Highly Efficient and Stable CO2 Reduction Photocatalyst with a Hierarchical Structure of Mesoporous TiO2 on 3D Graphene with Few-Layered MoS2

The development of photocatalysts of CO2, reduction based on stable and Earth-abundant materials is essential for utilizing solar energy and storing it in chemical forms. Here, we report the synthesis and characterization of a composite material consisting of a few layers of MoS2 on a hierarchical porous structure of mesoporous TiO2 and macroporous 3D graphene aerogel (TGM) as a high-performance, robust, noble-metal-free photocatalyst of CO2 reduction. The hierarchical structure contributed to the high photocatalytic catalyst performance, which was investigated by controlling the morphologies of the mesopores and macropores. By optimizing the relative amounts of each component and the configuration of the composite, a TGM system was fabricated. The resulting TGM showed a lower extent of charge recombination and a higher photocurrent density, and hence a higher CO photoconversion rate (92.33 mu mol CO/g.h) than those of other composite combinations, i.e., bare TiO2, TiO2-graphene, TiO2-MoS2, and TiO2-graphene multiple-layered MoS2. Also, the role of each component and the underlying mechanism in the catalysis of the reaction by TGM were investigated. The long-term stability of the TGM composite was tested and compared with that of a TiO2-graphene-Ag composite. Over the course of 15 cycles, the TGM composite retained its original conversion rate, while the activity of the TiO2-graphene-Ag composite decreased. The hierarchical porous structure with mesoporous TiO2 and a few layers of MoS2 on macroporous 3D graphene is expected to have great potential as an affordable, robust, high-efficiency CO-selective photocatalyst of CO, reduction.