Modified Polyvinylidene Fluoride Membrane Research Articles

Bioinspired multi-functional modified PVDF membrane for efficient oil-water separation

The pervasive issue of oily wastewater presents a critical environmental challenge, necessitating the development of advanced membranes that offer high purification efficiency, durability, and versatility. In this study, we introduce a novel bioinspired multifunctional membrane, synthesized by modifying polyvinylidene fluoride (PVDF) with fibrous two-dimensional carbides and nitrides (MXene) and silica (SiO2) nanoparticles, drawing inspiration from the complex structure of coral stones. The membrane was fabricated using the phase inversion technique, producing a robust material that achieves over 99% separation efficiency for oil–water mixtures. Beyond oil–water separation, the membrane exhibited exceptional performance in removing various contaminants from complex oily wastewater, including heavy metals, dyes, and phenol. Remarkably, the membrane maintained its high purification efficiency even after 5 consecutive cycles of oil–water separation and pollutant adsorption. This bioinspired multifunctional modified PVDF (MMP) membrane represents a major advancement in wastewater treatment technology, with significant potential for widespread application in the purification of complex oily wastewater.

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.

Modification of polyvinylidene fluoride membrane with ciprofloxacin to improve the bacteriostatic performance

The common polyvinylidene fluoride (PVDF) membrane itself is susceptible to membrane fouling, especially biofouling, which is a serious threat. In this study, PVDF membrane was modified with ciprofloxacin (CIP) through co-blending to investigate the filtration properties, bacterial inhibition and fouling resistance. Modified membranes were prepared by adding 0.3 g (MC0.3), 0.6 g (MC0.6), 0.9 g (MC0.9) and 1.2 g (MC1.2) CIP per 100 g casting solution. Among these modified membranes, MC0.6 showed the best filtration performances, with the pure water flux stabilized at about 416.67 L/(m2·h) and bovine serum albumin (BSA) rejection of 92.0% at a trans-membrane pressure of 0.1 MPa. The pore size was reduced, the average roughness was reduced to 29.4 nm, the contact angle was lowered to 68.9°, and the hydrophilicity was greatly improved. The width of the inhibition circle produced by MC0.6 was 0.35–0.45 mm, and the modified membrane showed good inhibition of non-specific bacteria and algal removal during urban river water filtration. The rejection of BSA was increased by 16.32% compared to the base membrane and the adsorption rate for BSA was reduced by 68.45%. In addition, the removal of conventional pollutants in urban river water by the modified membranes for was also improved. Compared with that of the base membrane, the removal of TN, NH3–N, TP and COD by MC0.6 was increased by 10.58%, 12.45%, 15.44% and 13.53%. The results showed that CIP co-blending modified PVDF membrane could effectively improve membrane performances and has good value for water treatment.

A comparison of three modification methods for polyvinylidene fluoride membrane grafting

Abstract UV-induced covalent bonding, UV-benzophenone (BP) embedding, and ozone-activated grafting methods were respectively used to graft 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) on polyvinylidene fluoride (PVDF) hollow fiber membrane surfaces via orthogonal test. The rejection rate, permeating flux, and pure water flux were chosen as comprehensive evaluation indexes to optimize the modification conditions. The optimal experimental conditions for UV-induced covalent bonding, UV-BP embedding, and ozone-activated grafting methods were obtained. Subsequently, three membranes were prepared by these three methods under their optimal modification conditions to compare their properties. The PVDF-g-AMPS-2 membrane obtained by the UV-BP embedding method exhibited the highest hydrophilicity and lipophobicity, and its water and underwater oil contact angles were respectively 66.0° and 146.6°. Besides, The PVDF-g-AMPS-2 membrane can resist the adhesion of oil with the underwater oil adhesion force of zero. What’s more, the PVDF-g-AMPS-2 membrane possessed the largest pure water flux (544.5 L/(m2·h·bar)), permeation flux (66.5 L/(m2·h·bar)), and recovered flux (205.7 L/(m2·h·bar)). By comparison, UV-BP embedding with simpler procedures can fabricate the AMPS modified PVDF membrane with superior performance, which has better application prospects in industrial scale-up production.

Characterization of Modified PVDF Membranes Using Fourier Transform Infrared and Raman Microscopy and Infrared Nanoimaging: Challenges and Advantages of Individual Methods.

