Chelating Zinc(II) in Crude Pheophorbide Gives It CO₂-Reducing Capability

Abstract

A pheophorbide-based photocatalyst prepared from water hyacinth (Pontederia crassipes) was developed for photocatalytic CO₂ reduction. Crude pheophorbide was prepared from the chlorophyll extract of fresh water hyacinth leaves by a sequential acid–base treatment. The successful conversion of chlorophyll to pheophorbide was indicated by the decreased absorbance intensity and slight red shift of the Qy band from around 662 nm to approximately 667 nm, indicating demetallation at the chlorophyll core as well as dephytylation. Preliminary photocatalytic investigation proved that the presence of a Zn center in pheophorbide resulted in its ability to convert CO₂ into CO and other organic compounds in water as the solvent under light irradiation. CO and organic molecules within a closed reaction system were detected and confirmed photocatalytic reduction of CO₂. However, bubbles formed during the process, probably owing to residual impurities carried in the crude chlorophyll precursor, degraded reactor stability. Additional purification and optimization therefore are required for further stability and effectiveness of the catalyst. Although this research is at the initial stage, this study demonstrates the feasibility of utilizing water hyacinth–derived pheophorbide–Zn complexes as potential organometallic photocatalysts for CO₂ reduction in support of green chemistry principles.