C3N5光催化制氢性能的系统研究

基于半导体的光催化制氢是解决当前日益增长的能源危机与环境污染等问题的有效选择之一.长期以来,设计具有不同结构与吸光特性的有机及无机半导体材料,开发廉价高效的助催化剂,构筑半导体异质结体系,探索实用研究装置等均受到广泛研究.其中氮化碳材料在过去十年中吸引了较大关注,但其光催化性能受到带隙较宽(代表材料C3N4的带隙为~2.7 e V)的限制.近年来,富氮型氮化碳(C₃N₅)材料因带隙更窄,在光催化污染物去除、光电能源转化和气体传感等领域被广泛研究,但其光催化制氢性能的系统研究尚未见报道.本文以3-氨基-1,2,4-三唑为原料,通过热处理制备C₃N₅,并对其光催化制氢性能进行了系统研究.X射线粉末衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、CHNS元素分析及红外光谱等表征结果确认成功制备了C₃N₅材料.同时,采用化学还原法(Na BH4为还原剂)负载Pt助催化剂并未对C₃N₅的结构及形貌造成影响;XRD,TEM及XPS结果表明,Pt以单质形态分散在C₃N₅材料上.紫外可见漫反射光谱(DRS)分析表明,C₃N₅在400~600 nm范围的可见光区具有强吸收,对600~800 nm范围的近红外光区也有一定的吸收能力.对Pt-C₃N₅材料的光催化制氢反应条件进行优化,以获得较好的催化活性.循环测试及光照后样品的XRD及DRS表明,C₃N₅具有良好的光催化稳定性.对比实验结果表明,负载1.0wt%Pt助催化剂时,C₃N₅的制氢速率约为C3N4的2.2倍.分析结果表明,比表面积及导带位置不是造成两种氮化碳材料光催化性能差异的主要因素.DRS、荧光光谱及光电流行为实验结果表明,C₃N₅具备更宽的可见光吸收范围,更窄的带隙及更快的光生e-/h+分离效率.采用包括原位红外在内的系列表征手段对水分子在材料表面的吸附性能进行研究,发现C₃N₅表面可以吸附更多的水分子,有利于表面水还原反应的进行.综上,本文为富氮型氮化碳材料的开发及其较高光催化活性的内在机制研究提供了新的见解.

Comprehensive investigation on robust photocatalytic hydrogen production over C3N5

Carbon nitride has drawn numerous eyes in the past decade, whereas the photocatalytic perfor-mance is significantly limited by its wide band-gap (～2.7 eV for C3N4) simultaneously. Recently, C3N5 with narrower band-gap has been reported, however, a systematically investigation on its photoac-tivity for H2 production has not been reported. The present work demonstrates the synthesis of C3N5 by thermal treatment of 3-amino-1,2,4-triazole, and the photocatalytic performance for H2 production of C3N5 is investigated comprehensively. Photocatalytic H2 production rate of C3N5 is ～2.2 times higher than that of C3N4 with 1.0 wt％ Pt as co-catalyst, and series of experiments are carried out to explore the behind elements accounting for the high photoactivity. Combining the results of DRS, PL and photocurrent, it is found that C3N5 possesses wider visible light absorption region, lower band-gap and quicker photogenerated e-/h+ separation efficiency. Moreover, charac-terizations including in-situ DRIFTS are adopted to monitor the adsorption property of H2O on C3N5, which plays a significant role in surface water reduction reaction, and higher amount of adsorbed H2O molecules on C3N5 is confirmed. The present work exhibits new insights into the high photo-catalytic performance of N-rich carbon nitride catalysts.