Photocatalytic H₂ production on trititanate nanotubes coupled with CdS and platinum nanoparticles under visible light: revisiting H₂ production and material durability

The photocatalytic production of molecular hydrogen (H₂) on ternary composites of Pt, CdS, and sodium trititanate nanotubes (NaₓH_(2−x)Ti₃O₇, TNTs) is examined in an aqueous 2-propanol (IPA) solution (typically 5 vol%) at a circum-neutral pH under visible light (λ > 420 nm). The H₂ production rates are dependent on the Pt-loading level, and the optimum production rate in the Pt/CdS/TNTs is approximately six times higher than that in Pt/CdS/TiO₂. A D₂O solution containing 5 vol% IPA leads only to the production of D₂ molecules, whereas increasing the IPA amount to 30 vol% leads to the production of DH molecules. This indicates that the Pt/CdS/TNTs composites enable H₂ production via true water splitting under our typical experimental conditions. X-ray photoelectron spectroscopy (XPS) analyses of the as-synthesized Pt/CdS/TNTs and those used for 6 and 12 h show that metallic Pt on the CdS/TNTs is less susceptible to oxidation than Pt on CdS/TiO₂. In addition, photocorrosion of CdS (i.e., sulfate formation) is significantly inhibited during the photocatalytic H₂ production reactions in the Pt/CdS/TNTs because of the efficient charge transfer via the TNTs framework. The Pt/CdS/TNTs samples are thermally more stable than Pt/CdS/TiO₂ and CdS/TNTs, effectively inhibiting the formation of CdO during the thermal synthesis. Detailed surface characterizations of the as-synthesized ternary composites are performed using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and XPS.