Construction Of Heterojunction Photocatalysts And Study On Their Degradation Of Norfloxacin

Fluoroquinolones（FQs）is a typical pollutant of pharmaceutical and personal care products.The residual FQs in aqueous environment would damage ecological environment and human health.Among all techniques,Photocatalytic driven by solar energy is considered to be one of the promising technologies to control FQs.At present,photocatalysis has some problems such as poor photoabsorption capacity and low efficiency of photogenerated electron-hole separation,limiting its application.In order to solve this scientific problems,heterojunction photocatalysts could improve photoabsorption and the efficiency of charge carriers separation.Based on this,controlling the surface-interface of one-dimensional（1 D）TiO₂ nanotube arrays（TiO₂ NTs）and two-dimensional（2 D）SnS₂ nanosheets:improving their contact rate,increasing the heterojunction interface contact area and the built-in electric fields,enhance the capacity of light absorption and promote charge carriers phase separation,migration and transfer.Norfloxacin was used as pollutant for photocatalytic degradation,SPV,TRPL,EPR and DFT techniques were conducted to investigate the charges carriers separating and transferring at surface-interface,the degradation paths and mechanism were also elucidated.The research results are as follows:（1）1D SnS₂/TiO₂ NTs photoelectrodes were synthesized by electrodeposition,and the effect of different deposition times on their properties were investigated.The photo electrode deposited for 5 min had highest photoelectochemical properties.The photo-response range of the photoelectrode is widened from 380 nm to 490 nm.The photocurrent density can reach up to 1.49 mA/cm²,which is 1.7 times of TiO₂ NTs.Under light irradiation,NOR degradation rate increased to 1.42 X 10^-2 min^-1,2.6 times higher than TiO₂ NTs.At the same time,LC-Ms technology was used to analyze the degradation path of NOR,which was mainly divided into three processes:defluorination,piperazine ring decomposition and decarboxylation.The radicals capturing experiments showed that,·O2^-,·OH and h⁺ were active radicals involved in NOR photoelectrocatalytic degradation.（2）1 D AgInS₂/TiO₂ nanotube array electrode was synthesized by ultrasonic assisted SILAR method,which increased their contact probability.Its photo-response range was widened to 665 nm after 10 cycles dipping.Photoelectron-conversion efficiency of AgInS₂/TiO₂ NTs was 3.61%,and its TPV response of 4.2 mV was about 8 times that of TiO₂ NTs.The interface separation of photogenerated electrons-holes and photoelectrocatalytic performance were improved effectively.The reaction rate was increased to 1.56×10^-2 min^-1,3.2 times higher than TiO₂ NTs,and higher than the synthetic AgInS₂/TiO₂ film photoelectrode 9.7×10-3 min^-1,the mineralization rate of NOR was increased from 18%to 38%.ESR and in-situ radicals capturing experiments showed that ·O2^-was the main active oxygen species,and ·OH and h+ were also involved in NOR degradation.（3）The separation,migration and transmission of charge carriers at the surface-interface were effectively promoted by increasing the contact area of the heterojunction interface.2D double heterojunction photocatalysts SnS₂/RGO/Ag with schottky and homologous schottky junctions were prepared by hydrothermal and UV reduction methods,and the lifetime of charge carriers was extended to 3.3 ns.SPVof SnS₂/RGO/Ag nanocomposites was value of 48μV,about 4 times than that of SnS₂.With RGO and Ag with certain amount,photocurrent density also increased from 25 μA/cm2 to 52 μA/cm²,and EIS arc decreased,indicating high photoelectrochemical properties and catalytic activity.After 150 min,the NOR photocatalytic degradation rate by SnS₂/RGO/Ag photocatalysts was as high as 2.0 X 1 0-2 min-1,1.8 times than that of SnS₂/RGO photocatalysts.The SnS₂/RGO/Ag photoelectrode showed degradation efficiency of 90%for NOR within 120 min.DFT calculation showed that RGO and Ag,as oxidative sites and reduction sites respectively,were involved in the production of reactive oxygen species.Radicals capturing experiment showed that ·O₂^-and ·OH were the main active oxygen species for NOR degradation.（4）In order to further optimize charges separation and transportion,2D double heterojunction photocatalysts AgInS₂/SnS₂/RGO were constructed with Type Ⅱ and homologous schottky junctions by two step hydrothermal methods,which increased charge carriers and promoted the separation,transportation of charge carriers at the bulk and surface/interface by increasing build-in fields effectively.The charges lifetime was prolonged to 6.89 ns,The SPV response of nanocomposites can be increased to 260 μV,21 and 12 times higher than that of SnS₂ and AgInS₂/SnS₂,and the photocurrent density is 72 μA/cm^-2,about three times than that of SnS₂,which indicates that the photoinduced charge carriers have higher spatial separation efficiency.After 90 min irradiation,the photocatalytic degradation rate was 3.3×10-2 min^-1,which was 5 times than that of SnS₂.The degradation efficiency of NOR by AgInS₂/SnS₂/RGO photoelectrode was 93%and TOC removal rate was increased from 16.3%to 49.5%.DFT results showed that RGO and AgInS₂ were the reduction sites and oxidizing sites in the reaction,respectively.It was found that ·O₂^-was the main active radicals,holes and ·OH all involved in NOR degradation.