Abstract: The high-quality ZnO/graphene nanostructured composites have wide application prospects in optoelectronic devices, sensors, photocatalysis, and other fields. In this study, bulk ZnO was used as the raw material to prepare ZnO nanoparticles, which were in-situ precipitated onto graphene nanosheets. The bulk ZnO was dissolved in a choline chloride-urea eutectic solvent, and then an ethanol-water mixed anti-solvent was dropwise added to precipitate ZnO nanoparticles in the presence of graphene nanosheets. After heat treatment, ZnO nanoparticle/graphene nanosheet composites (ZnO@G) were obtained. The physicochemical properties of the composites were characterized by TEM, XRD, ICP, Raman, FTIR, and UV-visible absorption spectroscopy, and their photocatalytic performance for methylene blue degradation was investigated. The results showed that ZnO nanoparticles were evenly dispersed on graphene surface, and thus expanding the light absorption range. The interface was connected via Zn-O-C bonds, providing an electron transfer channel between the two phases. By adjusting the composition ratio of the anti-solvent, the particle size and precipitation amount of ZnO can be controlled. ZnO@G can efficiently degrade methylene blue under both full-spectrum and visible light irradiations. The main active species were identified as superoxide radicals (O_2^(?-)) generated from the oxidation of H2O by photoinduced holes and the reduction of dissolved oxygen by photoinduced electrons. This work provides a novel method for transforming bulk ZnO into nanostructured ZnO and uniformly precipitating onto the surface of graphene sheets. The self-assembled ZnO@G enables efficient photocatalytic degradation of methylene blue, and the experimental results and presumed generation pathways of active species provide insights into the photocatalytic mechanism of ZnO/carbon composites.

Key words: deep-eutectic solvent, anti-solvent precipitation, ZnO nanoparticles, graphene nanosheets, self-assembly, photocatalysis

摘要： ZnO/石墨烯纳米结构复合材料在光电器件、传感器、光催化等领域展现出广阔的应用前景。本研究以体相ZnO为原料，将其溶解于氯化胆碱-尿素低共熔溶剂中，通过乙醇-水反溶剂沉淀法将ZnO纳米颗粒原位沉淀于石墨烯纳米片表面，经热处理后获得ZnO纳米颗粒/石墨烯纳米片(ZnO@G)复合材料。采用透射电子显微镜(TEM)、X射线衍射光谱(XRD)、拉曼光谱(Raman)、傅里叶变换红外光谱(FTIR)及紫外-可见吸收光谱等表征手段，研究了复合材料的物理化学性能，并考察了其光催化降解亚甲基蓝的性能。研究表明，ZnO纳米颗粒均匀分散于石墨烯表面，有效扩展了光吸收范围。界面处通过Zn-O-C键连接，为两相间提供了电子转移通道。通过调控反溶剂的组成，可实现对ZnO颗粒尺寸和沉淀量的精准调节。ZnO@G在全光谱和可见光照射下均能高效降解亚甲基蓝，其主要活性物种为光生空穴氧化H2O和光生电子还原溶解氧所生成的超氧自由基(O_2^(?-))。本工作提供了一种将体相ZnO转变为纳米结构并均匀沉积于石墨烯片表面的新方法，自组装形成的ZnO@G可高效光催化降解亚甲基蓝染料，实验结果和活性物种的产生路径对理解ZnO@G复合材料的光催化机制具有参考价值。

关键词: 低共熔溶剂, 反溶剂沉淀法, ZnO纳米颗粒, 石墨烯纳米片, 自组装, 光催化