The Study On Modification Of G-C₃N₄ By Carbon Materials In Molten Salt System And Its Photocatalytic Hydrogen Evolution Performance

Based on natural photosynthesis,solar photocatalysis using semiconductor is an emerging technology for green and sustainable development.As a two-dimensional polymer semiconductor photocatalyst,g-C₃N₄ has attracted wide attention due to its unique electronic structure,high chemical and thermal stability and nontoxicity.However,due to poor mass transfer during the reaction,the g-C₃N₄ synthesized by the traditional thermal condensation method is prone to excessive accumulate and cause it to form blocks between layers;incomplete condensation leads to low crystallinity,which is the reason for the low specific surface area,narrow visible light response range and fast recombination of charge.These shortcomings limit the photocatalytic performance of g-C₃N₄.Therefore,in this paper,molten salt was used to create a fluid environment to enhance the mass transfer of reactant molecules,and g-C₃N₄ was modified by introducing carbon materials that better conductivity,in order to promote the photocarrier separation efficiency of g-C₃N₄ and finally improve the photocatalytic performance effectively.Modify g-C₃N₄performances using two methods:The C-GLU/MS-CN complex with Donor-Acceptor（D-A）structure was prepared by thermal polycondensation using melamine and glucose（GLU）as precursors in molten salt system（LiCl,KCl）.GLU is carbonized in the high-temperature molten salt system to form graphene-like C-GLU nanosheets with high conductivity.Relying on the good mass transfer of the molten salt fluid,C-GLU is dispersed in the molten salt medium and composited in the surface of carbon nitride（MS-CN）.The formed C-GLU relies on good electrical conductivity facilitating the transport of charge carriers and acting as a co-catalyst to facilitate photocatalytic hydrogen production.The study shows that the C-GLU/MS-CN composite has higher carrier separation efficiency and wider light absorption range.After the calculation,the photocatalytic hydrogen production rate of 0.5 wt%C-GLU/MS-CN composite is 1.27 times as much as MS-CN.In molten salt system（LiCl–KCl）,π-conjugated C-PAN/MS-CN nanotubes were prepared by one-step thermal condensation of melamine and polyacrylonitrile（PAN）.Molten salt（LiCl–KCl）with a cubic structure acted as a template to guide melamine and its intermediates to form quadrilateral hollow nanotubes in low temperature.With the temperature rising,LiCl and KCl melted to facilitate the mass transfer.Carbonized PAN（C-PAN）nanosheets with a conjugate network structure formed in the molten salt system.On the one hand,it acted as partition plates confining the thermal condensation of melamine,which promoted the formation of condensedπ-conjugation MS-CN.On the other hand,combination of C-PAN with a conjugated network structure and MS-CN further expanded theπ-conjugated system.The study showed that C-PAN/MS-CN nanotubes exhibited increased crystallinity,enhanced carrier separation efficiency and enlarged specific surface area.The 1 wt%C-PAN/MS-CN nanotubes showed the optimum H₂ evolution rate,about 1.57 times that of MS-CN.