Preparation And Photocatalytic Performance Of Co Doped Alveolate G-C₃N₄ Composites

Photocatalytic technology is one of the most sustainable and environmental protection methods for hydrogen production from water decomposition and pollutant degradation.Graphite phase carbon nitride(g-C3N4)is a non-metallic semiconductor photocatalyst.It has been widely studied because of its non-toxic effect on the environment,low cost,excellent stability and good visible light response.However,the traditional g-C3N4 has some disadvantages,such as small specific surface area,insufficient visible light utilization,poor conductivity and high recombination rate of photogenerated electron holes,which limits its practical application.Therefore,g-C3N4 was modified by precursor selection and transition metal doping to obtain photocatalysts with excellent catalytic performance.The main contents are as follows:g-C3N4(U-CN,D-CN,M-CN)was prepared by using urea,dicyandiamide and melamine as precursors.The photocatalytic properties of g-C3N4 prepared by different precursors were studied by photocatalytic hydrogen production and photocatalytic degradation of methylene blue(MB).The experimental results show that D-CN has the largest specific surface area,the highest porosity,the highest electron hole separation efficiency and the best photocatalytic performance.The hydrogen evolution rate of D-CN(120.2?mol·h^-1·g^-1)is 1.68 and 2.19 times of that of U-CN and M-CN,respectively;the degradation rate of MB by D-CN after 6 hours of light is 34.0%,which is 1.12 and 1.36times of that of U-CN and M-CN,respectively.Using dicyandiamide and cobalt nitrate as raw materials,cobalt doped honeycomb g-C3N4 composite photocatalysts(X%Co/ACN,where x is 0,5,10,15,20)were prepared by hard template and simple calcination method.The thermal decomposition process of the prepared photocatalysts and the loading amount of cobalt in the materials were analyzed by DTA-TGA technique.The surface morphology of bulk g-C3N4(BCN)honeycomb g-C3N4(ACN)and Co doped composite photocatalysts were observed by scanning electron microscope(SEM).The nitrogen vacancy formation of the composite photocatalyst was confirmed by electron paramagnetic resonance(EPR).The effects of different experimental conditions and Co content on photocatalytic performance were studied by photolysis of hydrogen and photodegradation of MB.By measuring the active species in the process of photocatalytic reaction,the reaction mechanism was proposed.The results show that the maximum hydrogen evolution rate(472.2?mol·h^-1·g^-1)is 3.93 times of BCN and 38.4times of Co₃O₄ when the cobalt content is 10%(10%Co/ACN).After 6 hours of illumination,the decolorization rate of MB was 92.7%,which was 2.73 times and 1.50 times of that of BCN and ACN,respectively.The reaction kinetic rate constant of MB degradation(k=0.42 h^-1).In addition,the degradation process of MB dye was analyzed by LC-MS,and the possible degradation intermediates were proposed.