Hierarchical Porous TiO₂ Embedded Unsymmetrical Zinc–Phthalocyanine Sensitizer for Visible-Light-Induced Photocatalytic H₂ Production

Abstract

In this study, a novel visible-light-driven photocatalyst was designed based on unsymmetrical zinc–phthalocyanine photosensitizer on hierarchical porous TiO2 (HPT) semiconductor. The HPT material has been prepared by a simple self-formation route. The present work successfully uses zinc phthalocyanine with spectral response extended to 700 nm triggers light harvesting center and HPT semiconductors for high photocatalytic H2 production. This novel unsymmetrical zinc–phthalocyanine (PCH001) containing three tert-butyl and two carboxylic acid groups that act as “push” and “pull” electron transfer properties from the excited dye to the TiO2 conduction band. The carboxylic group in the sensitizer serves as an anchoring group on to the surface of TiO2 and to provide intimate electronic coupling between its excited-state wave function and the conduction-band manifold of the semiconductor. The excellent photophysical properties was governed further by choosing three tert-butyl groups which tuned the LUMO level of the sensitizer that provides directionality in the excited state in addition to low aggregation and high solubility. The Zn-PCH@TiO2 composites exhibited promising activity and enhanced stability a photocatalytic system for visible-light-induced hydrogen production from water. The photocatalyst (HPT-0.25) shows H2 production yield 2260 μmol and high turnover number (TON 18080) under visible/near IR light irradiation. Moreover, HPT-0.25 photocatalyst shows a broad visible/NIR light responsive range (400–800 nm) with high apparent quantum yields (AQY) of 7.15, 2.70, 11.57, 3.90, and 0.50% under λ = 420, 550, 690, 730, and 800 nm monochromatic light irradiation, respectively. The present work gives a new advance toward efficient solar energy conversion with promising visible/near IR light-driven photocatalytic activity.