High performance isotropic polyethersulfone membranes for heavy oil-in-water emulsion separation

Research Progress on Membrane Separation Technology for Oily Wastewater Treatment

This paper presents the research progress and future prospects of membrane separation technology for treating oily wastewater. It discusses various treatment methods tailored to different sources and characteristics of oily wastewater, summarizing the features of different membrane separation technologies and the latest advancements in their application. The paper concludes by emphasizing the need for future research to focus on developing environmentally friendly and efficient coupled membrane treatment technologies, optimizing membrane material design and enhancing the environmental benefits of oily wastewater treatment.

Intrinsically Conductive and Cu-Functionalized Polymer-Composite Membranes as Gas Diffusion Electrodes for CO2 Electroreduction

We introduced a new class of gas diffusion electrodes (GDEs) with adjustable pore morphology. We fabricated intrinsically conductive polymer-composite membranes containing carbon filler, enabling a pore structure variation through film casting cum phase separation protocols. We further selectively functionalized specific pore regions of the membranes with Cu by a NaBH4-facilitated coating strategy. The as-obtained GDEs can facilitate the electrochemical CO2 reduction reaction (CO2RR) at Cu active sites that are presented inside a defined and electrically conductive pore system. When employing them as free-standing cathodes in a CO2 flow electrolyzer, we achieved >70 % Faradaic efficiencies for CO2RR products at up to 200 mA/cm2. We further demonstrated that deposition of a dense Cu layer on top of the membrane leads to obstruction of the underlying pore openings, inhibiting an excessive wetting of the pore pathways that transport gaseous CO2. However, the presentation of Cu inside the pore system of our novel membrane electrodes increased the C2H4/CO selectivity by a factor of up to 3 compared to Cu presented in the dense layer on top of the membrane. Additionally, we found that gaseous CO2 could still access Cu in macropores after wetting with electrolyte, while CO2RR was completely suppressed in wetted nm-scale pores.

Enhancing oil-water emulsion separation via synergistic filtration using graphene oxide-silver oxide nanocomposite-embedded polyethersulfone membrane

This study introduces an innovative approach for enhancing oil-water emulsion separation using a polyethersulfone (PES) membrane embedded with a nanocomposite of graphene oxide (GO) and silver oxide (AgO). The composite membrane, incorporating PES and polyvinyl chloride (PVC), demonstrates improved hydrophilicity, structural integrity and resistance to fouling. Physicochemical characterization confirms successful integration of GO and AgO, leading to increased tensile strength, porosity and hydrophilicity. Filtration tests reveal substantial improvements in separating various oils from contaminated wastewater, with the composite membrane exhibiting superior efficiency and reusability compared to pristine PES membranes. This research contributes to the development of environmentally friendly oil-water separation methods with broad industrial applications.

Optimization of isotropic MoS2/PES membranes for efficient treatment of industrial oily wastewater

Elimination of tiny oil droplets nearly miscible with wastewater can be realized using membrane technology through ultrafiltration. The novelty of this work was to blend different phases of molybdenum disulfide (MoS2) in isotropic polyethersulfone (PES). We prepared isotropic PES membranes by optimizing nonsolvent vapour-induced phase separation (VIPS). Membranes were blended with MoS2 nanosheets of different phases to promote separation performance and antifouling resistance. FE-SEM revealed the flower-like surface morphology of MoS2 nanosheets. HR-TEM of MoS2 revealed 2H domains in the monolayer, flakes of a few layers and a d-spacing of 0.22 nm. Raman spectroscopy could be used to distinguish mixed-phase MoS2 from single-phase MoS2. Isotropic PES membranes modified with 70% 1T/2H MoS2 had a significantly high permeance to pure water (6911 kg m-2 h bar). The same membrane possessed a high efficiency of oil rejection of 98.78%, 97.85%, 99.83% for emulsions of industrial crude oil at 100, 1000 and 10 000 mg L-1, respectively. Removal of oil droplets from wastewater was dominated by a mechanism based on size exclusion. Isotropic PES modified with 2H MoS2 possessed superior oleophilicity, which resulted in low rejection of crude oil. Modified membranes showed excellent fouling resistance for three successive filtration cycles, as evidenced by enhanced antifouling parameters. Our study reveals how the phase composition of MoS2 nanosheets can significantly affect the performance of isotropic PES membranes during the ultrafiltration of oily wastewater.

