Photocatalytic performance of Pd decorated TiO2-CdO composite: Role of in situ formed CdS in the photocatalytic activity

We report an enhanced photocatalytic activity for TiO2-CdO composite for hydrogen generation from aqueous solution of Na2S + Na2SO3 compared to pure CdO and TiO2. An in situ conversion of CdO to CdS is observed during the photocatalytic reaction resulting in the formation of a CdO-CdS-TiO2 ternary composite, which play a role in the enhanced activity. Presence of Pd as a co-catalyst in the composite increases the hydrogen production nearly ten times. As prepared composite exists as anatase phase of TiO2 and cubic phase of CdO. Characterization of the catalyst by powder XRD, SEM and TEM suggest that a nanosized TiO2 exists as a dispersed phase on aggregated CdO. UV-visible absorption spectrum of the composite shows features of both CdO and TiO2. Composite sample exhibits increased photocurrent response and has increased fluorescence lifetime for the charge carriers compared to pure CdO and TiO2. A detailed characterization of the used catalysts clearly shows the formation of CdS phase besides TiO2 and CdO. This is the first report on the photocatalytic activity of TiO2-CdO system for hydrogen generation from water due to in situ bulk formation of CdS during the photocatalytic reaction. The in situ formed CdS in the composite enhances the photocatalytic activity in two ways: (i) CdS, whose conduction band is at higher negative potential than CdO and TiO2, can reduce H+ more efficiently and (ii) efficient separation of photogenerated charges can occur in this composite system, resulting in increased lifetime for the charge carriers. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.