Preparation Of An Ag₂CO₃/a-AgSiO/g-C₃N₄ Photocatalytic Heterojunction For The Photocatalytic Removal Of Indoor Formaldehyde

As one of the major indoor air pollutants,formaldehyde is a major health hazard and can cause a variety of diseases,making indoor formaldehyde pollution a major concern.Photocatalysis,an environmentally friendly technology with mild reaction and clean energy,can effectively remove formaldehyde from indoor air.However,the photocatalytic performance of single photocatalytic material is limited due to their limited light absorption capacity and fast photogenerated electron-hole complexation rate.Morphology control and construction of binary or ternary heterojunctions are effective strategies to solve these problems.In this thesis,a-AgSiO/g-C₃N₄ binary composites were prepared by loading a-AgSiO nanoparticles onto g-C₃N₄ nanosheets through a facile preparation method.Ag₂CO₃/a-AgSiO/g-C₃N₄ ternary composites were prepared by loading Ag₂CO₃ and a-AgSiO nanoparticles onto g-C₃N₄ nanosheets,while the morphological structure,chemical composition,energy band structure and photogenerated carrier separation efficiency of the materials were analyzed.Then,the photocatalytic performance and mechanism of formaldehyde removal were further investigated.The details of the study and the findings are as follows:1.Preparation and performance of a-AgSiO/g-C₃N₄ binary photocatalytic heterojunctionGraphitic carbon nitride nanosheets（CNNS）were prepared by acid etching,followed by the synthesis of a-AgSiO/g-C₃N₄ binary composite photocatalysts using a simple in situ precipitation method.The successful synthesis of a-AgSiO/g-C₃N₄ was demonstrated using XRD,FT-IR,and XPS characterization,and the composites were used for the study of photocatalytic removal of indoor formaldehyde.Through experimental investigation,a-AgSiO/g-C₃N₄ has good photocatalytic performance.Under the condition of reaction time 3h,initial formaldehyde concentration 1 mg/m³and humidity 20%,the efficiency of single CNNS and a-AgSiO photocatalytic removal of formaldehyde was 36.7%and 32.7%,respectively while the efficiency of a-AgSiO/g-C₃N₄ photocatalytic removal of formaldehyde was 69.2%,and its efficiency was still59.6%after five cycles.By analyzing the energy band structure and photogenerated carrier separation efficiency of a-AgSiO/g-C₃N₄,the enhanced photocatalytic performance was attributed to the Z-type heterojunction formed between CNNS and a-AgSiO.By conducting free radical tests,it was demonstrated that·OH and·O₂^-play a major role in the photocatalytic removal of formaldehyde.Through the above experimental analysis,a mechanism for the photocatalytic removal of indoor formaldehyde by a-AgSiO/g-C₃N₄ binary composite photocatalyst was proposed.2.Preparation and performance study of Ag₂CO₃/a-AgSiO/g-C₃N₄ ternary photocatalytic heterojunctionsTo further enhance the separation efficiency of photogenerated carriers,Ag₂CO₃/a-AgSiO/g-C₃N₄ ternary composite photocatalysts were synthesized by in situ precipitation and ion exchange methods and used for the study of photocatalytic removal of indoor formaldehyde XRD,FT-IR,XPS,and other characterization methods were used for the demonstration of the successful synthesis of Ag₂CO₃/a-AgSiO/g-C₃N₄.By introducing Ag₂CO₃ nanoparticles,the prepared Ag₂CO₃/a-AgSiO/g-C₃N₄photocatalytic removal of indoor formaldehyde was excellent,with an efficiency of81.9%at a reaction time of 3 h,an initial formaldehyde concentration of 1 mg/m³,and a humidity of 20%,which was superior to that of the a-AgSiO/g-C₃N₄ binary composite photocatalyst.Moreover,the material had excellent cycling stability,and the formaldehyde removal efficiency was still 72.7%after five cycles.The enhanced photocatalytic performance was attributed to the formation of a double Z-type ternary heterojunction between CNNS,a-AgSiO,and Ag₂CO₃.·OH and·O₂^-played a major role in the photocatalytic removal of formaldehyde through the analysis of the free radical test,energy band structure and photogenerated carrier separation efficiency of the material.According to the above experimental results,the mechanism for the photocatalytic removal of indoor formaldehyde by the Ag₂CO₃/a-AgSiO/g-C₃N₄ternary composite photocatalyst was proposed.