Degradation Of Nitrogen-containing Organics And Conversion Of NO₃^- And NO₂^- By Z-scheme Photocatalysts Supported With Copper And Silver

The rapid developments of industry and agriculture bring about the environmental pollution.The problem of groundwater polluted by organic dyes,nitrates（NO₃^-）,nitrites（NO₂^-）and sulfites(SO₃^2-)is becoming more and more serious.It is usually caused by the excessive use of fertilizers and pesticides containing nitrogen and sulfur as well as the arbitrary discharge of domestic sewage and industrial dye wastewater.The existences of these pollutants can not only harm the ecological system and destroy the ecological balance,but also seriously threaten the biological health.Therefore,degrading organic dyes and converting NO₃^-,NO₂^-and SO₃^2-in wastewater into non-polluting or usable substances such as nitrogen（N₂）and ammonium sulfate（（NH₄）₂SO₄）has become an urgent task.In the process of exploring effective technology for wastewater treatment,photocatalytsis has caused attention of researchers due to the advantages of low energy consumption,safety,high efficiency and environmentally friendly.The principle of photocatalysis can be used to design efficient photocatalyst to mineralize organic dyes into H₂O,CO₂and inorganic salt ions so as to achieve the purpose of the degradation of organic dyes.However,during the photocatalytic degradation of nitrogen-containing organic dyes,in addition to the mineralized products mentioned above,NO₃^-and NO₂^-will be generated,which also causes pollution to the water environment.Nevertheless,photocatalysis technology can not only degrade dyes,but also be used to convert inorganic salt ions in wastewater.In consequence,according to the actual situation,it is possible to use photocatalysis technology to directly convert NO₃^-,NO₂^-and SO₃^2-ions in wastewater into N₂and（NH₄）₂SO₄,or degrade nitrogenous organic pollutants while further convert the generated NO₃^-and NO₂^-into N₂.In the first section of the study,three novel photocatalysts,Z-scheme（Cu,Cu）/g-C₃N₄-（Cu,Cu）-WO₃（002）,Z-scheme（Cu,Ag）/g-C₃N₄-（Cu,Ag）-WO₃（002）and Z-scheme（Cu,Ru）/g-C₃N₄-（Cu,Ru）-WO₃（002）,were prepared by photo-assisted electrostatic self-assembly method to convert the harmful NO₃^-,NO₂^-and SO₃^2-into non-polluting or usable substances（N₂and（NH₄）₂SO₄）).The prepared photocatalysts were synthetically characterized by XRD,SEM,TEM,EDX,XPS,DRS,PL,TPR and EIS.The effects of different co-catalyst combinations on the activity and selectivity of the photocatalysts were evaluated.Also,the impacts of simulated solar light irradiation time,NO₃^-initial concentration and cycle times on the conversions of NO₃^-and SO₃^2-were studied.The results displayed that the Z-scheme（Cu,Ag）/g-C₃N₄-（Cu,Ag）-WO₃（002）photocatalyst can selectively convert NO₃^-to N₂,while the Z-scheme（Cu,Ru）/g-C₃N₄-（Cu,Ru）-WO₃（002）photocatalyst can selectively convertNO₃^-toNH₄⁺.Nevertheless,theZ-scheme（Cu,Cu）/g-C₃N₄-（Cu,Cu）-WO₃（002）photocatalyst hardly has selectivity for the conversion of NO₃^-.These three photocatalysts all exhibited relatively strong capabilities for converting SO₃^2-to SO₄^2-due to the existence of the highly active（002）plane of WO₃.Furthermore,the possible mechanisms on the photocatalytic conversions of NO₃^-and SO₃^2-caused by Z-scheme（Cu,M）/g-C₃N₄-（Cu,M）-WO₃（002）（M=Cu,Ag and Ru）photocatalysts were clarified.In the second part,the degradation of nitrogenous organic pollutants was combined with the conversion of inorganic salt ions on the basis of the first chapter.A dual Z-scheme Bi₂Mo O₆/Bi₂WO₆\Ag I\Ag photocatalyst was prepared via isoelectric point and continuous ion layer adsorption methods.The morphology,structure,composition and photoelectrical property of the acquired photocatalyst were investigated by multiple characterization techniques.The activity of the prepared photocatalyst was evaluated by degrading malachite green（MG）and converting the generated NO₃^-and NO₂^-ions into N₂.Meanwhile,the impacts of simulated solar light illumination time and solution p H on the photocatalytic degradation of MG were studied.The results revealed that the Z-scheme Bi₂Mo O₆/Bi₂WO₆\Ag I\Ag photocatalyst possesses high degradation ratio of MG and generation ratio of N₂under solar light irradiating for 180 min at p H=5.0.The cycle experiment and XRD test confirmed the preeminent stability and reusability of the photocatalyst.The trapping and electron spin resonance experiments verified that the holes played a vital part in the degradation of MG and electrons and·CO₂^-were in charge of the conversions of NO₃^-and NO₂^-ions.Finally,a probable mechanism on degradation of the nitrogen organic pollutants and conversion of the generated NO₃^-and NO₂^-ions induced by Z-scheme Bi₂Mo O₆/Bi₂WO₆\Ag I\Ag photocatalyst was put forward.