High performance nanofiber-supported thin film composite forward osmosis membranes based on continuous thermal-rolling pretreated electrospun PES/PAN blend substrates

Integration of adsorption, reduction, and filtration in PANI/PVDF nanofiber composite membrane for removal of Cr(VI)

Here, polyaniline/polyvinylidene fluoride (PANI/PVDF) nanofiber composite membrane was fabricated using electrostatic spinning technology to remove hexavalent chromium Cr(VI). The employment of PANI not only extremely enhanced the hydrophilic property of the nanofiber membrane, but also facilitated the transfer of Cr2O72- from water to the membrane. The PANI/PVDF membrane had an extremely excellent performance in getting rid of Cr(VI) and a quite large flux (250 L/m2 h). The maximum adsorption quantity of the membrane could reach 334.5 mg/g in which adsorption played 52.12% part and reduction played 47.87% part. The removal rate could reach nearly 100% immediately in the permeate solution under filtration while it needed 240 min to reach 100% only by static adsorption. Therefore, the interception of the membrane and the adsorption reduction of PANI had synergistic effect on removal of Cr(VI). Furthermore, the removal rate of Cr(VI) could still reach 95.97% after reused 8 times. The membrane showed a very good reusability and application prospect.

A Comprehensive Review of Performance of Polyacrylonitrile-Based Membranes for Forward Osmosis Water Separation and Purification Process

Polyacrylonitrile (PAN), with its unique chemical, electrical, mechanical, and thermal properties, has become a crucial acrylic polymer for the industry. This polymer has been widely used to fabricate ultrafiltration, nanofiltration, and reverse osmosis membranes for water treatment applications. However, it recently started to be used to fabricate thin-film composite (TFC) and fiber-based forward osmosis (FO) membranes at a lab scale. Phase inversion and electrospinning methods were the most utilized techniques to fabricate PAN-based FO membranes. The PAN substrate layer could function as a good support layer to create TFC and fiber membranes with excellent performance under FO process conditions by selecting the proper modification techniques. The various modification techniques used to enhance PAN-based FO performance include interfacial polymerization, layer-by-layer assembly, simple coating, and incorporating nanofillers. Thus, the fabrication and modification techniques of PAN-based porous FO membranes have been highlighted in this work. Also, the performance of these FO membranes was investigated. Finally, perspectives and potential directions for further study on PAN-based FO membranes are presented in light of the developments in this area. This review is expected to aid the scientific community in creating novel effective porous FO polymeric membranes based on PAN polymer for various water and wastewater treatment applications.

Graphene Quantum Dot-Added Thin-Film Composite Membrane with Advanced Nanofibrous Support for Forward Osmosis

Forward osmosis (FO) technology for desalination has been extensively studied due to its immense benefits over conventionally used reverse osmosis. However, there are some challenges in this process such as a high reverse solute flux (RSF), low water flux, and poor chlorine resistance that must be properly addressed. These challenges in the FO process can be resolved through proper membrane design. This study describes the fabrication of thin-film composite (TFC) membranes with polyethersulfone solution blown-spun (SBS) nanofiber support and an incorporated selective layer of graphene quantum dots (GQDs). This is the first study to sustainably develop GQDs from banyan tree leaves for water treatment and to examine the chlorine resistance of a TFC FO membrane with SBS nanofiber support. Successful GQD formation was confirmed with different characterizations. The performance of the GQD-TFC-FO membrane was studied in terms of flux, long-term stability, and chlorine resistance. It was observed that the membrane with 0.05 wt.% of B-GQDs exhibited increased surface smoothness, hydrophilicity, water flux, salt rejection, and chlorine resistance, along with a low RSF and reduced solute flux compared with that of neat TFC membranes. The improvement can be attributed to the presence of GQDs in the polyamide layer and the utilization of SBS nanofibrous support in the TFC membrane. A simulation study was also carried out to validate the experimental data. The developed membrane has great potential in desalination and water treatment applications.

Electrospun Nanofiber-Based Membranes for Water Treatment

Water purification and water desalination via membrane technology are generally deemed as reliable supplementaries for abundant potable water. Electrospun nanofiber-based membranes (ENMs), benefitting from characteristics such as a higher specific surface area, higher porosity, lower thickness, and possession of attracted broad attention, has allowed it to evolve into a promising candidate rapidly. Here, great attention is placed on the current status of ENMs with two categories according to the roles of electrospun nanofiber layers: (i) nanofiber layer serving as a selective layer, (ii) nanofiber layer serving as supporting substrate. For the nanofiber layer’s role as a selective layer, this work presents the structures and properties of conventional ENMs and mixed matrix ENMs. Fabricating parameters and adjusting approaches such as polymer and cosolvent, inorganic and organic incorporation and surface modification are demonstrated in detail. It is crucial to have a matched selective layer for nanofiber layers acting as a supporting layer. The various selective layers fabricated on the nanofiber layer are put forward in this paper. The fabrication approaches include inorganic deposition, polymer coating, and interfacial polymerization. Lastly, future perspectives and the main challenges in the field concerning the use of ENMs for water treatment are discussed. It is expected that the progress of ENMs will promote the prosperity and utilization of various industries such as water treatment, environmental protection, healthcare, and energy storage.

