离子热处理合成氮缺陷石墨相氮化碳及其光解水制氢性能

以尿素和二氰二胺为原料热聚合得到石墨相氮化碳,分别采用直接二次煅烧和熔盐离子热后热处理在不同温度下对产物进行后热处理,得到氮缺陷氮化碳CN和CNS。利用X射线衍射(XRD)、紫外-可见漫反射光谱(UV-Vis DRS)、透射电镜(TEM)等手段对所制备样品进行表征和分析,探讨了不同热处理温度和加热方法对催化剂微观聚合结构的影响;同时以光解水制氢为测试方法,考察了催化剂的可见光催化性能。结果表明,熔盐离子热更有利于氮化碳的层间聚合,得到高结晶度材料;在面内七嗪聚合单元中引入氮缺陷,产生末端氰基,优化电荷密度分布,增强电荷流动性;克服粒子尺寸效应,扩展催化剂的光吸收范围;当后热处理温度为500℃时,制备的CNS-500表现出优异的光解水制氢活性,是同温度下直接热处理得到的催化剂的3.84倍。

Ionothermal Synthesis of N-Deficient Graphitic Carbon Nitride with Enhanced Photocatalytic Hydrogen Evolution Activity

Graphitic carbon nitride(g-C3N4)was synthesized by thermal polymerization method using urea and dicyandiamide as raw materials.Then,g-C3N4 was treated at different temperatures by two post-heat treatment methods:direct secondary calcination and molten salt ionothermal post-heat treatment,respectively.As s results,different nitrogen-defected carbon nitride materials CN and CNS were obtained.The prepared samples were characterized and analyzed via X-ray diffraction(XRD),ultraviolet-visible diffuse reflectance spectrum(UV-Vis DRS),transmission electron microscopy(TEM),and so on.The effect of different heat treatment temperatures and heating methods on the microstructure of catalysts were discussed.The photocatalytic properties of catalysts were tested by H2 production from water splitting under visible light irradiation.The results showed that ionothermal post-heat treatment method was more conductive to interlayer polymerization of g-C3N4 than direct calcination,and high crystallinity materials were obtained.Nitrogen defects were introduced into the in-plane heptazine polymerization accompanying the production of terminal cyano groups.The strong electron absorption of cyano could optimize the charge density distribution and enhanced the charge fluidity.In addition,molten salt heat treatment increased porosity and expanded the light absorption range of CNS samples.CNS-500 prepared under 500℃ ionothermal post-heat treatment exhibited excellent photocatalytic hydrogen evolution activity,which was 3.84 times as high as that of the catalyst prepared by direct post-heat treatment at the same temperature.