-like technologies. Additionally, the top 10 countries with the highest number of publications on Fenton-like technologies over the past decade are shown in Figure 1b, among which China’s publication volume is far ahead, with 7,556 relevant papers, accounting for the vast majority of the total publications, indicating that China's research investment and output in the field of Fenton-like technologies far exceed those of other countries and regions.
图1 Publication Status of Relevant Literature on Fenton-like Technologies: (a) Annual Publication Volume from 2014 to 2023; (b) Publication Volume of the Top 10 Countries with the Highest Publication Volume (Data Source: CNKI and Web of ScienceTM)

Fig. 1 Publication of relevant papers on Fenton-like technology (2014—2023).(a) Annual volume of papers issued; (b) highest number of papers issued by each country (data from China National Knowledge Infrastructure and Web of scienceTM

Based on the problems in traditional homogeneous Fenton reactions, the Fenton-like technologies developed by researchers mainly include electro-Fenton technology, photo-Fenton technology, sono-Fenton technology, Fe3+ Fenton-like technology, and zero-valent iron (ZVI) Fenton-like technology, etc.[31, 32, 36-39] (Figure 2). Among them, ZVI Fenton-like technology degrades organic pollutants in water by generating ·OH and other reactive oxygen species through the corrosion of ZVI by H2O2[39-45], meaning that the degree of ZVI corrosion is positively correlated with the pollutant degradation capability of the system. Additionally, ZVI has gained popularity among researchers due to its low cost and environmentally friendly characteristics[40, 41, 43, 44]. Using ZVI instead of ferrous salts as the catalyst in Fenton's reagent, ZVI not only provides Fe2+ to the system but also facilitates the reduction reaction of Fe3+ on its surface, thereby achieving the Fe3+/Fe2+ cycle and effectively degrading organic pollutants in water while reducing the generation of iron sludge after the reaction[28, 41, 43, 44, 46-48]. Therefore, using "Fenton and Zero Valent Iron or ZVI or Fe0 and H2O2 or Hydrogen peroxide" and "Fenton and zero-valent iron" as keywords for searches in Web of ScienceTM and CNKI, the results are shown in Figure 3. In the past decade, a total of 1037 papers related to ZVI Fenton-like technology have been published both domestically and internationally, accounting for approximately 12.68% of the total publications on Fenton-like technology, showing an overall gentle upward trend, indicating that ZVI Fenton-like technology is an effective and promising Fenton-like remediation technology. Furthermore, using "Fenton and Zero Valent Iron or ZVI or Fe0 and H2O2 or Hydrogen peroxide and Organic Pollutant" and "Fenton and zero-valent iron and organic pollutants" as keywords for searches in Web of ScienceTM and CNKI, the results show that in the past decade, a total of 330 papers related to the application of ZVI/H2O2 Fenton-like technology in removing organic pollutants have been published (Figure 3), accounting for approximately 31.82% of the total publications on ZVI Fenton-like technology, indicating that ZVI/H2O2 Fenton-like technology can effectively degrade organic pollutants in water. Moreover, according to the publication analysis of ZVI/H2O2 Fenton-like technology applied to antibiotic pollution, the number of publications on the application of ZVI/H2O2 Fenton-like technology to antibiotic pollution accounts for approximately 18.79% of the total publications on the removal of organic pollutants by ZVI Fenton-like technology, indicating that the removal of antibiotics is a key concern for researchers. Due to the lack of a comprehensive summary of studies on the degradation of antibiotics in water by ZVI/H2O2 Fenton-like technology, this paper summarizes the main enhancement measures of ZVI/H2O2 Fenton-like technology and their impact on the system, elaborates and analyzes the degradation efficiency, mechanisms, advantages, and disadvantages of different enhancement measures in synergy with ZVI/H2O2 Fenton-like technology on the degradation of antibiotics in water, aiming to provide relevant suggestions for further research work on the degradation of antibiotics in water by ZVI/H2O2 Fenton-like technology.
图2 Clustering Map of Fenton-like Technology Keywords (Data Source: Web of ScienceTM)

Fig. 2 Keywords clustering diagram of Fenton-like technology (data from Web of scienceTM).(data from China National Knowledge Infrastructure and Web of scienceTM

图3 Publication Status of Relevant Literature on Zero-Valent Iron Fenton Technology at Home and Abroad (Data Source: CNKI and Web of ScienceTM)

Fig. 3 Domestic and foreign published papers on ZVI Fenton-like technology

3 Main Enhancement Measures of ZVI/H2O2 Fenton-like Technology and Their Impact on the System

The ZVI/H2O2 Fenton-like technology overcomes some bottleneck issues of traditional Fenton technology and is an effective method for treating high-concentration refractory organic wastewater. However, the ZVI/H2O2 Fenton-like technology itself still has problems such as the easy passivation and deactivation of ZVI and its dependence on an initially low pH value[32, 35]. Therefore, to enhance the removal efficiency of pollutants in water and broaden the applicability of the ZVI/H2O2 Fenton-like technology, researchers have proposed various enhancement measures to address the aforementioned issues. Currently, the main enhancement strategies for improving the ZVI/H2O2 Fenton-like technology can be categorized by their nature into physical modifications and chemical modifications, where physical modifications mainly include ball milling, pre-magnetization, ultrasonic treatment, and UV irradiation, etc.; chemical modification measures mainly include synthesizing nano-scale zero-valent iron, biochar loading, adding external oxidants, adding non-oxidizing promoters, acid washing, and metal doping, etc. In addition, the synergistic effect of multiple enhancement methods is also an important measure to improve the ZVI/H2O2 Fenton-like technology.

