The reduction of carbon dioxide to useful chemicals has received a great deal of attention as a strategy to reduce emissions of CO2 and as alternative to the depletion of fossil resources. As the chemical reduction of CO2 is energetically uphill due to its thermodynamic stability, this process involves a transfer of energy, usually derived either from light or electricity. Achievements in the fields of photocatalysis during the last decade sparked an increased interest in the possibility of using sunlight to reduce CO2, when many research groups began to check the CO2 reduction using a variety of semiconductors and photosensitizers, initially derived from efforts to split water into H2 and O2. Still, these photocatalysts used either as soluble photoactive molecules or solid materials, appear to be non-economically viable systems. Moreover, another problem of the CO2 photoreduction is the diversity of reaction products which range from formic acid, CO, formaldehyde, methanol, CH4 formed through a series of kinetically very challenging multi-electron, multi-proton transfer processes. Besides that, it is also difficult to control the selectivity of the photocatalytic reaction from water reduction with H2 generation to the less thermodynamically and kinetically favoured CO2 reduction. Whilst homogeneous photocatalytic systems have both advantages and disadvantages, the main issues are related to the low reduction rates, the use of expensive metals that is impractical on a large scale, and the need for sacrificial reductants. In many cases, the metal complexes do not serve as true catalysts, but rather are consumed stoichiometrically through a variety of deactivation pathways or at best exhibit a few turn overs. Similarly, several crucial obstacles limiting the efficiency of almost every oxide semiconductor photocatalyst are the high rate of charge-carrier recombination and the small activity under visible irradiation. It is desirable to develop materials with band-gaps corresponding to the solar spectrum, and with conduction band energies sufficiently energetic for the reduction of CO2. In this sense, modified TiO2 could absorb photons in the visible range. Titanium dioxide, the most known photocatalyst today, is an earth abundant and inexpensive material, and has very good chemical and photochemical stabilities. Several strategies can be applied to enhance the efficiency of TiO2 for CO2 reduction. In this presentation we will show our results on modified TiO2 photocatalyst that exhibits the highest productivity so far reported.

Modified titanium dioxide photocatalysts for solar fuels generation

247th National Meeting (2014)

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