Polymer materials are integral to diverse scientific fields, including chemical engineering and biochemical research, as well as analytical and physical chemistry. This study focuses on the characterization of modified poly(vinylidene fluoride) (PVDF) membranes from both physical and chemical perspectives. Unfortunately, current surface characterization methods face various challenges when simultaneously measuring diverse material properties such as morphology and chemical composition. Addressing this issue, we introduce infrared scattering scanning near-field optical microscopy (IR-sSNOM), a modern technique with the ability to overcome limitations and provide simultaneous topographical, mechanical, and chemical information. We demonstrate the capabilities of IR-sSNOM for investigation of four samples of PVDF membranes modified with 2-(methacryloyloxyethyl)trimethylammonium iodide and/or methacryloyloxyethyl phosphorylcholine in various ratios. These membranes, desirable for their specific properties, represent a challenging material for analysis due to their thermal instability and mechanical vulnerability. Employing Fourier transform infrared (FTIR) microscopy, IR-sSNOM, and Raman microscopy, we successfully overcame these challenges by carefully selecting the experimental parameters and performing detailed characterization of the polymer samples. Valuable insights into morphological and chemical homogeneity, the abundance of modifying side chains, and the distribution of different crystal phases of PVDF were obtained. Most notably, the presence of modifying side chains was confirmed by FTIR microscopy, the Raman spectral mapping revealed the distribution of crystalline phases of the studied polymer, and the IR-sSNOM showed the abundance of chemically diverse aggregates on the surface of the membranes, thanks to the unique nanometer-scale resolution and chemical sensitivity of this technique. This comprehensive approach represents a powerful toolset for characterization of polymeric materials at the nano- and microscale. We believe that this methodology can be applied to similar samples, provided that their thermal stability is considered, opening avenues for detailed exploration of physical and chemical properties in various scientific applications.

Synergistic Interaction of Ionic Liquid Grafted Poly(vinylidene Fluoride) and Carbon Nanotubes to Construct Water Treatment Membranes with Multiple Separation Properties.

In this study, the dual strategy of 1-butyl-3-vinylimidazolium bromide ionic liquid (IL) grafting and carbon nanotubes (CNTs) nanocomposition was applied to modify poly(vinylidene fluoride) (PVDF)-based membranes. The highly hydrophilic/oleophobic and fouling-resistant PVDF-g-IL/CNTs membranes with excellent separation efficiency were obtained by the nonsolvent-induced phase separation method with ethanol-water mixed solution as the coagulation bath. The grafted IL not only generated hydrophilic groups on PVDF chains but also acted together with the CNTs to induce the formation of hydrophilic β-crystalline phase of PVDF, which significantly improved the hydrophilicity and pore structure of the modified PVDF membranes. As a result, the pure water flux of the optimal membrane increased up to 294.2 L m-2 h-1, which was 5.2 times greater than that of the pure PVDF membrane. Simultaneously, the electrostatic interaction of the positive IL and the integration of CNTs enhanced adsorption sites of the membranes, producing exceptional retention and adsorption of dye wastewater and oil-water emulsion. This study presents a straightforward and efficient approach for fabricating PVDF separation membranes, which have potential applications in the purification of various polluted wastewater.

Plasma etching assisted fabrication of PDA/PEI modified PVDF membranes for oil/water emulsion separation

Plasma etching assisted fabrication of PDA/PEI modified PVDF membranes for oil/water emulsion separation

Simple surface modification of PVDF membrane via a quaternization of NM88B for efficient oil/water separation

Developing a stable MOF-modified membrane for efficient treatment of oily wastewater remains a challenge. In this study, NH2-MIL-88B(Fe) (NM88B) was deposited on the commercial polyvinylidene fluoride (PVDF) membranes, and grafted with perfluorohexane-1-sulfonic acid potassium salt (PFHx) to achieve quaternization modification. This reaction proceeds in an environmentally friendly manner due to the absence of any catalyst. The introduction of fluorine atoms through grafting PFHx resulted in the modified PVDF membrane (NPF) demonstrating remarkable underwater superoleophobic property with an underwater oil contact angle at ∼180°. In separation of various oil-water emulsions, the NPF membrane afforded a high permeation flux (up to 2043 L·m−2·h−1) and rejection rate (∼99 %). The oil rejection of NPF membrane was >99 % after 10 filtration cycles of n-hexadecane-water emulsion, and the pure water flux of the recovered membrane was kept at 82.65 % of the original flux, indicating a very good reusability and stability. Filtration of mixed dye/oil-water emulsions showed that the NPF membrane remove 99 % of both oil and dye from the mixture. This work provides a simple and stable modification of PVDF membrane, exhibiting remarkable underwater superoleophobicity and hydrophilicity, thereby harboring substantial prospects in the treatment of oily wastewater.

