Preparation And Photocatalytic Properties Of TiO₂ And Ag₂O Based Heterojunction Photocatalysts

In recent years,photocatalytic technology has made important progress in the degradation of pollutants.Compared with traditional chemical methods,photocatalytic technology has wider application prospects and better environmental protection performance.In the photocatalytic process,photosensitive semiconductor materials absorb light energy,generate electron-hole pairs,and use electron-hole pairs to degrade organic pollutants,thereby achieving the purpose of purifying water.However,the spectral response range of a single semiconductor photocatalyst is usually very narrow,and photogenerated carriers are often easily recombined,which affects its performance in degrading water pollutants.Therefore,combining semiconductors with different characteristics to establish heterojunction photocatalysts is an effective way to improve the photocatalytic degradation performance of semiconductors.Titanium dioxide（Ti O₂）is a low-cost readily available semiconductor material with good ultraviolet photocatalytic degradation activity but lacks visible light response capability.In contrast,silver oxide（Ag₂O）can excite photogenerated carriers under visible light,but has a higher recombination rate.This study investigates the photocatalytic performance of wide-bandgap commercial Ti O₂ and narrow-bandgap Ag₂O by compounding them with organic materials,such as phosphorus-doped graphene quantum dots（P-GQDs）;inorganic metal compounds,such as silver iodide（Ag I）and iron oxide（Fe₃O₄）,to prepare visible-light-responsive Ti O₂-based and Ag₂O-based heterojunction photocatalysts and study their photocatalytic performance in degrading organic dyes under visible light.In addition,the carrier transport mechanism in the heterojunction photocatalyst is analyzed,and the mechanism for improving photocatalytic activity is discussed.The main research content is as follows:（1）First,phosphorus-doped graphene quantum dots（P-GQDs）were successfully prepared by hydrothermal method using trinitronaphthalene(C₁₅H₉N₃O₆)and sodium hydrogen phosphate（Na₂HPO₄）as precursors.Then,by a simple solution adsorption method,the Ti O₂/P-GQDs/Ag I ternary catalyst was prepared by compounding Ti O₂,P-GQDs,and Ag I.The results show that under visible light,the Ti O₂/P-GQDs/Ag I（10 wt%）sample degraded 99.5%of the methyl orange solution（MO）within 30 minutes,much higher than the degradation rate of pure Ti O₂,Ti O₂/GQDs,and Ti O₂/GQDs/Ag I.This is attributed to the construction of the n-p-n heterojunction,which generates two tandem built-in electric fields after photoexcitation,significantly separating photogenerated carriers.（2）A binary catalyst of type II Ag₂O/Fe₃O₄ heterojunction was synthesized in one step using ferrous chloride tetrahydrate（Fe Cl₂·4H₂O）,ferric chloride hexahydrate（Fe Cl₃·6H₂O）and silver nitrate（Ag NO₃）as precursors.The results show that the Ag₂O/Fe₃O₄（10%）sample degraded 99.5%of MO within 15 minutes,higher than the degradation rate of pure Ag₂O and Fe₃O₄.This is attributed to the construction of the type II heterojunction,which greatly improves the separation efficiency of photogenerated electron-hole pairs and forms a photocatalytic-Fenton combined reaction system,greatly enhancing the utilization rate of photogenerated carriers.