3.1 Physics Assistance

Physical auxiliary methods such as ultrasound, ultraviolet (UV) irradiation, magnetization, and ball milling are commonly used to activate zero-valent iron (ZVI), thereby significantly enhancing the reactivity of the system and effectively degrading pollutants. For instance, Pan et al.[19] found that pre-magnetization could effectively promote the corrosion of zero-valent iron in the ZVI/H2O2 system by magnetizing zero-valent iron for 2 minutes under a static uniform magnetic field of 200 mT, thus improving its oxidative removal of antibiotics in water. Similarly, Du et al.[49] discovered that the ZVI/H2O2 system, activated by a weak magnetic field, could basically remove sulfamethoxazole (SMX) from water within 15 minutes.. Pan et al.[19] also enhanced the contaminant removal efficiency of the ZVI/H2O2 system by external UV irradiation. The results showed that within 60 minutes, the removal rate of SMT in water by the standalone ZVI/H2O2 system was less than 10%, whereas the removal rate of the UV/ZVI/H2O2 system significantly increased to 99.4%. Additionally, Ambika et al.[47] significantly improved the reactivity of ZVI by ball milling (10 hours) to strip the passivation film on the ZVI surface, thereby enhancing the ability of the ZVI/H2O2 system to simultaneously treat Cr(VI) and phenol in wastewater (Figure 4a). Segura et al.[31] utilized ultrasonic (5 minutes) assisted ZVI/H2O2 Fenton-like technology, which enhanced the reactivity of the ZVI/H2O2 system and greatly improved the mineralization rate of phenol in sewage. Chen et al.[37] adopted microwave (MW) synergistic ZVI/H2O2 Fenton-like technology to treat high-concentration landfill leachate. The results indicated that at 14 minutes, compared with the ZVI/H2O2 system, the COD removal rate of the MW-ZVI/H2O2 system significantly increased from 17.90% to 76.38% (Figure 4b). Although external auxiliary means can achieve effective removal and mineralization of pollutants, these methods often rely on excessively low initial pH and are costly, limiting the large-scale application of physically assisted ZVI/H2O2 Fenton-like technology.
图4 (a) Mechanism of Cr(VI) and Phenol Simultaneous Removal by Ball Milling mZVI/H2O2[47]; (b) Reaction Mechanism of MW-ZVI/H2O2 System for Treating High-Concentration Landfill Leachate[37]

Fig. 4 (a) Mechanism of simultaneous removal of Cr(VI) and phenol by ball milled mZVI/H2O2 47; (b) mechanism of MW-ZVI/H2O2 system treating high concentration landfill leachate37

3.2 Synthesis of Nano-scale Zero-valent Iron

In recent years, nanomaterials have become a research hotspot in the field of environmental remediation. Among them, nanoscale zero-valent iron possesses outstanding advantages such as high surface area, rapid kinetics, high reactivity, and small particle size, and is used to construct advanced oxidation systems to degrade pollutants in water50-53. For example, Zhang et al.54 successfully synthesized nanoscale zero-valent iron by the borohydride reduction method. The results showed that the degradation rate of Norfloxacin (NOR) by the nZVI/H2O2 system was over 95% within 40 minutes, with a mineralization rate of about 50%. Zha et al.55 used nanoscale zero-valent iron as a catalyst to enhance its reactivity with H2O2, thus oxidatively degrading 86.5% of Amoxicillin (AMX) in water and removing 71.2% of COD. Yi Yunqiang et al.56 found that under the same reaction conditions, compared with the traditional Fenton method, the degradation rate of Metronidazole (MNZ) and the removal rate of TOC in the nZVI/H2O2 system were 1.5 times and 7.1 times those of the Fe2+/H2O2 system, respectively. Additionally, Pirsaheb et al.57 successfully synthesized nanoscale zero-valent iron composites using Tragacanth gum extracted from Astragalus shrubs, effectively alleviating the bottleneck issue of nanoscale zero-valent iron being prone to agglomeration and deactivation. Within 60 minutes, the system's removal rate of AMX reached 90%. Similarly, Conde-Cid et al.58 successfully synthesized nanoscale zero-valent iron using black tea extract, significantly enhancing the reaction activity. The results showed that the nZVI/H2O2 system could remove more than 90% of Sulfadiazine (SDZ) within 1 hour. Machado et al.59 green-synthesized nanoscale zero-valent iron using oak leaf extract. The oak leaf extract enhanced the dispersion of zero-valent iron and the biodegradability of AMX, thereby enabling the nZVI/H2O2 system to completely remove AMX in the aqueous phase within 15 minutes (Figure 5a). Ouyang et al.60 successfully green-synthesized nanoscale iron-based composites using tea polyphenols, effectively improving the utilization of iron, thereby efficiently degrading Lincomycin in water and effectively reducing its ecological toxicity (Figure 5b). Although nanoscale zero-valent iron has excellent performance, its effectiveness is affected by some drawbacks. For instance, nZVI has high surface energy, making it highly prone to agglomeration, poor air stability, and easy to cause secondary pollution during preparation. Among these, using green extracts to synthesize nanoscale zero-valent iron can effectively overcome the problem of causing secondary pollution during preparation, showing great application prospects57-60.
图5 (a) Degradation Mechanism of AMX in nZVI/H2O2 System59; (b) Reaction Mechanism of nZVI/H2O2 Under Different pH Conditions60

Fig. 5 (a) Degradation mechanism of AMX in nZVI/H2O2 system59;(b) mechanism of nZVI/H2O2 system under different pH conditions60

