Enhanced photocatalytic CO2 valorization over TiO2 hollow microspheres by synergetic surface tailoring and Au decoration

The photocatalytic reduction of CO2 with H2O into valuable solar fuels is a sustainable solution for addressing the fossil energy crisis and mitigating the greenhouse effect. The exploitation of an efficient TiO2 photocatalyst for photocatalytic CO2 reduction is still urgently desirable but quite challenging. In this work, highly porous fluorinated TiO2 hollow microspheres with abundant exposed {001} facets and abundant surface defects (including Ti3+ and oxygen vacancies (V-o)) were fabricated via a fluoride-mediated self-transformation pathway, which were then decorated with multifunctional Au nanoparticles via in situ photochemical deposition. The photocatalytic CO2 reduction activity and selectivity were significantly enhanced over the as-prepared Au-modified TiO2 hollow microspheres under both full-spectrum and visible light illumination, because of the multiple synergetic effects of host-guest modifications in tuning light harvesting, charge separation, and CO2 adsorption and activation. First, the light harvesting capacity was enhanced because of the light trapping effect of hollow cavities together with the surface plasmon resonance (SPR) effect of surface decorated Au nanoparticles. Second, the charge transfer efficiency was significantly enhanced by simultaneously introducing {001}/{101} facet junctions and introducing Au/TiO2 Schottky junctions. In addition, surface CO2 adsorption and activation were enhanced owing to the strong affinity of decorated Au nanoparticles to CO2 molecules and abundant surface Ti3+ and V-o defect sites, significantly dominating the photocatalytic CO2 reduction reaction dynamics and pathway. This study not only demonstrates that synergetic host-guest engineering is a novel feasible avenue to design high-performance photocatalysts for photocatalytic CO2 reduction, but also offers new insights into integrated tuning of multiple photocatalytic processes.