Adsorption of Brilliant Red 2BE dye from water solutions by a chemically modified sugarcane bagasse lignin

A lignin resulting from acid hydrolysis of sugarcane bagasse in the process of bioethanol production from biomass (Mw = 1890 g mol−1) was purified and carboxy-methylated to obtain a macromolecule (CML), soluble in water at pH ≥ 4.5, with a degree of substitution (DS) of 0.46 ± 0.01 relative to C9 – the basic unit of lignins. This modified lignin was complexed with the Fe3+ ion (CML-Fe) and used as an adsorbent for the successful removal of Brilliant Red 2BE textile dye from aqueous solutions. The adsorbent was characterised by infrared spectroscopy and scanning differential calorimetry. The effects of pH, adsorbent dosage and shaking time on adsorption capacity were studied. In pH 2.0 the adsorption of the dye was maximum. The contact time to obtain equilibrium at 298 K was fixed at 12 h for the CML-Fe adsorbent. The Avrami fractional-order kinetic model provided the best fit to the experimental data compared with pseudo-first-order or pseudo-second-order kinetic adsorption models. For Brilliant Red 2BE dye, the equilibrium data were best fitted to the Sips isotherm model.