The Study On Modification And Photocatalytic Hydrogen Evolution Performance Based On G-C₃N₄

Semiconductor solar photocatalytic water splitting to produce hydrogen is considered to be the most promising means of hydrogen production.The development of high-efficient and stable visible-light photocatalyst becomes the research focus for photocatalytic water splitting to hydrogen production.Since 2009,Xinchen Wang et al.found that graphitic carbon nitride（g-C₃N₄）applied in photocatalytic water splitting,g-C₃N₄ has attracted wide attention due to its good chemical and thermal stability,proper band structure,low-cost raw materials,non-toxic.However,the photocatalytic activity of g-C₃N₄ was limited due to its the high charge carrier recombination rate and small specific surface area.Therefore,it is necessary to modify g-C₃N₄ to improve the charge carrier separation efficiency,increase the specific surface and improve its photocatalytic activity.This paper mainly uses two different schemes for modification,including the following two parts:Tannic acid（TA）and melamine were assembled into TA/melamine precursor by supramolecular self-assembly,and then carbonized TA（C-TA）/g-C₃N₄ composites were obtained by thermal condensation.The obtained C-TA/g-C₃N₄ composites showed good photocatalytic hydrogen evolution activity,in which the photocatalytic hydrogen evolution activity of 1wt%C-TA/g-C₃N₄ photocatalyst was 4.2 times higher than that of pristine g-C₃N₄.This is because tannic acid with a strong adhesion contains a large number of phenolic hydroxyl groups which can self-assemble with the amine groups of melamine to form TA/melamine aggregates.The TA on the surface of melamine can limit the melamine in the interior and promote the condensation of melamine to obtain more condensed g-C₃N₄.The obtained C-TA/g-C₃N₄ composites displayed a smaller layer spacing,which is beneficial to the transfer of charge carrier,and thus improving the photocatalytic activity.SPP-MS-g-C₃N₄ composite nanosquare tubes were obtained by regulating the condensation of melamine using sodium polyphosphate（SPP）in molten salt（MS）system.The photocatalytic hydrogen evolution activity of 0.5wt%SPP-MS-g-C₃N₄ composite cubic tube was 2.2 times higher than that of g-C₃N₄ obtained by direct molten salt synthesis.This is because the extremely strong solubility of SPP can promote the diffusion and contact of melamine in molten salt system,which is conducive to the formation of tubular g-C₃N₄.The results of N2 adsorption and desorption curve,UV-vis diffuse reflection spectra and electrochemical analysis showed that the obtained SPP-MS-g-C₃N₄ has a larger specific surface area,enhanced light absorption and higher charge carrier separation efficiency,and thus effectively improving the photocatalytic hydrogen production activity.