Graphite-like carbon nitride (g-C3N4)-based compounds have attracted considerable attention be-cause of their excellent photocatalytic performance. In this work, a novel direct Z-scheme system constructed from two-dimensional (2D) g-C3N4 nanoplates and zero-dimensional (0D) MoS2 quan-tum dots (QDs) was prepared through the combination of a hydrothermal process and microemul-sion preparation. The morphologies, structures, and optical properties of the as-prepared photo-catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectroscopy. In ad-dition, the photocatalytic performances of the prepared 2D/0D hybrid composites were evaluated based on the photodegradation of rhodamine B under visible-light irradiation. The results demon-strated that the introduction of MoS2 QDs to g-C3N4 greatly enhanced the photocatalytic efficiency. For the optimum 7% MoS2 QD/g-C3N4 photocatalyst, the degradation rate constant was 8.8 times greater than that of pure g-C3N4 under visible-light irradiation. Photocurrent and electrochemical impedance spectroscopy results further demonstrated that the MoS2 QD/g-C3N4 composites exhib-ited higher photocurrent density and lower chargetransfer resistance than those of the pure g-C3N4 or MoS2 QDs. Active species trapping, terephthalic acid photoluminescence, and nitro blue tetrazo-lium transformation experiments were performed to investigate the evolution of reactive oxygen species, including hydroxyl radicals and superoxide radicals. The possible enhanced photocatalytic mechanism was attributed to a direct Z-scheme system, which not only can increase the separation efficiency of photogenerated electron-hole pairs but also possesses excellent oxidation and reduc-tion ability for high photocatalytic performances. This work provides an effective synthesis ap-proach and insight to help develop other C3N4-based direct Z-scheme photocatalytic systems for environmental purification and energy conversion.%近年来,光催化技术作为一种"绿色"技术,在解决环境问题和能源危机等方面有着广泛的应用.新型可见光响应的半导体光催化材料g-C3N4具有二维(2D)纳米片结构,合适的禁带宽度(Eg=2.7 eV),优异的化学稳定性和低廉成本得到广泛的研究.但是,g-C3N4光催化剂本身的光生电子-空穴对复合几率高以及可见光响应范围窄等缺点,使其在光催化领域应用中具有一定的局限性.因此,提高g-C3N4半导体材料的光催化活性成为近年的研究热点.众所周知,Z型光催化体系的构筑不仅使材料具有较强的氧化还原能力而且有利于其光生电子-空穴的有效分离.但传统Z型光催化体系由于贵金属的引入、复杂的反应体系限制了其在实际领域中的应用.因此,构筑无电子介体的直接Z型光催化体系成为光催化领域的研究热点之一.与块状材料相比,零维(0D)量子点材料具有带隙可调性,可见光和近红外区域的强光收集能力等性能,在光催化领域具有广阔的应用前景.MoS2量子点具有优异的光学和电子性能,因此,在催化、荧光检测、生物成像领域有重要的应用价值.我们结合水热和微乳溶液法合成了直接Z型g-C3N4/MoS2 QDs(2D/0D)复合光催化材料,并采用X射线衍射(XRD)、X射线光电子能谱(XPS)、原子力显微镜(AFM),透射电子显微镜(TEM)以及紫外可见漫反射光谱(UV-vis)等表征方法对该催化剂的结构特征、微观形貌和光学性能进行分析.并研究了g-C3N4/MoS2 QDs复合材料在可见光下的光催化性能.XRD,XPS结果表明,复合材料由g-C3N4,MoS2组成.TEM和高斯分布结果表明,MoS2 QDs具有良好的分散性,其尺寸小于5 nm,g-C3N4纳米片由具有皱纹和不规则折叠结构的薄层组成,在g-C3N4/MoS2 QDs复合材料中可以看到少量的MoS2量子点沉积在片状g-C3N4的表面上.光催化性能测试结果进一步表明,7%MoS2 QDs/g-C3N4在可见光下具有优异的光催化性能:可见光照射12 min内,RhB的降解效率可达100%,降解速率常数是纯g-C3N4的8.8倍.为了进一步研究g-C3N4/MoS2异质结光催化剂的光催化机理,用对苯醌、乙二胺四乙酸二钠和丁醇进行了自由基捕捉剂实验.结果表明,超氧自由基在降解有机染料过程中起主要作用,羟基自由基和空穴在增强的光催化性能中发挥相对较小的作用.通过光电流测试、材料价带导带位置计算以及?O2-和?OH定量实验结果并结合文献分析认为,MoS2量子点和g-C3N4之间优良的界面接触以及由直接Z型结构产生的光生电荷载体的有效分离使其光催化性能得到显著提升.
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