Preparation And Photocatalytic Properties Of Coal-based Carbon Dots And Phosphate Heterojunction

Carbon dots（CDs）is a new carbon-based zero-dimensional material,which has multiple advantages and has been widely used in many fields.Especially in the study of photocatalysis,the performance of photocatalyst has been greatly improved by compounding other materials on carbon dots because of the excellent optical absorption,photogenerated electron transfer and up-conversion properties of carbon dots.On the one hand,by introducing molecular groups to change the functional groups on the surface of carbon dots,the photocatalytic effect of carbon dots can be improved.On the other hand,by compounding carbon dots with other semiconductor materials,the energy level structure of the catalyst can be adjusted.In this paper,carbon dots and phosphoric compounds are compounded to form heterojunctions.By adjusting the band gaps of phosphoric compounds,carbon dots are also used to enhance the absorption of visible light in composite materials.The photocatalytic properties of the composites are studied.The main research contents and achievements are as follows:（1）The heterostructure was formed by the combination of CDs and Ag₃PO₄,which regulated the band gap of the catalyst and improved the performance of the catalyst.In this paper,it is proposed for the first time to adjust the bandgap position of Ag₃PO₄ by fluorescent carbon dots（CDs）,in which CDs and Ag₃PO₄ need to maintain the same size to form heterojunctions.HRTEM,XRD and XPS were used to characterize the morphology,valence bond structure and element analysis of the heterojunction.The heterojunction not only enhanced the visible light absorption,the separation and transfer of photogenerated charges,but also changed the photocatalytic properties of Ag₃PO₄ from Photooxidation to photoreduction due to the great change of its band gap position.In addition,the heterostructures formed by CDs and Ag₃PO₄ exhibit unique temperature dependence of photocatalytic activity,and have higher photocatalytic stability than that of Ag₃PO₄ alone.Based on the comparative experiments and related characterization,we proposed a reasonable mechanism of photocatalytic reaction.Therefore,this work provides a new alternative way to adjust the energy band gap position or photocatalytic performance and to prepare new carbon-based heterostructures.（2）The heterostructure formed by the combination of CDs and BiPO₄ can also improve the performance of the catalyst,enhance the absorption of visible light and enhance the efficiency of the catalytic reaction.In the experiment,phosphoric acid modified carbon dots were synthesized by hydrothermal method and reacted with Bi（NO₃）₃ to prepare CDs@BiPO₄ composites.By controlling the size of CDs and BiPO₄ to form heterojunctions,the composite structure can improve the visible light absorption of the composites.HRTEM,XRD and XPS were used to characterize the morphology,element,valence bond structure and a series of performance tests.The results show that the complex formed by CDs and BiPO₄ not only improves the absorption of visible light,but also reduces the charge transfer impedance at the interface of the catalyst,which greatly improves the catalytic efficiency of the complex under visible light compared with the single CDs and BiPO₄.A reasonable mechanism is also analyzed,CDs enhances the visible light absorption of catalysts,and the photogenerated electrons act on the catalytic reaction system,thus increasing the reaction rate.Based on these results,a theoretical basis for the preparation of catalysts is also provided.