Fabrication Of Graphitic Carbon Nitride-based Nanocomposite Photocatalysts And Performance On H₂-production From Water Splitiing

The rapid development of science and technology brings convenience to human society,however,it also brings some negative effects.Especially in recent years,the global energy crisis and environmental pollution have seriously affected our lives and health.Since the discovery of hydrogen production by photocatalytic water splitting has been found by Japanese scientists in 1972,semiconductor-based photocatalysis harvest and convert of solar energy through water splitting to produce clean hydrogen energy is considered as a powerful strategy to settle increasing the global energy crisis and environmental issues.Traditional photocatalysts have many defects,such as high recombination rate of electron–hole pairs and the low solar energy utilization,which suppress their application.Therefore,developing a efficient,stable,visible light-driven photocatalyst is the major challenge.In recent years,graphite-like carbon nitride（g-C₃N₄）has attracted extensively attention in composite photocatalst system.Its comparatively simple synthesis process,good visible light absorption property and high stability make it a very attractive material for photocatalytic applications.Furthermore,g-C₃N₄ possesses an extremely high specific surface area,which could provide a suitable scaffold for other nanosized photocatalysts to achieve composites.However,pure g-C₃N₄ is restricted by their high recombination rate of photoinduced electron-hole pairs.In order to ehance the photocatalytic activity,we have tried a variety of attempts.In this dissertation,we followed three methods to improve photocatalytic activity of g-C₃N₄: one-step synthesis method to obtain Ag QDs/g-C₃N₄ photocatalysts,in-situ growth method to prepared CuS/g-C₃N₄ photocatalysts to increase the separation of the electron-hole pairs,synthesis g-C₃N₄ QDs composited with SnNb₂O₆ to improve the utilization of sunlight and photocatalytic activity.The details are as follows:（1）The Ag QDs/g-C₃N₄ photocatalysts are obtained by one-step method,which is simpler than photodeposition and the NaBH4 reduction reaction.We find that the plasmon resonance effect of Ag quantum dots can effectively improve the absorption intensity of the visible light and the utilization rate of the sunlight.On the other hand,the Ag quantum dots can act as co-catalyst to improve the separation rate of the electron-hole.The photocatalytic activity of Ag QDs/g-C₃N₄ photocatalysts were evaluated by H2-production from water splitting under visible light.The photocatalytic hydrogen production activity under visible light was significantly enhanced by Ag QDs modification.（2）We have synthesized the composites of CuS/g-C₃N₄ composites via a simple in-situ growth method.The electrons could transfer directly to CuS clusters from VB of g-C₃N₄ by IFCT under visible-light irradiation,which cause the partial reduction of CuS to Cu2 S.CuS/Cu2 S cluster could capture electrons,giving positive influence on the photocatalytic activity.In hydrogen evolution experiments,CuS/g-C₃N₄ composites exhibited efficient photocatalytic activity and excellent stability.（3）The CNQDs/SnNb₂O₆ photocatalsts were firstly synthesized by simple hydrothermal method.CNQDs could act as a good co-catalyst to capture electrons and improve the separation rate of the electron-hole.In other hand,CNQDs possess upconverison luminescence properties,which can improve the utilization of sunlight and ehance photocatalytic activity.