Piezo-photocatalysis Degradation Properties Of Graphite Carbon Nitride-based Composites

Direct conversion of clean and pollution-free solar energy into chemical energy is a major advantage of semiconductor photocatalytic technology,which provides a favorable solution for the energy crisis and environmental pollution.Graphite carbon nitride（g-C₃N₄）has been widely studied because of its narrow band-gap and wide visible light response range.However,its photocatalytic performance is restricted by low light energy utilization and high recombination ratio of photogenerated electrons and holes.The built-in electric field formed by the intrinsic or strain-induced directional electron separation can be used to improve the separation of photogenerated carriers and the photocatalytic efficiency of semiconductors materials.In this thesis,g-C₃N₄ and its composites were studied to enhance the catalytic activity of the materials through synergistic photocatalytic and piezoelectric catalysis.The results are as follows:1.By using urea as the precursor,g-C₃N₄ was prepared by high-temperature polycondensation.Carbon nitride with different nitrogen defects（Nv-C₃N₄）was prepared by heat-treating g-C₃N₄ in the N₂ atmosphere.Through the comparative study of Rh B degradation experiments under the conditions of light plus ultrasound,light only and ultrasound only,it is concluded that the appropriate number of nitrogen defects can make g-C₃N₄ exhibit the best piezoelectric photocatalytic degradation activity,and verify the performance of g-C₃N₄ piezoelectric catalytic activity.The catalytic performance of g-C₃N₄ was significantly enhanced by the synergistic effect of both piezoelectric and photocatalysis.The degradation rate of g-C₃N₄ by piezoelectric catalysis within 60 min gets to 23.43 percent.Compared with photocatalysis,the reaction rate constant of g-C₃N₄ piezoelectric synergistic photocatalysis increased by12.5 percent.The increase of ultrasonic time and ultrasonic power can improve the piezoelectric photocatalytic degradation performance of g-C₃N₄.2.BaTiO₃/g-C₃N₄ composite was prepared by the ultrasonic method.The successful construction of the heterojunction of BaTiO₃ and g-C₃N₄ enables the composite to exhibit an enhancement of catalytic activity under the synergistic effect of piezoelectric and photocatalysis.In the Rh B degradation experiment,the piezo-photocatalytic degradation rate of BaTiO₃/g-C₃N₄ composite material within 30minutes gets to 98.93 percent,and its piezoelectric photocatalytic reaction rate constant was increased by 2.04 times greater than that of photocatalysis.The mechanism of the enhancement of piezo-photocatalytic activity lies in that the built-in electric field of BaTiO₃/g-C₃N₄ heterojunction effectively promotes the separation of carriers and expands the light absorption wavelength range.The mechanism of action is that the built-in electric field of the BaTiO₃/g-C₃N₄ heterojunction effectively promotes the separation of carriers,and the degradation activity is enhanced under the synergistic effect of piezoelectric catalysis and photocatalysis.3.Composite films with g-C₃N₄ and PVDF were prepared by tape casting.The degradation experiments of Rh B under visible light and ultrasound confirmed that the g-C₃N₄/PVDF film had enhanced degradation performance under the synergistic action of piezoelectric catalysis and photocatalysis.The piezo-photocatalytic reaction rate constant is increased by 1.69 times compared with pure photocatalysis.Six cycles of degradation experiments showed that the composite membrane had excellent recyclability and recyclability.The composite film under low frequency vibration still remains the performance of piezoelectric degradation of Rh B,and the degradation rate of 200 ppm rhodamine B within 4 days holds to be 95.45 percent,indicating a potential to use micro-vibration in the environment to degrade organic pollutants.