Preparation And Photocatalytic Activity Of G-C₃N₄-based Photocatalytic Materials

Recently,Energy crisis and environmental pollution are two serious problems that humans face in the process of sustainable development.Semiconductor photocatalysis has gained more and more interest in the areas of energy storage and environmental remediation because of its using abundantly available solar energy.Graphite carbon nitride（g-C₃N₄）has been regarded as a promising non-metallic material in the field of photocatalysis research owing to its excellent photoelectric properties.However,the photocatalytic performance of g-C₃N₄ is limited due to low specific surface area,and high recombination rate of photo-generated electrons and holes.Hence,improving the specific surface area and restraining the recombination rate of photo-generated carriers is a hot topic,which can enhance the photocatalytic application of graphite carbon nitride（g-C₃N₄）.In consequence,in order to meet the requirements of practical application,the exploration of a feasible strategy to synthesize g-C₃N₄ with high photocatalytic activity is still a‘‘bottleneck’’.In the thesis,we have synthesized g-C₃N₄ with high specific surface area and g-C₃N₄-based photocatalytic materials.The main contents were discussed as follows:1.The g-C₃N₄ nanosheets with high specific surface area have been synthesized by gas phase template method by using dicyandiamide as precursor and ammonium chloride as a gas-phase template,respectively.The photocatalytic activity of as-prepared g-C₃N₄ was estimated by photocatalytic degradation of RhB aqueous solution under visible-light at ambient temperature.The weight ratio of ammonium chloride to dicyandiamide has an obvious effect on specific surface area,band gap and photocatalytic activity of g-C₃N₄.At an optimal weight ratio of ammonium chloride to dicyandiamide（5:1）,the as-prepared g-C₃N₄ nanosheets show the highest photocatalytic performance.2.The macro/mesoporous TiO₂/Au/g-C₃N₄ heterojunction photocatalysts have been prepared by using the tetrabutyl titanate and melamine as precursors and Au nano-particles as electronic media,respectively.Photocatalytic activity of as-prepared composites was estimated by photocatalytic degradation of RhB aqueous solution under visible-light at ambient temperature.The content of the Au nanoparticles had an important effect on photocatalytic activity of as-prepared samples.Under an optimal weight ratio of Au to TiO₂（1.5%）,the macro/mesoporous TiO₂/Au/g-C₃N₄ heterojunction photocatalysts show the highest photocatalytic performance.The improved photocatalytic performance may be attributed to the higher specific surface area and narrow band gap.According to active species trapping test results,the h⁺and·O₂^-are the main active species in the photocatalytic process,and the possible photocatalytic mechanism has been proposed.3.Nitrogen-riched g-C₃N₄/rGO photocatalysts have been prepared by using dicyandiamide as precursor and graphene oxide as electronic media via simple calcination method under the N₂/H₂atmosphere.The weight ratio of GO to dicyandiamide had an obvious effect on crystallisation degree,band gap structure and photocatalytic performance of as-prepared samples.Under optimal weight ratio of GO to dicyandiamide（2%）,the as-prepared photocatalyst shows the highest photocatalytic performance.That may be attributed to the narrow band gap and lower recombination rate of photo-generated electrons and holes.According to active species trapping test,the h⁺and·O₂^-are the main active species in the photocatalytic process.This work provides new insights to prepared high-efficient g-C₃N₄-based photocatalytic materials.