Preparation of CO2 responsive PVDF membranes using PDMAEMA‐PMMA‐PDEAEMA triblock copolymer

AbstractCO2‐responsive based separation membranes are attractive in the field of membrane separation, not only for their ability to modulate the pore size of the membrane in response to CO2 stimulation, but also for their ability to facilitate the removal of contaminants from the membrane surface. However, the introduction of CO2‐responsive polymers by simple blending often results in membranes that are not responsive enough to last. In this study, we synthesized a hooked triblock copolymer and used it as an additive to prepare CO2‐responsive PVDF membranes. The modified membrane combines the advantages of the PVDF material with the CO2 response of the triblock copolymer. It not only has good CO2 responsiveness, but also removes organic contaminants from the membrane surface well. The water flux of the hybrid membranes is 4 to 11 times higher than that of pure PVDF membranes, indicating that the triblock copolymer also has some porogenic ability. Surprisingly, the static contact angle on the membrane surface increased from 67° to 86° with the increase of the triblock copolymer content in the PVDF membrane. This suggests that modified PVDF membranes have some potential in the field of switchable oil–water separation.

Investigating mechanism of enhanced anti-fouling performance of MXene modified Janus MD membrane by XDLVO theory combined with surface elemental integration method

Organic membrane fouling is a major obstacle to the application of membrane distillation in low surface tension wastewater treatment. Membrane modification might be an effective way to mitigate membrane fouling. This study mainly explored the mechanism of enhanced anti-fouling performance of the MXene modified PVDF membrane by applying XDLVO theory combined with surface elemental integration (SEI) method. The rough membrane surfaces were first reconstructed using fractal function. Then, the interaction energy between low surface tension substances and the membranes before and after modification was calculated. The results showed that oil droplets and surfactant fouling were mainly caused by hydrophobic attraction due to Lewis acid-base (AB) interaction energy. By modifying the virgin PVDF membrane with MXene nanoparticles, the polar component of membrane surface tension (γAB) increased significantly, so that the interaction energy between all contaminants and membrane surface changed from attraction to repulsion. In addition, roughness weakened the interaction energy between contaminants and membrane surface but significantly lengthened the range of interaction distance, which together determined the ability of the membrane to attract or repel the contaminants. These findings may improve the understanding of the structure-effect relationship between membrane modification and anti-fouling ability, and provide new insights into the membrane modification for MD.

Effect of chitosan crosslinking time on the structure and antifouling performance of polyvinylidene fluoride membrane by surface gelation-immersion precipitation phase inversion.

Polyvinylidene fluoride (PVDF) porous membrane was prepared by a two-step method of surface gelation-immersion precipitation phase inversion. Chitosan/acetic acid solution and glutaraldehyde aqueous solution were sequentially sprayed onto the surface of the PVDF solution film, with chitosan crosslinking and gelation occurring simultaneously on the film surface. The solution film was then immersed in a coagulation bath to obtain a modified PVDF porous membrane. The effect of the crosslinking time of chitosan and glutaraldehyde on the structure and properties of the PVDF porous membrane was discussed. The results showed that with the prolongation of crosslinking time, the surface structure of the membrane changed from a dense skin layer to a porous structure; the porosity and the mean pore size of the modified PVDF membranes increased first and then decreased, and the contact angle gradually decreased. When the crosslinking time extended to 15 min, the water flux of modified membrane (M153) reached a maximum value. BSA dynamic cyclic filtration experiment showed that the retention rate (R) of the modified membrane was significantly improved, compared to 68.3% retention rate of the blank membrane (M000), but the crosslinking time had little effect on the retention rates of the four modified membranes. The antifouling data showed that the flux recovery rate of the blank membrane was 73.0%, while the flux recovery rate of the modified membrane can reach as high as 84.40%, and the irreversible pollution rate of the blank membrane was 27.7%, while the irreversible pollution rate of the modified membrane reduced to 15.6%. These results indicated that, after surface chitosan crosslinking, the hydrophilicity and antifouling properties of PVDF membranes were improved. PRACTITIONER POINTS: Modified PVDF membranes with crosslinking CS coating were prepared by a two-step method of surface gelation-immersion precipitation phase inversion. -OH groups and -NH2 groups of CS coating improve the hydrophilicity and the antifouling property of modified PVDF membranes. Modified PVDF membranes had larger mean pore size and higher porosity than unmodified membrane. Flux recovery rates of the modified membranes were higher than that of unmodified membrane. Pollution degree, reversible pollution rate, and irreversible pollution rate of modified membranes were lower than those of unmodified membrane.

