Photocatalytic Production of H₂ on Nanocomposite Catalysts

The photocatalytic production of H 2 in water with visible light using nanocomposite catalysts, which include quantum-sized (Q-sized) CdS, CdS nanoparticles embedded in zeolite cavities (CdS/zeolite), and CdS quantum dots (Q-CdS) deposited on KNbO 3 (CdS/KNbO 3 and Ni/NiO/KNbO 3 /CdS), is investigated. The rate of H 2 production in alcohol/water mixtures and other electron donors at λ ≥ 400 nm is the highest with the hybrid catalyst, Ni/NiO/KNbO 3 /CdS with a measured quantum yield, φ, of 8.8%. The relative order of reactivity as a function of catalyst is Ni(0)/NiO/KNbO 3 /CdS > Ni(0)/KNbO 3 /CdS > KNbO 3 /CdS > CdS/NaY-zeolite > CdS/TiY-zeolite > CdS, while the reactivity order with respect to the array of electron donors is 2-propanol > ethanol > methanol > sulfite > sulfide. In addition, the rates of H 2 production from water and water−alcohol mixtures are correlated with fluorescent emission spectra and fluorescence lifetimes. Irradiation of Ni/NiO/KNbO 3 /CdS proceeds via the partial reduction of Cd(II) to Cd(0) on the surface of CdS. The coupling of Ni(0)/NiO and Cd(0) on the surface of KNbO 3 appears to have some of the chemical principles of a Ni/Cd battery at high overvoltages. Evidence for the formation of nickel hydride as an important intermediate has been obtained.