A novel O-carboxymethyl chitosan-based hydrogel of an outstanding adsorption performance for removal of cationic Basic Red 12 dye from its aqueous solution

O-Carboxymethyl chitosan (O-CM-chitosan) hydrogel, prepared in our previous study, was investigated in this work for the first time as adsorbent for Basic Red 12 (BR 12) dye. With rising temperature (from 25 degrees C to 55 degrees C) and decreasing solution pH (from 9 to 4), a lowering in both adsorption capacity (from 703.47 to 400.79 mg/g) and removal efficiency (from 70.34% to 40.08%) was observed. A significant increase in adsorption capacity (from 342.75 to 621.39 mg/g) was observed with increasing initial dye concentration (from 400 to 1000 mg/L), while a decrease in removal efficiency (from 85.69% to 62.14%) was noted. Pseudo-second-order model fitted well the adsorption. Isotherms of adsorption conform to Langmuir model with a maximum monolayer adsorption capacity of 625 mg/g. The value of ?H degrees (-23.99 kJ/mol) implied exothermic nature of adsorption process. Values of ?G degrees indicated that the adsorption was spontaneous at low temperature and nonspontaneous at high temperature. The value of activation energy is equal to 13.071 kJ/mol. The dye removal percentage from the hydrogel was 88% at the first cycle. Thus, O-CM-chitosan hydrogel has promising and effective properties for removing BR 12 and similar dyes from aqueous media.