Step-by-step growth of HKUST-1 on functionalized TiO2 surface: An efficient material for CO2 capture and solar photoreduction

The present study reports on a simple preparation strategy of a hybrid catalyst, TiO2/HKUST-1, containing TiO2 anatase nanoparticles (NPs) with tailored morphology and photocatalytic activity coupled with a porous metal-organic framework (MOF), namely HKUST-1, as an advanced material for the CO2 photocatalytic reduction. In detail, TiO2/HKUST-1 catalyst was prepared via an easy slow-diffusion method combined with a step-by-step self-assembly at room temperature. The growth of crystalline HKUST-1 onto titania surface was achieved by functionalizing TiO2 nanocrystals, with phosphoesanoic acid (PHA), namely TiO2-PHA, which provides an intimate contact between MOF and TiO2. The presence of a crystalline and porous shell of HKUST-1 on the TiO2 surfaces was assessed by a combination of analytical and spectroscopic techniques. TiO2/HKUST-1 nanocomposite showed a significant efficiency in reducing CO2 to CH4 under solar light irradiation, much higher than those of the single components. The role of MOF to improve the photoreduction process under visible light was evidenced and attributed either to the relevant amount of CO2 captured into the HKUST-1 porous architecture or to the hybrid structure of the material, which affords enhanced visible light absorption and allows an effective electron injection from TiO2-PHA to HKUST-1, responsible for the photochemical reduction of CO2.