Epichlorohydrin-Crosslinked Nano-TiO₂/Plum Kernel Shell/Chitosan Hydrogel Beads for the Efficient Removal of Hexavalent Chromium from Aqueous Solutions

Abstract

The removal of hexavalent chromium [Cr (VI)] from industrial wastewater remains a significantenvironmental challenge due to its extreme toxicity and serious risks to both human health and the ecosystem.This study aims to develop and evaluate a sustainable and efficient adsorbent for Cr (VI) removal from aqueoussolutions. To achieve this, composite hydrogel beads composed of nano-TiO₂, plum kernel shell, and chitosanwere synthesized using a sol-gel method and crosslinked with epichlorohydrin (nTiO₂–PKS–Cts@ECH). Themorphological and structural characteristics of the biosorbent were analyzed using scanning electronmicroscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). Important operational factors, such aspH, adsorbent dose, contact time, and starting Cr (VI) concentration, were optimized using batch adsorptionexperiments. The equilibrium data were evaluated using the Langmuir, Freundlich, and Dubinin–Radushkevichisotherm models, with the Langmuir model showing the best fit, indicating monolayer adsorption and amaximum capacity of 97.09 mg/g. Kinetic analysis demonstrated that the adsorption process followed a pseudosecond-order model, suggesting that chemisorption, electrostatic attraction, and reduction collectively constitutethe rate-limiting steps. Overall, the findings highlight the high potential of nTiO₂–PKS–Cts@ECH as apromising and eco-friendly biosorbent for the effective removal of Cr (VI) from contaminated water systems