Pyridine-substituted zinc porphyrin/TiO2 nanoparticles for increased light harvesting and efficient photocatalysis

Metalloporphyrin-coated semiconductor nanoparticals may be one potential option for photodegradation of organic pollutants in watertreatment. To examine the function of lone pair electron-containing substituents in photocatalytic interfacial charge transfer mechanism, we synthesized three meso‑ substituted zinc porphyrins (Znpors) containing 4-pyridyl, 3-pyridyl and phenyl, denominated as 4-Pyr-Znpor, 3-Pyr-Znpor and Ben-Znpor, respectively. Density functional theory (DFT) calculations revealed similar electronic structrues and bandgaps of the three porphyrins, with clearly negaitive charges on the isosurface of pyridine substituents. Photoelectrochemical and impedance measurements reveal that 4-Pyr-Znpor/TiO 2 and 3-Pyr-Znpor/TiO 2 exhibit greater photocurrent response and lower charge transfer resistance as compared to Ben-Znpor/TiO 2 . Photodegradation of the organic pollutant AB1 using the composites suggests efficient photocatalysis ability of the three porphyrin-sensitized TiO 2 nanoparticals, with 4-Pyr-Znpor/TiO 2 exhibiting the highest degradation rate at the first 30 min. Our findings suggest that the pyridine substituent may attract holes and facilitate the charge separation efficiency, therefore enhancing the photocatalytic efficiency.