Modified Carbon Nitride By Copolymerization As Visible Light Photocatalyst For Hydrogen Evolution

Energy crisis and environmental pollution are two major concerns of the human society,therefore,the development of clean renewable energy sources is of great importance.Semiconductor photocatalytic technology,which could convert solar energy directly into storable chemical energy?for example,photocatalytic hydrogen evolution?,is of great potential to solve the energy and environmental problems.Graphitic carbon nitride?g-C₃N₄?,a new type of polymeric semiconductor material,has became a hotspot in the photocatalysis research,due to its visible light response,good thermal stability,light stability and environmental friendliness.Nevertheless,there are many shortcomings of pristine g-C₃N₄,such as narrow visible light response range,high recombination rate of photogenerated electron-hole pairs,small specific surface area and bad liquid phase dispersion.In this work,g-C₃N₄ was modified by organic molecule copolymerization to enhance the photocatalytic activity and extend the light response range.Moreover,a combination of theoretical calculation and experimental studies were employed to explore the mechanism of enhancement of photocatalytic activity.Specific contents were summarized as follows:?1?Modified g-C₃N₄ was synthesized by copolymerization of dicyandiamide and4,5-dicyano imidazole,and its light absorption range had been greatly extended.The photocatalytic activity of the as-prepared samples under visible light???420 nm?irradiation was evaluated by photocatalytic hydrogen production.The results indicated that copolymerization modified g-C₃N₄ showed the best activity when the mass ratio was 4,5-dicyano imidazole/dicyandiamide=0.05 g/3g.Then,N-CN_0.05,the sample with the highest activity,was exfoliated to nanosheets,and its photocatalytic activity under visible light irradiation was further improved.The characterization results reveal that the method combined copolymerization modification with liquid exfoliation could optimize the structure and morphology of pristine g-C₃N₄,enlarge the specific surface area,extend the light absorption range and improve the separation and transportation properties of photogenerated carriers,thus enhancing the photocatalytic activity.?2?In order to further understand the mechanism of copolymerization,phthalic nitrile,isophthalonitrile and terephthalonitrile were chosen as comonomers to prepare modified g-C₃N₄ photocatalysts,and the phthalic nitrile modified sample showed the best photocatalytic hydrogen production activity.By comparing the morphology and the hydrogen production performance of the as-prepared catalysts,a thorough investigation has been conducted to uncover the effects of copolymerization on the physicochemical properties of g-C₃N₄ photocatalyst.