Effect of Thermally Reduced Graphene on the Characteristics and Performance of Polysulfone Mixed Matrix Ultrafiltration Membranes

Ultrafiltration (UF) polymeric membranes are widely used in water treatment and support desalination and gas separation membranes. In this article, we enhance the performance of Polysulfone (PSF) mixed matrix membranes (MMMs) by dispersing different concentrations of thermally reduced graphene (TRG) nanofillers. The UF PSF-TRG MMMs were fabricated via the phase inversion process, and the impact of TRG loading on the characteristics of the membrane, including hydrophilicity, porosity, roughness, and morphology, were analyzed using a contact angle measurement, atomic force microscopy (AFM), scanning electron microscopy (SEM), and dynamic mechanical analysis. Incorporating TRG into the PSF matrix led to favorable effects in the instantaneous de-mixing during phase inversion, increasing the porosity and hydrophilicity of MMMs and improving the mechanical properties of the membranes. Moreover, membrane performance was examined to remove dispersed oil from oil-water emulsion and support air-dehumidification membranes. MMM performance in terms of flux and oil rejection was superior to the control PSF membrane. Incorporating 0.25% TRG into PSF resulted in a 70% water flux increase and higher oil rejection compared to the control PSF membrane. As a support for air-dehumidification membranes, the MMM also demonstrated enhanced humidity reduction and an over 20% increase in water vapor permeance over the control PSF membrane. These results indicate that the PSF-TRG MMMs are an excellent candidate for reliable oil-water separation and as a support for air-dehumidification membranes.

Quality attributes of CTVad1, a nanoemulsified adjuvant for phase I clinical trial of SpiN COVID-19 vaccine

Aim: To develop, characterize and evaluate an oil/water nanoemulsion with squalene (CTVad1) to be approved as an adjuvant for the SpiN COVID-19 vaccine clinical trials. Materials & methods: Critical process parameters (CPPs) of CTVad1 were standardized to meet the critical quality attributes (CQAs) of an adjuvant for human use. CTVad1 and the SpiN-CTVad1 vaccine were submitted to physicochemical, stability, in vitro and in vivo studies. Results & conclusion: All CQAs were met in the CTVad1 production process. SpiN- CTVad1 met CQAs and induced high levels of antibodies and specific cellular responses in in vivo studies. These results represented a critical step in the process developed to meet regulatory requirements for the SpiN COVID-19 vaccine clinical trial.

A Competitive Study Using Electrospinning and Phase Inversion to Prepare Polymeric Membranes for Oil Removal

Polyacrylonitrile (PAN) is a popular polymer that can be made into membranes using various techniques, such as electrospinning and phase inversion. Electrospinning is a novel technique that produces nonwoven nanofiber-based membranes with highly tunable properties. In this research, electrospun PAN nanofiber membranes with various concentrations (10, 12, and 14% PAN/dimethylformamide (DMF)) were prepared and compared to PAN cast membranes prepared by the phase inversion technique. All of the prepared membranes were tested for oil removal in a cross-flow filtration system. A comparison between these membranes' surface morphology, topography, wettability, and porosity was presented and analyzed. The results showed that increasing the concentration of the PAN precursor solution increases surface roughness, hydrophilicity, and porosity and, consequently, enhances the membrane performance. However, the PAN cast membranes showed a lower water flux when the precursor solution concentration increased. In general, the electrospun PAN membranes performed better in terms of water flux and oil rejection than the cast PAN membranes. The electrospun 14% PAN/DMF membrane gave a water flux of 250 LMH and a rejection of 97% compared to the cast 14% PAN/DMF membrane, which showed a water flux of 117 LMH and 94% oil rejection. This is mainly because the nanofibrous membrane showed higher porosity, higher hydrophilicity, and higher surface roughness compared to the cast PAN membranes at the same polymer concentration. The porosity of the electrospun PAN membrane was 96%, while it was 58% for the cast 14% PAN/DMF membrane.