Novel bentonite modified PVDF membrane for desalination of synthetic-produced water by vacuum membrane distillation

ABSTRACT Membrane distillation (MD) has emerged as a highly promising method for the treatment of intricate and heavily contaminated water sources, such as those containing oily wastewater. The present study endeavors to advance the field by designing and evaluating a novel nanocomposite membrane comprised polyvinylidene fluoride (PVDF) and Bentonite (BNT) for application in vacuum membrane distillation (VMD) processes targeted at treating oily wastewater. A series of five nanocomposite flat sheet membranes were meticulously fabricated, incorporating varying quantities of bentonite (ranging from 0 to 0.8 g). Systematic characterizations were meticulously undertaken to comprehensively elucidate the influence of BNT incorporation on the structural and functional attributes of the developed membranes. These encompassed an array of analytical techniques, including Fourier Transform Infrared Spectroscopy (FTIR), atomic Force Microscopy (AFM), X-Ray diffraction (XRD), field emission scanning electron microscopy (FESEM), contact angle measurements (CA), as well as assessments of membrane thickness, porosity, pore size, and pore size distribution. The findings distinctly showcased the successful integration of BNT within the PVDF matrix, which correspondingly led to discernable augmentations in membrane surface roughness, hydrophobicity, and porosity. Employing consistent operational conditions involving a feed temperature of 50°C, a vacuum pressure of 30 kPa, and a NaCl solution with a concentration of 14.75 g/L, VMD experiments were systematically conducted. The empirical outcomes revealed that the incorporation of BNT notably conferred substantial enhancements upon the nanocomposite membrane’s performance. The pinnacle achievement was evidenced in a flux rate of 34 L/m2.h and a remarkable NaCl rejection rate of 99.92%, a result achieved by the nanocomposite membrane incorporating the highest content of BNT additives.

Adapting virus filtration to continuous processing: Effects of product and process variability on filtration performance.

Virus filtration (VF) is an important unit operation in the manufacture of biotherapeutics that provides robust removal of potential virus contaminants. Small virus removal can be impacted by the low operating pressures and potential depressurization events that are often associated with continuous operations where increased operational flexibility for higher loading at low flux and low pressure is required. In this study, we evaluated the impact of low flux (7 LMH) and pressure interruptions on minute virus of mice (MVM) removal. We used long-term filtrations conducted to a target throughput of 1000 L/m2 with four different monoclonal antibodies on small-scale hollow fiber virus filters with a hydrophilic modified polyvinylidene fluoride membrane. These conditions are certainly challenging for any VF operation and ensuring robust viral clearance under such conditions is critical to the design and implementation of continuous VF. Planova BioEX filters effectively removed MVM at 4 log or greater when run continuously for up to 6 days. Interestingly, pressure increases associated with filter fouling over the duration of long-term filtrations were shown to be reflective of load material variability and could be remediated by implementation of an inline prefilter. Pressure interruptions had minimal impact on overall MVM logarithmic reduction value. Effective virus removal was achieved with pressure increases being largely product-specific, which demonstrates the capability of the virus filter to remove virus independent of pressure increases that are expected to occur with increased protein load.

