石墨烯负载的金属氧化物纳米颗粒的可控制备及催化性能

采用直接浸渍法、过氧化氢均相氧化沉积法和氨水催化水解法制备了石墨烯负载的铁、钴、镍金属氧化物纳米颗粒.研究了三种沉积方法对颗粒尺寸分布的影响;采用透射电子显微镜、傅里叶变换红外光谱、X射线衍射和X射线光电子能谱表征了催化剂的形貌与结构.用过氧化氢均相氧化沉淀法可制得粒径分布最均匀的纳米颗粒.过氧化氢的氧化作用可使石墨烯表面的氧化基团含量最大化,为纳米颗粒提供了足够的吸附与成核点.氨水加速了金属离子的水解与成核,导致纳米颗粒的粒径增大与不均.以苯甲醇氧化为探针反应考察了催化剂的性能.催化剂的活性按以下顺序逐渐下降:过氧化氢辅助沉积法>直接浸渍法>氨水催化水解法,与纳米颗粒尺寸增长趋势一致.纳米催化剂颗粒尺寸与其活性的良好关联性显示,发展石墨烯负载尺寸可控的纳米催化剂的方法具有重要意义.

Controllable synthesis and catalytic performance of graphene-supported metal oxide nanoparticles

The size of nanoparticles plays a crucial role in their performance. In this article, three methods, i.e., direct impregnation, homogeneous oxidative precipitation with hydrogen peroxide, and ammonia-catalyzed hydrolysis, were applied to synthesize iron, cobalt, and nickel metal oxide nanoparticles supported on graphene. The influence of the three deposition methods on particle size distribution was investigated. Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of the catalysts. The highest dispersion and the most uniform particle size distribution were obtained by the hydrogen peroxide homogeneous oxidative precipitation method. Hydrogen peroxide favors the maximization of the oxygen-containing groups on graphenes, thereby providing sufficient absorption and nucleation sites to give a high dispersion of nanoparticles. In contrast, ammonia accelerates the nucleation speed and results in the largest particle size and inhomogeneity. The catalytic properties of the graphene-supported metal oxide nanoparticles were tested with the oxidation of benzyl alcohol as a probe reaction. The reaction activity decreased in the following order: catalysts prepared by hydrogen peroxide-assisted deposition > direct impregnation > ammonia-catalyzed hydrolysis. The decrease in reaction activity was consistent with the order of increasing catalyst particle sizing shown in transmission electron microscopy images. The catalytic relevance of the particle size showed a necessity for the development of effective methods for size-controlled nanocatalyst synthesis on graphenes.