摘要
Semiconductor photocatalytic technology is widely recognized as one of the most promising technologies to solve current energy and environmental crisis, due to its ability to make effective use of solar energy. In recent years, graphite carbon nitride(g-C3N4), a new type of non-metallic polymer semiconductor photocatalyst, has rapidly become the focus of intense research in the field of photocatalysis because of its suitable bandgap energy, unique structure, and excellent chemical stability. In order to improve its intrinsic shortages of small specific surface area, narrow visible light response range, high electron-hole pair recombination rate, and low photon quantum efficiency, a simple method was utilized to synthesize Br-doped g-C3N4(CN–Br X, X = 5, 10, 20, 30), where X is a percentage mole ratio of NH4 Br to melamine. Experimental results showed that Br atoms were doped into the g-C3N4 lattice by replacing the bonded N atoms in the form of C–N=C, while the derived material retained the original framework of g-C3N4. The interaction of Br element with the g-C3N4 skeleton not only broadened the visible-light response of g-C3N4 to 800 nm with an adjustable band gap, but also greatly promoted the separation efficiency of the photogenerated charge carrier and the surface area. The photocurrent intensity of bare CN and CN–Br X(X = 5, 10, 20, 30) catalysts is calculated to be 1.5, 2.0, 3.1, 6.5, and 1.9 μA, respectively. And their specific surface area is measured to be 9.086, 9.326, 15.137, 13.397, and 6.932 m2/g. As a result, this Br-doped g-C3N4 gives significantly enhanced photocatalytic reduction of Cr(VI), achieving a twice enhancement over g-C3N4, with high stability during prolonged photocatalytic operation compared to bare g-C3N4 under visible light irradiation. Furthermore, an underlying photocatalytic reduction mechanism was proposed based on control experiments using radical scavengers.
半导体光催化技术不仅可将太阳能转化为化学能,还能直接降解和矿化有机污染物,在解决能源短缺和治理环境污染等方面具有广阔的应用前景.然而传统的TiO2光催化剂具有较大的禁带宽度(3.2 eV),使得材料只能吸收紫外光(仅占太阳光的4%)且量子产率较低.因此,研究和开发新型的本身具有可见光响应的光催化材料在实际应用中具有重要的指导意义.g-C3N4作为一种非金属有机聚合物n型半导体,因具有合适的禁带宽度、独特的电子结构和良好的化学稳定性,迅速成为光催化领域的研究热点.但是,由于g-C3N4本身存在比表面积小、可见光响应范围狭窄和光生电子-空穴对分离效率低等缺陷,极大限制了其光催化实际应用.为了解决该问题,人们进行了很多尝试来改善石墨相氮化碳光催化材料的光催化活性.研究表明,非金属元素掺杂是一种有效且常用的提高g-C3N4光催化性能的方法.例如,通过高温煅烧三聚氰胺和氧化硼混合物可制备掺B的g-C3N4,g-C3N4结构中的H元素被B取代, B的掺杂大大提高了g-C3N4的光催化活性;利用氟化铵和三聚氰胺合成F掺杂的g-C3N4, F原子与g-C3N4中心或边缘的C键合,将部分sp2杂化的碳原子转化为sp3杂化,降低了材料的平面性,从而使材料的析氢性能和催化苯氧化生成苯酚的能力有了明显提高;使用氯化铵和双氰胺作为前驱体制备Cl掺杂的g-C3N4, Cl元素的引入使g-C3N4晶格变形,带隙变窄,电荷迁移效率提高,光催化效率显著改善.基于上述结果,并考虑到原子的电负性和大小等因素的影响,我们采用简单的一步法合成了系列Br掺杂的g-C3N4光催化剂CN–BrX.通过X射线衍射(XRD)、红外光谱(FTIR)和电子显微镜(SEM、TEM)等手段对材料的结构进行了表征,并结合元素分析(EA)和光电子能谱(XPS)研究了其形成机理.采用光催化还原Cr(VI)效率、光催化产双氧水浓度以及光催化氧化NO能�
基金
国家自然科学基金(21603271).
