(73c) Photocatalytic Reduction of CO2 to Fuels by Brookite-Containing Mixed-Phase TiO2 Nanocrystals

Photocatalytic reduction of CO₂ to fuels (CO, methane, methanol, etc) by sunlight is potentially a promising sustainable energy technology that not only reduces greenhouse gas emissions but also produces renewable fuels. TiO₂ has been widely used as a photocatalyst due to its low cost, high stability, and non-toxicity.  TiO₂ naturally occurs as three polymorphs: anatase, brookite and rutile. Among them, only TiO₂ anatase, rutile or anatase-rutile mixed phase (P25) have been studied for CO₂ photoreduction. Brookite phase is much less studied as a photocatalyst and has not been studied for CO₂ photoreduction so far.  In this work, brookite containing mixed-phase (e.g., anatase-brookite, anatase-brookite-rutile) TiO₂ nanocrystals have been synthesized through a hydrothermal method with a good control in brookite phase fraction. The catalysts are well characterized by UV-vis, XRD, SEM, TEM, BET, and FTIR analysis. The experiments of photocatalytic CO₂ reduction with water vapor using the prepared catalysts are conducted under simulated sunlight irradiation. CO and CH₄ are the major reduction products measured by a gas chromatograph (GC) equipped with thermal conductivity detector (TCD) and flame ionization detector (FID). The interfacial charge transfer between the different phase nanocrystals and CO₂ reduction mechanisms are also investigated in this study.