Chitosan coated cotton-straw-biochar as an admirable adsorbent for reactive red dye

Abstract

Cotton straw generated biochar was coated with chitosan using oxalic acid as a crosslinking agent. This chitosan-oxalic acid-biochar composite was characterized and analyzed for adsorption of synthetic azo-dye Reactive Red 21. Batch as well as column studies in fixed bed mode were carried out. The monolayer adsorption capacity was found to be 125.1 mg g−1 at pH 5.0, with just 90 min of adsorption highlighting this as super-sorbent material. Langmuir as well as Redlich-Peterson isotherms exhibited best fit models with the experimental data. Kinetics studies suggested a pseudo second order adsorption process in agreement with Langmuir isotherm. The thermodynamics of adsorption disclosed the fact that process is purely enthalpy-driven, spontaneous, and exothermic in nature. The presence of biopolymer, organic cross-linker, and biowaste altogether in a single adsorbent material led to an excellent super-sorbent for the dye. The effect of cationic, anionic, and non-ionic surfactants on the adsorption efficiency has also been studied.

Keywords

• Chitosan-oxalic acid-biochar
• Adsorption
• Reactive red 21
• Water treatment
• Dyes