3.3 Biochar Loading

Biochar (BC) has gained popularity in various fields due to its advantages such as low cost, high performance, and wide availability of production materials, showing a very promising development prospect61-64. To improve the stability and dispersion of zero-valent iron (ZVI), thereby enhancing the reaction efficiency of the ZVI/H2O2 Fenton-like system, researchers have proposed using biochar as a carrier for zero-valent iron. For instance, Mao et al.63 prepared biochar by pyrolyzing Miscanthus and fabricated biochar-supported nanoscale zero-valent iron (BC/nZVI) via a liquid-phase reduction precipitation method, effectively alleviating the severe agglomeration issue of nZVI particles, thus improving the degradation efficiency of the ZVI/H2O2 Fenton-like system for ciprofloxacin (CIP) in water, with a CIP removal rate above 70% (Figure 6a). Zhang et al.64 prepared biochar from bamboo wood chips and synthesized biochar-supported nanoscale zero-valent iron (nZVI-BC) using traditional liquid-phase reduction methods. The characterization results of nZVI-BC showed that BC can enhance the adsorption of ornidazole (ONZ) antibiotics and alleviate the agglomeration of nZVI. Compared to the 48.3% ONZ removal rate in the nZVI/H2O2 system, the reaction activity of nZVI-BC with H2O2 is higher, with the nZVI-BC/H2O2 system removing over 63% of ONZ within 12 minutes, and when the nZVI/BC mass ratio is 1:2, the highest ONZ removal rate reaches 80.1% (Figure 6b). Despite the good loading performance and low cost of biochar, it still faces issues such as slow adsorption rates, large usage amounts, and potential secondary pollution caused by migration with water flow. Based on the enhancement of ZVI/H2O2 Fenton-like technology through biochar modification, future research could further focus on improving the adsorption performance of biochar and overcoming its potential to cause secondary pollution.
图6 (a) Degradation Mechanism of CIP in the BC/nZVI /H2O2 System63; (b) Reaction Mechanism of ONZ Degradation by the nZVI-BC/H2O2 Process64

Fig. 6 (a) Degradation mechanism of CIP in BC/nZVI /H2O2 system63;(b) degradation mechanism of ONZ in nZVI-BC/H2O2 technology64

3.4 Exogenous Oxidants

Advanced oxidation technology is one of the effective treatment methods for removing antibiotic pollutants in water because it generates highly oxidative radicals such as hydroxyl radicals (·OH) and sulfate radicals (SO4-·), which further attack and degrade pollutants65, 66. Therefore, some researchers have improved the generation of highly oxidative radicals in the ZVI/H2O2 Fenton-like system by adding external oxidants, significantly enhancing the system's pollutant removal efficiency. For example, Wu et al.65 significantly reduced the pH value of the ZVI/H2O2 Fenton-like system and simultaneously acidified the pollutants by externally adding persulfate (PS). Within 30 minutes, the degradation rate of SMT (50 mg/L) reached up to 96%, and another eight typical PPCPs (i.e., bisphenol A, indomethacin, norfloxacin, tetracycline, paracetamol, carbamazepine, phenacetin, and sulfamethoxazole) in the same water sample were also efficiently degraded (degradation rates of 77%~100%). Similarly, Li et al.66 enhanced the corrosion rate of iron in the ZVI/H2O2 system and the decomposition rate of H2O2 by adding PS, significantly improving the removal efficiency of erythromycin (ERY) in wastewater. Within 90 minutes, the system completely degraded ERY (Figure 7). Although adding external oxidants can significantly enhance the pollutant removal efficiency of the ZVI/H2O2 Fenton-like system, it may cause secondary pollution from sulfate radicals, posing a threat to the ecological environment and human health.
图7 Degradation Mechanism of ERY in PS/ZVI/H2O2 System66

Fig. 7 Degradation mechanism of EPY in PS/ZVI/H2O2 system66

3.5 Addition of Non-Oxidizing Promoters

One effective method to address the bottleneck issues of the Fenton reaction is to regulate the Fe3+/Fe2+ cycle by altering the coordination environment of iron, thereby promoting the generation of strongly oxidative radicals such as ·OH[53, 67]. Currently, the most extensively studied approach is introducing complexing agents with multiple coordination sites to construct a complexing agent-Fenton-like system. Moreover, some complexing agents possess reducing capabilities themselves; introducing organic or inorganic reducing agents with reductive functions into Fenton or Fenton-like systems can promote the Fe3+/Fe2+ cycle and the generation of ·OH within the system, thus enhancing its pollution removal efficiency[68, 69]. For instance, Ouyang et al.[68] used tea polyphenols, which have both complexing and reducing abilities, as promoters to lower the pH of the reaction system and effectively promoted the Fe3+/Fe2+ cycle in the ZVI/H2O2 system, significantly improving the removal efficiency of lincomycin (Lincomycin, LCM). The pollutant could be degraded by more than 97% around 90 minutes, and compared with the ZVI/H2O2 system alone, its degradation rate constant increased about 26 times, while greatly reducing secondary pollution. Similarly, Ouyang et al.[70] found that using oxalic acid, hydroxylamine hydrochloride, and ascorbic acid as reductive promoters could also reduce the system pH, promote iron corrosion, and effectively enhance the degradation efficiency of the ZVI/H2O2 system for LCM, completely degrading the pollutant within 90 minutes. Hwang et al.[71] utilized ascorbic acid as a complexing agent to improve the reaction efficiency of the ZVI/H2O2 system, and results showed that the system could almost completely remove endosulfan from the aqueous phase within 24 hours. Additionally, the research group led by Fang Zhanqiang[69] enhanced the ZVI/H2O2 Fenton-like system by externally adding tea extract with antioxidant properties. Results indicated that extracts from different types of tea all promoted the removal of NOR by the ZVI/H2O2 Fenton-like system, among which green tea extract (Green tea extract, GT) had the best effect on promoting the ZVI/H2O2 Fenton-like system. GT could effectively promote the Fe3+/Fe2+ cycle, increasing the NOR removal rate from 56.69% to 97.68%, while the reaction rate was improved by 5.3 times. The research group also used guava leaf extract and eucalyptus leaf extract as green promoters for the ZVI/H2O2 Fenton-like system, which significantly improved the reaction efficiency and overcame the bottleneck problems of low reagent utilization and narrow applicable pH range in the ZVI/H2O2 Fenton-like system (Fig. 8a, b))[72, 73]. Cao et al.[74] employed Moringa seed extract as a bioflocculant, effectively dispersing zero-valent iron in the system and improving the mineralization rate of pollutants in leachate (72.6%), which is 1.21 times higher compared to the ZVI/H2O2 system without Moringa seed extract (Fig. 8c). Zou Yachen et al.[75] used gelatin extracted from animals as a coagulant aid, which could almost completely remove copper ions, nickel ions, and lead ions from wastewater within 60 minutes, and its sludge production was only 20% of the traditional Fenton system (Fig. 8d). Furthermore, Ling et al.[76] introduced chloride ions into water by adding sodium chloride, accelerating the corrosion of ZVI by H2O2 and the formation of ROS, thereby improving the degradation efficiency of organic pollutants. Oral et al.[77] used pyrite as a promoter, suppressing ZVI particle aggregation, significantly lowering solution pH, and enhancing iron dissolution, thereby markedly improving the removal of diclofenac by the ZVI/H2O2 system.
图8 (a) Reaction Mechanism of NOR Removal in Water by Guava Leaf Extract/ZVI/H2O2 System[70]; (b) Reaction Mechanism of NOR in Water by Eucalyptus Leaf Extract/ZVI/H2O2 System[71]; (c) Reaction Mechanism of Landfill Leachate Treatment by Moringa Seed Extract/ZVI/H2O2 System[74]; (d) Reaction Mechanism of Copper Ion Removal from Wastewater by Bone Glue/ZVI/H2O2 System[75]

