Graft copolymerization of acrylic acid on kraft lignin to enhance aniline adsorption from aqueous solution

Abstract

Kraft lignin from bamboo was modified by grafting with acrylic acid to improve its capacity to adsorb aniline, a typical aromatic organic pollutant. Characterization of the copolymer structure and morphology indicated that lignin was successfully grafted by acrylic acid. Batch experiments showed that after graft copolymerization, the modified lignin had an enhanced aniline adsorption capacity (89.89 mg/g) as compared with the original lignin (6.61 mg/g). A kinetics study showed that the adsorption process followed pseudo-second-order kinetics, and the activation energy (Ea) was 10.22 kJ/mol. The equilibrium data were consistent with the Langmuir equation. The maximum monolayer capacity was 108.7 mg/g, which is higher than those of most reported lignin-based adsor-bents. Thermodynamic values indicated that adsorption of aniline on the modified lignin is an exothermic process and spontaneous in nature due to the negative value of ΔH and ΔG. Consequently, graft copolymerization of acrylic acid on lignin appears to be a promising modification process to enhance the aniline adsorption capacity from aqueous solution. Application: Information from this study can help mills prepare a better lignin adsorbent.