Surface Modification Of Membranes Research Articles

Surface treatment optimization of mixed cellulose ester membrane by cold plasma treatment to improve apple juice clarification

This study aimed to determine the optimal conditions for the surface modification of mixed cellulose ester (MCE) microfiltration membrane by cold plasma (CP) for apple juice clarification. Response surface method using central cubic design (CCD) was employed for the optimization of the membrane surface modification process. Plasma gas type (oxygen, carbon dioxide, and air), power (10, 15, and 20 W), and exposure time (120, 180, and 240 s) were used as the factors for cold plasma surface modification. The results revealed the surface modification of the MCE membrane using air as plasma gas with plasma power and exposure time equal to 10 W and 180 s resulted in the maximum permeate flux in apple juice clarification. The results of scanning electron microscope, and atomic force microscope confirm the effect of CP treatment on the membrane surface roughness. Fourier transform infrared spectroscopy showed the incorporation of the hydroxyl group into the membrane surface due to CP treatment which affected the surface contact angle and hydrophilicity. The CP treatment of the membrane significantly affects the membrane resistances. Also, the surface modification of the MCE membrane using the CP treatment process in optimal conditions is an effective method for clarifying apple juice.

Ultrafiltration membrane modified via synergistic integration of quaternary ammonium compounds bactericidal activity and g-C3N4 photocatalysis: Toward superior antibiofouling and self-cleaning property

Fouling, particularly biofouling caused by microbial adhesion and subsequent biofilm formation, limits the widespread applications of membrane-based technologies. Although integrating contact-killing agents (i.e., quaternary ammonium compounds, QACs) to fabricate antibiofouling membranes has been proven as an effective approach to mitigate this issue, the long-term effectiveness of the modified membranes after foulants covering remains a challenge. Herein, hydrophilic photocatalyst nanosheet g-C3N4 (NCN) was introduced into QAC-modified ultrafiltration (UF) membranes to address this limitation. Results showed that the hydrophilic surface of NCN can improve the antiadhesion properties of hydrophobic QAC modified membranes. Moreover, NCN can degrade organic and inorganic pollutants on QAC modified membrane surface under visible light, thereby restoring the antibacterial ability of QAC. Furthermore, the composite QAC/NCN modified membrane demonstrated long-term stability with sustained remarkable antibacterial performance even after numerous fouling-chemical cleaning cycles. These findings underscore the efficacy of the synergistic integration of contact-killing bactericidal activity and photocatalysis as a versatile and promising solution for combating biofouling, thereby contributing to the advancement of membrane technology in environmental remediation applications.

Swelling-assisted surface grafting strategy for multichannel antifouling membranes: Reconstruction of surface pore structure and applications in microalgae harvesting and blood purification

Membrane fouling remains a major challenge in membrane separation. The modification of hydrophilic membrane surfaces can mitigate irreversible fouling deposition, thereby improving antifouling properties. Effective surface modification strategies are essential techniques for developing highly efficient antifouling membranes. In this work, a swelling-assisted surface grafting strategy was proposed for multichannel antifouling membranes, where various lengths of polyvinylpyrrolidone (PVP) brushes were grafted on the surface of polysulfone membrane using reversible addition-fragmentation chain transfer polymerization. The successful grafting of PVP polymer brushes was confirmed using Fourier transform infrared spectrometer and X-ray Photoelectron Spectroscopy. Changes in membrane morphology and pore structure were observed via scanning electron microscope and atomic force microscope. During the grafting process, the amphiphilic macromolecules formed through grafting were selectively swelled by graft solvent, leading to the formation of mesopores in both the surface layer and sublayer of the membrane, which formed additional water transport channels. The introduction of hydrophilic polymer brushes and the change of pore structure significantly boosted the hydrophilicity and permeability of the membranes. As a result, the water contact angle decreased from 85° to 42°, accompanied by an approximate 3.24-fold increase in pure water flux (PWF). Due to superior hydrophilicity, modified membranes demonstrated exemplary performance in microalgae harvesting, boasting a microalgae retention rate nearing 100 % and low fouling resistance (2.12 × 1012 m−1). In algal filtration experiments, a confocal laser scanning microscope was employed to assess the activity of filtered algae on the membrane surface. The prepared membranes effectively maintained the bioactivity of algae while also achieving a high flux recovery rate (90.7 %) following filtration and cleaning. Furthermore, in blood cell compatibility tests, the modified membranes exhibited resistance to blood cell adhesion and sustained a low hemolysis rate (0.06 %). Overall, this strategy offers unique insights into the fabrication of antifouling surfaces and shows considerable promise for large-scale applications in microalgae harvesting and blood purification.

