Synthesis Of Bismuth Phosphate Series Photocatalysts And Their Application In Photocatalytic Conversion Of Nitrite

With the rapid development of modern industry and agriculture,the concentration of nitrite anion in water bodies has been significantly rising.At present,the nitrite has been considered as a common inorganic environmental contaminant,which presents a serious toxicity to human health.And as a result,it is very necessary for us to remove the nitrite anion in drinking water in order to satisfy the requirement of human health.In recent years,various kinds of semiconductors used to photocatalytic reaction have received the widespread attentions.Photocatalysis is particularly suitable for the conversion of nitrite because of its simple and environmentally friendly process by utilizing the clean,inexhaustible and easily accessible resources of solar energy.Based on the investigation,it was considered that the bismuth phosphate（BiPO₄）can better satisfy the requirements of the conversion of nitrite.However,we found two serious defects in the field of photocatalysis that retard the photocatalytic capacity: firstly,as a wide band-gap semiconductor the BiPO₄ powder is active only under ultraviolet-light excitation,which accounts for less than 5.0 % of the entire solar spectrum.Therefore,it is too inefficient to harness solar energy by only using pure BiPO₄.How to utilize solar energy is quite a problem.Secondly,the high recombination rate of electron-hole pairs always led to the low semiconductor quantum efficiency.How to efficiently restrain the recombination of electron-hole pairs is another problem.In order to overcome the problem above,we prepared Er³⁺:Y₃Al₅O₁₂/BiPO₄ and Er³⁺:YAlO₃@（PdS/BiPO₄）/（Au/rGO）/CdS composite photocatalytic system by using sol-gel,hydrothermal,deposition-precipitation,ultrasonic-assisted and calcination methods to improve the photocatalytic efficiency.Upconversion luminescence agent is a useful selection to convert low energy（long wavelength）light to high energy（short wavelength）light,which can effectively activate the wide band-gap photocatalyst.Therefore,it can broaden the solar-light absorption region to strengthen solar-light photocatalytic activity.On the other hand,composited with narrow-gap semiconductor,loaded co-catalysts on semiconductor and structured mediator were used to promote the separation of photo-generated electrons and holes,resulting in high photocatalytic activity.In this article,the phase structures and crystallite sizes of prepared photocatalyst was characterized by X-ray diffractometer（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,energy dispersive X-ray spectroscopy（EDX）,X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared spectroscopy（FT-IR）,Raman spectroscopy.The effect of upconversion luminescence agent was evaluated via UV-vis diffuse reflectance spectra（DRS）and Photoluminescence（PL）spectroscopy.In addition,the photocatalytic activity of prepared photocatalyst was evaluated via photocatalytic conversion of nitrite under simulated solar-light irradiation.The effects of irradiation time,photosource kinds,electron and hole sacrificial agent and cycling times on the photocatalytic capability of Er³⁺:Y₃Al₅O₁₂/BiPO₄ and Er³⁺:YAlO₃@（PdS/BiPO₄）/（Au/rGO）/CdS were studied.Through the research,it was indicated that compositing with the up-conversion luminescent material could improve the utilization efficiency of sunlight.And composited with narrow-gap semiconductor,loaded co-catalysts on semiconductor and structured mediator could enhance the photocatalytic activity of photocatalyst.This research may provide a potential way by utilizing solar energy efficiently for converting nitrite and other contaminants released into the environment.