Modifications Of Layered Bi₂WO₆ Catalyst And Its Visible-light Photocatalytic Performance For The Abatement Of Low-concentration Indoor Toluene

Recently,indoor air pollution has attracted increasing attention.Photocatalytic oxidation technology as a promising green process for indoor VOCs purification under mild reaction conditions has become a research hotspot.However,narrow visible light utilization range and high recombination ratio of photoexcited pairs have inhibited its practical application.In this dissertation,layered Bi2WO6 catalysts were modified by semiconductor coupling and defect engineering methods to enhance its visible-light utilization and photocatalytic performance towards toluene removal.Moreover,a series of characterization methods were employed to disclose the inherent structure-performance relationship.Futhermore,the effect of other indoor air pollutant(NO)on the photo-degradation process of toluene was analyzed via in situ DRIFT measurement.Firstly,layered MoSe2/Bi2WO6 composite photocatalyst was synthesized via a simple bath sonication method and the amount of MoSe2 was optimized as well.The study demonstrated that 1.5%-MOSe2/Bi2WO6 catalyst showed the highest activity with a degradation rate of nearly 80%during three-hour visible-light irradiation.Based on the characterization results,the p-n heterojunctions between MoSe2/Bi2WO6 composites with strong interlayer interactions could effectively broaden the visible light absorption range and increase the separation ratio of photo-generated electron and hole pairs.More oxidative radicals would be generated due to the rising of available photoinduced pairs,which was beneficial for the photocatalysis.What's more,the-OH and h+ were regarded as the major active species based on the results of radical-trapping experiments.Secondly,layered a-Fe2O3/Bi2WO6 heterojunctions with strong interlayer interaction were fabricated through a facile in situ growth method.Experimental results showed that the optimized 4%-a-Fe2O3/Bi2WO6 composite photocatalyst had better photocatalytic performance,whose k value(0.3469 h-1)was much higher than that of pure Bi2WO6(0.0749 h-1).The characterization results indicated that the introduction of a-Fe2O3 could greatly improve the utilization of visible light.In addition,it was further demonstrated that the recombination ratio of photoexcited electron-hole pairs was greatly reduced owing to the heterojunction effect between ?-Fe2O3 and Bi2WO6,which benefitted the photocatalytic process.Finally,Bi-deficient monolayered Bi2WO6 nanosheets were successfully synthesized through a facile hydrothermal method under acid conditions given the fact that surface defects in materials could provide extra active sites and tune the band structure of semiconductors as well.And then it was obtained the 1.0M-mBWO sample with the highest photocatalytic activity by adjusting the concentration of H2SO4.The photocatalytic oxidation efficiency of toluene for 1.0M-mBWO sample nearly reached 100%within three hours and its relative apparent rate constant was 32 times higher than that of pristine Bi2WO6 nanosheets.The characterization studies had showed that the formation of strong protonated hydroxyl group around Bi vacancies could lead to the transfer of photogenerated electrons to vacancies sites,thereby benefitting the separation of electron-hole pairs.Futhermore,the Bi defects were beneficial for the adsorption and activation of reactant molecules,thereby lowering the energy barrier of the reaction and promoting the photocatalytic process.Moreover,in situ DRIFT technology was used to analyze the effecting mechanism of toluene photo-degradation in the presence of NO.It was found that the presence of NO would somewhat inhibit the photocatalytic oxidation of toluene and some nitrogen-containing compounds could be generated.