Gold nanoparticles-sensitized wide and narrow band gap TiO2 for visible light applications: a comparative study

Gold nanoparticles (AuNPs)-sensitized wide band gap TiO2 (Au/P-TiO2) and narrow band gap TiO2 (Au/M-TiO2) nanocomposites were prepared using an electrochemically active biofilm. The optical and structural properties of the Au/P-TiO2 and Au/M-TiO2 nanocomposites were characterized using standard techniques. The surface plasmon resonance (SPR) absorption characteristics of the AuNPs on the TiO2 surface extended the absorption edge of P-TiO2 and M-TiO2 to the visible light region. The photocatalytic activity of the Au/P-TiO2 and Au/M-TiO2 nanocomposites was evaluated by the photodegradation of methylene blue and methyl orange, and 2-chlorophenol under visible light irradiation, where Au/M-TiO2 nanocomposite exhibited enhanced photocatalytic activity compared to the Au/P-TiO2 nanocomposite and P-TiO2 and M-TiO2 nanoparticles. Furthermore, the higher photoelectrochemical performance of the Au/M-TiO2 nanocomposite compared to the Au/P-TiO2 nanocomposite and P-TiO2 and M-TiO2 nanoparticles further support its higher visible light active behavior under visible light irradiation. The pronounced photoactivities of the Au/M-TiO2 nanocomposite in the visible region were attributed to the interfacial synergistic effects of the two phenomena, i.e. the SPR effect of AuNPs and the defect-induced band gap reduction of M-TiO2 nanoparticles. The present work provides a newer insight into the development of nanocomposites of noble metals and defective metal oxides with high efficiency in the field of visible light-induced photoactivity.