Towards the Optimization of Nanoporous Copolymer Membranes for Use As Heavy Metal Adsorbers

Due to their small size, the effective removal of aqueous heavy metals ions is a substantial challenge in the area of water treatment. To this end, nanoporous membranes synthesized from self-assembled copolymer precursors show potential for the separation and/or capture of these aqueous species. Using the self-assembly and nonsolvent-induced phase separation (SNIPS) procedure, we have synthesized tunable poly(acrylonitrile-r-oligo(ethylene glycol) methyl ether methacrylate-r-glycidyl methacrylate) membranes. Due to their well-defined structure, narrow pores (≲ 5 nm), and amenability to chemical modification, these membranes act as effective substrates for adsorptive groups which can capture and remove divalent aqueous heavy metal contaminants. As such, amino acid moieties—including L-cysteine and L-glutamic acid—were grafted onto membrane substrates. The grafting reaction was optimized through a fractional factorial design-of-experiments approach towards the effective capture of metals including divalent copper, lead, and nickel. Reaction conditions such as the graft molecule concentration, mole fraction of the zinc chloride catalyst, temperature, and reaction duration were manipulated in order to increase the capacity of the adsorptive membranes. Subsequent batch tests were employed to elucidate adsorption equilibria and capacity measurements. Furthermore, a custom-built miniaturized flow cell enabled the creation of well-defined solute breakthrough curves which probe the adsorption phenomena under dynamic conditions.