Synthesis and surface modification of TiO₂-based photocatalysts for the conversion of CO₂

Among all greenhouse gases, CO₂ is considered the most potent and the largest contributor to global warming. In this review, photocatalysis is presented as a promising technology to address the current global concern of industrial CO₂ emissions. Photocatalysis utilizes a semiconductor material under renewable solar energy to reduce CO₂ into an array of high-value fuels including methane, methanol, formaldehyde and formic acid. Herein, the kinetic and thermodynamic principles of CO₂ photoreduction are thoroughly discussed and the CO₂ reduction mechanism and pathways are described. Methods to enhance the adsorption of CO₂ on the surface of semiconductors are also presented. Due to its efficient photoactivity, high stability, low cost, and safety, the semiconductor TiO₂ is currently being widely investigated for its photocatalytic ability in reducing CO₂ when suitably modified. The recent TiO₂ synthesis and modification strategies that may be employed to enhance the efficiency of the CO₂ photoreduction process are described. These modification techniques, including metal deposition, metal/non-metal doping, carbon-based material loading, semiconductor heterostructures, and dispersion on high surface area supports, aim to improve the light absorption, charge separation, and active surface of TiO₂ in addition to increasing product yield and selectivity.