Direct-coating of cellulose hydrogel on PVDF membranes with superhydrophilic and antifouling properties for high-efficiency oil/water emulsion separation

As a well-known natural and innocuous plant constituent, cellulose consists of abundant hydroxyl groups and can tightly adsorb onto material surfaces hydrogen bonding, resulting in a superhydrophilic surface. In this work, the hydrophobic polyvinylidene fluoride (PVDF) membranes were modified by immersing them in cellulose hydrogel using a simple one-step process. The modified PVDF membrane exhibited excellent resistance to fouling and oil adhesion, making it highly effective in separating various oil-in-water emulsions. The cellulose-modified PVDF membranes achieved a high oil rejection rate (>99 %) and a maximum separation flux of 2675.2 L·m−2·h−1. Furthermore, even an oil-in-water emulsion containing bovine serum albumin maintained a steady permeation flux after four filtration cycles. Additionally, these cellulose-modified PVDF membranes demonstrated excellent underwater superoleophobicity across a wide range of pH levels and high saline conditions. Overall, these cellulose-modified superhydrophilic PVDF membranes are sustainable, environmentally friendly, easily scalable, and hold great promise for practical applications in oily wastewater treatment.

Modification of Polyvinylidene Fluoride (PVDF) Membrane by Polymer Blending with Phase Inversion Method

One of the simplest approaches to improve membrane performance is to increase the hydrophilicity of the membrane. This article describes the manufacture of activated polyvinylidene fluoride (PVDF) based membranes using PVP and chitosan as organic additives, with the specific aim of increasing the hydrophilicity of the membranes. Variations of dope solution were made by adding 1% by weight of PVP and 1, 2, and 3% by weight of chitosan into three different PVDF polymer solutions. The effect of additives on the membrane was obtained by evaluating chemical functional groups by ATR-FTIR, morphological changes by SEM, and filtration performance. SEM images show that the presence of additives changes the morphological structure of the membrane. This change also had a significant impact on the membrane performance, as evidenced by the increased permeability of the pure water solution and the removal of dissolved humic acid. Overall, modified PVDF membranes with 1% by weight of PVP and 1, 2, and 3% by weight of chitosan resulted in much better permeability than unmodified PVDF membranes due to their excellent hydrophilicity.

Hydrophobic modification of polyvinylidene fluoride membranes in supercritical carbon dioxide fluids

Polyvinylidene fluoride (PVDF) membranes exhibit exceptional chemical stability and find applications in various fields, including building membranes, flexible sensors, blood purification, and seawater desalination. Nevertheless, the hydrophobic performance of PVDF membranes in these applications is subpar and requires enhancement. Supercritical carbon dioxide (scCO2) fluid demonstrates a beneficial expansion effect on PVDF membranes and exhibits good solubility with fluorine reagents. This study employs scCO2 as a medium to introduce a fluorine reagent onto the surface of PVDF membranes, forming a layer of low surface energy substance that significantly improves the membrane's hydrophobicity. The results indicate the feasibility of hydrophobic modification of PVDF membranes using scCO2 as a medium, leading to improved hydrophobic properties. When using a fluorine reagent with a relatively large molecular weight, PVDF membranes in scCO2 fluid at 110 °C and 20–25 MPa for 4 h results in a substantial improvement in the hydrophobicity of the PVDF membrane, with the contact angle reaching 117.2° (compared to the primitive membrane's 80°). Scanning electron microscopy (SEM) analysis confirms the presence of a layer of low surface energy material on the modified PVDF membrane surface. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses demonstrate that the hydrophobic modification using scCO2 enhances the crystallinity and thermal stability of the PVDF membrane, raising the thermal cracking temperature from 425.3 °C to 450.5 °C. Fourier-transform infrared spectroscopy (FT-IR) reveals clear absorption peaks of the fluorine reagent at 1740 cm−1 and 1211 cm−1. Nuclear magnetic resonance (NMR) confirms the presence of characteristic peaks of hydrogen on the fluorine reagent, confirming the embedding of the hydrophobic reagent onto the PVDF membrane surface. This modification method holds significant potential for guiding the development of hydrophobic surfaces, contributing to carbon neutrality, and meeting environmental sustainability goals.

