Assembling ultrafine TiO2 nanoparticles on UiO-66 octahedrons to promote selective photocatalytic conversion of CO2 to CH4 at a low concentration

The improvement of CO2 conversion efficiency over semiconductor photocatalysts is usually restricted by their poor CO2 adsorption capacity. In this work, a zirconium-based organic framework (UiO-66) was introduced as an effective CO2 adsorbent to couple with TiO2 photocatalyst. The designed two-step strategy endowed the TiO2/UiO-66 composite with hierarchical porous structure, which ensured the sufficient exposed catalytic sites and a high CO2 uptake of 78.9 cm(3) g(-1). In consequence, a high CH4 production rate of 17.9 mu mol g(-1) h(-1) with 90.4 % selectivity was achieved in a mild gas-solid system using water as electron donors. Interestingly, the photocatalytic efficiency reached the similar level to that of pure CO2 atmosphere even under diluted CO2 condition (<= 2%). Further, the enhanced mechanism was discussed in detail to present the superiority of such designed composite structure from the aspects of CO2 enrichment and exposure of sufficient catalytic sites.