Shedding light on hydroxyquinoline-based ruthenium sensitizers with a long-lived charge carrier to boost photocatalytic H2 evolution
Three new hydroxyquinoline-coordinated ruthenium(II) sensitizers bearing a polypyridyl derivative anchor (R1, R2 and R3) were synthesized that could tether to visible light sensitization over a Pt–TiO2 system for hydrogen production. The highest hydrogen production yield of 225.2 μmol was obtained and a turnover number (TON) of 1734 (for 6 h) over R1/Pt–TiO2. The photoactivity of the as-prepared sensitizers was found to be predominantly influenced by the longer lifetime of the metal-to-ligand-charge transfer (MLCT) states and suitable redox properties of Ru(II) species in the heteroleptic complexes. Measurement of the binding kinetics revealed a comprehensive relationship between the adsorption behaviour of dyes onto a TiO2 surface and ligand influence on the hydrogen evolution activity. The dependence of the hydrogen generation rate was systematically screened at different dye concentrations (0.05–1.0 μmol/10 mg TiO2) and the results were correlated with their pertinent adsorption properties. The operational parameters like, pH of the medium and noble metal loading were taken into account for optimal photocatalytic performance.