Construction Of BIOCOOH-based Photocatalysts And Their Performances For Photocatalytic Degradation TC-HCl In Water

As new contaminants,antibiotics are ubiquitous in the whole ecological environment,and the superbugs and resistance genes caused by antibiotics may bring serious threats to the ecological environment and human being health.The low treatment efficiency and the risk of the diffusion of superbugs and resistance genes of traditional biological treatment methods limit it application in antibiotics pollution treatment.Similarly,physical treatment methods cannot destroy the molecule of antibiotic,it just removes antibiotic from solution to adsorbent or other materials.A t the same time,traditional chemical treatment methods have the disadvantages of high energy consumption and other potential risks.As a green chemical treatment technology,photocatalytic technology,based on semiconductor photocatalysts,has attracted much attention for its economical,efficient,and eco-friendly.Photocatalyst is the key of photocatalytic technology.Bismuth oxide formate（Bi OCOOH,BCH）is a layered bismuth-based photocatalyst with eco-friendly and harmless elements.However,the large bandgap（～3.4 e V）and low utilization rate of visible light of BCH severely limit its application in the field of photocatalysis.I n this paper,BCH was used as the base photocatalyst and a series of modification strategies such as non-metallic element semiconductor loading,metal deposition,heterostructure construction,combined with sodium percarbonate（SPC）were used to improve its photocatalytic efficiency.Tetracycline hydrochloride（TC-HCl）was used as the target contaminant.The removal efficiency,influence factors,reaction mechanism,and so on of TC-HCl removal via the obtained photocatalysts were detailedly investigated.The cytotoxicity of TC-HCl after photocatalytic degradation and the feasibility of photocatalytic technology in the treatment of TC-HCl wastewater were explored.This study provides a series of strategies for improving the photocatalytic activity of wide-bandgap semiconductors and an effective method for removing antibiotics in water.（1）A black phosphorus/red phosphorus（BP/RP）heterojunction was obtained by condensation reflux using commercial red phosphorus as raw material.And then hierarchical red phosphorus/black phosphorus/bismuth oxide formate（RP/BP/BCH）double heterostructures with abundant oxygen vacancies（OVs）was obtained by hydrothermal process and its photocatalytic activity was investigated by degradation of TC-HCl with different light sources and various natural water matrices.Compared with BCH,the photocatalytic activity of RP/BP/BCH obviously enhanced.Under simulated solar light irradiation,a 60.5%of TC-HCl was removed by3%RP/BP/BCH.And the rate constant of 3%RP/BP/BCH was 2.95 times than that of BCH.Traces of small molecular organics were beneficial to improving photocatalytic efficiency.The process of photocatalytic degradation and the cytotoxicity of intermedia products of TC-HCl were discussed via High Performance Liquid Chromatography-Mass Spectrometer（HPLC-MS）,three-dimensional fluorescence spectroscopy（3D-EEMs）,and antibacterial properties test.Based on the results of trapping experiments and electron spin resonance（ESR）tests,superoxide radical（·O₂^-）was the most significant reactive oxygen species.The enhanced photocatalytic activity was ascribed to two reasons:1)double heterojunctions structure enhanced the separation efficiency of carriers,2)the introduction of OVs and BP/RP expanded the response range of light.This work provides a feasible strategy that non-metallic element semiconductor is used to modify the wide band gap semiconductor to enhance the phot ocatalytic efficiency.（2）In view of the drawbacks of low photocatalytic efficiency and the effusion of P element for RP/BP/BCH.Herein,a visible light responsive self-assembled micro-flowers of ultrathin bismuth oxide formate nanosheets supported by inert gold nanoparticles composite photocatalyst（Au/Bi OCOOH,Au/BCH）via hydrothermal method was prepared.Compared with bare BCH,the photocatalytic activity of Au/BCH significantly improved.2.0%Au/BCH possessed the highest rate constant of 0.0054 min^-1for degradation of TC-HCl,which was nearly 13.5 times higher than that of bare BCH.The intermedia products were analyzed by 3D EEMs and HPLC-MS,and the antibacterial ability of intermediate products with 2.0%Au/B CH significantly descended by the E.coli toxicity test.In order to explore the potential of practical applications,photocatalytic experiments were also implemented through different water sources matrices and solar light irradiation.The excellent photocatalytic activity owned to the enhanced separation of charge carriers and light absorption ability by the surface plasmon resonance（SPR）effect of Au nanoparticles.（3）For the disadvantage of expensive of Au in Au/BCH,in this study,a Zn Fe₂O₄/Bi OCOOH（ZFO/BCH）heterojunction photocatalyst was prepared by a two-step hydrothermal method using an economical narrow-band semiconductor zinc ferrite as the modifier.It was found that the photocatalytic activity of ZFO/BCH greatly improved.After 120 min of photocatalytic reaction,the removal rates of TC-HCl and ciprofloxacin（CIP）by ZFO/BCH（1:1）were 92.81%and 59.05%,respectively.The study found that common anions(Cl^-,NO₃^-,SO₄^2-,and CO₃^2-)and humic acid（FA）had side effect on the removal of TC-HCl,and FA had the most inhibitory effect.It was found that h⁺,·OH,and·O₂^-all participated in the degradation process of TC-HCl.The degradation intermediates of TC-HCl and CIP were analyzed by 3D-EEMs and HPLC-MS,and the possible degradation pathways were proposed.By the E.coli toxicity test,the toxicity of TC-HCl and CIP was greatly reduced after photocatalytic degradation.The prepared photocatalyst had good stability.After 1000 h of photocatalytic reaction,the removal rate of TC-HCl by ZFO/BCH（1:1）still reached 88.35%.Finally,the practical application performance of the prepared photocatalysts was also investigated.（4）In view of the potential risk of effusion of metal ion from ZFO/BCH,in this study,bismuth oxide iodate（Bi OIO₃,BIO）-modified BCH composite photocatalysts Bi OIO₃/Bi OCOOH（BIO/BCH）were prepared by a two-step hydrothermal method.In order to further improve the utilization of visible light,graphene oxide（GO）was supported by mechanical stirring and the graphene oxide-BIO/BCH（GO-BIO/BCH）composite photocatalyst was prepared.It was found that 10%GO-BIO/BCH（1:1）had the highest photocatalytic activity,and the removal rate of TC-HCl reached 92.21%after120 min irradiation of visible light.The removal efficiency of TC-HCl was greatly improved by photocatalysis combined with SPC,and the removal rate of TC-HCl reached 99.14%within 60 min.It was found that common anions and dissolved organic matter in water could reduce the removal rate of TC-HCl,but they had little effect on the final removal rate of TC-HCl.Via the free radical trapping experiments and ESR tests,it was found that·O₂^-and·CO₃^-were the main active oxygen radicals in the degradation process of TC-HCl,and·OH was the minor active oxygen radicals.In addition,the intermediate products in the degradation process of TC-HCl were analyzed,and it was found that the cytotoxicity of the treated TC-HCl solution greatly reduced.Finally,the practical performance of the prepared photocatalyst was investigated by different light sources and different water sources matrices.In order to facilitate the recovery and reuse of the obtained photocatalyst,a gelatin aerogel-supported catalysts was obtained and continuous flow experiments were carried out,and the prepared photocatalysts had good stability.