Cu(II)-imprinted poly(vinyl alcohol)/poly(acrylic acid) membrane for greater enhancement in sequestration of copper ion in the presence of competitive heavy metal ions: Material development, process demonstration, and study of mechanisms

It is a great challenge that a certain type of heavy metals such as copper is separated in the presence of competing metals. In this study, a novel Cu(II)-imprinted poly(vinyl alcohol)/poly(acrylic acid) membrane (Cu-IM) was prepared by semi-interpenetrating polymer network technique for selective copper removal from aqueous solution. The morphology, surface chemistry, stability, and copper adsorption performance of the Cu-IM were investigated. The Cu-IM exhibited a superior chemical stability in different severe environments. The batch adsorption studies showed that the adsorption of copper was highly pH-dependent, and the maximum adsorption reached 1.284 mmol/g at pH 5.0. The adsorption process was well described by the Langmuir isotherm model and the intraparticle pore diffusion model. Compared with nonimprinted PVA/PAA membrane, the Cu-IM exhibited a higher selectivity for copper, with relative selectivity coefficient of 7.78 for Cu²⁺/Zn²⁺. Besides, the Cu-IM possessed a high reusability for copper uptake and could maintain 96.25% of the original capacity for copper after 8 repeated cycles. In addition, the filtration studies indicated the Cu-IM could remove copper efficiently with the total treatment volume of 1370 bed volume to meet the EPA standard when the initial copper concentration was as high as 0.348 mM. The copper removal efficiency in the copper/zinc binary mixed solution can still retain 95.69% of that in single copper solution. Finally, the FTIR and XPS studies revealed that the carboxyl and hydroxyl groups played key roles in the copper uptake.