Combining experimental and molecular computational approaches for enhanced removal of organic and inorganic pollutants via diafiltration using chitosan with permanent cationic charges.

Environmental and public health concerns have intensified due to the persistence, bioaccumulation, and toxicity of organic and inorganic pollutants in aquatic systems. To address this issue, we modified chitosan polymer incorporating permanently charged quaternary ammonium groups, enhancing its efficiency to remove five emerging contaminants: arsenic (V) (As(V)) as arsianate, chromium (VI) (Cr(VI)) as dichromate, tetracycline (TC), ciprofloxacin (CIP), and amoxicillin (AMX). Crucially, this study combines experimental validation with density functional theory (DFT) simulations to provide a mechanistic understanding of the molecular interactions governing contaminant retention. The integrated approach reveals how electrostatic forces, hydrogen bonding, and steric effects contribute to pollutant binding under varying conditions of pH (3.0-11.0), ionic strength (0.0-1.00 mol L NaCl), and contaminant concentrations (1-100 mg L). The system demonstrated high removal efficiencies 98 % for As(V), 95 % for Cr(VI), 75 % for TC and CIP, and 60 % for AMX with respective maximum retention capacities (MRCs) of 112, 97.4, 632.3, 185.6, and 420 mg g. DFT calculations strongly supported these results, elucidating binding mechanisms and electronic interactions between the functionalized biopolymer and each contaminant. The combination of diafiltration and tailored polymer design offers a robust, insightful platform for the remediation of contaminated water, highlighting the value of mechanistic modeling in advancing environmental technologies.