Simultaneous realization of direct photodeposition and high H₂-production activity of amorphous cobalt sulfide nanodot-modified rGO/TiO₂ photocatalyst

To realize highly efficient hydrogen production of graphene-based photocatalysts, it is greatly important to increase more interfacial active sites onto graphene. In this work, the highly efficient CoS_x-rGO (reduced graphene oxide)/TiO₂ composite photocatalyst was synthesized via a simple two-step method, including the hydrothermal loading of rGO nanosheets onto TiO₂ nanoparticles and the subsequent photodeposition process of CoS_x nanodots (0.5–2 nm) on the rGO nanosheets. Photocatalytic experimental results confirmed that the CoS_x-rGO/TiO₂ photocatalyst displayed a distinctly higher photocatalytic H₂-evolution activity than the TiO₂ photocatalyst. The highest hydrogen-production efficiency of obtained CoS_x-rGO/TiO₂ (10%) achieved 256.97 μmol·h⁻¹, which was distinctly higher than that of TiO₂ (4.41 μmol·h⁻¹), rGO/TiO₂ (20.19 μmol·h⁻¹) and CoS_x/TiO₂ (132.67 μmol·h⁻¹). According to the results of various characterizations and tests, the synergistic-effect mechanism of CoS_x nanodots and rGO nanosheets is proposed to explain the increased photocatalytic performance of CoS_x-rGO/TiO₂ photocatalytic material, namely the rGO nanosheets cause the quick transfer of photo-induced carriers from TiO₂ to CoS_x nanodots, and then CoS_x nanodots work as hydrogen-production active sites to quickly generate H₂. The present study may offer innovative ideas for the preparation and application of new highly efficient and inexpensive photocatalytic materials.

增加石墨烯界面产氢活性位点是提升石墨烯基光催化材料的一种重要方法。在本研究中, 通过简单的两步法合成了高效的CoS_x-rGO/TiO₂复合光催化剂, 即首先利用水热法将rGO纳米片负载到TiO₂纳米颗粒上, 随后再通过光沉积的方法在rGO纳米片表面沉积CoS_x纳米点 (0.5–2 nm)。光催化实验结果表明, 光催化剂CoS_x-rGO/TiO₂相比于TiO₂具有更高的光催化析氢活性。其中CoS_x-rGO/TiO₂(10%) 光催化剂的产氢性能达到256.97 μmol•h^-1, 明显高于TiO₂ (4.41 μmol•h^-1)、rGO/TiO₂ (20.19 μmol•h^-1)和CoS_x/TiO₂(132.67 μmol•h^-1)。根据各种表征测试结果, 提出了CoS_x纳米点和rGO纳米片协同增强TiO₂光催化产氢性能的作用机理, 即rGO纳米片作为良好的电子转移介质可以将TiO₂上的光生电子快速转移至CoS_x, 随后CoS_x纳米点作为产氢活性位点快速产生H₂。本研究可以为新型高效光催化材料的制备和应用提供新的思路。