Enhanced photocatalytic production of molecular hydrogen on TiO2 modified with Pt–polypyrrole nanocomposites

Abstract

Titanium dioxide was modified with Pt–polypyrrole nanocomposites through the in situ simultaneous reduction of Pt(IV) and the oxidative polymerization of pyrrole monomers at ambient temperature. The modified powders were characterized using X-ray photoelectron spectroscopy (XPS), dark-field scanning transmission electron microscopy (DF-STEM), infrared spectroscopy (IR) and by the determination of the BET surface area by nitrogen adsorption. Photocatalytic hydrogen production tests were performed employing 75 ml aqueous solution containing 2250 μmol methanol as the sacrificial electron donor. The obtained results show that 0.5 and 1.0 wt% Pt and polypyrrole, respectively, are the optimum ratios for high photocatalytic H₂ production rates. The amount of H₂ evolved during 5 h of UV-vis illumination of the suspension of Pt–polypyrrole modified TiO₂ powder is three times higher than that obtained with Pt-loaded TiO₂ prepared by a photochemical deposition method. The photonic efficiencies of the H₂ production employing 75 ml aqueous solution containing 370 mmol methanol were calculated to be 10.6 ± 0.5 and 4.5 ± 0.2% for TiO₂ modified with Pt–polypyrrole nanocomposites and for Pt-loaded TiO₂ prepared by a photochemical deposition method, respectively. A synergistic effect between Pt nanoparticles and polypyrrole leading to a better separation of the charge carriers is proposed to explain the enhanced reactivity of the newly synthesized photocatalyst.