Ag-decorated TiO2 nanofibers as Arrhenius equation-incompatible and effective photocatalyst for water splitting under visible light irradiation

Abstract The decoration of titanium oxide nanostructures with noble metal forming nanoparticles and a nanofibrous morphology can result in overcoming the electron-hole fast recombination problem and enhancing the activity of this important photocatalyst under the visible light irradiation spectra. In this study, Ag-decorated TiO2, with different Ag contents, was synthesized in nanoparticulate and nanofibrous forms. Synthesis of Ag-decorated nanofibers was performed by calcination of titanium isopropoxide/silver nitrate/polyvinylpyrrolidone electrospun nanofiber mats at 700 °C. To prepare the nanoparticles, the initial electrospun sol–gel was dried, crushed and finely ground before the calcination process. As a photocatalyst for the water photosplitting process under visible light irradiation, the rate of hydrogen production was strongly affected by nanomorphology, Ag content, and reaction temperature. Typically, due to electron confinement in the 0D nanostructure, the nanofibrous morphology markedly enhanced the hydrogen evolution rate, by almost 8-fold compared with the nanoparticles. The hydrogen production rates for the samples containing 1 wt% Ag were 5.5 and 120 mmol H2/gcat for the nanoparticles and nanofibers, respectively. For both formulations, increasing the silver content led to enhancement of the hydrogen production rate; however, the influence was clearer in the case of the nanoparticles. Investigation of the photocatalysis mechanism indicated that the localized surface plasmon of the silver nanoparticles was the main parameter resulting in the observed high photocatalytic activity under visible light irradiation. Compared to the huge effort done by researchers in this field, this study draws attention to the strong influence of nanofibrous morphology in enhancing photocatalytic activity compared to nanoparticulates and the negative influence of reaction temperature on the proposed photocatalyst reactivity. Industrially, obtaining high yield at low temperature is an economic target.