Hydrophilic modification and anti-fouling properties of PVDF membrane via in situ nano-particle blending

Preparation of hydrophilic PVDF membranes through in situ assembly of phytate-polyethyleneimine-Fe3+ for efficient separation of herbal volatile oil from oily water

In the realm of oil-water separation technologies, membrane-based separation emerges as an efficacious approach. Nevertheless, crafting a hydrophilic membrane capable of effectively segregating herbal volatile oil remains a formidable challenge. Our study introduces a facile in situ assembly strategy for fabricating a double-crosslinked composite coating comprising phytate (PA)-polyethyleneimine (PEI) polyelectrolyte complexes and PA-Fe3⁺ assemblies. The PA within the PA-PEI/Fe3⁺ coatings form a double cross-linking layer through interactions with amine groups and metal ions, thereby enhancing interfacial interactions and structural integrity of the membranes. Consequently, the resultant PVDF/PA-PEI/Fe3⁺ membranes exhibit improved coating stability, pronounced hydrophilicity, and exceptional antifouling capabilities, rendering them highly suitable for the separation of diverse herbal volatile oil-in-water emulsions. Furthermore, they possess the capability for reuse with an average retention ratio exceeding 90% and a pure water flux reaching up to 3200 L·m⁻2·h⁻1. Additionally, they demonstrate long-term stability and resistance to corrosion. With a simplistic yet efficient preparation process, the PVDF/PA-PEI/Fe3⁺ membrane holds significant potential for the extraction of oils from herbal volatile oil-in-water emulsions.

Antifouling CuO@TiO2 coating on plasma-grafted PAA/PES membrane based on photocatalysis and hydrogen peroxide activation

Because of the small size effect leading to the high bandgap of TiO₂ P25, the photocatalytic membrane using this photocatalyst has low antifouling efficiency. This study prepared CuO@TiO₂ composite photocatalyst with a lower bandgap than TiO₂ P25 and used it as antifouling coatings on the PES membrane with PAA intermediate adhesive layer. PAA was grafted onto the surface of the PES membranes through free radicals generated by the cold plasma treatment of the PES membrane. The composite photocatalysts were characterized by FTIR, SEM-EDS, TEM-EDS, XRD, BET, UV-Vis DRS, XPS, and ESR methods demonstrating high surface area (51.0 m²/g), decreased bandgap, and the formation of active free radicals under UV light irradiation. Under photocatalysis and hydrogen peroxide activation, the degradation of AB260 (acid blue 260) catalyzed by 10%CuO@TiO₂ reached about 92% after 60 min. Besides, the photocatalytic and antifouling activities of CuO@TiO₂/PAA/PES membranes are high and stable over five continuous cycles. The water flux of the modified membrane was not significantly influenced and only decreased about 10% compared to the pristine membrane. In addition, the flux recovery ratios (FRR) of fouled membranes treated by photocatalysis were almost 100%.

Micro-polluted water resources treatment by PVDF-TiO2 membrane combined with Fe2+/sodium dithionite (DTN)/O2 pre-oxidation process

Modifying PVDF membrane by blending hydrophilic nano TiO₂ has been highly concerning, but its practical application is not well investigated. In this study, PVDF-TiO₂ membrane was employed in two modes to treat micro-polluted raw water for the first time, direct membrane filtration and pre-oxidation assists membrane filtration. At two filtration modes, the PVDF-TiO₂ membrane had comparable rejection capability to the unmodified PVDF membrane, as the removal of permanganate index (COD_Mn) was 0.26-0.72 mg/L, UV₂₅₄ was 0.0070-0.0618 cm^-1, turbidity was 1.60-4.49 NTU, and the total number of colonies was 360-23,780 CFU/mL. As for raw water treatment, using Fe²⁺/sodium dithionite (DTN)/O₂ system as the pre-oxidation process to assist the filtration of the PVDF-TiO₂ membrane was feasible. After optimization, the applicable conditions of the Fe²⁺/DTN/O₂ process were DTN dosage at 100 mg/L and a C_Fe/C_DTN of 1:4. As a result, the effluent qualities of the PVDF-TiO₂ membrane significantly improved. It was investigated that atrazine (ATZ), COD_Mn, UV_254, and turbidity reduced, which was realized by the synergic effects of the pre-oxidation by free radicals and flocculation by iron. Pre-oxidation of the Fe²⁺/DTN/O₂ process could also enhance the permeability of the PVDF-TiO₂ membrane from 53.6 to 58.0 L/(m²·h), nearly two times the PVDF membrane. Besides, the practical fouling of the PVDF-TiO₂ membrane was stably alleviated by the reduced R_t, R_re, and R_ir, mainly due to constraining the internal pore fouling effectively.