Enhanced water permeability and fouling resistance properties of ultrafiltration membranes incorporated with hydroxyapatite decorated orange-peel-derived activated carbon nanocomposites

Hydroxyapatite-decorated activated carbon (HAp/AC) nanocomposite was synthesized and utilized as a nanofiller to fabricate a novel type of polyethersulfone (PES) nanocomposite ultrafiltration (UF) membranes. Activated carbon (AC) derived from orange peel was synthesized by low-temperature pyrolysis at 400 °C. A hydroxyapatite/AC (HAp/AC) nanocomposite was developed by a simple one-pot hydrothermal synthesis method. The UF membrane was fabricated by intercalating HAp/AC fillers into PES casting solution by the non-solvent induced phase separation (NIPS) process. The prepared membranes exhibited a lower water contact angle than the pristine PES membrane. The hybrid membrane with 4 wt% HAp/AC nanocomposite displayed 4.6 times higher pure water flux (~660 L/m² h) than that of the pristine membrane (143 L/m² h). In static adsorption experiments, it was found that the amount of humic acid (HA) and bovine serum albumin (BSA) adsorbed by the HAp/AC-PES hybrid membrane was much lower than that of the original membrane due to the electrostatic repulsive forces between them and the surface of the membrane. Irreversible fouling was reduced from 33 to 6 % for HA and from 46 to 8 % for BSA after HAp/AC was incorporated into the PES matrix. After 7 cycles of water-BSA-water, the HAp/AC-PES hybrid membrane maintained a high pure water flux of 540 L/m² h with an excellent flux recovery ratio (FRR), demonstrating the long-term stability of the membranes. The developed UF membranes outperformed the original PES membranes in terms of permeability, selectivity, and antifouling.

Zwitterionic silica nanogel-modified polysulfone nanoporous membranes formed by in-situ method for water treatment

We report a simple methodology to prepare nano-porous polysulfone membranes using zwitterionic functionalized silica nanogels with high BSA protein rejection and antifouling properties. The zwitterionic silica precursor was prepared by reacting 1,3-propane sultone with 3-aminopropyl triethoxysilane under an inert atmosphere. The precursor was in situ hydrolyzed and condensed in the polysulfone nanoporous membrane network by one-pot acidic phase inversion. The prepared membranes were characterized to establish their physicochemical nature, morphology, and basic membrane properties such as permeation, rejection, and recovery. The zwitterionic membranes showed improved hydrophilicity, membrane water uptake (∼83.5%), water permeation, BSA protein rejection (>95%), and dye rejection (congo red: >52% (∼6-fold increase); methylene blue: ∼15% (∼2-fold increase)) were improved without compromising the membrane flux and fouling resistance. Overall, we report an easy fabrication method of efficient nanocomposite zwitterionic ultrafilter membranes for water treatment with excellent flux, protein separation, filtration efficiency, and antifouling behavior.

Improved permeability and antifouling performance of polyethersulfone ultrafiltration membranes tailored by hydroxyapatite/boron nitride nanocomposites

To extend the use of polyethersulfone (PES) ultrafiltration membranes in water process engineering, the membrane's wettability and anti-fouling properties should be further improved. In this context, hydroxyapatite/boron nitride (HAp/BN) nanocomposites have been prepared and intercalated into PES membranes using a non-solvent-induced phase separation process. High-quality 2D transparent boron nitride nanosheets (BN NSs) were prepared using an environmentally friendly and green-template assisted synthesis method in which 1D hexagonal hydroxyapatite nanosheets (HAp NRs) were uniformly distributed and hydrothermally immobilized at 180 °C. SEM, XRD, and Raman spectroscopy techniques were used to characterize the HAp/BN nanocomposites. PES membranes intercalated with various nanocomposite amounts (0-4 wt %) were also characterized by permeability, porosity, and contact angle measurements. Additional pathways for water molecule transport were promoted by the high surface area of the BN NSs, resulting in high permeability. Membrane wettability and antifouling properties were also improved by the inclusion of negative charge groups (OH^- and PO₄^3-) on HAp. Hybrid membranes containing 4 wt% HAp/BN showed the best overall performance with ∼97% increase in water flux, 90% rejection of bovine serum albumin (BSA), high water flux recovery ratio, low irreversible fouling, and high reversible fouling pattern. The intercalation of HAp/BN with the PES matrix therefore opens up a new direction to enhance the PES UF membranes' hydrophilicity, water flux, and antifouling capacity.