溴掺杂石墨相碳化氮对Cr(VI)光催化还原性能的提高

引用本文: 汪勉, 曾玉彬, 董国辉, 王传义. 溴掺杂石墨相碳化氮对Cr(VI)光催化还原性能的提高[J]. 催化学报, 2020, 41(10): 1498-1510. doi: S1872-2067(19)63435-2 shu

Citation: Mian Wang, Yubin Zeng, Guohui Dong, Chuanyi Wang. Br-doping of g-C₃N₄ towards enhanced photocatalytic performance in Cr(VI) reduction[J]. Chinese Journal of Catalysis, 2020, 41(10): 1498-1510. doi: S1872-2067(19)63435-2 shu

溴掺杂石墨相碳化氮对Cr(VI)光催化还原性能的提高

a 武汉大学动力与机械学院, 流体机械与动力工程装备技术湖北省重点实验室, 湖北武汉 430072;
b 陕西科技大学环境科学与工程学院, 陕西西安 710021
基金项目:
国家自然科学基金（21603271）.

摘要: 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（3.2eV），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能力评价了CN-BrX的光催化活性，并进行了光催化反应过程动力学拟合和循环实验.通过理论计算（DFT）、紫外-可见漫反射光谱（UV-vis DRS）、荧光光谱（PL）、光电流（PC）和比表面积（BET）等测试分析了材料的光催化活性增强机理，并通过活性物种捕获实验深入探究了其光催化还原Cr（VI）的反应机理.结果表明，CN-BrX（CN-Br30除外）保留了g-C₃N₄的基本骨架，其中Br元素以取代碳氮杂环中N原子的形式均匀分布于g-C₃N₄结构中.引入的Br元素可以明显降低材料的禁带宽度，拓宽其可见光响应范围，加快光生载流子的分离效率，并增大其比表面积，从而使得改性材料具有更高的光催化氧化还原活性.此外，在Cr（VI）光催化还原过程中，光生e^-，·OH和H₂O₂均起着重要作用.

关键词:

English

Br-doping of g-C₃N₄ towards enhanced photocatalytic performance in Cr(VI) reduction

a Hubei Key Laboratory of Accoutrement Technique in Fluid Machinery and Power Engineering, School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, Hubei, China;
b School of Environmental Science and Engineering, Shaanxi University of Science and Technology, Xi'an 710021, Shaanxi, China
Received Date: 25 February 2020
Revised Date: 27 March 2020
Fund Project:
This work was supported by the National Natural Science Foundation of China (21603271).

Abstract: 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-BrX, X=5, 10, 20, 30), where X is a percentage mole ratio of NH₄Br 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-BrX (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.

Key words:

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沈阳化工大学材料科学与工程学院沈阳 110142

溴掺杂石墨相碳化氮对Cr(VI)光催化还原性能的提高

English

Br-doping of g-C₃N₄ towards enhanced photocatalytic performance in Cr(VI) reduction

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