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

Abstract

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 TiO2quasi 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.