The Modification Of G-C₃N₄ For Its Photo-catalytic Performance

As a two-dimensional semiconductor photocatalytic materials,graphitic carbon nitride（g-C₃N₄）has attracted a lot of attention for its advantages such as simple composition and preparation method,moderate forbidden band width（2.7 e V）,excellent thermal and chemical stability,etc.And it possesses huge potential in the field of hydrogen evolution from water decoposition,in order to meet the urgent need of the society for clean renewable energy.However,the stacked lamellar structure limits the specific surface area（SSA）.And the band gap is relatively big for the absorption of visible light,which hinders its utilization of visible light.These lead to the poor photocatalytic performance.Therefore,a large number of modification strategies have been developed to improve the electronic structure and morphology of g-C₃N₄.Based on this,the foam g-C₃N₄was modified by changing morphology and doping which can directly influence the electronic structure of g-C₃N₄in this paper,aiming to improve its photocatalytic performance by regulating the band structure.In this paper,the tungsten element with the best doping effect was selected through the preliminary experiment at first.Then,taking foam g-C₃N₄as main research object,different amount of W-doped foam g-C₃N₄were successfully prepared by direct grinding and calcination of raw materials.The photocatalytic performance of the W-doped g-C₃N₄samples were significantly better than that of the pure foam g-C₃N₄,and the average rate of hydrogen evolution could reach 18 times larger than that of pure foam g-C₃N₄.Besides,the optimal hydrogen evolution rate was better than a large proportion of other photocatalysts.In addition,the change of photocatalytic performance with the increase of amount of tungsten strengthened first and then weakened with the optimal amount at 0.7 wt%.Through the characterization analysis of the XRD spectra,Raman spectra,EDS energy spectra and XPS spectra of mixed samples,it was proved that the tungsten formed W-C in the skeleton of the g-C₃N₄lattice,which made it possible for charge to transfer between them.Besides,the amount range should be controlled within 1 wt%,basing on the premise that the structure of the g-C₃N₄will not be destroyed by tungsten.The increase of SSA introduced by a large number of pores on the surface of the W-doped samples which is the main reason for the enhancement of photocatalytic performance.In addition,the temperature-dependent photoelectronic properties of W-doped g-C₃N₄were systematically studied,and the sensitivity to temperature response was estimated by fitting.Besides,the temperature-dependent photocatalytic properties of W-doped g-C₃N₄were characterized.Finally,the optimal reaction temperatures for foam g-C₃N₄（70 ^oC）and bulk g-C₃N₄（55 ^oC）were obtained by comprehensively considering the disappearing time of the absorption peak and the reaction kinetic constants corresponding to different temperature.The results provide a reference for the practical application temperature of W-doped g-C₃N₄photocatalysis.