SrCO3-modified brookite/anatase TiO2 heterophase junctions with enhanced activity and selectivity of CO2 photoreduction to CH4

Utilizing the abundant solar energy to chemically convert CO₂ into high-energy chemical fuels such as CO, CH₄ or CH₃OH offers a way to address the serious concerns about the increasing atmospheric CO₂ levels and the depletion of fossil fuels. Herein, a series of SrCO₃-modified TiO₂ composites have been synthesized by adding SrCl₂ into a TiCl₄ hydrothermal reaction solution. It is found that brookite TiO₂ quasi nanocubes with high phase purity (denoted as pristine TiO₂) can be derived from the TiCl₄ reaction solution, and the additive Sr²⁺ ions lead to the formation of SrCO₃-modified TiO₂ heterophase junctions (HPJs) containing brookite nanorods and anatase nanoparticles. When used the SrCO₃-modified TiO₂ HPJs (hereafter denoted as SrCO₃/HPJs) as photocatalyst for CO₂ photoreduction, significantly enhanced activity and selectivity for CO₂ photoreduction to CH₄ can be achieved as compared to the pristine TiO₂. Especially, 1.0% SrCO₃/HPJs composite shows CH₄/CO production activities of 19.66/2.64 μmol g⁻¹ h⁻¹ with an overall photoactivity of 162.6 μmol g⁻¹ h⁻¹, which is 12.3 times of the pristine TiO₂ that shows an overall photoactivity of 13.2 μmol g⁻¹ h⁻¹ with CH₄/CO production activities of 0.79/3.46 μmol g⁻¹ h⁻¹. The brookite/anatase TiO₂ HPJs can effectively promote the photogenerated charge separation and restrain the interfacial charge recombination, and the SrCO₃ species on the TiO₂ HPJs can act as an efficient synergistic catalyst to improve the CO₂ adsorption and activation abilities, and thus cause the enhanced activity and selectivity for CO₂ photoreduction to CH₄. This work represents the first example of coupling TiO₂ HPJs with alkaline earth metal carbonates for efficient CO₂ photoreduction.