Removal of direct Red‐31 and direct Orange‐26 by low cost rice husk: Influence of immobilisation and pretreatments

Abstract

Abstract The aim of the present study is to investigate the influence of free, carboxymethyl cellulose (CMC) immobilised, PVA–alginate immobilised, and HCl treated rice husk on the removal of Direct Red‐31 and Direct Orange‐26 dyes. The biosorption capacity of the rice husk increased with HCl treatment (67.39 and 45.34 mg/g) and decreased with PVA–alginate immobilisation (9.73 and 10.03 mg/g) as compared to the free biomass (65.56 and 45.58 mg/g) at 200 mg/L dye concentration for Direct Red‐31 and Direct Orange‐26, respectively. Equilibrium data were best described by Langmuir Type 1 for Direct Red‐31 and Direct Orange‐26 (free, CMC immobilised, PVA–alginate immobilised, and HCl treated). Best correlation coefficients for Direct Red‐31 and Direct Orange‐26 using free, CMC immobilised, PVA–alginate immobilised, and HCl treated rice husk were obtained for pseudo‐second order and Elovich kinetic models. Values of Gibbs free energy (Δ G °) and enthalpy change (Δ H °) indicated that reaction was spontaneous and endothermic in nature at the studied temperatures. FT‐IR studies showed the involvement of carbonyl, carboxyl, and amide groups in the biosorption process. SEM exhibited the morphological changes on the biosorbent surface and BET analysis to determine the surface area is also carried out.