Hemin-Modified Multi-Walled Carbon Nanotube-Incorporated PVDF Membranes: Computational and Experimental Studies on Oil-Water Emulsion Separations

The separation of oil/water emulsions has attracted considerable attention for decades due to the negative environmental impacts brought by wastewater. Among the various membranes investigated for separation, polyvinylidene fluoride (PVDF) membranes have shown significant advantages of ease of fabrication, high selectivity, and fair pore distribution. However, PVDF membranes are hydrophobic and suffer from severe fouling resulting in substantial flux decline. Meanwhile, the incorporation of wettable substrates during fabrication has significantly impacted the membrane performance by lowering the fouling propensity. Herein, we report the fabrication of an iron-containing porphyrin (hemin)-modified multi-walled carbon nanotube incorporated PVDF membrane (HA-MWCNT) to enhance fouling resistance and the effective separation of oil-in-water emulsions. The fabricated membrane was thoroughly investigated using the FTIR, SEM, EDX, AFM, and contact angle (CA) analysis. The HA-MWCNT membrane exhibited a water CA of 62° ± 0.5 and excellent pure water permeance of 300.5 L/m2h at 3.0 bar (400% increment), in contrast to the pristine PVDF, which recorded a CA of 82° ± 0.8 and water permeance of 59.9 L/m2h. The hydrophilic HA-MWCNT membrane further showed an excellent oil rejection of >99% in the transmembrane pressure range of 0.5−2.5 bar and a superb flux recovery ratio (FRR) of 82%. Meanwhile, the classical molecular dynamics (MD) simulations revealed that the HA-MWCNT membrane had greater solvent-accessible pores, which enhanced water permeance while blocking the hydrocarbons. The incorporation of the hemin-modified MWCNT is thus an excellent strategy and could be adopted in the design of advanced membranes for oil/water separation.

Efficient removal of lead ions from aqueous solution by graphene oxide modified polyethersulfone adsorptive mixed matrix membrane

In this study, we report the combined effect of graphene oxide (GO) and polyvinylpyrrolidone (PVP) for the heavy metal removal efficiency of polyethersulfone (PES) membranes. PVP with four different amounts of GO was infused in the membrane matrix by the physical blending method. Characterizations such as porosity, contact angle, water flux and Fourier transform infrared spectroscopy were conducted for all prepared membranes. Viscid behavior of polymer dope solution was examined to understand the phase separation phenomena better. PVP enhanced the GO distribution within the membrane surface to some extent via hydrogen bond. The addition of nanoparticles enhanced the membrane physicochemical properties with water permeation, Pb²⁺ rejection and adsorption capacity. Permeate flux of modified membrane (m4) was found to be 150.21 L/m²h and it is 8.03 times higher than unmodified membrane (m0). Besides, all fabricated membranes were evaluated for Pb²⁺ rejection from synthetic wastewater and rejection % of m4 (80.6%) had increased twofold than m0 (38.9%). Membrane cleaning was performed using different methods and the best results were achieved with a concentration of 0.05 wt% sodium hypochlorite under pH 7 and further reused for the filtration test. Moreover, adsorption isotherm was tested using Freundlich and Langmuir models and the Langmuir model offered the best fitting.

Superhydrophilic polyethersulfone (PES) membranes with high scale inhibition properties obtained through bionic mineralization and RTIPS

Reverse thermally induced separation (RTIPS) was used to obtain a separation membrane with a better internal structure for a higher water flux and a surface that could easily form a hydration layer. In comparison to the traditional modification method, this work focused on the aspect that the internal structure obtained by changing the membrane-making method provided easier adhesion conditions for the dopamine/TiO₂ hybrid nanoparticles (DA/TiO₂ HNPs) obtained by biomimetic mineralization. It provided a basis for exploring the variation in adhesion with the water bath temperature and the amount of titanium added through the study of turbidity point, SEM images, water contact angle, thermogravimetric test, EDX, AFM, XPS, FTIR and other test results. The SEM images proved that the membrane obtained through the RTIPS method had a porous surface and spongy internal structure, furthermore, additional polymers were adsorbed. Use of EDX demonstrated that biomimetic mineralization prevented the production of agglomerated titanium dioxide. XPS and FTIR spectra confirmed the introduction and immobilization of HNP aggregation. Moreover, a decrease in the surface roughness and water contact angle further suggested an improvement in the hydrophilicity of the modified membrane. The introduction of HNP at a higher water bath temperature helped increase the water flux up to ten times, moreover, the oil-water separation efficiency could still reach over 99.50%. Lastly, a cycle test of the modified membrane under the optimal conditions helped confirm that the membrane forming conditions at this time could provide a better environment for the formation of the hydrophilic layer, which was conducive to the recycling of the separation membrane. In summary, more fixed more hydrophilic particles could be obtained through the RTIPS method based on biomimetic mineralization to prevent the accumulation of titanium dioxide, thus helping improve permeability and anti-fouling of the membrane.

