The promoted effect of a metal-organic frameworks (ZIF-8) on Au/TiO2 for CO oxidation at room temperature both in dark and under visible light irradiation

A gold nanoparticle catalyst supported on the ZIF-8 (a metal-organic frameworks) modified TiO2 (Au/ZIF-8-TiO2) was prepared by self-assembly together with solvothermal and deposition-precipitation methods, which its performance of catalytic oxidizing CO was evaluated and compared with that of Au/TiO2 and Au/ZIF-8, respectively. It was found that the incorporation of ZIF-8 into Au/TiO2 could remarkably enhance the catalytic activity of Au/TiO2 both in dark and under visible light irradiation. The characterization result of Au/ZIF-8-TiO2 showed that the sheet of ZIF-8 was distributed on the surface of TiO2 microspheres to enhance the surface roughness of TiO2, which could effectively limit the migration and aggregation of Au nanoparticles (i.e., enhancing the dispersion of Au nanoparticles at support) due to its large surface area and porousness. Moreover, Au/ZIF-8-TiO2 owned a higher surface electron density of both Au nanoparticles and TiO2 as compared to Au/TiO2. It is proposed that ZIF-8 with abundant delocalized electrons of π bond could act as an electron donor for TiO2 and Au in the structure of Au/ZIF-8-TiO2, but it act as an electron transfer mediator to promote the electron transfer between Au and TiO2 induced by the localized surface plasmon resonance of Au nanoparticles under visible light irradiation. These behaviors would promote the adsorption and activation of CO and O2 at Au or TiO2 sites, resulting in the enhanced CO oxidation.