Kinetic and isotherm studies on the adsorption of ionic liquids from aqueous solutions by carboxymethyl cellulose modified with sodium methacrylate sulfonate.

A novel carboxymethyl cellulose (CMC) graft copolymer (CMC-g-PSMAS) was successfully synthesized by grafting sodium methacrylate sulfonate (SMAS) onto CMC. The resulting CMC-g-PSMAS was used to absorb 1-allyl-3-methylimidazole chloride ([Amim]Cl) ionic liquid. The effects of different experimental factors such as monomer dosage, temperature and time on the grafting yield were systematically studied. Adsorption studies demonstrated that the adsorption equilibrium could be achieved within 60 min. The theoretical maximum adsorption capacity of CMC-g-PSMAS for [Amim]Cl reached 69.2 mg·g^-1. Compared to several kinetic and isothermal models, the adsorption process of [Amim]Cl onto CMC-g-PSMAS could be well-described by the pseudo-second-order model (R² = 0.991) and the Langmuir model (R² = 0.999), which was a typical chemical adsorption process. Adsorption thermodynamics analyses at 25 °C revealed that the adsorption process was spontaneous (ΔG = -33.37 KJ·mol^-1) and exothermic (ΔH = -56.52 KJ·mol^-1). The adsorption capacity of CMC-g-PSMAS was 35.3 mg·g^-1 after eight cycles, indicating its good stability and recyclability. As a consequence, CMC-g-PSMAS was efficient in the adsorption of [Amim]Cl, which could be a potential candidate for removing ionic liquids in aqueous environments.