Fig. 8 (a) Mechanism of guava leaf extract/ZVI/H2O2 system to remove NOR in water; (b) mechanism of eucalyptus leaf extract/ZVI/H2O2 system to remove NOR in water; (c) mechanism of landfill leachate treatment by Moringa oleifera seed extract/ZVI/H2O2 system; (d) mechanism of removing copper ions in wastewater by bone glue/ZVI/H2O2 system

In summary, chelating agents can form relatively stable complexes with Fe3+ or Fe2+, thereby maintaining the solubility of Fe3+ and Fe2+ and enhancing the Fenton-like reaction activity. Furthermore, when the chelating agent added to the ZVI/H2O2 Fenton-like system has reducing capability, an appropriate amount of reducing chelating agent can effectively promote iron cycling and thus improve the Fenton-like reaction efficiency. When the introduced promoter contains acidic groups and exhibits acidity, it often reduces the pH value of the system, promotes iron corrosion, and effectively enhances the decontamination efficiency of the system. Additionally, coagulant aids can also effectively disperse zero-valent iron in the system, increase iron utilization, and thus enhance reaction efficiency. It is worth noting that using reducing green promoters (such as plant extracts) to enhance ZVI/H2O2 Fenton-like technology, such as tea polyphenols and tea extract, can often alleviate the agglomeration of iron, reduce the pH of the system, effectively promote iron cycling, and greatly reduce secondary pollution, showing great application potential. However, the promoters used in current research often have the problems of high cost or difficult preparation; therefore, future research can focus on finding low-cost, environmentally friendly, and easily prepared green promoters.

3.6 Pickling

The surface of zero-valent iron (ZVI) is prone to passivation in the environment, which greatly increases the consumption of ZVI. Meanwhile, passivation significantly reduces the corrosion rate and reactivity of ZVI, making it difficult to continuously release Fe2+, reducing the removal efficiency of pollutants in the reaction system and leading to the formation of some iron sludge, thus limiting the large-scale application of ZVI/H2O2 Fenton-like technology [42,78-83]. Therefore, some researchers have adopted acid-washing modification of ZVI to remove the passivation layer on its surface, thereby improving its reactivity and pollution removal efficiency. Wang Qi et al. [84] applied acid-washing to remove the passivation film on the surface of ZVI powder, significantly enhancing the reactivity of ZVI. In the acid-washed ZVI/H2O2 system, aniline in water was completely degraded within 10 minutes, and the removal rates of chromium and antimony reached up to 99% at 90 minutes, achieving simultaneous removal of three pollutants in wastewater (Figure 9a). Liang et al. [35] found that acid-washed ZVI promoted the precipitation of Fe2+ and the generation of strong oxidizing radicals in the system, greatly improving the reactivity. Under the reaction condition of 40°C, the water content of the sludge treated by the acid-washed ZVI Fenton-like system decreased to 54.81 wt%, which was 18.47% less than that of the ZVI/H2O2 system, significantly improving the sludge dewatering performance (Figure 9b). Huang Ting et al. [48] showed that the rate of wastewater treatment by the acid-modified ZVI/H2O2 system was significantly improved, with a COD removal rate of 20% at 2 hours, effectively increasing the B/C ratio and improving the biodegradability of wastewater. Therefore, acid modification can significantly enhance the reactivity and pollution removal performance of ZVI, reduce the amount of H2O2 used, and decrease the production of iron sludge. However, there are non-negligible problems with the acid modification method, such as the consumption of large amounts of acid reagents, the loss of ZVI, and the secondary pollution easily caused by waste acid and iron salts after modification.
图9 (a) Schematic Diagram of the Mechanism for Simultaneous Removal of Aniline, Hexavalent Chromium, and Antimony by ZVI/H2O2 Process84; (b) Reaction Mechanism of Acid Washing-Zero Valent Iron Fenton-like System35

Fig. 9 (a) Mechanism of simultaneous removal of aniline, Cr(Ⅵ) and antimony by ZVI/H2O2 process84; (b) mechanism of pickling-ZVI Fenton-like system35

