Cross-linked chitosan and iron-based metal-organic framework decoration on waste cellulosic biomass for pharmaceutical pollutant removal

Abstract

Biocompatible composite adsorbents were developed by incorporating Fe-based metal-organic framework (MIL-101) and cross-linked chitosan (Ch) onto cinnamon bark (CNM) waste for tetracycline (TC) removal. The synthesized MIL-101 decorated cinnamon (MIL-101@CNM) and chitosan-functionalized MIL-101@CNM (Ch/MIL-101@CNM) composites were thoroughly characterized, and the effects of key adsorption parameters were examined. The required adsorbent dosage and equilibrium time were reduced by half compared to MIL-101@CNM (60 mg, 180 min) with Ch/MIL-101@CNM (30 mg, 90 min). Moreover, adsorption capacity also increased from 9.60 mg g⁻¹ to 33.77 mg g⁻¹. Adsorption data were conformed to the Dubinin-Radushkevich isotherm model for both adsorbents, while the Elovich model showed the best fit for MIL-101@CNM and the pseudo-first-order kinetic model for Ch/MIL-101@CNM, indicating distinct adsorption mechanisms and heterogeneous surface interactions. It was observed that pH played dominant role and since both surface and adsorbent were protonated in TC solutions at acidic pH, efficiencies decreased due to electrostatic repulsion. In addition, adsorption processes were exothermic and spontaneous. Increasing humic acid (HA) concentrations also decreased the adsorption rate. After five cycles, TC adsorption decreased from 91.31 % to 76.12 % for MIL-101@CNM and from 98.59 % to 85.03 % for Ch/MIL-101@CNM, confirming their suitability for reuse. The proposed biocomposites offer significant potential for real-world applications, demonstrating sustainable and promising removal of both pharmaceutical and a wide range of anionic and cationic organic dyes from various water sources.