Effects of Ag loading on structural and photocatalytic properties of flower-like ZnO microspheres

Flower-like Ag/ZnO samples were successfully fabricated via a simple and cost efficient method without surfactants. The morphologies, structural and optical properties of Ag/ZnO samples with various Ag content were investigated. The samples were systematically characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N-2 adsorption desorption isotherm, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). It was found that ZnO was wurtzite phase and metallic Ag particles were wrapped by ZnO nanosheets. Compared with pure metallic Ag, the binding energy of Ag 3d for the Ag/ZnO samples distinctly shifted to the lower binding energy, which was attributed to the interaction between ZnO and Ag. With the increase of Ag content, surface plasmon absorption band of Ag/ZnO samples was obviously widened; meanwhile, PL intensity was decreased. The photocatalytic performance of Ag/ZnO samples were carried out by the degradation of methylene blue (MB) solution under visible light irradiation. The deposition of a certain amount of Ag was beneficial to the improvement of photocatalytic activity. The degradation rate of the Ag/ZnO sample with Ag/Zn ratio 1/20 was greater than fourfold times faster than that of ZnO. It was suggested that photoexcited electrons transferred from Ag to ZnO due to surface plasmon resonance (SPR), which could effectively reduce the recombination of electron-hole pairs and prolong lifetime of the electron-holes pairs, promoting the degradation efficiency. The deposition of a large amount of Ag was unfavorable for the formation of flower-like Ag/ZnO samples, and caused the decrease of specific surface area and the aggregation of Ag nanoparticles, leading to the reduction of photocatalytic performance. (C) 2016 Elsevier B.V. All rights reserved.

通过一种简单且经济高效的无表面活性剂的方法，成功制备了花状的Ag/ZnO样品。研究了不同Ag含量的Ag/ZnO样品的形貌、结构和光学性质。利用X射线粉末衍射（XRD）、透射电子显微镜（TEM）、扫描电子显微镜（SEM）、N₂吸附 - 脱附等温线、漫反射光谱（DRS）、X射线光电子能谱（XPS）和光致发光光谱（PL）对样品进行了系统表征。发现ZnO为纤锌矿相，金属Ag颗粒被ZnO纳米片包裹。与纯金属Ag相比，Ag/ZnO样品中Ag 3d的结合能明显向低结合能方向移动，这归因于ZnO和Ag之间的相互作用。随着Ag含量的增加，Ag/ZnO样品的表面等离子体吸收带明显变宽；同时，光致发光强度降低。通过在可见光照射下对亚甲基蓝（MB）溶液的降解来评估Ag/ZnO样品的光催化性能。一定量Ag的沉积有利于光催化活性的提高。Ag/Zn比为1/20的Ag/ZnO样品的降解速率比ZnO快四倍以上。这表明由于表面等离子体共振（SPR），光激发电子从Ag转移到ZnO，这可以有效减少电子 - 空穴对的复合并延长电子 - 空穴对的寿命，从而提高降解效率。大量Ag的沉积不利于花状Ag/ZnO样品的形成，并导致比表面积减小和Ag纳米颗粒的聚集，从而导致光催化性能降低。（C）2016 Elsevier B.V. 保留所有权利。