β-Cyclodextrin Immobilized in Geophagic Clay Sheets for the Absorption of Dyes From Wastewater Using a Fixed-Bed Method.

Abstract

Industrial wastewater contaminated with synthetic dyes remains a critical environmental concern due to their persistence, toxicity, and poor biodegradability. In this study, β-cyclodextrin (βCD) functionalized geophagic clay was evaluated as an adsorbent under continuous flow fixed-bed conditions. Structural characterization confirmed successful βCD immobilization, with SEM/EDS showing carbon-enriched agglomerated sheets, the FTIR spectra exhibiting new O-C stretching bands at 1152 and 1025 cm^-1, and XRD patterns indicating lattice reorganization with enhanced basal reflections and new peaks at 17.9° and 25.1°. Performance testing demonstrated that an optimized 3-cm bed height achieved 93% RhB removal within 3 min 57 s, while MO removal exceeded 96% at 50 ppm. Regeneration studies showed strong reusability, with the composite retaining over 80% efficiency after five adsorption-desorption cycles. Kinetic modeling revealed that RhB uptake followed the pseudo-second-order model (R² > 0.99), confirming chemisorption dominated by electrostatic attraction and hydroxyl-mediated hydrogen bonding. In contrast, MO adsorption on βCD clay was well described by both pseudo-first-order (R² = 0.99) and pseudo-second-order (R² = 0.98) models, reflecting a dual mechanism of rapid diffusion-controlled physisorption and stable chemisorption via cavity inclusion and hydrogen bonding. These findings highlight the synergistic role of βCD functionalization in enhancing adsorption capacity, selectivity, and reusability for industrial dye remediation.