{'fraction_non_alphanumeric': 0.04092071611253197, 'fraction_numerical': 0.0196078431372549, 'mean_word_length': 4.726829268292683, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Enhancement of Salt Rejection and Water Flux by Crosslinking-Induced Microstructure Change of N- substituted Polybenzimidazole Membranes

Crosslinked or non-crosslinked ultrathin semipermeable membranes based on the N -butylated and N -butylsulfonated polybenzimidazole (BPBI and BSPBI) were successfully prepared by spin-coating method. Structural characterization by FTIR and WAXD revealed that the N -substitution and the crosslinked structure of PBI suppressed the hydrogen bonding and increased the d -spacing. Furthermore, positron annihilation lifetime spectroscopy (PALS) clearly showed the pore radius change from 0.27-0.29 nm to 0.33 nm by crosslinking. As a result, the enhancement of water flux and NaCl rejection was achieved by the crosslinking of the BPBI and BSPBI. Especially, the crosslinked N -butylsulfonated PBI (CL-BSPBI) membrane significantly improved not only salt rejection but also water flux (NaCl rejection : 46 %, water flux : 22.1 L m -2 h -1 ) compared to those of non-crosslinked BSPBI one (NaCl rejection : 11 %, water flux : 1.88 L m -2 h -1 ) due to both the Donnan effect and the formation of larger pores in the membrane, respectively.