Preparation Of Several Z-scheme Photocatalyst And Investigation On The Degradation Of Organic Pollutants And Simultaneous Hydrogen Production Under Solar Light

With the rapid development of industry and the massive exploitation and use of fossil fuels,environmental pollution and energy shortage are becoming increasingly serious.How to avoid environmental pollution and search for green and sustainable new energy sources are becoming an urgent problem for researchers.In recent years,with the continuous development of photocatalytic technology,all kinds of high-efficiency semiconductor photocatalysts have been widely used in research on the photocatalytic degradation of organic pollutants and water splitting for hydrogen production.By combining solar energy with photocatalysts,the organic pollutant in the wastewater can be degraded and the water can be split to produce hydrogen.In the process of achieving the above goals,it is necessary to select the suitable photocatalyst.However,most high-efficiency semiconductor photocatalysts have the wide band-gaps.These photocatalysts can only be activated by absorbing the high-energy ultraviolet light,which only accounts for about 5%in the sunlight spectrum.Therefore,onefold wide band-gap semiconductor photocatalyst has a low utilization rate of solar energy,which results in a very low quantum efficiency in the photocatalytic reactions.In addition,the photo-generated electron-hole pairs of onefold semiconductor photocatalyst are easy to recombine,which results in a low photocatalytic activity in the photocatalytic degradation of organic pollutants simultaneous hydrogen production.In this study,Z-scheme photocatalytic system is constructed by combining a wide band-gap semiconductor and a narrow band-gap semiconductor,which can not only broaden the photoresponse range of the Z-scheme photocatalytic system,but also make it have a more negative conduction band(CB)potential and a more positive valence band(VB)potential and obtain the strong redox ability.Moreover,in order to further enhance the activity of Z-scheme photocatalytic system for the degradation of organic pollutants and simultaneous hydrogen production,Z-scheme photocatalytic system is improved by the following methods.(1)The metal nanoparticles acted as conductive channel are introduced into the Z-scheme photocatalytic system,which can quickly transfer the photo-generated electrons(e-)on the CB of one semiconductor photocatalyst to the VB of another semiconductor photocatalyst and recombine with its photo-generated holes(h+)on the VB.It effectively inhibits the recombination of photo-generated electron-hole pairs in the Z-scheme photocatalytic system,and makes the Z-scheme photocatalytic system show a high photocatalytic activity.(2)The metal nanoparticles used as co-catalyst are introduced into the Z-scheme photocatalytic system,which can increase the active sites of hydrogen production and significantly enhance the efficiency of hydrogen production.(3)The semiconductor photocatalyst with specific crystal planes is selected to construct the Z-scheme photocatalytic system.The photo-generated e-and photo-generated h+of Z-scheme photocatalytic system can be concentrated on different crystal planes of the semiconductor photocatalyst,respectively,which can realize the effective separation of the photo-generated electron-hole pairs in the Z-scheme photocatalytic system.(4)The up-conversion luminescent material is introduced into the Z-scheme photocatalyst system.The up-conversion luminescent material can absorb infrared light(IR)from sunlight and emit ultraviolet light(UV)and visible light(VS).These ultraviolet light and visible light can further intensify the activations of wide band-gap semiconductor and metal nanoparticles,respectively,which can effectively improve the utilization rate of solar energy for the Z-scheme photocatalyst system.The experimental results show that the improved Z-scheme photocatalytic system has higher photocatalytic activity than the unimproved Z-scheme photocatalytic system.In the second chapter,NaNbO3 and Sn3O4 photocatalysts were synthesized by hydrothermal method and solvothermal method,respectively.Z-scheme NaNbO3-Au-Sn3O4 photocatalyst was prepared by ultrasonic dispersion and calcination methods.Its photocatalytic activity was evaluated by degradation of carbofuran under sunlight irradiation.In addition,the influence factors such as sunlight irradiation time,NaNbO3 and Sn3O4 mole ratio,cycle number and pesticides types on the photocatalytic activity of Z-scheme NaNbO3-Au-Sn3O4 photocatalyst were investigated.The research results show that Z-scheme NaNbO3-Au-Sn3O4 photocatalyst has a high photocatalytic activity.It can be used as an efficient photocatalyst for photocatalytic degradation of carbofuran in wastewater.In the third chapter,Z-scheme Ag/g-C3N4-Ag-Ag3PO4(110)photocatalyst was prepared by photo-assisted isoelectric point method.Its photocatalytic activity was evaluated by photocatalytic degradation of levofloxacin(LEV)and simultaneous hydrogen production under visible light irradiation.Besides,the influence factors such as visible light irradiation time,types of sacrificial agents,initial pH of the solution,the amount and used times of photocatalysts were studied systemically.The research results indicate that the prepared Z-scheme Ag/g-C3N4-Ag-Ag3PO4(110)photocatalyst displays a high photocatalytic activity and stability in the processes of the photocatalytic degradation of LEV and simultaneous hydrogen production.Finally,the photocatalytic reaction mechanism on the degradation of organic pollutants and simultaneous production hydrogen caused by Z-scheme Ag/g-C3N4-Ag-Ag3PO4(110)photocatalyst is proposed.In the fourth chapter,a high-efficiency Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst was prepared successfully via photo-assisted isoelectric point method.Its photocatalytic activity was evaluated by photocatalytic degradation of malachite green(MG)and simultaneous hydrogen production under sunlight irradiation.Furthermore,some influence factors such as sunlight illumination time,NaYF4:Er,Yb,Tm and Bi-BiOBr/Bi mole ratio and cycle number on the performance of Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst were investigated.The experimental results show that the as-prepared Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst exhibits excellent photocatalytic activity on the photocatalytic degradation of MG and simultaneous hydrogen production.Finally,the possible mechanism of photocatalytic degradation MG and simultaneous hydrogen production caused by Z-scheme BiVO4(040)-Bi-(NaYF4:Er,Yb,Tm@BiOBr)/Bi photocatalyst are proposed.It is wished that the research results could provide a feasible strategy for effective treatment of wastewater containing MG and simultaneous hydrogen production by using solar energy.