Noble metal modified reduced graphene oxide/TiO2 ternary nanostructures for efficient visible-light-driven photoreduction of carbon dioxide into methane

• The effect of noble metal doping on rGO/TiO2 was extensively investigated.
• Noble metal nanoparticles were doped onto rGO/TiO2 through a simple polyol process.
• All modified samples displayed enhanced photoactivity toward CO2 photoreduction.
• Platinum-modified rGO/TiO2 ternary nanocomposite showed the highest photoactivity.
• The optimum weight percentage of Pt to rGO/TiO2 was shown to be at 2 wt.%.

The design and architecture of visible-light-active photocatalysts is a key aim among material scientists for the efficient utilization of renewable solar energy. In this paper, a series of noble metal (Pt, Pd, Ag and Au) nanoparticles supported on reduced graphene oxide/TiO2 (GT) were successfully synthesized through a dual step process. In the first step, GT nanocomposites were prepared using a solvothermal method. The as-prepared hybrid nanostructures were subsequently employed as supporting materials for the dispersion of metal nanoparticles. A simple polyol process was used to respectively reduce metal ions (PtCl62−, Pd2+, Ag+, and AuCl4−) into metal (Pt, Pd, Ag and Au) nanoparticles on GT. The three-component nanocomposites exhibited enhanced photocatalytic activities toward the photoreduction of CO2 into CH4 gas under the irradiation of typical daylight bulbs. This was attributed to the multiplex phenomena such as an enhanced utilization of visible light, efficient electron transfer in the noble metal-doped GT nanojunctions and interfacial electron transfer in the reduced graphene oxide (rGO) sheets, as evidenced by UV–vis and PL characterizations. Among the noble metals studied, the Pt-doped GT nanocomposites showed the highest efficiency in reducing CO2. A total CH4 yield of 1.70 μmol/gcat was achieved after 6 h of light irradiation, which was 2.6 and 13.2 folds higher in comparison to GT and commercial P25, respectively. Based on the experimental results obtained, a plausible mechanism for the photocatalytic process associated with Pt-GT was proposed.

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