The Impact of Central Metal Ions in Porphyrin Functionalized ZnO/TiO2 for Enhanced Solar Energy Conversion

Abstract

The photochemistry of porphyrins and metalloporphyrins has drawn immense research interest because of their diverse catalytic activity and biological relevance. Porphyrin sensitized devices for efficient visible light photocatalysis (VLP) and dye sensitized solar cells (DSSC) are emerging as green alternate to ruthenium dye based devices. In this review, we provide an overview of the ultrafast dynamics and role of metal ions in electron transfer processes in porphyrin sensitized devices. We have discussed some of our relevant works on biologically important organic pigments, Hematoporphyrin (HP) and Protoporphyrin IX (PP) as photosensitizer to the solar devices. Our study on HP functionalized ZnO nanorod (NR) arrays shows efficient electron migration from photoexcited HP to the host ZnO NRs leading to successful realization of twin applications of HP-ZnO nanohybrids in efficient VLP and DSSC. Another study reveals the role of iron ion and its oxidation states in electron transfer processes in HP functionalized titania. From the practical application point of view, use of porphyrin-based photocatalytic devices for water decontamination is very important, given the fact that water from natural resources contains metal ions (Fe³⁺ and Cu²⁺ especially). We have synthesized and characterized a PP-ZnO nanohybrid for a flow-type photocatalytic solar device for a prototype water decontamination plant using visible light. We explored the role of metal ions, specifically, iron (III) and copper (II) in the test water with a model contaminant, methylene blue (MB) and rationalized our observations from femtosecond to picosecond resolved electronic spectroscopic studies.