Study On Preparation And Properties Of Oxygen-doped G-C₃N₄Photocatalyst Active In Visible Light

Utilizing solar energy to solve the problem of environmental pollution andenergy shortage is one of the major research topics in21century. The photocatalytictechnology can make full use of the oxidation and reduction of photogeneratedcarriers, which could degradate the organic pollutants and split water to generatehydrogen directly.A new-type polymeric organic semiconductor, graphitic carbon nitride （g-C₃N₄）,was investigated in this study. We reported that oxygen heteroatoms and carbonnanotubes （CNTs） were successfully introduced into g-C₃N₄, resulting in improvedoptical absorption properties, an enhanced separation efficiency of photogeneratedcarriers, and thus high visible-light photoactivity. The as-prepared samples werecharacterized by XRD、BET、SEM、XPS、IR、Raman、UV-Vis DRS、PL andphotoelectrochemical measurement. The aim of this study is to explore the possiblephotocatalytic mechanism and understand the enhanced photoactivity for themodified g-C₃N₄photocatalyst. The main researchs were listed as following:（1） O-doped g-C₃N₄was successfully synthesized by a facile H2O2hydrothermalapproach. To obtain the high photocatalytic activity, catalysts treated at differenttemperature were tested by methylene blue degradation and water splitting undervisible light irradiation. The result showed that The result indicates that the averageH2evolution rate (37.5mmol h^-1) on the O-doped g-C₃N₄is2.5times higher than that(15.2mmol h^-1) on the g-C₃N₄. It was found that the O-doping induced nitrogenvacancies into the bandgap the g-C₃N₄, resulting in harvesting more visible-lightphotons, hindering the recombination of photogenerated carriers and producing a highquantum yield in photocatalytic reaction.（2） A series of g-C₃N₄/CNTs composites with low-doped CNTs was prepared byutilizing cyanamide and CNTs as the precursors. The results indicated that themodification did not change the lattice structure, molecule skeleton and surface areaof the g-C₃N₄while it contributed to the efficient separation of photogeneratedcarriers and improved photocurrent response over the g-C₃N₄/CNTs. The photocurrent response and the H2evolution rate on the g-C₃N₄/CNTs were2.03and2.35times respectively than those over the pure g-C₃N₄.（3） In combination with the methods of the O-doping and the CNTs-loadingmentioned above, study was carried out to investigate the coupling effect on thephotocatalytic performance of the Oxygen-doped g-C₃N₄/CNTs. It showed the H2evolution rate on the as-synthesized catalyst was68.6μmol h^-1, which is nearly equalto the sum of that on the g-C₃N₄/CNTs (38.7μmol h^-1) and the O-doped g-C₃N₄(37.5μmol h^-1). Our findings present a new potential route to improve the photocatalyticperformance of g-C₃N₄and may be significative for the applications in sustainablechemistry and actual industry.