Self-assembly of nitrogen-doped TiO2 with exposed {001} facets on a graphene scaffold as photo-active hybrid nanostructures for reduction of carbon dioxide to methane

Abstract

Tailored synthesis of well-defined anatase TiO2-based crystals with exposed {001} facets has stimulated incessant research interest worldwide due to their scientific and technological importance. Herein, anatase nitrogen-doped TiO2 (N-TiO2) nanoparticles with exposed {001} facets deposited on the graphene (GR) sheets (N-TiO2-001/GR) were synthesized for the first time via a one-step solvothermal synthetic route using NH4F as the morphology-controlling agent. The experimental results exemplified that GR was uniformly covered with anatase N-TiO2 nanoparticles (10–17 nm), exposing the {001} facets. The percentage of exposed {001} facets in the N-TiO2-001/GR nanocomposites was calculated to be ca. 35%. Also, a red shift in the absorption edge and a strong absorption in the visible light range were observed due to the formation of Ti-O-C bonds, resulting in the successful narrowing of the band gap from 3.23 to 2.9 eV. The photocatalytic activities of the as-prepared photocatalysts were evaluated for CO2 reduction to produce CH4 in the presence of water vapor under ambient temperature and atmospheric pressure using a low-power 15 W energy-saving daylight lamp as the visible light source—in contrast to the most commonly employed high-power xenon lamps—which rendered the process economically and practically feasible. Among all the studied photocatalysts, the N-TiO2-001/GR nanocomposites exhibited the greatest CH4 yield of 3.70 μmol·gcatalyst −1, approximately 11-fold higher activity than the TiO2-001. The enhancement of photocatalytic performance was ascribed to the effective charge anti-recombination of graphene, high absorption of visible light region and high catalytic activity of {001} facets relative to the {101} facets.