Effect of deposition method on metal loading and photocatalytic activity of Au/CdS for hydrogen production in water electrolyte mixture

Abstract

Au nanoparticles of size ranging 2–6 nm were deposited over hexagonal CdS using three conventional metal deposition methods namely; deposition precipitation (DP), incipient wet impregnation (WI), photo-deposition (PD) and a recently reported KI method by our group [1]. The later involves reduction of Au3+ ions with iodide ions. XRD results confirmed the formation of CdS hexagonal phase from as prepared cubic phase at 600 °C under the N2 atmosphere. Transmission electron spectroscopy (TEM), diffused reflectance spectroscopy (DRS), X-Ray fluorescence (XRF), ICP-OES and photoreactions were conducted to study the effect of Au particle size, Au loading and Au plasmonic properties on H2 production activity. It was found that surface plasmon resonance (SPR) is directly linked to Au particle size. Among all four methods, 3 wt.% Au deposited over hexagonal CdS by KI method with mean Au particle size of 4 nm showed highest performance for hydrogen production from water electrolyte mixture under visible light irradiation (>420 nm and a flux of 35 mW/cm2). XPS results of Au/CdS prepared by KI method showed that Au is exclusively present in zero oxidation state before and after photocatalytic H2 production testes indicating the stable nature of Au/CdS catalyst. The H2 production activity of Au/CdS catalysts prepared by different metal deposition methods and H2 production mechanism in a water-electrolyte is discussed in detail.