Controllable Preparation And Enhanced Photocatalytic Activity Of Sliver Chromate And Its Composites

The solar energy can be converted into the storable chemical energy by photocatalytic technoloy,which is promising used in the organic pollutant degradation,the water spliting for hydrogen production,the carbon dioxide reduction,the antivirus sterilization and the organic compound synthesis.As a key family of the photocatalysts,Ag-based semiconductors attract more attentions due to their excellent photosensitive and high charge transfer rate.It is found that metal Ag with 4d¹⁰configurations participating in band design can not only raise the valance band level and lower the conduction band level of semiconductors,but also increase the delocalization of the orbital electrons.Silver chromate?Ag2CrO4?is one of the important photocatalysts with narrow band gap?¹.8 eV?and small electron effective mass?⁰.46 m₀?,thus it is expected for Ag₂CrO₄ showing a desired photocatalytic performance under visible light irradiation.However,the main topics of Ag-based photocatalysts are how to fully utilize their photosensitivity and further improve their photostability.In this work,a systematic investigation is established to further improve the photocatalytic activity and stability of Ag2CrO4 by the morphology controling,the band modufication and the carbon material coupling strategies.The main results are as follows:Ag₂CrO₄ photocatalysts are prepared by microemulsion,precipitation,and hydrothermal methods,in order to investigate the effect of preparation methods on the structure and visible-light photocatalytic activity of Ag₂CrO₄ crystals.It is found that the photocatalytic activity of the prepared Ag₂CrO₄ was highly dependent on the preparation methods.The sample prepared by microemulsion method exhibits the highest photocatalytic efficiency on the degradation of methylene blue?MB?under visible-light irradiation.The enhanced photocatalytic activity could be ascribed to the smaller particle size,higher surface area,relatively stronger light absorption,and blue-shift absorption edge,which result in the adsorption of more MB molecules,shorter diffusion process of more photogenerated excitons,and stronger reducing ability of the photogenerated electrons.Ag-cotaining semiconductors have attracted significant attention because of the unique photosensitivity that provides these materials with visible-light photocatalytic activity.This study systematically investigates the correlation among the photophysicochemical performance,crystal structure,electronic structure,and photocatalytic activity and stability of three Ag-containing photocatalysts Ag₂MO₄?M=Cr,Mo,W?prepared by microemulsion based on experimental and theoretical results.Results show that the photocatalytic activity and stability of the three photocatalysts strongly depend on the light absorption performance of these photocatalysts.Ag₂CrO₄ has the best light absorption performance,exhibiting the highest photocatalytic activity for methylene blue degradation under visible-light irradiation that is 3.5 and 1.5 times those of Ag₂MoO₄ and Ag₂WO₄,respectively.Meanwhile,the photocatalytic stability follows the same light absorption performance order.The theoretical calculation shows that stronger crystal field and smaller Ag–O distance lower the conduction band bottom of Ag₂CrO₄ and Ag₂WO₄,respectively.This reduction in conduction band causes the band gap,light-absorption,and subsequent photocatalytic activity and stability of these photocatalysts to differ.Ag₂CrO₄-graphene oxide?Ag₂CrO₄-GO?composites are prepared by a facile precipitation method.The resulting Ag₂CrO₄-GO composites exhibit excellent photocatalytic activity and stability towards the degradation of the dyes and phenol in aqueous solution under visible-light irradiation.The optimal composite with 1.0 wt%GO content shows the highest photocatalytic activity for MB degradation,which is3.5 times that of pure Ag2CrO4 particles.The enhanced photocatalytic activity is mainly attributed to the formation of Ag2CrO4-GO Z-scheme heterojunction that can not only facilitate the separation and transfer of the photogenerated charge carriers,but also preserve a strong oxidation and reduction ability.The high photocatalytic stability is due to the successful inhibition of the photocorrosion of Ag₂CrO₄ by transferring the photogenerated electrons of Ag₂CrO₄ to GO.Photocatalytic CO₂ conversion into solar fules based on graphite carbon nitride?g-C₃N₄?photocatalyst arouses much attetntion due to the promose on simultaneously addressing the environmental and energy crisis.In this study,a ternary Ag₂CrO₄/g-C₃N₄/GO composite photocatalyst is established via an electrostatic self-assembly strategy.Coupling Ag2CrO4 nanoparticles and GO nanosheets with g-C₃N₄ greatly increases the light absorption,promotes the charge separation and provides abundant active sites of composite photocatalyst.The ternary Ag₂CrO₄/g-C₃N₄/GO composite photocatalyst shows an enhanced CH₃OH and CH₄production,giving CO₂ conversion of 1.03?mol g^-1 with TOF value of 0.3 s^-1,which is 2.3 times that of pristine g-C3N4.Both radical scavenger experiment and charge effective mass calculation illustrate that a direct Z-scheme mechanism is suggested for better understanding this enhanced photocatalytic activity.