Construction Of Z-scheme Catalytic System And Its Application In Sonocatalytic Degradation Of Organic Contaminants

In recent years,sonocatalytic technology combined with ultrasound and semiconductor photocatalyst has been used in the treatment of organic pollutant wastewater due to its strong mineralization ability,clean and pollution-free advantages.Some semiconductor photocatalysts have been widely used in sonocatalytic degradation of organic pollutants due to their simple manufacture and high activity.Under ultraviolet irradiation,the semiconductor photocatalyst titanium dioxide?TiO₂?can produce free radicals with high catalytic activity and degrade various organic pollutants adhering to the photocatalyst surface.However,there are three major drawbacks for TiO₂.First,the absorption range of light is small.Second,photo-generated electrons and holes are easy to recombine.Third,TiO₂ can not simultaneously possess strong redox ability.These problems seriously limit the practical application of TiO₂.In order to solve these problems,researchers have carried out a lot of experiments.In 2013,the direct Z-scheme has been proposed by Yu et al.The direct Z-scheme can solve the three problems mentioned above to a certain extent,which attracted wide attention.In this study,different band-gap semiconductor photocatalysts were compounded to broaden the response range of light.In addition,by adding conductive channels to accelerate the electron transfer from one photocatalyst conduction band to the valence band of another photocatalyst,the electrons holes recombination of the photocatalyst itself can be effectively suppressed,while retaining the strong redox ability.In order to improve the degradation of organic pollutants,the Z-scheme catalytic system was improved to form a double Z-scheme sonocatalytic system.Meanwhile,the valence bands of the positive potential of two semiconductor photocatalysts were retained to form a larger oxidative degradation surface,thus improving the efficiency of sonocatalytic degradation of organic contaminants.In the first part,mMBIP-MWCNT-In₂O₃?mMBIP:BiPO₄ with monoclinic monazite structure and MWCNT:multiwalled carbon nanotube?composite was prepared by hydrothermal and calcination methods.The samples were characterized by XRD,SEM,DRS,EDX,FT-IR and XPS.The degradation activity of sonocatalysts was evaluated by degradation of norfloxacin under ultrasound irradiation.The sonocatalytic activity of mMBIP-MWCNT-In₂O₃ composite is evaluated through the degradation of norfloxacin in aqueous solution under ultrasonic irradiation.Meanwhile,the impacts of ultrasonic irradiation time,used times and scavengers on the sonocatalytic degradation efficiency are researched by using UV-vis spectroscopy.Subsequently,several scavengers are used to confirm the formation of the hydroxyl radical?·OH?and hole?h⁺?for elucidating the sonocatalytic degradation mechanism.In the second part,an ortho-symmetric double?OSD?Z-scheme SnO₂\CdSe/Bi₂O₃ sonocatalyst is skillfully designed and synthesized via ultrasonic-assisted isoelectric point method and then the sonocatalytic activity is studied under ultrasonic irradiation in the degradation of organic contaminants.The effects of ultrasonic irradiation time,sonocatalyst dosage,initial Rhodamine B concentration,organic dye kind and used times are investigated systemically.The formation of·OH and h⁺are confirmed by using tertiary butanol and oxalate,respectively.The Rhodamine B can completely be degraded under given experimental conditions such as 10 mg/L Rhodamine B solution,1.00 g/L OSD Z-scheme SnO₂\CdSe/Bi₂O₃ dosage and 150 min ultrasonic process.The formation of mainly intermediate products is studied by Liquid Chromatography-Mass Spectrometry.Moreover,the sonocatalytic reaction mechanism caused by OSD Z-scheme SnO₂\CdSe/Bi₂O₃ is presented.