3.7 Metal Doping

By strengthening the ZVI/H2O2 Fenton-like technology through metal doping, electron transfer reactions between different metals can promote the precipitation of Fe2+, enhance the catalytic activity and utilization of zero-valent iron as well as the generation of ·OH, thereby improving the reaction efficiency of the Fenton-like technology[85]. Jiang et al.[86] significantly improved the reactivity of ZVI by loading Cu metal particles on micrometer-sized zero-valent iron particles, greatly enhancing the removal efficiency of TC contaminants in aqueous solutions by the Fenton-like system, with a TC removal rate as high as 98% within 3 minutes. Chen et al.[87] recovered manganese from the cathode materials of spent lithium-ion batteries for hydrothermal synthesis of MnO2/ZVI composites, which significantly enhanced the catalytic activity of zero-valent iron, with the degradation rate of SDZ in the system reaching about 98.6% at 60 minutes (Figure 10a). Xia et al.[88] prepared Fe-Cu bimetallic materials via a simple electrodeposition process as Fenton-like catalysts. The results showed that when Cu accounted for 25% of the material, the Cu heteroatoms enhanced the ability of adjacent Fe atoms to adsorb H2O2, thereby promoting the generation of more ·OH in the system, while independent Cu clusters also inhibited surface passivation of the catalyst, allowing the Fe-Cu/H2O2 system to remove over 99% of phenol within 30 minutes, and the catalyst could be reused sustainably up to 10 times (Figure 10b). Bao et al.[89] introduced the lanthanide metal cerium (Ce) into the iron-based material (Fe-MIL-101), and the introduction of Ce accelerated electron transfer in the system, significantly improving the catalytic performance of the iron-based material; the degradation efficiency of NOR (10 mg/L) increased from 50.1% to 94.8% within 60 minutes. Although metal doping can significantly enhance catalytic activity, issues such as difficult preparation and high cost limit its large-scale application. By simply introducing other metal ions or synergistically removing wastewater containing metal ions, these problems can be overcome to a certain extent. For example, Yang Bo et al.[90] promoted the corrosion of zero-valent iron and reduced sludge production by introducing copper ions into the ZVI/H2O2 system, and the synergistic effect of copper ions further promoted the generation of ·OH, significantly enhancing the reaction performance; the system could basically completely degrade methylene blue under near-neutral conditions.
图10 (a) Reaction Mechanism of Hydrothermal Conversion of Cathode Materials of Lithium-Ion Batteries into MnO2/ZVI Composites87; (b) Schematic Diagram of the Reaction Mechanism of Fe-Cu Bimetallic Materials88

Fig. 10 (a) Hydrothermal conversion of Li-ion battery cathode materials into MnO2/ZVI composites: mechanis87; (b) mechanism of Fe-Cu bimetallic material88

3.8 Others

In addition to the aforementioned enhancement methods, researchers have also strengthened ZVI/H2O2 Fenton-like technology by preparing metal-organic frameworks and synthesizing graphene composite iron-based materials. Xie et al.[91] successfully prepared zero-valent iron metal-organic frameworks (Metal-organic frameworks, MOFs) embedded in a carbon-based structure, and obtained derivatives (Fe-MOF-based iron/carbon hybrid material, FMC) through direct pyrolysis of MOFs. The carbon structure promotes electron transfer and reaction activity within the system, thereby efficiently degrading and mineralizing AMX in water, with removal and mineralization rates of 100% and 60.41%, respectively, after 1 hour (Figure 11a). Li Yuhui et al.[92] used waste activated carbon as the carbon source and prepared red mud-based zero-valent iron material (ZVI/RM) through a two-step method of reduction roasting-magnetic separation, improving the utilization rate of zero-valent iron. The system can completely degrade Rhodamine B and SDZ pollutants in water within 10 minutes. Additionally, Masud et al.[93] synthesized graphene nano iron-based material (rGO-nZVI) using reduced graphene oxide (Reduced graphene oxide, rGO), significantly enhancing the reaction activity of the system and the adsorption performance of the material, achieving almost complete removal of 12 different PPCPs mixed in water within 10 minutes (Figure 11b).
图11 (a) Schematic Diagram of the Synthesis and Reaction Mechanism of FMC91; (b) Schematic Diagram of the Reaction Mechanism of the rGO-nZVI/H2O2System93

Fig. 11 (a) The synthesis of FMC and its mechanism91; (b) Mechanism of rGO-nZVI/H2O2 system93

3.9 Synergistic Effects of Multiple Reinforcement Methods

Although individual modification techniques have shown good enhancement effects, they often present issues such as high energy consumption and cost. Therefore, researchers have proposed combining two or more modification techniques to overcome these problems. Pan et al[19] built upon pre-magnetized zero-valent iron (pre-Fe0) with additional UV irradiation. The results showed that pre-magnetized ZVI could achieve a faster corrosion rate under UV irradiation. Applying the UV/pre-Fe0/H2O2 process could completely remove antibiotics such as SMT, oxytetracycline (OTC), and TC within 30 minutes, while the mineralization rate of SMT was as high as 92.1% (Fig. 12a). Tian et al[94] enhanced the conventional ZVI-EF process by adding a certain amount of MoS2, applying ultrasonic treatment for 20 seconds to disperse it, and then introducing air to excite the reaction in direct current mode under constant current conditions. The results indicated that this process could completely degrade SMT within 10 minutes, whereas the degradation rate of the traditional ZVI-EF process was only 19.4% (Fig. 12b). Huang Danwei et al[95] prepared micron-scale sulfidated zero-valent iron (S-ZVI) through mechanical ball milling. SEM and XRD characterization results showed that FeS replaced the passivation film (iron oxide) on the surface of ZVI, accelerating electron transfer from ZVI to H2O2, thereby increasing the release rate of Fe2+. The constructed S-ZVI/H2O2 system could rapidly and thoroughly degrade all selected pollutants; tetracycline could be completely degraded in 20 seconds, and the apparent rate constant of phenol degradation was 51 times that of the ZVI/H2O2 system (Fig. 12c). Similarly, Feng et al[96] prepared sulfidated zero-valent iron (S-ZVI) through mechanical ball milling to enhance its reactivity and efficiently activate H2O2 to oxidize various organics over a wide pH range. Mondal et al[36] utilized UV irradiation in synergy with nZVI/H2O2 technology to remove CIP from water under near-neutral pH conditions. The results indicated that CIP could be completely removed within 25 minutes, with a relatively high mineralization rate (Fig. 12d). Conde-Cid et al[58] green-synthesized nano-zero-valent iron using black tea extract and further employed photocatalytic-assisted nZVI/H2O2 systems, which could completely remove SDZ from water within 5 minutes (Fig. 12e). Wan et al[97] synthesized Ce0/Fe0-reduced graphene oxide (Ce0/Fe0-RGO) nanocomposites using chemical reduction methods. RGO alleviated the agglomeration of Ce0 and Fe0, improving the catalyst's stability. The removal rate of SMT reached 99% at 30 minutes, with a mineralization rate as high as 73%.
图12 (a) Reaction Mechanism of UV/pre-Fe0/H2O2 Process for Antibiotic Degradation[19]; (b) Reaction Mechanism of MoS2-Enhanced ZVI-EF Process for SMT Degradation[94]; (c) Reaction Mechanism of S-ZVI/H2O2 Process for Pollutant Degradation[95]; (d) Reaction Mechanism of UV/nZVI/H2O2 for CIP Removal in Water[36]; (e) Reaction Mechanism of Photocatalytic-nZVI/H2O2 Process for SDZ Removal in Water[58]

