Forward osmosis is a promising technology. However, it has many characteristics that need improvement for better function. A team of researchers tried to find out if nanofiber interlayers could be a solution.
What is Forward Osmosis?
Forward osmosis (FO) is a membrane-based technology still in its early stages.
According to Science Direct, it has a number of potential uses in the treatment of water, including desalination. Using a draw solution with a higher osmotic pressure than seawater, the FO process can directly desalt seawater as a feed solution.
This technology has a low possibility of membrane fouling and low energy usage. However, the absence of high-performance FO membranes hampered the widespread application of FO.
Generally speaking, a high-performance FO membrane should have strong antifouling performance, high water permeability, low structural parameters (S value), low salt permeability, and stable chemical characteristics. Nanofiber-supported FO membranes have become more and more popular among them.
Challenges of FO Membranes
Phys.org shows that thin-film composite (TFC) FO membranes are made of porous substrates and ultra-thin polyamide (PA) selective layers. It has exceptional permeability and selectivity. But the issue is minimizing the total S value of FO membranes while resolving the trade-off between water permeability and solute selectivity.
On the other hand, Polyvinylidene Fluoride (PVDF) is a semi-crystalline polymer with repeating units. It is frequently used to create water treatment membrane materials due to its robust mechanical and stable chemical properties. The challenge for this polymer is creating a defect-free and reliable PA separation layer using interfacial polymerization on an electrospun nanofibrous substrate (PVDF) with wide open surface pores (IP). Another concern is how to effectively alleviate the internal concentration polarization (ICP) phenomenon and membrane fouling.
To address these problems, Miao Tian and Tao Mao from Northwestern Polytechnical University worked with their team members to develop a dual-layer PVDF nanofiber-supported TFC FO membrane. Their findings, published in Frontiers of Environmental Science & Engineering, provide a theoretical framework for investigating and developing high-water flux and anti-pollution TFC FO membranes for practical wastewater treatment. They also provided insight into the behavior of foulants on the membrane surface.
Forward Osmosis Study
The work successfully electrospun a layered PVDF nanofiber substrate with an ultrathin (~1 µm) fine fiber interlayer on top (average fiber diameter 40-60 nm). A PA selective layer was created via IP on the aforementioned nanofibrous substrate with various physicochemical properties. The impact of the electrospun nanofiber interlayer and drying duration on the intrinsic separation FO performance was investigated using FESEM and AFM.
Model foulants (sodium alginate and bovine serum albumin) in both the feed solution (FS) and draw solution were used to investigate the separation performance of the dual-layer nanofibrous FO membranes (DS). When utilizing 1.5 M NaCl versus deionized water in the active layer facing draw solution mode, the dual-layer nanofibrous substrate demonstrated a flux of 30.2 LMH, outperforming the single-layer nanofibrous substrate.
ALSO READ: Soft-tissue Regeneration Possible Through a Nanofiber-Hydrogel
Fouling Test and Findings
Assuming the foulants were present in both the FS and DS during the fouling test, the water flux could be effectively increased without compromising the water/solute selectivity. The cleaning and fouling tests also revealed that the dual-layer nanofibrous TFC FO membrane was more durable. This study shows how crucial the interlayer enhances the TFC FO membrane.
The interlayer improved the PA layer's selectivity during long-term use and cleaning. To put it briefly, the study offers a theoretical framework for investigating and developing high-water flux and anti-pollution TFC FO membranes for real-world wastewater treatment.
RELATED ARTICLE: Novel Lightweight Nanofiber Material Protects Against Space Debris and Better Than Existing Bulletproof Technology
Check out more news and information on Nanofibers in Science Times.
