Study On Preparation And Performance Of Visible Light Responsive Semiconductor Photocatalysts

The rapid expansion of the population,coupled with the swift progress of industrialization and urbanization,has resulted in a plethora of ecological issues.The pollutants with slow degradation such as dyes,pesticides and antibiotics are potentially harmful to ecosystems and human health,and these pollutants are consumed in large quantities worldwide,causing pure drinking water to become more scarce and expensive as they are released into water resources.Conventional treatment technologies for biological processes are not highly effective in removing these contaminants.Therefore,it is essential to develop efficient and sustainable methods for the removal of these pollutants.Semiconductor photocatalysis is an effective,inexpensive and environmentally friendly technology for decomposing various aqueous organic pollutants and is playing an increasingly important role in pollutant degradation.However,numerous developed semiconductor photocatalysts have limited their applications due to the lack of favorable compatibility between strong redox ability and visible light response range.The design and preparation of highly stable and active semiconductor photocatalytic materials in photocatalytic reactions is still a major challenge.In this paper,semiconductor nanocomposites were synthesized mainly on the basis of g-C₃N₄ using Zn₃V₂O₈,Ag I and Ag₃PO₄ as additives.Through the synergistic effect among the components,the light trapping ability and charge transfer rate of the materials were improved,which in turn enhanced the photocatalytic activity.The main methods and details are as follows:（1）Dual Z-scheme ternary semiconductor heterojunction photocatalysts were synthesized using g-C₃N₄（CN）,Zn₃V₂O₈（ZV）and Ag I（A）as the main raw materials by simple thermal polycondensation and in-situ chemical precipitation,respectively,and the catalysts were employed for the photocatalytic degradation of organic pollutants under simulated sunlight irradiation.The results showed that the synthesized dual Z-scheme heterojunction photocatalyst g-C₃N₄/Zn₃V₂O₈/Ag I（ZV/CN/A）exhibited superior photocatalytic activity compared with pure g-C₃N₄,Zn₃V₂O₈,Ag I and their binary composites.The best photocatalytic efficiency of the ZV/CN/A sample for MB degradation reached 92%.A dual Z-scheme heterojunction,with its increased redox capacity and accelerated electron transfer rate,was credited for the enhanced photocatalytic degradation performance.The detection of active oxygen experiment verified that the non-radical ¹O₂ in the photocatalytic system plays a major role in the removal of MB,while the free radical h⁺plays a minor role.The mechanism of charge transfer in the photocatalytic process was investigated based on the energy band potential.（2）Porous HNO₃-g-C₃N₄（H-CN）was prepared by vacuum thermal polycondensation using nitric acid-treated melamine as a precursor,and the composites（AP/H-CN）of Ag₃PO₄loaded on H-CN substrate were further prepared by in-situ precipitation method.The loading of Ag₃PO₄ significantly improved the photocatalytic degradation efficiency of the composite.AP/H-CN（20）showed a maximum degradation efficiency of 98.5%for the drug carbamazepine（CBZ）within 60 min.The catalyst exhibited a wide p H applicability which could effectively degrade CBZ in acidic,neutral and alkaline environments in experiments examining the effect of various operating parameters on the photocatalytic degradation of CBZ.The experimental data of active species detection revealed that h⁺,·O₂^–,and·OH were all involved in the photocatalytic process,with h⁺playing the most crucial effect.In addition,based on the analysis of CBZ degradation products,the main degradation intermediates of CBZ were identified.The introduction of Ag₃PO₄ forms the S-scheme charge transfer pathway resulting in enhanced visible light utilization as well as lower recombination efficiency of photogenerated carriers.