Preparation And Application Of Graphite Phase Carbon Nitride-based Photocatalyst

Two-dimensional graphite phase carbon nitride（g-C₃N₄）is widely used as a visible light responsive photocatalyst due to its special thermal and chemical stability,appropriate energy band structure and low cost.However,the photocatalytic properties of the original g-C₃N₄ are limited by the rapid recombination of photo-generated electron-hole pairs,limited surface area and low-efficiency light absorption.In this paper,g-C₃N₄-based composites with enhanced photocatalytic performance were prepared by the strategy of element doping and the construction of heterojunction,and applied to the photocatalytic oxidation of NO,hydrogen production and degradation of pollutants,etc.The main contents are as follows:Synthesis and photocatalytic properties of B,K co-doped g-C₃N₄ nanosheets.The strategy of multi-element co-doping and two-step heat treatment was adopted to modify g-C₃N₄.In the two thermal polymerization processes at the temperature of 600 and 700°C,B and K were introduced into different positions in the structure of g-C₃N₄,respectively,to synthesize the g-C₃N₄ nanosheets（KBCN）modified by B and K co-doping.The effects of different doping elements on the structure and photocatalytic performance of the prepared catalysts were also investigated.And the optimum preparation conditions were determined by adjusting the proportion of doping elements.The experimental results showed that the introduction of B element not only adjusts the distribution and transfer of electrons in the in-plane structure of g-C₃N₄ and inhibits the recombination of carriers,but also endows the samples with enhanced light absorption capacity.On the basis of B-doping,K element is introduced into the interlayer structure as the channel of electron transfer,which provides a reasonable path for the electron transfer between the inter layers.The synergistic effect of B-doping and K-doping promoted the redistribution and transfer of electrons in the structure of g-C₃N₄,and the photocatalytic NO oxidation and hydrogen production activity of KBCN were significantly improved after optimization.Combined with a series of optical/electrical performance tests,the enhanced photocatalytic mechanism was investigated.Construction and photocatalytic NO oxidation properties of Ni Co P/B-doped g-C₃N₄schottky heterojunction.The strategy of combining element doping and constructing schottky junction was adopted to further inhibit recombination of carriers.On the basis of the previous work,using B-doped g-C₃N₄ nanosheets as the substrate material,the Ni Co P/B-doped g-C₃N₄Schottky heterojunction was constructed by co-precipitation and vapor deposition.The effects of the loading of Ni Co P and different loading amounts on the performance of photocatalytic NO oxidation were explored.The results show that,based on the enhanced intrinsic catalytic activity of B-doped g-C₃N₄,the existence of Ni Co P with good conductivity promotes the transfer of photoelectrons,which tend to transfer to Ni Co P.The existence of Schottky barrier effectively inhibits the transferred electrons from returning to B-doped g-C₃N₄,which inhibits the recombination of photo-generated electron-hole pairs and increases the number of effective photo-generated electrons.In addition,the loading of Ni Co P effectively improved the absorption of the composite in the region of visible light.By adjusting the loading ratio,the optimal loading ratio was determined.The optimal sample photocatalytic NO removal efficiency reached 80%.The high mineralization efficiency indicated that less NO₂ was generated in the reaction process,and the secondary pollution was alleviated.The quantitative experimental results of superoxide radicals showed that the increase in the number of superoxide radicals was the main reason for the high-efficiency photocatalytic NO oxidation performance.Study on the construction and photocatalytic performance of W₁₈O₄₉/B-doped g-C₃N₄ Z-scheme heterojunction.In order to further increase the species and number of active oxygen species and improve carrier separation and transport efficiency.The Z-scheme heterojunction was constructed by growing W₁₈O₄₉ with oxygen vacancies on B-doped g-C₃N₄ nanosheets by solvothermal method.The effects of modification and different loading amounts of W₁₈O₄₉ on the structure,optical/electrical properties and photocatalytic performance were investigated.The results of ESR and reactive oxygen species quantification experiments showed that the construction of Z-heterojunction satisfied the conditions for the composite to produce superoxide radical and hydroxyl radical at the same time,and the species and number of ROS species were significantly increased.The synergistic effect of B-doping and Z-scheme charge transfer route enhanced the separation and transfer efficiency of photogenerated electrons and holes.In addition,the existence of abundant oxygen vacancies in W₁₈O₄₉ induces the local surface plasmon resonance（LSPR）effect,which broadened the light absorption region of the composite to the region of near infrared.The generated hot electrons were injected into the B-doped g-C₃N₄,and the existence of two electron transfer paths further improved the concentration of the effective electrons.Compared with the single component,the W₁₈O₄₉/B-doped g-C₃N₄ showed excellent photocatalytic NO oxidation performance,and the optimized photocatalytic NO removal rate of the sample reached 64%.