Classification of Nanomaterials and the Effect of Graphene Oxide (GO) and Recently Developed Nanoparticles on the Ultrafiltration Membrane and Their Applications: A Review

The emergence of mixed matrix membranes (MMMs) or nanocomposite membranes embedded with inorganic nanoparticles (NPs) has opened up a possibility for developing different polymeric membranes with improved physicochemical properties, mechanical properties and performance for resolving environmental and energy-effective water purification. This paper presents an overview of the effects of different hydrophilic nanomaterials, including mineral nanomaterials (e.g., silicon dioxide (SiO2) and zeolite), metals oxide (e.g., copper oxide (CuO), zirconium dioxide (ZrO2), zinc oxide (ZnO), antimony tin oxide (ATO), iron (III) oxide (Fe2O3) and tungsten oxide (WOX)), two-dimensional transition (e.g., MXene), metal-organic framework (MOFs), covalent organic frameworks (COFs) and carbon-based nanomaterials (such as carbon nanotubes and graphene oxide (GO)). The influence of these nanoparticles on the surface and structural changes in the membrane is thoroughly discussed, in addition to the performance efficiency and antifouling resistance of the developed membranes. Recently, GO has shown a considerable capacity in wastewater treatment. This is due to its nanometer-sized holes, ultrathin layer and light and sturdy nature. Therefore, we discuss the effect of the addition of hydrophilic GO in neat form or hyper with other nanoparticles on the properties of different polymeric membranes. A hybrid composite of various NPs has a distinctive style and high-quality products can be designed to allow membrane technology to grow and develop. Hybrid composite NPs could be used on a large scale in the future due to their superior mechanical qualities. A summary and future prospects are offered based on the current discoveries in the field of mixed matrix membranes. This review presents the current progress of mixed matrix membranes, the challenges that affect membrane performance and recent applications for wastewater treatment systems.

Surface Mineralization of the TiO2-SiO2/PES Composite Membrane with Outstanding Separation Property via Facile Vapor-Ventilated In Situ Chemical Deposition

Conventional polymeric membranes are broadly employed in water treatment processes; however, most of them suffer from relatively low water permeance and severe membrane fouling phenomena owing to their relatively hydrophobic nature. In this work, a novel class of inorganic-organic composite membranes was developed through a newly developed vapor-ventilated in situ chemical deposition method, where the Ti and Si precursors were first hydrolyzed and then conferred into metal oxides to form a continuous TiO₂-SiO₂ modification layer. Owing to the distinct physicochemical properties, the Ti and Si precursors were leveraged as quasi-molecular regulators to tune the membrane surface chemistry and pore aperture (within the nanoscale) to benefit highly efficient water purification by underpinning the rapid transport of water molecules and featuring an excellent fouling-resistant and fouling-releasing property against typical pollutants. The as-developed TiO₂-SiO₂/PES composite membrane showed a high water permeance of 187.4 L·m^-2·h^-1·bar^-1, together with a relatively small mean pore aperture of 4.2 nm, showing an outstanding permeating efficiency among state-of-the-art membranes with a similar separation accuracy. This study provides a paradigm shift in membrane materials that could open avenues for developing high-performance inorganic-organic composite membranes for complex wastewater treatment.

Impacts of Sulfuric Acid on the Stability and Separation Performance of Polymeric PVDF-Based Membranes at Mild and High Concentrations: An Experimental Study

This study investigated the effects of an aqueous acidic solution at typical concentrations on polymeric polyvinylidene fluoride (PVDF)-based membranes. Flat-sheet PVDF-based membranes were completely embedded in sulfuric acid at varying concentrations. The effect of the acid concentration after a prolonged exposure time on the chemical, mechanical and physical properties of the membrane were checked via FE-SEM, EDX (Energy-Dispersive Spectrometer), FTIR, XRD, tensile strength, zeta potential, contact angle, porosity, pure water flux measurement and visual observation. The result reveals prompt initiation of reaction between the PVDF membrane and sulfuric acid, even at a mild concentration. As the exposure time extends with increasing concentration, the change in chemical and mechanical properties become more pronounced, especially in the morphology, although this was not really noticeable in either the crystalline phase or the functional group analyses. The ultimate mechanical strength decreased from 46.18 ± 0.65 to 32.39 ± 0.22 MPa, while the hydrophilicity was enhanced due to enlargement of the pores. The flux at the highest concentration and exposure period increased by 2.3 times that of the neat membrane, while the BSA (Bovine Serum Albumin) rejection dropped by 55%. Similar to in an alkaline environment, the stability and performance of the PVDF-based membrane analyzed in this study manifested general deterioration.

Ultrasonication favors TiO2 nano-particles dispersion in PVDF ultrafiltration membrane to effectively enhance membrane hydrophilicity and anti-fouling capability

The influence of ultrasonication on membrane performance was investigated by two ultrasonication modes, direct and indirect ultrasonication as pretreatment, and simply improved PVDF-TiO₂ membranes' performance was systematically compared. Ultrasound intensity of 100% and ultrasonication time ranged from 1 to 2 h positively affect membrane permeability. Characterization results manifested that membrane structure was eventually optimized with an even nano-TiO₂ dispersion by direct ultrasonication. Analysis of surface roughness reflected that PVDF-TiO₂ (MS-U2) surface morphological pattern was peak-valley structure that resisted fouling greatly. A good fitting of experimental result and Tansel's simulation illustrated that anti-fouling ability was realized direct ultrasonication modified membrane. PVDF-TiO₂ (MS-U2) membrane showing the lowest |τ| reflecting the time required to reach a certain level of the fouling degree was the lowest. Relying upon modified Hermia's model analysis, protein blockage within the membrane pore was one major fouling mechanism; surface blockage degree of PVDF-TiO₂ (MS-U2) was relative slight. Fouling mechanism analyzed by two models reflected that PVDF-TiO₂ (MS-U2) membrane exhibited a higher anti-protein fouling ability during cross-flow filtration process.