Study On The Z-scheme Photocatalysts Modified By Several Co-catalysts To Convert Organic Dyes To （NH₄）₂SO₄

In recent years,with the development and progress of society,organic dyes containing N and S elements are more and more widely used.But the attendant is that a large amount of organic dyes containing N and S elements in wastewater are discharged into rivers and lakes,causing great harms to the environment and ecosystem.In theory,organic dyes containing N and S elements can be mineralized into water,carbon dioxide and some inorganic acid ions,such as NO₃^-,SO₄^2-,NO₂^-and SO₃^2-by photocatalytic technology.However,the generated NO₂^-and SO₃^2-still have a negative impact on the environment.In fact,the ideal mineralization products should be NH₄⁺,NO₃^-and SO₄^2-.The generated NH₄⁺can combine with NO₃^-and SO₄^2-,respectively,to form the main parts of the fertilizer NH₄NO₃ and（NH₄）₂SO₄.Therefore,in order to effectively convert the organic dyes containing N and S elements in wastewater into NH₄⁺,NO₃^-and SO₄^2-,it is essential to design and develop appropriate photocatalysts.Currently,the Z-scheme photocatalyst is widely used.Because it can not only inhibit the electron and hole recombination in the two semiconductors,but also widen the optical response range.In order to enhance the conversion ratio,the co-catalysts on the surface of the Z-scheme photocatalyst can selectively adsorb and convert acid ions.Therefore,the selection and matching of catalyst can greatly enhance the conversion ratio of organic dyes containing N and S elements,forming the main components of fertilizers NH₄NO₃ and（NH₄）₂SO₄.In the first part of the study,we successfully prepared（Cu,Pd）-NiGa₂O₄/BiVO₄by using light-assisted chemical reduction combined with high-temperature calcination methods.In this study,the Z-scheme（Cu,Pd）-NiGa₂O₄/BiVO₄photocatalyst with Cu and Pd as double co-catalysts was used to convert organic dyes.The X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,energy dispersive X-ray spectroscopy（EDX）and X-ray photoelectron spectroscopy（XPS）were used to characterize the chemical composition,microstructure and valence bond structure of the samples.The absorption edges and bandgaps of the samples were analyzed and calculated by UV-Vis diffuse reflection spectroscopy（DRS）.Photoluminescence spectroscopy（PL）,transient photocurrent response（EIS）and electrochemical impedance（TPR）electrochemical analysis were used to investigate the electron and hole pairs recombination of the sample.Some influence factors,deposited order,molar proportion and deposited amount of Cu and Pd on the photocatalyst activity are considered.The effects of irradiation time,NO₂^-and SO₃^2-concentrations and catalyst used times on the photocatalytic conversion of organic dyes are also evaluated.The results display that the Z-scheme（Cu,Pd）-NiGa₂O₄/BiVO₄ photocatalyst has an excellent performance in the conversions of NO₂^-and SO₃^2-.Also,NH₄⁺as a main product can be generated in the actual photocatalytic conversion of organic dyes.It is wished that this work could provide a feasible route to convert organic dyes in wastewater to selectively generate NH₄⁺and SO₄^2-,forming（NH₄）₂SO₄（the main ingredient of fertilizer）,respectively.In the second part of the study,we synthesized three Z-scheme CuPd-SrTiO₃/Bi₂O₃（SB）,CuPd-SrTiO₃/Bi₂O₃（AA）and CuPd-Sr TiO₃/Bi₂O₃（HH）photocatalysts by using three reducing agents（sodium borohydride（SB）,ascorbic acid（AA）and hydrazine hydrate（HH））.The XRD,SEM,TEM,EDX and XPS are used to characterize the chemical composition,microstructure and valence bond structure of the samples.The absorption edge and bandgaps of the samples are analyzed and calculated using DRS.The recombination of electron and hole pairs is studied by using PL,TPR and EIS electrochemical analysis.In addition,the effects of irradiation time,photocatalyst kinds and used times of catalysts on photocatalytic conversion of organic dyes are also investigated.The results show that the Z-scheme CuPd-SrTiO₃/Bi₂O₃（SB）,CuPd-Sr TiO₃/Bi₂O₃（AA）and CuPd-Sr TiO₃/Bi₂O₃（HH）photocatalysts prepared by three different reducing agents all show the outstanding photocatalytic activities.However,the Z-scheme CuPd-SrTiO₃/Bi₂O₃ photocatalyst obtained from NaBH₄ as a reducing agent has the best photocatalytic activity.Finally,it can be speculated that the three Z-scheme Cu Pd-SrTiO₃/Bi₂O₃ photocatalysts all have a good application prospect in the conversion of organic dyes into the main component of fertilizer（NH₄）₂SO₄.