Polymer-agro-waste composites for removal of Congo red dye from wastewater: adsorption isotherms and kinetics

Composites of sawdust and sugarcane molasses with styrene-maleic acid copolymer [(SD-SMA) and (SM-SMA)] were successfully synthesized by suspension polymerization and used as adsorbents for removal of Congo red (CR) dye from aqueous solution. The surface morphology of composite beads was observed under scanning electron microscope, which revealed highly porous surface. Maximum 20 wt.% sawdust and 10 wt.% sugarcane molasses loading were achieved in respective composite. Adsorption of CR was performed in batch process. The effect of initial solution concentration, amount of composite dose, and biomaterial content into the composite were investigated to test the adsorption efficiency and adsorption capacity of these composite beads at pH 7. Adsorption efficiency of 90 and 48% was observed in 2 h using SM-SMA and SD-SMA composites, respectively. The equilibrium data was analyzed using Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models. Adsorption onto SD-SMA composites followed the Langmuir model whereas Freundlich model was obeyed by SM-SMA composite beads. Pseudo-second-order kinetics was followed by both types of composites with good correlation coefficient values. The results indicates that SD-SMA and SM-SMA composite beads can be considered as potential adsorbent for the CR dye removal from aqueous solutions.