Tailored nanofiltration membrane for enhanced antibiotic desalination by surface modification using branched quaternary triethanolamine assembly

Surface modification of nanofiltration membranes is a productive approach to improve separation performance. In this study, we synthesized branched bis- and tris-quaternary assemblies, denoted as BQTE and TQTE, through the quaternization reaction of triethanolamine with 1,4-bis(bromomethyl)benzene and 1,3,5-tris(bromomethyl)benzene. These assemblies were then grafted onto a nascent polyamide (PA) membrane via forming ester bonds. This modification induced the formation of nanobubbles within the PA matrix due to reaction heat-induced gas expansion during grafting. Compared to TQTE, BQTE had fewer hydroxyl-quaternary ammonium entities, resulting in a much looser PA film. Additionally, the positively charged quaternary ammonium groups reduced the negative charge and mitigated Donnan exclusion against ions. Both PA-BQTE and PA-TQTE membranes demonstrated exceptional performance in antibiotic desalination. Specifically, PA-BQTE had a water permeance of 9.7 L·m-2·h-1·bar-1 in a 10 g·L-1 NaCl solution, with a NaCl/tetracycline selectivity of 42.5. Furthermore, these modified membranes demonstrated improved antifouling property and enhanced resistance to chlorine, underscoring their potential for practical applications.

Fouling-resistant superhydrophobic polyketone membranes modified with fluorine-containing silica for water-in-oil emulsion separation

Membranes for water-in-oil (W/O) emulsion separation require high emulsion permeance, oil purity selectivity, high water-fouling resistance, and reusability. Therefore, a functional membrane structure that satisfies these needs is required. Herein, we describe the effective modification of a membrane surface by forming functional silica particles on a porous polyketone (PK) membrane to form a hierarchical membrane structure with enhanced roughness and superhydrophobicity. We also demonstrate the potential application of the membrane for W/O emulsion separation based on enhanced performance and fouling resistance. Membranes were fabricated by forming silica particles on a porous PK membrane by a sol–gel method using tetraethoxysilane (TEOS). By modifying these silica particles with fluoroalkyl silane (FAS), a superhydrophobic membrane with a high contact angle of up to 162° was fabricated. The resulting FAS-modified membrane had higher permeance with regard to a toluene W/O emulsion than an unmodified PK membrane or a commercially available polyvinylidene fluoride (PVDF) membrane. It was possible to recycle the FAS-modified membrane by simply washing it in toluene to remove external fouling. This effective membrane surface modification helps to enhance both emulsion permeance and fouling resistance during W/O emulsion separation.

A green bulk modification for imparting a green VIPS membrane with antifouling properties

