Abstract
The increasing release of synthetic dyes in industrial effluents poses major environmental challenges. This study evaluated raw (SHR) and 0.1 M H(3)PO(4) acid-treated (SHT) sorghum husks as low-cost adsorbents for removing Congo Red (CR) from aqueous solutions. SHT achieved a maximum removal efficiency of 85.26% at 40 mg dosage and pH 2, outperforming SHR (76.17% at pH 3 and dosage of 45 mg). Langmuir isotherm analysis demonstrated higher adsorption capacity for SHT (77.14 mg/g) compared to SHR (57.55 mg/g), inferring improved monolayer coverage after treatment. Kinetic modeling indicated that SHR followed a pseudo-first-order model, while SHT was better explained by a pseudo-second-order model, indicating chemisorption as the dominant mechanism. Thermodynamic results confirmed spontaneous and endothermic adsorption with positive enthalpy change (ΔH) values of 13.52 kJ/mol for SHR and 25.26 kJ/mol for SHT at 40 °C. Regeneration studies demonstrated that SHT retained over 65% desorption efficiency after six cycles, highlighting good reusability. FTIR revealed that Congo Red sorption onto treated sorghum husk is governed by hydrogen bonding, π-π stacking interactions, and possibly electrostatic attractions involving functional groups like hydroxyls, amines, and aromatic rings. These findings indicate that acid-treated sorghum husk is an effective, sustainable, and economical alternative to commercial adsorbents for azo dye removal in wastewater treatment.