Fig. 12 (a) Mechanism of antibiotics degradation by UV/pre-Fe0/H2O2 process19; (b) mechanism of MoS2 enhanced ZVI-EF process for SMT degradation94; (c) mechanism of pollutants degradation by S-ZVI/H2O2 process95; (d) mechanism of CIP removal in water by UV/nZVI/H2O2 36; (e) mechanism of SDZ removal in water by photocatalysis-nZVI/H2O2 process58

In summary, different enhancement measures can effectively improve the reaction efficiency of ZVI/H2O2 Fenton-like technology for degrading organic pollutants through various pathways. Therefore, the main effects of the aforementioned enhancement measures on improving ZVI/H2O2 Fenton-like technology were summarized, and the results are shown in Figure 13. By analyzing Figure 13, it can be seen that the effects of different enhancement measures all include increasing the reactivity of zero-valent iron, while the modification pathways of zero-valent iron by different enhancement measures vary. Physical enhancement measures such as ball milling, magnetization, and ultrasonication improve its reactivity by promoting the corrosion of zero-valent iron; nano-scale zero-valent iron has advantages such as high surface area and high reactivity due to its ultrafine particle size; biochar loading can reduce the agglomeration of zero-valent iron and also has an adsorption effect on pollutants; adding oxidants improves its reactivity by promoting the corrosion of zero-valent iron and lowering the system's pH value; adding non-oxidizing promoters, based on the effects of added oxidants, often can improve the stability and dispersion of zero-valent iron and effectively promote iron cycling; acid washing enhances the corrosion rate of zero-valent iron by stripping its passivation film; metal doping enhancement measures not only improve the corrosion efficiency of zero-valent iron and accelerate electron transfer but also have a synergistic catalytic effect on the system by the doped metal itself; the synergistic action of multiple enhancement measures can combine the advantages of each measure to efficiently enhance the system's reactivity, but its operation is often more complex. In addition, these enhancement measures also have non-negligible problems, such as ecological risks associated with the preparation process and existence of nano-scale zero-valent iron itself; enhancement measures like adding oxidants, acid washing, metal doping, and biochar loading may cause secondary pollution; physical auxiliary measures such as ball milling, UV irradiation, and magnetization are too costly. In contrast, using green extracts (plant extracts) with chelating and reducing capabilities as promoters to enhance ZVI/H2O2 Fenton-like technology can reduce the system's pH value to some extent, effectively improve the coordination environment of iron and promote iron cycling effectively, while greatly reducing the generation of secondary pollution, having the advantages of low cost, high efficiency, and environmental friendliness, and possessing great application potential.
图13 Main Effects of Different Reinforcement Measures on Improving ZVI/H2O2-Based Fenton-Like Technology

Fig. 13 The main role of different measures in improving ZVI/H2O2 Fenton-like technology

4 ZVI/H2O2 Fenton-Like Technology for Degradation Efficiency and Mechanism of Antibiotics in Water

In recent years, the ZVI/H2O2 Fenton-like technology has been widely used for the removal of antibiotics in water, but the research in this area has not been well summarized so far. Therefore, this paper summarizes the remediation efficiency and main mechanisms of the ZVI/H2O2 Fenton-like technology in degrading antibiotics in water, as shown in Table 1. According to Table 1, different enhancement measures have varying effects on the removal of the same antibiotic contaminant. For example, Pan et al.[19] used pre-magnetization to promote the corrosion of zero-valent iron in the ZVI/H2O2 system, resulting in an approximately 5% higher removal efficiency of the antibiotic SMT compared to the standalone ZVI/H2O2 system; the decontamination efficiency of the ZVI/H2O2 system was enhanced by about 90% through external UV irradiation; when both enhancement measures were applied synergistically, SMT could be completely removed, the reaction time was halved, and the mineralization rate of SMT reached 92.1%. This indicates that the antibiotic SMT is not easily oxidatively degraded by the standalone ZVI/H2O2 system, and auxiliary enhancement measures can effectively improve its removal efficiency. The enhancement effect of standalone UV irradiation is much better than that of standalone pre-magnetization, possibly because SMT can be directly photolyzed effectively, and the significant improvement in reaction efficiency when both are applied simultaneously is due to the synergistic effect between UV irradiation and pre-magnetization. Another example is Pirsaheb et al.[57] using Tragacanth gum for the green synthesis of nano zero-valent iron to construct a ZVI/H2O2 Fenton-like system, which achieved a 51% removal rate of CIP at 60 minutes, while Mao et al.[63] prepared a nanoscale zero-valent iron Fenton-like system loaded on Miscanthus biochar via liquid-phase reduction, capable of removing over 70% of CIP within 40 minutes, indicating that apart from Fenton-like oxidation and the complexation of nano zero-valent iron with CIP, biochar further enhances the system's decontamination efficiency by improving the dispersion of nano zero-valent iron and simultaneously adsorbing a certain amount of pollutants. Additionally, the same enhancement measure shows significantly different removal efficiencies for different antibiotic contaminants. Pirsaheb et al.[57] successfully synthesized nano zero-valent iron using Tragacanth gum, and at 60 minutes, the removal rates of AMX and CIP by the ZVI/H2O2 Fenton-like system were 90% and 51%, respectively, suggesting that AMX is more readily complexed by nano zero-valent iron or oxidized by Fenton-like reactions compared to CIP. Notably, the removal efficiency of the same enhancement measure for the same antibiotic contaminant also varies. Fang Zhanqiang’s research group[69] used six kinds of tea extracts as green promoters to enhance the ZVI/H2O2 Fenton-like system for the removal of NOR in water, and after 120 minutes, the degradation rate of NOR ranged from 98.84% to 63.94%, indicating that in addition to the enhancement method, the functional groups and properties of the promoter itself are key factors affecting the decontamination efficiency when enhancing the system with external promoters.
表1 不同强化措施去除水中抗生素的修复效能及其作用机理

