Sorghum husks as potential low cost adsorbent for Congo red adsorption

The increasing release of synthetic dyes in industrial effluents poses major environmental challenges. This study evaluated raw (SHR) and 0.1 M H₃PO₄ 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.