Plasmonic coinage metal-TiO2 hybrid nanocatalysts for highly efficient photocatalytic oxidation under sunlight irradiation

The conventional methods of Au co-catalyst deposition onto TiO2 surfaces generally do not offer fine tuning of the metal-TiO2 interface for enhanced photoactivity because of the non-uniform distribution of the size and shape of metal nanodeposits. Hence, this study demonstrated the comparative co-catalysis activity imparted to TiO2 by as-prepared coinage metal (Au, Ag and Cu) quantum dot particles of similar sizes (3-5 nm) as a function of their plasmonic interactions with TiO2 under visible light irradiation. The physiochemical and interfacial properties of metal-TiO2 composites are studied by optical band gap, XRD, XPS, TEM, surface area, time resolved spectroscopy, current-voltage characteristics, GC and GC-MS analysis. It was revealed that the optical band gap is shifted to 2.9 eV from 3.2 eV of bare TiO2 and the specific surface area, 50 m(2) g(-1), of TiO2 is notably reduced to 20-33 m(2) g(-1) after metal nanoparticles impregnation (M-TiO2) that were found to exist in the Au-0 and Ag-0, and Cu+2 oxidation states. The average relaxation time approximate to 18 mu s (bare TiO2) < 20 mu s (Cu-TiO 2) < 24 mu s (Au-TiO2) < 27 mu s (Ag-TiO2) of photo-excited charge species and the highest conductance value 1.65 x 10(-7) S of Ag-TiO2 as revealed by current-voltage studies strongly established that Ag-TiO2 interface acts as a better electron sink to capture and store photogenerated electrons, thus displaying superior photocatalytic activity than Au/or Cu-TiO2 interfaces. Thus, Ag-TiO2 exhibited the highest rate constant k = 4 x 10(-2) min(-1) relative to k = 2.7 x 10(-2) min(-1) (Au-TiO2) and k = 1.93 x 10(-2) min(-1) (Cu-TiO2) for the oxidative degradation of benzaldehyde and nitrobenzaldehyde, respectively, to CO2 under direct sunlight (40-50 mW cm(-2)) exposure.