BackgroundMembrane preparation and membrane modification processes have long involved the use of toxic solvents. The present work proposes to only use envrionmentally-friendly solvents for both the fabrication and the surface modification of hydrophobic microfiltration membranes. In addition, coating processes for membrane modification are essentially surface modification processes. However, spray-coating may be a suitable method for both surface and bulk modification. MethodsAfter dissolving poly(vinylidene fluoride) in dimethylsulfoxide, membranes were formed by the vapor-induced phase separation process, and then modified using an aqeous solution of an amphiphilic copolymer containing poly(ethylene glycol) methyl ether methacrylate units. Then, a variety of physicochemical techniques were employed to characterize the membrane structure and prove the effectiveness of the surface/bulk modification. Antifouling tests in static and dynamic conditions were conducted. Significant findingsIt is possible to reduce the water contact angle of the top surface of the membrane from 135° to 0° and that of the bottom surface from 126° to 0° within <10 s, indicating successful hydrophilization of the membrane on the one hand, and top-to-bottom modification, despite solely exposing the top surface to the spray, on the other hand. This conclusion was confirmed by deidcated surface chemistry analyses. Besides, the membranes maintained their original highly porous and symmetric structure with light effects on surface porosity and pore size following the spray-coating process. The drasting improvement of hydrophilicity resulted in effective mitigation of fibrinogen adsorption (reduced by 85 %) and Escherichia coli adhesion (reduced by 86 %). Fouling during cyclic filtration involving a bacterial suspension was also effectively reduced with a flux recovery ratio of 53 % (against 37 % for a commercial hydrophilic membrane) and an irreversible flux decline ratio of 47 % (against 63 % for a commercial hydrophilic membrane) in the conditions of the test.

Sheep bone powder modified PVDF membrane for highlyefficient oil-in-water emulsion separation

BackgroundThe wetting properties and roughness modification of membrane surfaces are crucial for their application in emulsion separation. However, traditional membrane modification methods suffer from high cost, complex preparation, and secondary pollution. MethodsIn this study, a novel, simple, and economical interfacial engineering method was developed using tannic acid (TA), sodium alginate (SA), and sheep bone powder (BP) as raw materials. Through vacuum filtration, these materials were deposited onto polyvinylidene fluoride (PVDF) membrane to fabricate superhydrophilic/underwater superoleophobic filtration membrane (PDBS). BP induced surface roughness and wetting properties to the membrane, while preserving the porous structure of the substrate membrane. The complex formed by TA and SA encapsulated BP onto the surface of PVDF microfiltration membrane, enhancing its mechanical properties. Significant FindingsThe prepared membrane exhibited a membrane flux of 347 Lm−2h−1 bar−1 and a separation efficiency of 99.9 % for emulsified oil. Furthermore, after soaking in NaCl solution for 30 h, the membrane still showed excellent stability. Therefore, this study developed a new membrane surface modification strategy with promising application prospects in oily wastewater treatment.

Surface modification of inter-polymer cation exchange membrane by controlled loading of polyaniline/metal particles for improved electrodialytic performance during mono-/bi-valent ions separation

Separation/recovery water hardness (Ca2+/Mg2+), toxic (Ni2+), and micro-nutrient (Zn2+) metal ions, are important for the water purification and resources recovery. Previously conducting polymer (polyaniline-PANI) and metal nanoparticles coated cation exchange membranes (CEMs) are reported for electrodialytic separation of mono- and bi-valent ions. However, a comparative study under similar experimental conditions must assess their suitability. We achieved the surface modification of inter-polymer CEM by PANI or metal nanoparticles (Cu or Ni) by ion exchange process followed by reduction to improve the membranes mono-valent selectivity. Different surface-modified interpolymer cation exchange membranes (CEMs) were examined and characterized for their morphological, physicochemical, electrochemical properties, stabilities, and electrodialytic transport properties. It was observed that PANI/metal nanoparticles surface modification of IPC membrane showed fine control over hydrophilic/hydrophobic behaviour, and permselectivity, which may be fine-tuned according to the requirements. Further, electro-transport of mono-valent ions was unaltered, while reported pore-sieving strategy restricted the transport (leakage) of bi-valent ions. Pristine IPC membrane showed 68.8–61.2 % leakage of bi-valent ions, while surface modified IPC-PANI membranes exhibited an 8.4 % leakage of Ca2+, corresponding to 0.99 kW h kg−1 removal of salt and a current efficiency of 78.9 %. These information revealed the suitability of IPC-PANI membrane for separation/recovery of micro-nutrient (Ca2+, Mg2+, and Zn2+) and toxic (Ni2+) bi-valent cations from water systems by electrodialysis.

