Metal Doped TiO₂ Photocatalysts for CO₂ Photoreduction

Abstract

Greenhouse gases such as CO 2 , CH 4 and CFCs are the primary causes of global warming. Worldwide, people are exploring techniques to reduce, capture, store CO 2 gas and even convert this gas in to some useful chemicals. CO 2 can be transformed into hydrocarbons in a photocatalytic reaction. The advantage of photo reduction of CO 2 is to use inexhaustible solar energy. Knowledge of elementary steps in photocatalytic CO 2 reduction under UV irradiation is required in order to improve the photo efficiency of the photocatalyst. A semiconductor photocatalyst mediating CO 2 reduction and water oxidation needs to absorb light energy, generate electron hole pairs, spatially separate them, transfer them to redox active species across the interface and minimize electron hole recombination. This requires the semiconductor to have its conduction band electrons at higher energy compared to the CO 2 reduction potential while the holes in the valence band need to be able to oxidize water to O 2 . A single semiconductor does not usually satisfy these requirements. Some recent developments in this field have been moves towards rational photocatalyst design, the use of highly active isolated Ti-species in mesoporous and microporous materials, metal-doping of TiO 2 , development of catalysts active at longer wavelengths than can be achieved with commercially available titania etc. The use of transition-metal loaded titanium dioxide (TiO 2 ) has been extensively studied as a photocatalyst in photoreactions. Unlike traditional catalysts drive chemical reactions by thermal energy, semiconducting photocatalysts can induce chemical reactions by inexhaustible sunlight and convert CO 2 in to the useful hydrocarbons. In this review article we will cover different aspects of metal doped nano structured TiO 2 photocatalysts, used to convert/reduce CO 2 in to useful hydrocarbons.