Abstract:

Lignin-based ion-imprinted polymer(L-ⅡP) was prepared via graft copolymerization of sodium lignosulfonate(SL) and acrylamide(AM) with using Cr(VI) as template ion, acrylamide as functional monomer, N, N-methylene-bis-acrylamide as crosslinker and ammonium persulfate as initiator. Then the L-ⅡP's structure and adsorption performance on Cr(VI) were studied. The preparation conditions of L-ⅡP were optimized by single factor experiment and orthogonal experiment. The structure of L-ⅡP was characterized by FT-IR, SEM-EDS and pore size analysis. The adsorption experimental data were fitted by quasi-first-order kinetic equation, quasi-second-order kinetic equation, Langmuir and Freundlich isothermal adsorption equation, and the reuse of L-ⅡP was discussed. FT-IR analysis showed that the grafting copolymerization of sodium lignosulfonate and AM was successful. SEM images showed that L-ⅡP had more porous structure than lignin non-ionic imprinted polymer(L-NIP). L-ⅡP was a kind of mesoporous material with pore size of 3-5 nm and 10-20 nm. When the mass of template ion, functional monomer, sodium lignosulfonate and crosslinker were 10 mg, 0.2 g, 100 mg and 0.6 g, respectively, and the reaction was performed at 60 ℃ for 24 h, the obtained L-ⅡP exhibited the best adsorption performance of Cr(VI). The optimum adsorption conditions at room temperature were pH value of 2 and initial concentration of Cr(VI) of 800 mg/L.The adsorption of Cr(VI) was described well with the pseudo-second-order model with R² of 0.980 1, when L-ⅡP was used as absorbent. And the adsorption isotherm was consistent with the Langmuir model with q_mof 24.94 mg/g and R² of 0.992. The results indicated that the adsorption of Cr(VI) by L-ⅡP was a monolayer adsorption dominated by chemical adsorption. The selectivity coefficients of L-ⅡP for Cr(VI) of Cu(Ⅱ) and Cr(Ⅲ) were 5.925 and 7 respectively, indicating of its excellent selective adsorption properties. L-ⅡP had good reusability, after 5 times of adsorption/desorption, the adsorption capacity could still retain more than 80% of the maximum adsorption capacity.

Key words: sodium lignosulfonate, ion-imprinted polymer, selective adsorption, Cr(VI)