Super-hydrophobic ceramic membrane with dense and robust silane grafting for efficient water-in-oil emulsion separation

Separate water from water-in-oil (W/O) emulsions is essential in oil resources recycling and wastewater treatment. Hydrophobic ceramic membranes (HCM) have shown great potential in the dehydration of W/O emulsions but developing high-performance HCM is still a challenge due to the difficulty in hydrophobic modification of ceramic membranes. In this study, an HCM with high grafting density and robust structure was prepared by the grafting silane coupling agent onto an attapulgite (ATP) ceramic membrane. The hexadecyltrimethoxysilane (HDTMS) was chosen for membrane surface modification considering its reaction activity and stability based on molecular dynamic simulation. The effect of the HDTMS contents in the grafting solution and reaction time on the membrane properties were examined. The ATP membrane grafted by HDTMS solution with a content of 9600 ppm for 24 h had a water contact angle of 161° and oil permeability larger than 2207.5 L·m−2·h−1·bar−1 (LMHB). When dealing with W/O emulsions with a water content of 10000 ppm, the steady permeability, permeability recovery ratio, and water rejection of ATP-based HCM was 362 LMHB, 97 %, and 99 %, respectively. Ascribe to the –OH-rich nature of ATP, the performance of HCM in this work is superior to most membranes including Al2O3, ZrO2, and SiC. Hydrophobic-modified ATP provides a new idea for the development of high-performance HCM based on natural mineral ceramics.

Mesoporous Silica-Based Membranes in Transdermal Drug Delivery: The Role of Drug Loss in the Skin.

Compared to other forms of drug administration, the use of Transdermal Drug Delivery Systems (TDDSs) offers significant advantages, including uniform drug release profiles that contribute to lower side effects and higher tolerability, avoidance of direct exposure to the gastrointestinal tract, better patient compliance due to their non-invasive means of application and others. Mesoporous silica membranes are of particular interest in this regard, due to their chemical stability and their tunable porous system, with adjustable pore sizes, pore volumes and surface chemistries. While this allows for fine-tuning and, thus, the development of optimized TDDSs with high loading capacities and the desired release profile of a given drug, its systemic availability also relies on skin penetration. In this paper, using a TDDS based on mesoporous silica membranes in Franz cell experiments on porcine skin, we demonstrate surprisingly substantial drug loss during skin penetration. Drug passage through porcine skin was found to be dependent on the age and pre-treatment of the skin. pH and temperature were major determinants of drug recovery rates as well, indicating drug loss in the skin by enzymatic metabolization. Regarding the TDDS, higher loading obtained by SO3H surface modification of the mesoporous silica membranes reduced drug loss. Still, high loss rates in the skin were determined for different drugs, including anastrozole, xylazine and imiquimod. We conclude that, beyond the fine-tuned drug release profiles from the mesoporous silica membrane TDDS, remarkably high drug loss in the skin is a major issue for achieving desired skin penetration and, thus, the systemic availability of drugs. This also poses critical requirements for defining an optimal TDDS based on mesoporous silica membranes.

Biofouling control of thermophilic bacteria in membrane distillation

Previously, fouling of MD membranes was perceived to be minimal due to the operational conditions preventing bacterial growth. However, recent studies presented fouling of MD membranes, largely due to various halophilic and thermophilic bacterial. The current study presented potential of antibacterial cellulose nanocrystals (CNCs) capped silver nanoparticles (AgNPs) towards biofouling control in MD water desalination processes. Interestingly, the CNCs were used as capping and reducing agent in a microwave mediated synthesis of AgNPs. The green synthesis approach of AgNPs and its successful use in MD processes was reported for the first. The MD experiments were carried out using a series of modified PVDF membranes and feed solution spiked with a thermophilic G. stearothermophilus. Upon evaluation of fouled membranes, particularly PVDF, PVP-equipped PVDF, and f-CNTs-modified PVDF, the surface energy of interactions were −131 mJ/m2, −31.5 mJ/m2, −28.6 mJ/m2, suggesting favorable interaction between the membranes and bacterial foulant. The findings of this study were supported by fouling layer and bacterial growth as seen from scanning electron microscopy, atomic force microscopy and Fourier transform infrared results. Upon membrane surface modification using CNCs-capped AgNPs, bacterial growth on membrane surface was reduced. Specifically, the positive cohesion energy between the CNCs-capped AgNPs-modified PVDF membrane and thermophilic bacterial foulant was + 63.2 mJ/m2, distinctly proving reduced fouling. The findings were supported by 5.5 % flux decay of the modified membrane compared to 79.3 % flux decay of virgin PVDF membrane. This suggested a long-term membrane integrity in thermophilic bacterial contaminated feed solutions during the MD water desalination.

