Green Synthesis Of Iron Nanocomposites And Their Adsorption And Fenton-like Oxidation Mechanism For Antibiotics In Water

With the increasing detection frequency and concentration of antibiotics in various environments,the harm they bring to the ecosystem and human health has become increasingly prominent,which has aroused the academic community’s general attention.Adsorption and advanced oxidation process and their combination are the core directions for the removal of antibiotic residues in wastewater.As a result,various adsorbents and catalysts have been developed.However,the development of sustainable functional nanomaterials remains one of the most challenging scientific problems in environmental pollution control.Therefore,this paper focuses on the synthesis and application of green multifunctional nanomaterials with both adsorption and catalytic properties.The main research contents and results are as follows:（1）Given the combined pollution of oxytetracycline（OTC）and Cu（II）in aquaculture wastewater,iron-manganese nanocomposites（Fe/MnNPs）with high removal activity for OTC and Cu（II）were developed and synthesized,and the removal efficiency of OTC and Cu（II）in swine wastewater was 99.9%and 55.6%,respectively.Scanning electron microscopy（SEM）and nitrogen adsorption-desorption isotherm showed that Fe/MnNPs were elliptic particles of 20-40 nm with mesoporous properties,a specific surface area of59.5 m²/g,total pore volume of 0.386 cm³/g and average pore diameter of 5.27 nm.Fourier infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）showed that there were hydroxyl,carboxyl and amino functional groups on the surface.Zeta potential indicates that Fe/MnNPs maintain a high negative charge density between p H 1-11.These surface properties enable Fe/MnNPs to remove OTC and Cu（II）by pore filling,hydrogen bonding and electrostatic attraction,and the adsorption process follows the pseudo-second-order kinetic model and Langmuir isothermal model.In addition,the complexation reaction and adsorption bridging between OTC and Cu（II）improved the removal efficiency,and their adsorption capacities are up to 164.0 mg/g and 33.9 mg/g,respectively.（2）In view of the high adsorption performance and potential catalytic properties of Fe/MnNPs,Fe/MnNPs were combined with sodium persulfate（PDS）to construct a pre-adsorption/Fenton-like oxidation system for efficient removal of OTC and Levofloxacin（LEV）.The results showed that the adsorption capacities of Fe/MnNPs reached 58.8 and192.3 mg/g for OTC and LEV,respectively,and the materials also exhibited good catalytic activity,resulting in the oxidative degradation efficiency of the Fe/MnNPs/PDS system for both OTC and LEV exceeding 99.9%,while PDS alone could only remove 26.6%of OTC and 29.0%of LEV.In addition,it was found that Fe/MnNPs can not only act as catalysts to trigger electron transfer activation of PDS to generate different reactive oxygen species such as·OH,·O₂^-和¹O₂（free radical mechanism）,but also act as electron transfer mediators to mediate the shuttle of electrons from pollutants to PDS for oxidative degradation of pollutants（non-free radical mechanism）.The study then combined the identification of OTC and LEV degradation products to propose the degradation pathways and removal mechanisms of OTC and LEV.Finally,the results show that the oxidation system has a good potential for application with the removal efficiency of 94.3%and 85.4%for OTC and LEV in municipal wastewater,which only decreased by 5.6%and 14.5%,respectively.（3）In view of the high degree of agglomeration of Fe/MnNPs which is not favorable for the acquisition of active sites,graphene was used as a carrier for the modification of the material.Subsequently,green tea extract was used as a reducing agent to green synthesize reduced graphene oxide/iron nanoparticles（rGO/FeNPs）,focusing on the effect of synthesis conditions on the removal activity of rGO/FeNPs and the synthesis mechanism of the material.Response surface analysis indicated that the concentration of green tea extract is a most important parameter for the synthesis and activity of rGO/FeNPs.Raman,XRD and XPS results indicated that the abundance of oxygen-containing functional groups on the GO surface was reduced to form rGO in the presence of green tea extract,and the reduction and chelation of tea polyphenols converted Fe³⁺mainly to amorphous iron（and ferrous）polyphenol complex nanoparticles.In addition,AFM,FTIR and TG results showed the existence of organic coating on rGO/FeNPs,and these results indicated that green tea extracts acted as reducing and capping agents during the synthesis process.Finally,more than 50 chemical components were identified in green tea extract using GC-MS and LC-MS,among which catechins were the main reducing agents for the synthesis of rGO/FeNPs,while amino acids,phenolic acids,organic acids,carbohydrates and alkaloids were mainly used as capping agents to make the materials stable and biocompatible.（4）Highly active rGO/FeNPs have been synthesized,and this section focuses on the adsorption performance of rGO/FeNPs on mitoxantrone（MTX）and the adsorption mechanism.The results showed that the synergistic effect of rGO and FeNPs improved the agglomeration of nanoparticles and increased the specific surface area of the composites,resulting in a higher adsorption efficiency of the composite rGO/FeNPs on MTX（99.9%）than rGO（77.5%）and FeNPs（53.1%）,with an adsorption capacity of 95.2 mg/g.The nitrogen adsorption-desorption isotherm showed that the surface area of rGO/FeNPs was63.1 m²/g,the pore volume was 0.376 cm³/g,and the average pore size was 23.8 nm.FTIR analysis showed that functional groups such as hydroxyl and carboxyl groups on the surface.The Zeta potential showed that the surface charge of rGO/FeNPs decreases from-1.8 to-39.9 m V as p H increases from 2.5 to 11.These unique surface properties enable rGO/FeNPs to achieve efficient adsorption of MTX throughπ-πstacking effect,pore filling,hydrogen bonding and electrostatic attraction.The dominant mechanism isπ-πstacking between rGO-richπ-electrons and MTX.The adsorption process follows the pseudo-second-order kinetic model and Langmuir isotherm model.Finally,the results show that rGO/FeNPs has a good potential for application with the removal efficiency of 99%for MTX in wastewater.（5）In view of the high adsorption of rGO/FeNPs on MTX and its potential catalytic performance,rGO/FeNPs were combined with H₂O₂ to construct a pre-sorption/Fenton-like oxidation system.The results showed that the material exhibited excellent catalytic activity,and the removal efficiency of rGO/FeNPs/H₂O₂ oxidation system for MTX could reach 99.9%,which was about 9 times higher than that of H₂O₂ alone.The EPR indicated that rGO/FeNPs can activate H₂O₂ to produce·OH,·O₂^-and ¹O₂.In addition to the heterogeneous catalytic reactions,the increased concentration of Fe³⁺/Fe²⁺and hydroxyl products indicates the participation of homogeneous Fenton reaction induced by leached iron ions.Electrochemical measurements showed that rGO/FeNPs could not only activate H₂O₂ by triggering electron transfer,but also act as an electron transfer mediator to mediate the shuttle of electrons from MTX to H₂O₂,leading to the oxidative degradation of MTX.LC-MS and ECOSAR results showed that the degradation process of MTX involved the destruction or hydroxylation of anthraquinone,which resulted in a comprehensive reduction of acute and chronic toxicity.Finally,the results showed that the oxidation system has a good application potential with an efficiency of 93.6%for the removal of MTX from municipal wastewater.