Table 1 Remediation efficiency and mechanism of different strengthening measures to remove antibiotics in water

Strengthening measures Antibiotic Initial concentrationof antibiotics Catalyst dosage H2O2 dosage InitialpH Reactiontime Remediation efficiency Main mechanism Ref
Physical modification Place ZVI in 200 mT magnetic field for 2 min SMT 400 mg/L 0.3 mmol/L 0.3 mmol/L 7.3 60 min About 5% higher than ZVI/H2O2 system

Promote ZVI corrosion;

Promote ROS production;

Fenton-like oxidation

19
6 W UV SMT 400 mg/L 0.3 mmol/L 0.3 mmol/L 7.3 60 min 99.4%

Direct Photolysis;

Fenton-like oxidation

19
Weak magnetic field SMX 20 μmol/L 56 mg/L 0.1 mmol/L 3~4 15 min Almost completely removed

Promote ZVI corrosion;

Fenton-like oxidation

49
Synthesis of nZVI Borohydride reduction method NOR 100 mg/L 100 mg/L 20 mmol/L 3~4 40 min 95%

Adsorption;

Complexation;

Fenton-like oxidation

54
Borohydride reduction method AMX 50 mg/L 500 mg/L 6.6 mmol/L 3 21 min 86.5%

Adsorption;

Fenton-like oxidation

55
Liquid phase reduction method MNZ 80 mg/L 500 mg/L 3.24 mmol/L 3.02 5 min 100% Reduction followed by oxidation 56
Green Synthesis of Tragacanth gum AMX,CIP —— 765 mg/L 20 mmol/L 3.5 60 min

AMX 90%

CIP 51%

Complexation;

Fenton-like oxidation

57
Green Synthesis of Black tea extract SDZ 50 μM 1.92 mmol/L 1.92 mmol/L 4 60 min 90%

Adsorption;

Reduction;

Fenton-like oxidation

58
Green Synthesis of oak leaves extract AMX 10 mg/L 0.024 mmol/L 0.31 mmol/L 3 15 min 100%

Biodegradation;

Reduction;

Fenton-like oxidation

59
Green Synthesis of Tea polyphenols LCM 20 mg/L 100 mg/L 1 mmol/L 5.8 90 min 94%

Chelation;

Fenton-ike oxidation

60
Biochar loading Biochar was produced by the pyrolysis of miscanthus floridulus CIP 100 mg/L 400 mg/L 20 mmol/L 3~4 40 min 70%

Adsorption;

Fenton-like oxidation

63
Biochar was produced via pyrolysis of bamboo sawdust ONZ 100 mg/L 300 mg/L 12 mmol/L 3 12 min 80.10%

Adsorption;

Fenton-ike oxidation

64
External oxidant PS 9 different PPCPs 50 mg/L 8 mmol/L 2 mmol/L 7 30 min 77%~100%

Reduces pH and acidifies contaminants;

Fenton-like oxidation

65
PS ERY 1 mg/L 22.4 mg/L 0.09 mmol/L 6 90 min 100%

Promote ZVI corrosion;

Fenton-like oxidation

66
Addition of non-oxidative promoter Tea polyphenols LCM 20 mg/L 500 mg/L 1 mmol/L 5.8 90 min 97%

Chelation;

Tea polyphenols chelated first and then reduced iron ions;

Fenton-like oxidation

68

Oxalic acid;

Hydroxyla mine hydrochloride;

Ascorbic acid

LCM 20 mg/L 500 mg/L 1 mmol/L 5.8 90 min 100%

Introduction of acidic groups;

Promoters chelated first and then reduced iron ions;

Fenton-like oxidation

70
Green tea extract (GT), Black tea extract (BT), Yellow tea extract (YT), Dark tea extract (DT), White tea extract (WT), Oolong tea extract (OT) NOR 10 mg/L 500 mg/L 1 mmol/L 7 120 min

GT 98.84%,

BT 87.92%,

YT 80.11%,

DT 79.16%,

WT 68.03%,

OT 63.94%

Promote the iron cycle;

Fenton-like oxidation

69
Metal doping Microscale Fe/Cu bimetallic particles’ catalysis TC 50 mg/L 5000 mg/L 50 mmol/L 3 3 min 98%

Improve ZVI reactivity;

Fenton-like oxidation

86
Hydrothermal synthesis of MnO2/ZVI composites from Li-ion battery cathodes SDZ 20 mg/L 200 mg/L 6 mmol/L 3 60 min 98.60%

Improve ZVI reactivity;

Fenton-like oxidation

87
Novel Ce-mediated Fe-MIL-101 (Fe/Ce-MIL-101) NOR 10 mg/L 300 mg/L 20 mmol/L 7 180 min 100%

Improve ZVI reactivity;

Accelerate electron transfer;

Fenton-like oxidation

89
Others Metal-organic frameworks (MOFs) derived zero-valent iron embedded in the carbon matrix structure named FMC. AMX 20 mg/L 100 mg/L 5 mmol/L 4 60 min 100%

Accelerate electron transfer;

Fenton-like oxidation

91
Two-steps method including reducing roasting and magnetic separation was implemented by reutilizing red mud as iron sources and activate carbon as reducing agent. SDZ 20 mg/L 100 mg/L 1 mmol/L 3 10 min 100%

