Covalently bound Eosin Y on chitosan as a removable photosensitizer for ranitidine degradation

Abstract

Developing visible-light-responsive materials that enable pollutant removal is essential for advancing greener water treatment technologies. In this work, a chitosan–Eosin Y conjugate (CTS–EOY) was synthesized through carbodiimide coupling to produce a biodegradable and low-toxicity photosensitizer that operates homogeneously in aqueous media. Importantly, the biopolymeric nature of CTS–EOY allows its recovery from the reaction medium after treatment, addressing key limitations associated with freely dissolved dyes. The conjugate preserves the characteristic optical properties of Eosin Y while exhibiting modified excited-state behavior associated with its restricted environment within the biopolymer matrix. Ranitidine (RAN), a widely detected pharmaceutical and precursor of N-nitrosodimethylamine, was selected as a model contaminant to evaluate the environmental performance of the material. Under visible-light irradiation (525 nm), CTS–EOY achieved nearly 90% RAN removal within 2 h. Mechanistic studies demonstrated that degradation proceeds predominantly through singlet-oxygen–mediated pathways, with secondary contributions from triplet–substrate interactions, rather than through hydroxyl-radical-driven oxidation typical of advanced oxidation processes. LC-QToF/MS analysis identified five major transformation products, enabling the proposal of an environmentally relevant degradation route involving both Type I and Type II photosensitized pathways. Overall, this work highlights CTS–EOY as a sustainable biopolymer-supported photosensitizer for visible-light degradation of pharmaceutical pollutants combining efficient photodegradation with low toxicity and post-treatment recoverability, offering an energy-efficient alternative to conventional oxidation approaches.