Photocatalytic Water Decomposition Performance Of Graphite Phase Carbon Nitride Matrix Composites

Graphite phase carbon nitride(g-C3N4)has become a hotspot in the field of photocatalytic water spliting,because of its non-toxic,high efficiency,non-metallic composition,simple preparation process,suitable band gap and good chemical stability.However,when thinking of the characteristics of g-C3N4,there are many problems such as small specific surface area,serious photo-generated electron-hole recombination,low quantum efficiency and large band gap.These asoects eriously restrict its large-scale application in the field of energy,environment and photocatalysis.Therefore,to obtain a considerable visible light response of the photocatalytic water splitting efficiency,it is necessary to optimize and modify the g-C3N4.In this paper,we foucus on the improving the photogenerated electron-hole separation efficiency of g-C3N4 based samples.The structure and properties of the catalysts are tested by the X-ray diffraction(XRD),transmission electron microscopy(TEM),UV-Vis spectroscopy,fourier transform infrared spectroscopy(FTIR),.X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM),and thermogravimetric analysis(TG),and etc.Finally,the photocatalytic performance of the samples is evaluated by photocatalytic water splitting.The main contents are as follows:1 The g-C3N4 is obtained by calcining urea at the temperature of 550?.The TiO2/g-C3N4 heterojunctions are synthesized by a hydrothermal method using g-C3N4 and titanium tetrachl oride as precursors.The g-C3N4 can be converted to thinner nanosheets during the hydrothermal process.Results show that this heterojunction structure ensures the effective separation of photogenerated carriers.2 The results show that TiO2/g-C3N4-3 can reach the optimum hydrogen production rate of 154?mol ·h-1.Then the stability of the catalyst is also studied.We can find that the heterojunction photocatalyst shows the good stability by comparing the XRD,TEM and XPS results before and after hydrogen production.3 Hydrogen-evoluted photocatalyst of TiO2/g-C3N4 and oxygen-evoluted photocatalyst of WO3 and BiVO4 are used to form Z system under the using of redox medium,and to promote the formation of H2 and O2.The quantum efficiency(AQY)of 4.94%and 4.01%are achieved with LED monochromatic light at wavelengths of 365 and 405 nm,respectively.4 The Ni(OH)2/g-C3N4 heterojunction structure is synthesized by hydrothermal method using the obtained carbon nitride and nickel chloride as precursors.The g-C3N4 has been converted to thinner nanosheets with the growth of Ni(OH)2.And during the formation process,the specific surface area of g-C3N4 and layered Ni(OH)2 with(001)exposed facet are obtained.Based on their photocatalytic water splitting performance,the effective separation of photogenerated carriers can be concluded.5 We use the electrochemical workstation to study the photocurrent response ability of Ni(OH)2/g-C3N4.The results show that the photocurrent response of heterojunction Ni(OH)2/g-C3N4 is greatly improved compared with g-C3N4.By optimizing the content of Ni(OH)2,we obtained the hydrogen production rate of 14.2 ?mol·h-1 and the oxygen production rate of 7.2 ?mol·h-1 with the more than 20 hours stable activity.Under the visible light irradiation of 405 nm,the external quantum efficiency(AQY)can reach 1.48%.