The forward osmosis (FO) process suffers from unfavorable internal concentration polarization (ICP) of the solute within the support layer of thin-film composite forward osmosis (TFC-FO) membranes. To lower the ICP effect, a support layer with low tortuosity, high porosity, and interconnected pores is necessary. In the present investigation, sodium bicarbonate has been presented as a simple pore-forming agent to decline the ICP within a poly­(ethersulfone) substrate. In particular, the porous poly­(ethersulfone) support layer was fabricated by embedding sodium bicarbonate into the casting solution to form CO2 gas bubbles in the substrate during phase inversion in an acidic nonsolvent. Experimental results revealed that the separation performance of the TFC-FO membranes significantly improved. The most water-permeable membrane was prepared in the acidic nonsolvent (TFC-SB.3) and it demonstrated a water flux of 26.6 LMH and a reverse salt flux of 3.6 gMH in the FO test. In addition, the TFC-SB.3 membrane showed an 85% increase in water permeability (2.13 LMH/bar) with negligible change in salt rejection (94.3%). Such observations were based on the increase of substrate porosity and the improved connectivity of the finger-like channels through in situ CO2 gas bubbling that alleviate the ICP phenomena. Therefore, the current study presents a simple, scalable method to design a high-performance TFC-FO membrane.

The stability and compatibility of a nanomaterial in a substrate matrix are a tough challenge in preparing thin-film nanocomposite membranes. In this study, we fabricated a ternary nanocomposite membrane substrate consisting of polyethersulfone (PES), quaternary graphene oxide (QGO), and sulfonated polyethersulfone (SPES). First, SPES was blended with the PES substrate, and then different concentrations of QGO were incorporated within this substrate. The effect of QGO on the substrate morphology, hydrophilicity, and porosity was analyzed via scanning electron microscopy, water contact angle measurement, and gravimetric methods, respectively. The optimum loading of QGO significantly enhanced the hydrophilicity, porosity, and water permeability of the PES/SPES support layer. In addition, the effect of QGO on the polyamide rejection layer morphology and performance was thoroughly investigated. The result shows that a thin, smooth, and defect-free polyamide (PA) layer was formed on hydrophilic QGO-based substrates. Intrinsic separation performance data verified these results, where the PA layer formed on the QGO-based substrate presented the highest water permeability. The forward osmosis test also demonstrated the positive impact of QGO incorporation on the performance of membrane substrates. The optimal TFC-QS0.5 (containing 0.5 wt % of QGO) membrane has a water flux of 24.4 LMH in the forward osmosis mode and 32.1 LMH in the pressure-retarded osmosis mode when using a 1 M NaCl draw solution and deionized water feed solution.

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A substrate with good physicochemical properties is essential for minimizing unpleasant internal concentration polarization phenomena in a forward osmosis (FO) process. In this study, graphene oxide-graf t-poly(2hydroxy ethyl methacrylate) (GO-g-PHEMA, GP) nanoplates with different weight ratios were prepared for the first time using a combination of click chemistry and reversible addition−fragmentation chain-transfer polymerization. Then, high-efficiency thin-film nanocomposite (TFN) FO membranes were fabricated using GP-modified polysulfone (PSf) substrates. The influence of the structure parameter and concentration of GP on the substrate and polyamide (PA) active layer properties were systematically studied using various characterization methods. The obtained results indicated that the morphologies of the GPmodified PSf substrates were more porous, and the pure water flux, surface hydrophilicity, and mean pore size of the substrates considerably improved. Furthermore, the GP/PSf-based TFN membranes showed thicker, rougher, and permeable PA active layers than the baseline PSfbased TFC membrane. In the case of TFN-FO membranes, the water permeability noticeably increased, and the structural parameter effectively declined. Additionally, the FO performance dramatically improved (e.g., the water flux of TFN-GP 21 0.4 reached 32.6/15.6 LMH under PRO/FO configuration). According to the results, it can be concluded that 0.4 wt % of GP 21 nanofiller (GO/ PHEMA ratio of 2:1) was the optimal blend concentration. Also, the modified membranes showed a noticeable performance in Caspian seawater desalination.

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