Harnessing Hofmeister Salt Effects for Confined Photosensitized Oxidation in a Porphyrin-Based Supramolecular Nanoreactor

Abstract

Coexisting inorganic ions and multiple water-soluble organic dyes in saline wastewater often compromise substrate selectivity and photosensitized efficiency, creating challenges for effective pollutant dye removal. To overcome these limitations, we developed a heterogeneous supramolecular photosensitized system based on a microporous porphyrin organic cage (HP3C) and investigated its size-selective photosensitized behavior toward water-soluble dyes, together with the salt-regulated confined enrichment effect. Photophysical studies revealed that HP3C efficiently generated reactive oxygen species (ROS) under light irradiation, including singlet oxygen (1O2) and superoxide radicals (O2•–). Under 440–445 nm light irradiation, HP3C exhibited molecular-size-dependent photosensitization. Indigo carmine (IC), with molecular dimensions compatible with the cage cavity, achieved rapid decolorization within 10 min with a rate constant of 0.336 min–1, which is approximately 20-fold higher than those of geometrically mismatched dyes. Notably, the presence of salts, particularly Na2SO4, further enhanced IC decolorization with the rate constant increasing to 0.514 min–1, an approximately 1.5-fold enhancement over the salt-free system. Hofmeister analysis and DFT calculations suggest that salting-out-induced dehydration promoted IC enrichment toward the hydrophobic cage of HP3C, enabling confined oxidation through shortened substrate–ROS diffusion pathways. This work establishes a salt-assisted confined photosensitization strategy for selective decolorization of water-soluble dye pollutants in saline environments.