Surface modification of polyacrylonitrile nanofiber membrane by Bimetallic organic frameworks for enhanced antibacterial properties

With the increasing environmental degradation, bacterial contamination is threatening human health. Thus, it is crucial to develop an efficient and safe antimicrobial strategy. In this work, the polyacrylonitrile (PAN) nanofiber membranes contained Co/Zn-metal organic framework (Co/Zn-MOF@PAN) were fabricated via electrospinning technique and surface modified method. The optimal preparation condition for nanofiber membranes were further regulated by adjusting 2-methylimidazole (2-MIM) concentration and secondary growth time. The antibacterial activity of Co/Zn-MOF@PAN against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were determined by turbidimetry and plate colony-counting methods. As the 2-MIM concentration and secondary growth time increased, the hydrophilicity and surface roughness of Co/Zn-MOF@PAN nanofiber membranes increased. In addition, when the 2-MIM concentration was 0.16 mol/L, the Co/Zn-MOF@PAN nanofiber membranes had an antibacterial rate of over 99% against E. coli and S. aureus., and the minimum inhibitory concentration (MIC) value of Co/Zn-MOF@PAN nanofiber membranes was 0.75 mg/mL. It could be indicated that Co/Zn-MOF@PAN nanofiber membranes exhibited an excellent antibacterial effect. The main antibacterial mechanism of nanofiber membranes was that ROS produced by MOFs could destroy the physiological activities of the bacteria lead to death. The Co/Zn-MOF@PAN nanofiber membranes will have a wide range of applications value in the fields of antibacterial packaging materials and sterilization of water resources.

Surface Modification of Polyethylene Terephthalate Track-Etched Membranes by 2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl Acrylate for Application in Water Desalination by Direct Contact Membrane Distillation.

In this work, the surfaces of poly (ethylene terephthalate) track-etched membranes (PET TeMs) with pore sizes of 670-1310 nm were hydrophobized with 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate (DFHA) by photoinitiated graft polymerization. Attenuated total reflection FTIR spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) coupled to an energy-dispersive X-ray spectrometer (EDX), and contact angle measurements were used to identify and characterize the TeMs. The optimal parameters for graft polymerization were determined as follows: polymerization time of 60 min, monomer concentration of 30%, and distance from the UV source of 7 cm. The water contact angle of the modified membranes reached 97°, which is 51° for pristine membranes. The modified membranes were tested for water desalination using direct contact membrane distillation (DCMD) method. The effects of membrane pore size, the degree of grafting, and salt concentration on the performance of membrane distillation process were investigated. According to the results obtained, it has been concluded that large pore size hydrophobic TeMs modified by using DFHA could be used for desalinating water.

Surface Modification of PVDF and PTFE Hollow Fiber Membranes for Enhanced Nitrogen Removal in a Membrane-Aerated Biofilm Reactor

Surface Modification of PVDF and PTFE Hollow Fiber Membranes for Enhanced Nitrogen Removal in a Membrane-Aerated Biofilm Reactor

Opting for polyamines with specific structural traits as a strategy to boost performance of enzymatic membrane reactors