Adsorption;

Fenton-like oxidation

92
Reduce graphene oxide (rGO) to support nZVI to synthesize rGO-nZVI nanohybrid. 12 different PPCPs 0.2 mg/L 407 mg/L 10 mmol/L 3 10 min 95%~99%

Adsorption;

Fenton-like oxidation

93
Combination UV/pre-magnetized ZVI SMT, OTC, TC

SMT 400 mg/L,

OTC 800 mg/L,

TC 800 mg/L

0.3 mmol/L 0.3 mmol/L 7.3 30 min 100%

Promote ZVI corrosion;

Promote ROS;

Direct Photolysis;

Fenton-like oxidation

19
MoS2 as highly efficient co-catalyst enhancing the performance of ZVI based electro-Fenton process SMT 10 mg/L 224 mg/L —— 4 10 min 100%

MoS2 co-catalysis;

Promote the iron cycle;

Fenton--ike oxidation

94
Mechanochemically Sulfidated ZVI TC 0.2 mM 120 mg/L 2 mmol/L 3 20s 100%

Accelerated electron transfer and iron precipitation;

Fenton-like oxidation

98
UV/nZVI/H2O2 CIP 10 mg/L

5

mmol/L

1 mmol/L 6.5~7.5 25 min 100%

Improve ZVI reactivity;

Fenton-like oxidation

36
Green synthesis of nZVI from Black tea extracts with synergistic photocatalysis SDZ 50 μmol/L 1.92 mmol/L 1.92 mmol/L 4 5 min 100%

Direct Photolysis;

Adsorption;

Reduction;

Fenton-like oxidation

58
The nanocomposites Ce0/Fe0-reduced graphene oxide (Ce0/Fe0-RGO) SMT 20 mg/L 500 mg/L 8 mmol/L 7 30 min 99%

Adsorption;

Fenton-like oxidation

97
At present, the Fenton-like technology strongly relies on the initial low pH value, which limits the large-scale industrial application of this technology. Therefore, whether different enhancement measures can effectively broaden the working pH range of the ZVI/H2O2 Fenton-like system is a key indicator for evaluating its practical feasibility. As can be seen from Table 1, on the basis that antibiotics in water can be completely or almost completely removed by the enhanced system, additional UV irradiation, green synthesis of nano zero-valent iron with tea polyphenols, addition of PS, addition of tea polyphenols, oxalic acid, hydroxylamine hydrochloride, ascorbic acid, and tea extract, etc., can effectively broaden the working pH range of the ZVI/H2O2 Fenton-like system, overcoming the bottleneck problem of the system's reliance on the initially low pH. However, the costs of additional UV irradiation, tea polyphenols, and ascorbic acid are high, and the synthesis of nano zero-valent iron and the addition of PS can easily cause secondary pollution. Therefore, enhancing the ZVI/H2O2 Fenton-like system with additional tea extract can broaden the system’s working pH range, promote iron cycling, and thus enhance the efficiency of the Fenton-like reaction. It is a cost-effective and environmentally friendly means of effective decontamination.

5 Conclusions and Prospects

Antibiotics are widely used due to their broad antibacterial spectrum, strong bacteriostatic ability, and low cost. However, the frequent detection of antibiotics in the environment and their continuously increasing concentrations pose potential threats to ecosystems and human health. Advanced oxidation technologies are commonly employed for the removal of organic pollutants in wastewater. Among them, the ZVI/H2O2 Fenton-like technology, as an improved version, can better address issues associated with traditional homogeneous Fenton reactions, such as strong dependence on initial low pH, high reagent consumption, and large amounts of iron sludge. Nevertheless, current research on the degradation of antibiotics in water by ZVI/H2O2 Fenton-like technology has not been well summarized. Therefore, this paper statistically analyzes the research status of ZVI/H2O2 Fenton-like technology for removing antibiotics from water both domestically and internationally. The results indicate that Fenton-like technologies are generally showing vigorous development, with ZVI/H2O2 Fenton-like technology being the current research focus and possessing good application potential. The main enhancement measures of the current ZVI/H2O2 Fenton-like technology and their impact on the system were summarized, finding that these enhancement measures mainly improve the catalytic activity of zero-valent iron, thereby enhancing reaction efficiency. The degradation efficiency, mechanisms, advantages, and disadvantages of different enhancement measures synergizing with ZVI/H2O2 Fenton-like technology for degrading antibiotics in water were described and analyzed, revealing that the addition of green extracts (natural plants) is a cost-effective and environmentally friendly enhancement measure. Finally, to further improve the reaction efficiency, economic benefits, and reduce secondary pollution of ZVI/H2O2 Fenton-like technology in removing antibiotics from water, based on the existing problems, the following suggestions for its future development are proposed in this paper.
(1) The vast majority of antibiotics are attacked and degraded by ·OH during the reaction process, while the reaction of ZVI with H2O2 mainly produces highly oxidative active radicals ·OH. In future research, various improvement measures can be taken to promote the iron cycle in the system, thereby enhancing the system's reactivity to produce more ·OH for the degradation of pollutants, thus further improving the efficiency of the reaction in removing contaminants.
(2) Adding promoters in the ZVI/H2O2 Fenton-like system to enhance reaction efficiency has good application prospects. Future research can explore suitable green promoters (plant extracts with acidic groups, complexing ability, and reducing ability) to improve the ZVI/H2O2 Fenton-like technology, enabling it to reduce the system pH and effectively promote iron cycling while greatly reducing secondary pollution, thereby developing a Fenton-like technology with a wide pH working range, low cost, high efficiency, and environmental friendliness.
(3) Currently, some researchers have adopted different methods to further enhance the contaminant removal efficiency of zero-valent iron Fenton-like technology, but some methods are too costly, such as pre-magnetized zero-valent iron, external UV irradiation, and synthesis of nano-scale zero-valent iron. Considering the possibility of large-scale application of zero-valent iron Fenton-like technology, future research should further investigate the economic benefits and feasibility of improvement measures.
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