Loose nanofiltration membrane with highly-branched SPEI/PEI assembly for dye/salt textile wastewater treatment

Salt accumulation is inevitable in the conventional textile wastewater treatment, which hardly realize the effectively remove of dye and recover of water. Loose nanofiltration (NF) membrane with highly hydrophilic surface and loose structure has been demonstrated as an optimal choice for efficient dye/salt separation. This study develops a loose NF membrane via the layer-by-layer (LbL) assembly of highly-branched sulfonated polyethyleneimine (SPEI)/polyethyleneimine (PEI) and mussel-inspired post-crosslinking. Different molecular weights of highly-branched SPEI are synthesized. Effects of LbL assembly and cross-linking process, SPEI molecular weight and crosslinker type are investigated systematically. It is found that the membrane prepared with the assembly of SPEI10k/PEI and crosslinked by catechol exhibits low roughness (Ra = 3.56 nm), high hydrophilicity (WCA = 44.07°) and negatively-charged membrane surface (ζ = −16.39 mV). As a result, the membrane achieves an ultrahigh permeability (~ 36.89 LMH/bar), excellent dyes retention (> 99.37% to Congo red), as well as low rejection to salts (2.47% to NaCl). The novel loose NF membrane developed in this work therefore shows a promising prospect in practical industrial textile wastewater treatment.