Charge tunable thin-film composite membranes by gamma-ray triggered surface polymerization

Rackel Reis,Mikel C Duke,Raymond R Dagastine,Ludovic F Dumée,Blaise L Tardy,Daniel Oldfield,John D Orbell

doi:10.1038/s41598-017-04900-5

Rackel Reis, Mikel C Duke + Show 5 more

Open Access

https://doi.org/10.1038/s41598-017-04900-5

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Abstract

Thin-film composite poly(amide) (PA) membranes have greatly diversified water supplies and food products. However, users would benefit from a control of the electrostatic interactions between the liquid and the net surface charge interface in order to benefit wider application. The ionic selectivity of the 100 nm PA semi-permeable layer is significantly affected by the pH of the solution. In this work, for the first time, a convenient route is presented to configure the surface charge of PA membranes by gamma ray induced surface grafting. This rapid and up-scalable method offers a versatile route for surface grafting by adjusting the irradiation total dose and the monomer concentration. Specifically, thin coatings obtained at low irradiation doses between 1 and 10 kGy and at low monomer concentration of 1 v/v% in methanol/water (1:1) solutions, dramatically altered the net surface charge of the pristine membranes from −25 mV to +45 mV, whilst the isoelectric point of the materials shifted from pH 3 to pH 7. This modification resulted in an improved water flux by over 55%, from 45.9 to up 70 L.m−2.h−1, whilst NaCl rejection was found to drop by only 1% compared to pristine membranes.

Highlights

The nature and distribution of chemical functional groups across the surface of thin-film composite (TFC) membranes is critical to the tuning of the selectivity of membrane materials in relation to seawater desalination and other applications including foods processing[1]
This is consistent with a previous study on a PA hollow fiber forward osmosis (FO) membrane treated with N-methyl pyrrolidone as a function of the impact of oxidation resistance post-treatment[8]
The increasing monomer concentrations led to increased grafted film with a thickness estimated at ~300 nm which in turn caused flux decline of 81%15. This trend demonstrated that polymerization kinetic rates were favored with increasing monomer concentration and total irradiation dose

Summary

Introduction

The nature and distribution of chemical functional groups across the surface of thin-film composite (TFC) membranes is critical to the tuning of the selectivity of membrane materials in relation to seawater desalination and other applications including foods processing[1]. The excellent salt and organic rejection capability of poly(amide) (PA) TFC membranes is due to a combination of the material’s free volume, which corresponds to the spaces between the macromolecular chains, and to the nature of the electrostatic repulsions at the liquid/membrane interface, i.e. the Donnan Layer[2]. Such electrostatic interactions are influenced by the polar moieties that are present on the surface of the membrane material[3]. This study demonstrates for the first time the feasibility and potential of irradiation-induced grafting onto functional thin-film membrane materials as a more sustainable and cost-effective approach than other methods with a potential for specific selectivity and tailored performance

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