Synthesis of Cross-linked Carboxyl Modified Polyvinyl Alcohol and its Application in Selective Adsorption Separation of Cu(II) from Cd(II) and Ni(II)

Abstract

A cross-linked copolymer (XL-P(AA-co-VAc)) of vinyl acetate and acrylic acid was prepared using azobisisobutyronitrile as initiator and N,N’-methylenebisacrylamide as crosslinker. Then, XL-P(AA-co-VAc) was reacted with ethanol to prepare a crosslinked carboxyl modified polyvinyl alcohol (XL-P(AA-co-VA)). The as-prepared XL-P(AA-CO-VA) hydrogel was characterized by FTIR, XRD, SEM and BET, and investigated as an selective heavy metal ion adsorbent. The adsorption characteristics of the XL-P(AA-CO-VA) hydrogel were studied with a aqueous solution containing ternary metal ions Cu(II), Cd(II) and Ni(II). It was found that XL-P(AA-CO-VA) can selectively adsorb Cu(II) in competition with Cd(II) and Ni(II), and the selectivity coefficients of 48 (βCu(II)/Cd(II)) and 80 (βCu(II)/Ni(II)) were obtained. The kinetics were demonstrated to match well with the pseudo-second order kinetics model with the rate constants (K2, g/(mg•min)) of 3.71✕10− 4, 0.0011 and 0.0015 for Cu(II), Cd(II) and Ni(II), respectively. The equilibrium adsorption of Cu(II) to the XL-P(AA-CO-VA) hydrogel follows the Langmuir adsorption model with qmax of 41.27 mg/g and KL of 0.94 L/mg. The thermodynamic studies indicate that ΔG0 was negative and increased with temperature, and the adsorption process of XL-P(AA-CO-VA) for Cu(II) ion was spontaneous and exothermic. ΔH and ΔS were − 56.57 kJ/mol and − 171.18 J·(mol·K)−1, respectively. The XL-P(AA-CO-VA) hydrogel is of interest for the selective separation of Cu(II) from industrial wastewater containing Cd(II) and Ni(II).