Formation and structural evolution of biphenyl polyamide thin film on hollow fiber membrane during interfacial polymerization

A novel reverse osmosis hollow fiber membrane was prepared by interfacial polymerization from 3,3′,5,5′-biphenyl tetraacyl chloride and m-phenylenediamine on a polysulfone hollow fiber membrane. The structural evolution of biphenyl polyamide thin film during interfacial polymerization was monitored by attenuated total reflectance infrared, X-ray photoelectron spectroscopy and atom force microscopy. The relationship between the structure and separation properties of the membranes was investigated. Results show that the biphenyl polyamide thin film had a three-layer structure: a loose initial layer with a low cross-linked structure, a dense middle layer with a high cross-linked structure and a loose surface layer with a low cross-linked structure. The dense middle layer had an intrinsic cross-linked structure with over 86.0% amide bonds (–CONH–) and below 14.0% carboxylic groups (–COOH), mainly responsible for separation. A growth model of the biphenyl polyamide thin film was proposed to describe the structural evolution process during interfacial polymerization.