微波水热两步法合成高可见光响应Ag2S/ZnO及其光催化性能、机理

在不同的制备条件下,通过微波水热两步法获得了一系列Ag₂S/ZnO光催化剂,采用X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、紫外-可见漫反射吸收光谱(UV-Vis/DRS)、扫描电子显微镜(SEM)和N₂吸附-脱附等测试手段对产物结构和形貌进行了表征。结果表明,产物以六方纤锌矿ZnO为主,其晶型结构并未随着反应温度和Ag₂S物质的量的增加而改变。Ag₂S的引入显著增强了光催化剂在可见光区的吸收,使吸收边带发生红移,同时抑制了ZnO(001)晶面的生长。另外,所得产物的形貌随着Ag₂S物质的量的增加从爆米花状转变为少量的柱体颗粒,且BET比表面积经过复合后明显减小。以罗丹明B为目标降解物,研究并比较了一系列Ag₂S/ZnO光催化剂对罗丹明B的光降解性能。结果表明,n_Ag2S/n_ZnO=1:10时,光催化剂在紫外光、可见光和模拟日光的照射下具有最好的光催化效果,优于目前应用最广泛的市售P25。另外,所制备的光催化材料Ag₂S/ZnO经4次循环使用后,其降解效率没有明显下降,表明该催化材料具有一定的光催化稳定性。经捕获实验研究发现,在Ag₂S/ZnO的光催化反应中空穴起主要作用,并根据绝对电负性估算了复合材料Ag₂S/ZnO的能带位置,据此提出了可能的光催化反应机理。

Photocatalytic Performance and Photolysis Mechanism of Ag2S/ZnO with Visible-Light Response Prepared by Microwave Hydrothermal Two-Step Method

Under different synthetic condition, the Ag₂S/ZnO photocatalyst with visible-light response was prepared by microwave hydrothermal two-step method. The phase structures, physicochemical properties and morphologies were well-characterized via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption (UV-Vis/DRS), Scanning electron microscopy (SEM) and N₂ adsorption-desorption tests. Results indicate that the synthetic product is mainly hexagonal wurtzite ZnO, of which phase structure has been changed with the temperature of reaction and the n_Ag2S/n_ZnO increased. The presence of Ag₂S enhances the light absorption of the photocatalyst under the visible-light region, redshifting the absorption band, and suppresses the growth of ZnO along the (001) crystal plane. In addition, with the n_Ag2S/n_ZnO increased, the morphology of synthetic Ag₂S/ZnO realizes a transformation from the shape of popcorn to cylinder, moreover, the BET values reduce obviously. Compared to pure ZnO, when the n_Ag2S/n_ZnO was 1:10, the composite performs the highest photocatalytic activity to degrade Rhodamine B under the irradiation of ultraviolet, visible and simulated sunlight, far superior than P25 which was the most widely used at present. Moreover, there is no significant change in the degradation efficiency of Ag₂S/ZnO 200° 1-10 after four times of recycling, which shows the photocatalytic stability to a certain extent. In addition, the capture experiments proved that holes brought out main effect on the photocatalytic reaction of Ag₂S/ZnO. Accordingly, a potential reaction mechanism was proposed.