Preparation Of Bi-Ag Composite Photocatalyst And Research On Its Photocatalytic Performance

Semiconductor photocatalyst technology is a kind of green energy-saving,efficient and environmental protection technology rising in recent decades.The well-designed artificial semiconductor photocatalyst can generate H2 from water cracking as energy storage products,and can degrade organic pollutants,reduce CO2,oxidize formaldehyde and so on[1-4].Traditional semiconductor photocatalysts,such as TiO2,have the following disadvantages:1)the wide band gap limits the absorption of visible light.2)The low quantum efficiency affects the photodegradation efficiency.3)In the process of photocatalytic reaction,photogenerated electrons and holes are easily combined,which reduces the photocatalytic activity.Although the new semiconductor photocatalyst prepared by modification can make up for the above shortcomings to a certain extent.However,these new semiconductors still can not give full play to their excellent performance when used alone.Therefore,the composite of two or more semiconductors can not only make up for the defects of a single photocatalyst,but also improve the photocatalytic activity.In this project,bismuth based and silver based semiconductors are prepared to improve the response of semiconductors to visible light,and two or more semiconductors are combined to improve the redox ability,the mechanism of photocatalysis was discussed.The details are as follows:(1)BiOCl/Bi3O4Cl photocatalyst was synthesized by hydrothermal method usingBi(NO3)3·5H2O and NaCl as raw materials and adjusting the pH value of the solution;A series of AgBr/BiOCl/Bi3O4Cl photocatalysts were prepared by changing the content of AgNO3 and NaBr.The composite photocatalyst was characterized by XRD,SEM,XPS and UV-Vis DRS.The results show that the composite semiconductor photocatalyst has been successfully prepared.Under simulated visible light conditions,Rhodamine B was used as degradation product to test the degradation performance.The results showed that when m(AgBr):m(BiOCl/Bi3O4Cl)was 0.3,the photocatalytic performance of AgBr/BiOCl/Bi3O4Cl was the best,and the degradation rate of Rhodamine B was more than 95%in 80 min.The results show that both single and 0.3AgBr/BiOCl/Bi3O4Cl composite photocatalysts have good photoelectric properties.The photocatalyst still has good photocatalytic activity after five times of recycling.(2)Tetrahedral Zn2SnO4 was successfully prepared by hydrothermal method using ZnCl2,SnCl4·4H2O and CH4N2O as raw materials.AgI was deposited on the surface of Zn2SnO4 by chemical precipitation method.The structure,morphology and chemical states of the elements were characterized by XRD,SEM and XPS.Taking doxycycline hydrochloride as the target pollutant,the photocatalytic degradation of doxycycline hydrochloride was studied.When the doping ratio m(AgI):m(Zn2SnO4)was 0.10,the degradation effect of doxycycline hydrochloride was the highest within 120 min of visible light irradiation,and the degradation rate reached 96%.The photocatalytic degradation cycle experiment of 0.10AgI/Zn2SnO4 composite catalyst was carried out.After five cycles,the catalyst still had strong activity.This excellent photocatalytic degradation ability is attributed to the successful construction of Z-scheme heterostructure between Zn2SnO4 and AgI.This structure can accelerate the separation of photogenerated carriers,therefore,the absorption efficiency of the semiconductor to visible light is enhanced and its redox ability is improved.(3)In order to explore the photodegradation ability and photocatalytic activity between BiOBr and CdS,a series of BiOBr/CdS composites with different doping ratios were prepared by one-step hydrothermal method.The composite materials were characterized by XRD,SEM,UV-Vis DRS and XPS,and Rhodamine B was used as the target degradation product,The photocatalysis performance was tested.The results show that the photocatalytic activity of the composite photocatalyst is much higher than that of pure CdS and BiOBr nanoparticles.Under visible light irradiation,when the doping ratio m(BiOBr)/m(CdS)is 0.3,the photocatalytic performance of 0.3 BiOBr/CdS is the best,and the photodegradation efficiency reaches 81.2%within 100 min.This is due to the cross band structure between CdS and BiOBr.This structure improves the utilization of solar energy in the visible wavelength range,speeds up the migration efficiency of photo induced electrons,and is conducive to the migration of photo generated electron hole pairs.The efficient separation of photo generated electron hole pairs reduces the recombination probability to a certain extent,and greatly improves its catalytic performance.