Recent trends in photocatalytic materials for reduction of carbon dioxide to methanol

One of the promising approaches to alleviate the problems associated with energy crisis and global warming is through photocatalytic reduction of CO2 to hydrocarbon fuels. Ultimately, photocatalytic processes utilize solar energy to convert CO2 into hydrocarbon fuels by deploying effective photocatalysts. Among the solar fuels produced from CO2 photoconversion, methanol is a versatile feedstock for producing numerous chemicals in the industry. The success of a photocatalytic conversion process hinges on the type of photocatalyst material. Although TiO2 is considered a very viable candidate due to its availability, non-toxicity, ease of synthesis and affordability, its large band gap and inability to absorb in the visible region has necessitated research into other materials. For several years researchers have reported different viable materials for this process leading to improvements in the catalytic activity. However, actualizing the conversion efficiency desired from the solar energy to produce fuels still requires modification of existing materials and discovery of new ones. The objective of this review is to provide an in-depth systematic information on different photocatalysts that have been used over the years and discuss factors that influence their effectiveness. Various modification methods for tuning the properties and improving the performance of photocatalysts are discussed. Composites or heterostructures synthesized through these modification methods are also evaluated. Comparative analysis of the performance of these composites or heterostructures with that of TiO2 is presented in this review followed by useful, applicable suggestions and recommendations for future progress.