Preparation And Photocatalytic Performance Of V₂O₅-Ag₂O/g-C₃N₄ Composites Photocatalys

In recent years,with the continuous improvement of human living standards and the rapid development of industrial productivity,a large amount of non-degradable industrial waste water is discharged into the environment,posing a great threat to the human health.Photocatalysis is an advanced oxidation process that can be used for the destruction of organic pollutants in a simple and efficient manner,and avoids causing secondary pollution.Although TiO₂ remains of great interest as a model system,a low quantum yield,following its wide bandgaps and fast recombination of the photoinduced electron and holes,limits its use for photocatalytic degradation of organic pollutants.Therefore,this paper focus on the research of semiconductor with high efficience,stablility and wide range of visible light response.(1).Melamine was selected as the precursor to prepare g-C₃N₄ by high-temperature calcination method.The g-C₃N₄ based Ag₂O/g-C₃N₄composites were synthesized via a hydrothermal method.Ag₂O/g-C₃N₄ displayed increased visible light absorption property with a significant red-shift of the absorption edge to visible region as compared to pure g-C₃N₄.A 400W Sodium lamp was employed as the visible-light source and methylene blue(MB)was utilized as model of organic pollutant to investigate the effect of Ag₂O dosage,composites amount and initial concentration on photocatalytic activity of composites.The result shows that Ag₂O/g-C₃N₄(the mass ratio of Ag₂O and g-C₃N₄to be2.5:1)composites exhibited the highest photocatalytic activity and about 86.62%of MB can be degraded after 180min under visible light irradiation in the presence of2.5Ag₂O/g-C₃N₄ composites,which was about 2.56 and 2.32 times higher than that of g-C₃N₄ and Ag₂O,respectively.The degradation rate of MB was 91.35%and 95.97%when the amount of composites was 1.0 g/L and initial concentration of MB was 15 mg/L,respectively.The repetition tests shows that Ag₂O/g-C₃N₄composites have an excellent stability and applicability.The active species trapping and quantification experiments indicated that the holes(h⁺)were the main active species in photocatalytic reaction process.The p-n heterojunction between Ag₂O and g-C₃N₄ was formed and it is favorable to the transport of photogenerated carriers and enhanced photocatalytic activity.(2).V₂O₅ was prepared by an in-situ synthesis method,using ammonium metavanadate as feedstocks.The V₂O₅-Ag₂O/g-C₃N₄composites were synthesized via a hydrothermal method.The edge of V₂O₅-Ag₂O/g-C₃N₄ composites has a significant red shift and the composites exhibited stonger the visible-light absorption property compared to that of V₂O₅.The 15%V₂O₅-Ag₂O/g-C₃N₄composites with MB degradation rate of 98.42%exhibit the highest photocatalytic activity of under visible-light irradiation for 180min,which was about 10.07 and 2.28 times higher than that of V₂O₅and 2.5Ag₂O/g-C₃N₄composites,respectively.The optimized reaction conditions obtained through orthogonal experiments were that the amount of composites was 0.5g/L and initial concentration of MB was 5mg/L.Meanwhile,V₂O₅-Ag₂O/g-C₃N₄composites show excellent stability and applicability.The active species trapping and quantification experiments indicated that the holes(h⁺)were the major active species for the V₂O₅-Ag₂O/g-C₃N₄ photocatalytic system and the recombination process of V₂O₅ and Ag₂O adopts Z-scheme visible-light-driven mechanism,which has contributed to effectively hinder the recombination of photogenerated carriers and enhance photocatalytic activity of composites.