A novel method of surface modification on thin-film-composite reverse osmosis membrane by grafting hydantoin derivative

Abstract

Membrane degradations by biofouling and free chlorine oxidation are the major obstacles for aromatic polyamide thin-film-composite (TFC) reverse osmosis (RO) membranes to realize high performance over a long period of operation. In this work, a hydantoin derivative, 3-monomethylol-5,5-dimethylhydantoin (MDMH), was grafted onto the nascent aromatic polyamide membrane surfaces by the reactions with active groups (e.g., acyl chloride groups) in the surfaces. The grafted MDMH moieties with high reaction activity and free chlorine could play as sacrificial pendant groups when membranes suffer from chlorine attacks, and the chlorination products N-halamines with strong antimicrobial function could sterilize microorganisms on membrane surfaces and then regenerate to MDMH. This was designed as a novel means to improve both chlorine resistances and anti-biofouling properties of the aromatic polyamide TFC RO membranes. Attenuated total reflectance mode Fourier transform infrared spectroscopy (ATR-FTIR) revealed that the MDMH-modified membranes had two characteristic bands at 1772 and 1709 cm −1 corresponding to two carbonyl groups in hydantoin ring. This suggested the successful grafting of MDMH onto the membrane surfaces, which was further confirmed and quantified by X-ray photoelectron spectroscopy (XPS) analysis. After modification with MDMH, the membrane surface hydrophilicity increased obviously as contact angles decreased from 57.7° to 50.4–31.5°. But, there was no obvious change in membrane surface roughness after modification. The MDMH-modified membranes were shown to possess high chlorine resistances with small changes in water fluxes and salt rejections after chlorination with 100–2000 ppm h chlorine at pH 4. The chlorinated MDMH-modified membranes demonstrated obvious sterilization effects on Escherchia coli and substantial preventions against microbial fouling. Therefore, the MDMH-modified membranes offer a potential use as a new type of chlorine resistance and anti-biofouling TFC RO membranes.