Enzymatic membrane reactor (EMR) is a type of continuous-flow bioreactor offering easy separation and reuse of biocatalyst while giving opportunities to improve its performance. However, simultaneous enhancement of activity and stability of enzyme while retaining high membrane permeability poses a challenge for a single reactor. Herein, we propose a new method to optimize EMR system − by employing cationic polyelectrolytes with selected molecular weight, backbone, and amino group type for modification of membrane surface; after we have evaluated the effect of polyamine chemistry and membrane properties on each aspect of EMR performance. Polydopamine (PDA)-assisted co-deposition of polyamines (polyethyleneimine (PEI), PEI-graft-poly(ethylene glycol) (PEI-g-PEG), poly(allylamine hydrochloride) (PAH), and poly(diallyldimethylammonium chloride) (PDADMAC)) was used as the modification method; the membranes were characterized by water permeability, water contact angle (WCA), zeta potential (ZP), FTIR spectra, and SEM/EDX; and EMRs were assessed by biocatalytic activity at various pH, flux, immobilization yield and efficiency (activity recovery), enzyme leakage, pH/storage and thermal stability, and reusability. In this work, EMRs with immobilized alcohol dehydrogenase (ADH) showed activities up to 8.9 mU/cm2, retained up to 86 % of initial activity in three conversion cycles without any reduction in flux, and allowed to increase non-optimal pH activity (pH 10) by up to 81 % and improve storage stability by up to 53 % compared to the free enzyme. We discovered statistically significant (p < 0.01) relationships between: (1) polyamine backbone type (linear vs branched) and membrane permeability; (2) membrane isoelectric point and immobilization yield; and (3) membrane WCA and immobilization efficiency. To our knowledge, this is the first systematic study of the effect of polyelectrolyte chemistry on performance of immobilized enzyme − which showed the method’s strong potential for customizing properties and maximizing the productivity of EMRs.

Novel membrane modifications for pressure retarded osmosis as a new way for sustainable power generation from salinity gradients

Pressure retarded osmosis (PRO) is a novel technology that allows power to be generated from high-salinity resources. To achieve a high power density, a high-salinity solution should be used on the draw side together with high hydraulic pressure, thus the PRO process requires a membrane that has high salt rejection and high pressure resistance. The reverse osmosis (RO) membranes can be potential candidates for the PRO process. In this study, commercial RO membranes with different surface modifications were examined: O2 plasma, polydopamine (PDA) and tannic acid (TA). Improved water permeability and salt rejection were obtained after modification. The membranes were also tested with a high salinity solution (175 g/L NaCl) in a PRO mode. Due to the improved water permeability and high salt rejection of the surface-modified membrane, the commercial RO membrane showed enhanced power density (3 W/m2) in comparison to the pristine membrane (2 W/m2).

Recent 10-year development on surface modification of polymeric hollow fiber membranes via surface coating approach for gas separation: a review

Recent 10-year development on surface modification of polymeric hollow fiber membranes via surface coating approach for gas separation: a review

High-performance lithium batteries achieved by electrospun MXene-Enhanced cation-selective membranes

Conventional separators applied in lithium batteries face limitations like low porosity, poor electrolyte wettability, lower cation selectivity, and thermal instability, which impact battery performance and safety characteristics. Besides the challenge in separator design, transition metal ion migration from positive electrodes during cycling greatly accelerates capacity fading because of unrestricted diffusion of transition metal cation across the separator. This study explores an innovative strategy for the separator design by incorporating MXene (spraying MXene solution on both sides of the separator), a two-dimensional material, into electrospun Polyacrylonitrile/Polyetherimide membranes with the function of cation selection. Li+ can be accelerated, and its transference number increases along with the anion limitation in the MXene layer. Ni, Co, and Mn ion dissolution from the positive electrode is inhibited due to the cation selectivity of the MXene layer. Leveraging electrospinning advantages, the resultant membranes exhibit high porosity, excellent liquid absorption, mechanical strength, and superior thermal properties. Benefiting from MXene's layered structure and excellent adsorption ability, the membrane significantly inhibits the dissolution of transition metal ions while enabling smooth lithium deposition due to its cation selectivity. Eventually, the Li||NMC811 batteries deliver outstanding cyclic performance (91.3 % capacity retention after 200 cycles) and robust lithium dendrite suppression (800 h of stable cycling). Moreover, the MXene-modified membrane demonstrates exceptional electrolyte wettability, significantly improving ionic transference number (0.67) and conductivity (1.6 mS/cm). Modification of membrane surfaces with MXene offers insights into addressing transition metal ion migration from the positive electrode material perspective, providing a promising avenue for high-performance LIBs.

