Preparation and Characterization of Thin-Film Composite Membrane with Nanowire-Modified Support for Forward Osmosis Process

Ze-Xian Low,Qi Liu,Ezzatollah Shamsaei,Huanting Wang,Xiwang Zhang

doi:10.3390/membranes5010136

Abstract

Internal concentration polarization (ICP) in forward osmosis (FO) process is a characteristic problem for asymmetric thin-film composite (TFC) FO membrane which leads to lower water flux. To mitigate the ICP effect, modification of the substrates’ properties has been one of the most effective methods. A new polyethersulfone-based ultrafiltration membrane with increased surface porosity and high water flux was recently produced by incorporating Zn2GeO4 nanowires. The composite membrane was used as a substrate for the fabrication of TFC FO membrane, by coating a thin layer of polyamide on top of the substrate. The substrate and the nanowires were characterized by a range of techniques such as SEM, XRD, and contact angle goniometry. The water permeability and molecular weight cut-offs (MWCO) of the substrate; and the FO performance of the TFC membrane were also determined. The Zn2GeO4-modified membrane showed ~45% increase in water permeability and NaCl salt rejection of 80% under RO mode. In FO mode, the ratio of water flux to reverse solute flux was also improved. However, lower FO flux was obtained which could be due to ICP. The result shows that Zn2GO4 nanowire may be used as a modifier to the substrate to improve the quality of the polyamide layer on the substrate to improve the flux and selectivity, but not as effective in reducing ICP. This work demonstrates that the incorporation of nanomaterials to the membrane substrate may be an alternative approach to improve the formation of polyamide skin layer to achieve better FO performance.

Highlights

Global water crisis and clean water shortage have remained one of many pressing development challenges of all time
This work demonstrates that the incorporation of nanomaterials to the membrane substrate may be an alternative approach to improve the formation of polyamide skin layer to achieve better forward osmosis (FO) performance
The incorporation of nanomaterials to the membrane substrate may be an alternative approach to improve the formation of polyamide skin layer to achieve better FO performance

Summary

Introduction

Global water crisis and clean water shortage have remained one of many pressing development challenges of all time. The thick and dense support layers, necessary to withstand large hydraulic pressures causes ICP [9]. Because this ICP effect is unperturbed by stirring [10], modifying the support layers is essential to reduce ICP effect in TFC membrane [9]. Zn2GeO4-nanowire-modified PES membrane exhibits increased number of nanopores in the active layer leading to enhanced water flux [32], which may be beneficial as a substrate for FO membrane. The modified PES substrate may exhibit better FO performance either via (i) the reduction in ICP by increasing porosity or reducing thickness and tortuosity; or (ii) formation of a polyamide layer with. The incorporation of nanomaterials to the membrane substrate may be an alternative approach to improve the formation of polyamide skin layer to achieve better FO performance

Results and Discussion

FO Membrane Performance

Experimental Section

Conclusions