Recent Progress in Microfiltration/Ultrafiltration Membranes for Separation of Oil and Water Emulsions

Oily wastewater has become one of the leading causes of environmental pollution. A massive quantity of oily wastewater is released from industries, oil spills, and routine activities, endangering the ecosystem's sustainability. Due to the enormous negative impact, researchers put strenuous efforts into developing a sustainable solution to treat oily wastewater. Microfiltration/ultrafiltration membranes are considered an efficient solution to treat oily wastewater due to their low cost, small footprint, facile operation, and high separation efficiencies. However, membranes severely fouled during the separation process due to oil's adsorption and cake layer formation, which shortens the membranes' life. This review has critically discussed the microfiltration/ultrafiltration membrane synthesizing methods and their emulsion's separation performance. In the end, key challenges and their possible solutions are highlighted to provide future direction to synthesize next-generation membranes.

Freely switchable super-hydrophobicity and super-hydrophilicity of sponge-like poly(vinylidene fluoride) porous fibers for highly efficient oil/water separation

Highly efficient oil/water separation ability is a prerequisite for the actual application of the membranes in oily sewage treatment, which is closely related to the surface feature and the porous structure of the membranes. In this work, the electrospun poly(vinylidene fluoride) (PVDF) porous fibers were firstly fabricated through blend-electrospinning with poly(vinyl pyrrolidone) (PVP) and then treating in distilled water. The results showed that the fibers exhibited the sponge-like porous structure, and a few PVP was reserved in the fibers due to the relatively good interaction between PVDF and PVP. The fibrous membrane exhibited high porosity, super-wettability with freely switchable super-lipophilicity and super-hydrophilicity. The oil adsorption capacities as well as the oil and water fluxes were measured, and the oil adsorption capacities were varied in the range of 22.7-76.0 g/g, and oil and water fluxes were 54,737.3 and 56,869.9 L/(m²h), respectively. Specifically, the PVDF porous fibrous membranes showed excellent separation abilities and they could highly efficiently separate oil from oil-in-water emulsions or separate water from water-in-oil emulsions, accompanied with the extremely high water or oil flux. This work confirms that the PVDF membranes composed of the porous fibers can be used in wastewater treatment.

Synchronous removal of emulsions and organic dye over palladium nanoparticles anchored cellulose-based membrane

Membrane is a considerable precursor for emulsions separation and organic dyes degradation used in water purification and oil reclamation. However, the tedious preparation method, the surface smears easily, and low degradation efficiency, these characteristics usually significantly hinder its applicability toward wastewater governance. Herein, a green, facile, and efficient fabrication strategy to prepare a bi-functional palladium nanoparticles (PdNPs)-loaded bacterial cellulose membrane (BCMPd) is proposed. A tri-functional bacterial cellulose membrane (BCM) was obtained by percolating bacterial cellulose (BC) on a basal membrane, and BCM served as a support, reducing agent, and stabilizer in the subsequent reduction of PdNPs. Bi-functional BCMPd was successfully obtained and used for continuously removing emulsions and reducing methylene blue (MB) from simulated wastewater via the integration of physical sieving and chemical reaction. Meanwhile, the enhancement factors for the water transfer ability and demulsification capacity correlated directly with the wettability and surface structure of BCMPd. Furthermore, the dosage of BC was adjusted to reveal the mechanism for the enhanced water transferability and demulsification capacity. Notably, PdNPs of BCMPd decreased Fermi potential difference between BH_4- and MB, accelerating the electron transfer of the reduction reaction and thus exhibiting a remarkable MB degradation efficiency. Together, the information obtained in this work can be useful for comprehensively addressing the bottleneck of forming a cost-effective, eco-friendly, and bi-functional membrane reactor, providing an alternative approach for better treatment of complex wastewater.

Three-dimensional superhydrophilic polyvinyl alcohol–formaldehyde composite sponges with suitable pore sizes for high efficiency emulsion separation

PVA/PVF and PVA–COOH/PVF composite sponges with excellent emulsion separation performance.