In-situ surface modification of a reverse osmosis membrane with acrylic polymers: Transport and retention of a small neutral organic micropollutant

Highly selective in-situ surface grafting approaches were designed to improve the rejection of 1H-benzotriazole (BTA) by a reverse osmosis (RO) membrane. A commercial FT30 membrane was grafted in-situ for the first time with 2-(diethylamino)ethyl methacrylate (DEAEMA) and 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), respectively, and compared with the state-of-the-art polydopamine (PDA) modification method. The TMSPMA grafting enhanced the BTA rejection from 88.4% to 98.4%, with a minor drop in water permeability (0.3%) compared to the pristine membrane. The FT30-TMSPMA membrane performed considerably better than the FT30-DEAEMA and FT30-PDA membranes. The improved rejection after TMSPMA modification can be ascribed to enhanced steric exclusion and hydrophobic interactions. The boosted hydrophobicity of the FT30-TMSPMA membranes is the result of the hydrophobic nature of the propyl/methyl groups present in TMSPMA, resulting in an 11.3% and 8.8% higher selectivity of BTA compared to the pristine FT30 and FT30-PDA membrane, respectively. The A/B ratio (which indicates the membrane selectivity to water against the solute) of the FT30-TMSPMA membrane increased by 714%, which is the highest enhancement compared to other modified materials reported in the literature until now. This new modification approach is thus highly promising for membrane functionalization to improve the rejection of small neutral organic micropollutants.

Contribution of graphene oxide (GO)-containing polydimethylsiloxane (PDMS) binder to the surface modification of electrospun PVDF membrane towards development of photothermal vacuum membrane distillation (PVMD)

Given the scarcity of water and energy resources and their potential to escalate into future crises, water and energy have emerged as the paramount challenges of the present century. To address these challenges, simultaneously, a novel membrane distillation (MD) technique named photothermal MD (PMD) has come to the forefront in recent years. The PMD is rapidly advancing, particularly in the field of desalination, towards increasing the use of sustainable solar energy. In this work, the surface of poly(vinylidene fluoride) (PVDF) electrospun membrane was turned into a photothermal surface by binding graphene oxide (GO) nanosheets using a binder solution made of polydimethylsiloxane (PDMS) with different concentrations (0.1, 0.5, 1, 2, 3 wt%). Subsequently, the environmentally-friendly low-pressure plasma polymerization method was employed to polymerize perfluorodecyl acrylate (PFDA) monomers on the surface of coated electrospun membrane to achieve an omniphobic surface. In this regard, the contact angles of water, oil, and ethanol/water (70/30 v/v) solution on the surface of the coated membranes were measured to be 144°, 124.4°, and 120.8°, respectively. Compared to the uncoated electrospun membrane, the one coated with GO-containing binder solution with optimum PDMS concentration of 0.1 wt%, showed a significant increase in flux by 41 % at 1 sun irradiation during photothermal vacuum MD (PVMD). In the PVMD process, the conventional method of feed heating was substituted with membrane surface heating utilizing solar energy. Additionally, vacuum was employed to facilitate the passage of water vapor through the membrane pores. This increment was further highlighted by salt rejection remained constant at 99.9 %. It was also found that PDMS concentration in the GO-containing binder solution adversely affects the membrane efficiency, exhibiting a decreasing trend from 54.1 % to 17.5 % when PDMS concentration increases from 0.1 to 3 wt%. Additionally, the long-term performance assessment of the prepared membrane coated with the binder solution with optimum PDMS concentration of 0.1 wt% demonstrated its acceptable resistance against wetting by the NaCl aqueous solution (35 g/L) containing 0.3 mM sodium dodecyl sulfate (SDS).