Abstract: A surface molecular imprinted layer-by-layer (SMILbL) film was fabricated on a polyethersulfone (PES) porous membrane substrate for selective filtration of cations and anions. The LbL deposition procedure and the ultraviolet (UV) cross-linking of the modified membrane were monitored by attenuated total reflection-infrared (ATR-IR) spectra. The SMILbL-PES membrane with 4.5 bilayers of diazoresin (DAR)/poly(acrylic acid) complexed with 5,10,15,20-tetrakis(4-(trimethylammonio)-phenyl)-21H,23H-porphyrin tetratosylate (PAA-Por4+) effectively reduced the permeation velocity of Por4+ after washing the Por4+ template out. In comparison to a control film DAR/PAA-modified PES membrane (ConLbL-PES) in a dialysis experiment, the SMILbL-PES membrane exhibited better selectivity for permeation of 5,10,15,20-tetraphenyl-21H,23H-porphine-p,p',p'',p'''-tetrasulfonic acid tetrasodium hydrate (Por4-) against permeation of Por4+. In pressure-driven transport experiments, the SMILbL-PES membrane showed a much longer blocking time for Por4+ than for Por4-, indicating the selective loading of Por4+ into the SMILbL film. The surface charge of the SMILbL-PES membrane after Por4+ loading was higher than that of other membranes, resulting in an enhanced rejection ability of the SMILbL?PES membrane to Por4+ caused by Coulomb repulsion. A possible mechanism was proposed as follows. The binding sites generated through imprinting in the SMILbL-PES membrane enable loading of a larger amount of Por4+. The stronger repulsion between Por4+ and the SMILbL film may cause the main contribution to the selective rejection of Por4+. It can be easily imagined that this concept can be extended to the construction of composite membranes from other imprinting systems.
Template and target information: 5,10,15,20-tetrakis(4-(trimethylammonio)-phenyl)-21H,23H-porphyrin tetratosylate, Por⁴⁺

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