The Preparation And Evaluation Of MoO₃ Composites With Enhanced Photocatalytic Degradation Efficiency For Typical Organic Pollutants

As an emerging environmental treatment technology,photocatalytic technology had attracted more attention in treating organic pollutants due to its simple equipment,low cost,and no secondary pollution.Obtaining efficient,safe and stable catalysts was a key issue in the application of photocatalytic technology.MoO3 had a narrow band gap(2.85-3.2 eV)with high visible light absorption efficiency.As a highly active photocatalyst,it had a very broad application prospect in photocatalytic degrading emerging pollutants.However,the low quantum yield of MoO3 still limit its efficiency,and the MoO3 are was often combined with other compounds to obtain higher catalytic activity.Construction of heterojunction structure was a commonly used method to reduce the recombination of photogenerated electron-hole pairs.Moreover,the heterojunction structure could reduce the band gap to improve the visible light adsorption.The photo-generated electron-hole separation mechanism of the p-n heterojunction formed between ?-MoO3 and TiO2 nanotubes was studied,and the Z-scheme heterostructure formed between h-MoO3 and AgBr nanoparticles was investigated.By using pyrene and trimethoprim as typical organic pollutants,the catalytic performance of ?-MoO3/TiO2 nanotubes and AgBr/h-MoO3 composites were thoroughly investigated under sunlight and visible light,and the mechanism for the promoted catalytic performance of the matherials and the degradion processes of the contaminants were revealed.The main researches and conclusions are as follows:1)A highly solar active ?-MoO3/TiO2 nanotubes catalyst was prepared by calcining the solid-state decomposition derived ?-MoO3 and hydrothermal synthesized TiO2 nanotubes.Using pyrene as a model PAH,the photocatalytic activity of ?-MoO3/TiO2 nanotubes was evaluated under solar light irradiation,and the mechanism of improved photocatalytic activity was investigated by experiments and material characterizations.The results showed that the p-n heterojunction formed between(3-MoO3 and TiO2,which reduced the band gap energy of TiO2,and the photocatalytic activity of the composite was improved via obtaining higher visible light utilization efficiency and promoting the separation of electrons and holes.The degradation rate(k)of pyrene by 1%?-MoO3/TiO2 nanotubes is 5.3 times and 1.5 times of ?-MoO3 and TiO2(anatase),respectively.Moreover,the ·OH and holes were found to play major roles in the photodegradation of pyrene.According to LC-MS analysis,six intermediates of pyrene catalytic degradation were identified to infer the possible photodegradation pathway of pyrene.2)Trimethoprim was selected as a model organic pollutant to explore the mechanism of photocatalytic activity of AgBr/h-MoO3 composite under sunlight.The h-MoO3 was successfully prepared by hydrothermal method,then the AgBr was loaded on the surface of h-MoO3 by simple precipitation method.The Z-scheme heterostructure of AgBr/h-MoO3 composite offters the material with highly solar and visible light active.The catalytic degradation rate of trimethoprim was up to 97%by 1:2AgBr/h-MoO3 under simulated sunlight for 20 minutes,and only 30 minutes were required to reach complete degradation.In addition,1:2AgBr/h-MoO3 also showed excellent visible light catalytic activity.The degradation rate of trimethoprim was as high as 95%by 1:2AgBr/h-MoO3 under visible light irradiation for 30 min.Rradical quenching experiments further showed that O2 was the main active species in the photocatalytic degradation of trimethoprim,followed by 1O2,h+,and e-.The role of ·OH was almost negligible.Six intermediates of trimethoprim photodegradation were identified by LC-MS.According to the three transformation pathways of trimethoprim:hydroxylation,demethylation,and cleavage,the pathways of trimethoprim degradation were deduced.In terms of mechanism,the Z-scheme heterojunction formed between AgBr and h-MoO3 could effectively promote the charge transfer of photo-generated carriers and reduce the recombination rate of photo-generated carriers.This made it have excellent catalytic activity under sunlight and visible light.