(381n) Silicene As a Novel Nanofiller for Thin Film Nanocomposite Forward Osmosis Membrane

Forward osmosis (FO) is an emerging membrane desalination process which gained popularity due to its energy-efficiency and lower propensity to membrane fouling. In FO, osmotic pressure gradient drives water molecules from the saline feed towards highly ionic draw solution. However, selection of appropriate draw solutes and FO membranes remains a challenge towards wide implementation of FO technology. Particularly, in thin film composite TFC-FO membranes, internal concentration polarization is a common problem. A phenomenon that reduces the effective osmotic pressure difference in the support layer and thus, the water flux. This study employs silicene nanoflowers as membrane support fillers to reduce the effect of internal concentration polarization by tuning the TFC-FO membrane structural (S) parameter.

Silicene was synthesized via magnesiothermic reduction of silica nanoparticles then characterized via XRD, TEM, N₂ adsorption-desorption test, and XPS. The nanoflowers were pulverized, sieved and then incorporated into polyethersulfone (PES) dope solution. Silicene/PES dope solutions with different filler loading were casted via phase inversion technique and used as support for TFC-FO membrane. On the silicene/PES, thin selective polyamide layer was deposited through interfacial polymerization of 2 wt% aqueous m-phenylenediamine and 0.15 w/v% trimesoyl chloride in n-hexane. The resulting silicene/PES TFC FO membranes were characterized using SEM, TEM, FTIR, porosity test and contact angle measurements.

Relative to the control PES TFC-FO, permeation tests reveal overall improvement in water flux for silicene/PES TFC FO membranes. This was attributed to decrease in S parameter, which was correlated to the increased porosity and reduced thickness of the support layer. This resulted in reduced water and draw solute tortuous paths which, in effect, enhanced the effective osmotic pressure difference across the FO membrane. This study demonstrates the potential of silicene, a silicon analogue of graphene as nanofiller, for TFC-FO membranes with improved water flux.

This research was supported by the National Research Foundation of Korea (NRF) under the Ministry of Science and ICT (No. 2016R1A2B1009221 and 2017R1A2B2002109) and the Ministry of Education (No. 22A20130012051(BK21Plus)).