Content area
Full Text
INTRODUCTION
Reverse osmosis (RO) membranes are widely used in desalination and water treatment (Kheriji et al. 2015; Ricci et al. 2016). In addition, RO membranes are applied in a variety of separation operations in environmental, chemical, and food manufacture sectors (Akbari et al. 2015). Being high in thermal, mechanical, and hydrolytic stability, polyamide membranes of advanced thin-film composites (TFC) dominate the RO membrane market (Zuo et al. 2014). The TFC membranes are composed of three polymers: an outer ultra-thin polyamide layer, a microporous middle polysulfone support, and a polyester web that acts as a substrate (Safarpour et al. 2015). Each layer can be independently modified to optimize selectivity and/or mechanical strength.
The ultra-thin polyamide layer is generally formed by interfacial polymerization of m-phenylenediamine (MPD) in aqueous phase and trimesoyl chloride (TMC) in organic phase (Ng et al. 2013; Kim et al. 2014; Jahangiri et al. 2015). Further development of TFC membranes demands excellent water permeability without sacrificing salt rejection ability (Shao & Kurth 2013; Tu et al. 2014). The aromatic polyamide TFC membranes with high water flux and satisfactory salt rejection ability were synthesized by MPD/TMC interfacial reaction in the presence of different types of additives, such as alcohols, ethers, sulfur-containing compounds, and monohydric aromatic compounds. Among the additives, dimethyl sulfoxide (DMSO) was reported to enhance water flux. Being able to dissolve both polar and nonpolar compounds, DMSO is used as a solvent for extractive distillation (Shen et al. 2015). Also, since it is miscible in water as well as in a wide range of organic solvents, it is utilized in chemical reactions as well as in biochemistry and cell biology processes (Dominik et al. 2014; Kurt et al. 2014).
According to Kim et al. (2005), the presence of DMSO in the aqueous phase during MPD/TMC interfacial reaction enhances the miscibility between the aqueous and the organic phases (by reducing the solubility difference of the two immiscible solutions), thereby facilitating the diffusion of MPD into the organic TMC phase. The consequence is modification of surface morphology, variation in polymer chain organization, and change of molecular nature during the formation of TFC membranes. On the other hand, glycerol is a passive flux-preserving agent commonly employed to prevent loss of porosity during oven drying (Kuehne et al....