Modification Of Graphitic Carbon Nitride And Its Application In Hydrolysis Of Water To Hydrogen Production

The semiconductor photocatalytic technology can use solar energy to directly decompose water into hydrogen,which provides an effective way to solve environmental pollution and energy shortage.Polymer semiconductor graphite carbon nitride?g-C₃N₄?is a novel non-metallic functional material.Because of its unique energy band structure and photoelectric properties,it has received extensive attention in the photocatalytic field of photocatalytic splitting of water for H₂ production,degradation of pollutants,chemical synthesis,CO₂ reduction and so on.However,the low specific surface area and high photogenerated electron-hole recombination rate limit its practical application seriously.At present,the methods for modification of g-C₃N₄ include semiconductor coupling,elemental doping,morphological control,surface modification and so on.The main research contents and results of this paper are as follows:?1?Construction and Photocatalytic Performance of 2D/1D g-C₃N₄/CdS HeterojunctionA series of g-C3N4/CdS composites were prepared by ultrasonic-deposition method.The effects of CdS content and different preparation methods on the photocatalytic activity of composites were explored,and the factors and rules that affect their photocatalytic properties were also discussed.The results showed that the introduction of CdS nanowires formed an inorganic/organic heterojunction on the surface of g-C₃N₄,which significantly enhanced the photocatalytic hydrogen production activity.The photocatalytic activity of the product that the mass ratio of CdS to g-C3N4 was 0.1 was best.?2?Post-heat treatment of B/F co-doped g-C₃N₄ and its photocatalytic propertiesThe B/F co-doped g-C₃N₄?CN-B/F-x?were prepared by thermal polymerization with ionic liquid as dopant,dicyandiamide and urea as precursors?mass ratio of 1:1?.The screening results showed that the photocatalytic performance of CN-B/F-1 prepared with[Epin]BF₄ as doping source was the best,and it was calcined to prepare the post-thermal treatment B/F co-doped g-C₃N₄?r-CN-B/F?.The effect of post-heat treatment on the structure,morphology,specific surface area and photocatalytic property of it was explored.The results showed that B and F were doped on the CN framework and the surface respectively,and the post-heat treatment contributed to more compact layer accumulation and the increase of the specific surface area.In particular,the decrease of the graphite C on the catalyst surface,the increase of the B doping amount and the optimization of the structure of the conjugated aromatic ring promoted the separation and transfer of charge carrier.Therefore,the photocatalytic performance of r-CN-B/F was significantly improved.?3?Activation of In-situ B/F Co-doped g-C₃N₄ and Its Photocatalytic ActivityThe in-situ B-F co-doped g-C₃N₄?p-CN-BF?and bulk B-F co-doped g-C₃N₄?p'-CN-BF?were prepared by double thermal polymerizations with ionic liquid[Emim]BF₄as B-F doping source,dicyandiamide and urea as precursors?mass ratio of 1:1?.The effects of post-heat treatment and different doping methods with B-F on their structure and photocatalytic property were investigated.Studies showed that compared with bulk doping,the in-situ doping method can effectively dope B and F to the CN framework and the surface respectively.The B in the skeleton not only helped to increase visible light absorption,but also helped to build porous structures.Through co-doping and post-activation of B-F,p-CN-BF has been greatly improved in carrier generation,separation and transfer.Therefore,it exhibited higher photocatalytic hydrogen production performance,which were 2.5 and 1.7 times that of bulk B-F co-doped?p'-CN-BF?and B-F source of[Epin]BF₄?r-CN-B/F?respectively.