Exploring the potential of nanofillers for advanced thin film nanocomposite forward osmosis membranes fabrication

摘要

Novel and promising forward osmosis (FO) is a membrane-based separation with significant potentials for the desalination process. While this technology offers various benefits, overcoming its internal concentration polarization (ICP) and membrane fouling in polyamide (PA) skin layer remain as a challenge. In this study, three types of novel thin film nanocomposite (TFN) membranes were synthesized by either coating a typical PA film over the surface of substrate made of polysulfonehalloysite nanotubes (HNTs) or embedding HNTs and titanium dioxide (TiO2)/HNTs nanocomposites into PA thin layer formed over a typical polysulfone (PSF) substrate. These approaches aim to reduce membrane fouling and/or ICP during FO applications. In the first stage of this study, both hydrophilicity and porosity of the substrate were increased using HNTs. The results obtained from filtration experiments showed that the TFN membrane prepared with incorporation of 0.5 wt% HNTs (TFN 0.5) demonstrated the most satisfactory results by exhibiting high water permeability and low reverse solute flux in both FO and pressure retarded osmosis (PRO) configurations. This improvement can be ascribed to the fact that the structural parameter (S value) of TFN membrane is much lower compared to that of control thin film composite (TFC) membrane (0.37 vs 0.95 mm), leading to reduced ICP effect. In the second stage of this study, both hydrophilicity and surface roughness of TFN membranes increased with incorporation of HNTs into PA layer. In the FO mode, the fabricated TFN FO membrane in this study exhibited significantly higher fouling resistance compared to the control TFC membrane. As an indication to reversibility of fouling in TFN FO membrane, it was also found that more than 96% permeate flux could be recovered after a simple water rinsing process. In the third stage of this study, TiO2/HNTs nanocomposites synthesized via one-step solvothermal method were used as nanofillers in the preparation of TFN membranes for the FO application. With respect to separation performance, it was discovered that the TFN membrane incorporated with 0.05% (w/v) TiO2/HNTs (TFN 0.05) exhibited the best performance due to its high water permeability and low reverse solute flux when tested using 10 mM sodium chloride (NaCl) feed solution and 2.0 M NaCl draw solution under two different membrane configurations. Compared to the control membrane (without TiO2/HNTs incorporation), the fabricated TFN 0.05 membrane could offer up to 90% higher water flux and exhibited significantly better antifouling affinity against bovine serum albumin (BSA). The results revealed that fouling in the TFN 0.05 membrane was completely reversible. As a conclusion, it was found that modifying the PA skin layer of composite membrane using TiO2/HNTs as nanofillers could give the most promising results, improving not only membrane permeability and selectivity but also its antifouling property.