The structure and hydrophilicity of MWCNT-COOH /TiO2 modified PVDF membrane

MWCNT-COOH/TiO2 modified PVDF ultrafiltration membrane was created using a blended modification process with carboxyl carbon nanotubes (MWCNT-COOH) and TiO2 nanoparticles as modification additives in order to further enhance the hydrophilicity of the PVDF membrane surface. Using the techniques of scanning electron microscopy, Fourier transform infrared spectrum, and a water angle of engagement analyzer, the membrane’s structure and hydrophilicity were identified. Investigations were conducted into the effects of various MWCNT-COOH dosages on membrane structure and hydrophilicity. The results of the investigation indicated that 0.03 g of MWCNT-COOH in the casting solution was the ideal dose. The manufactured MWCNT-COOH/TiO2 modified PVDF ultrafiltration membrane had the best hydrophilicity.

Lithiated Phosphoryl Cellulose Nanocrystals Enhance Cycling Stability and Safety of Quasi-Solid-State Lithium Metal Batteries.

Cycling stability and safety are two of the main challenges facing lithium metal batteries with metallic lithium as anodes. Quasi-solid-state lithium metal batteries based on gel polymer electrolytes are one of the important development directions for lithium metal batteries addressing those challenges. Herein, we prepare lithiated phosphoryl cellulose nanocrystals (PCNC-Li) as a modification material for poly(vinylidene fluoride) (PVDF) gel polymer electrolyte to improve cycling stability and safety of quasi-solid-state lithium metal batteries. The synthesized PCNC-Li tends to form a uniform network structure on the surface of the PVDF membrane, in which the phosphoryl groups grafted regularly on celluloses can regulate the transport of lithium ions. As a result, a more uniform ion flux and more stable lithium anode interface support an obviously improved cycling stability for lithium metal batteries. Moreover, the introduction of the PCNC-Li coating layer makes the modified PVDF membranes have a better thermal stability and an enhanced mechanical strength, which is beneficial for improvement of safety of lithium metal batteries. This work provides a new alternative to fabricating a better composite gel polymer electrolyte for lithium metal batteries.

Modification of PVDF membrane for harvesting of Nannochloropsis sp. and its cleaning results

One of the biggest challenges in implementing microalgae-based biofuels is the effective harvesting process. Filtration membrane has become one of the flexible methods in microalgae harvesting. This study investigated the harvesting of Nannochloropsis sp. using a modified PVDF membrane at various LiCl as an additive with N-methyl-2-pyrrolidone (NMP) solvent. Harvesting of Nannochloropsis sp. with PVDF membrane has never been reported before. The addition of LiCl can improve the performance of PVDF membrane due to LiCl has a great affinity for water, resulted in inducing the formation of the pore structure of membrane. The optimum membrane composition was determined at various LiCl additive from 1% to 3% (w/w). The hydrophilicity of the membrane increased as indicated by the increasing of water permeance, which were 516, 546, 660, and 614 l m−2h−1 bar−1 for neat PVDF, PVDF/LiCl-1, PVDF/LiCl-2, and PVDF/LiCl-3 membrane, respectively. PVDF/LiCl-2 membrane showed the highest water permeance and the highest total average permeance (150 l m−2h−1 bar−1) with 100% rejection of Nannochloropsis sp. harvesting. The membranes was cleaned using sodium hypochlorite, citric acid, and nitric acid. The SEM results showed that the membrane after cleaning appears the algae particles in the membrane pore. Furthermore, algae particles were almost not visible on cleaned membrane. The FTIR results showed an absorption at 3401 cm−1, which was a characteristic of the hydrogen N–H bond, also including a typical amide uptake (C=O) at 1648 cm−1 indicating protein appearance. Moreover, the cleaned membrane did not appear any absorption that indicates the foulant.

Preparation of GO@DCN nanocomposite modified PVDF membranes for improved membrane performance and exploration of formation mechanism

Two-dimensional nanocomposite membranes (NCMs) have attracted increased attention, but the effects of nanomaterials on membranes and phase inversion mechanisms are still unclear. In this study, graphene oxide (GO) was combined with nitrogen defect-modified g-C3N4 (DCN) nanosheets by grinding to obtain GO@DCN, with subsequent doping into polyvinylidene fluoride (PVDF) by non-solvent induced phase separation (NIPS) to prepare a series of hydrophilic NCMs. The thermodynamic ternary phase diagram of NCMs is reported for the first time. Compared with pure PVDF, the phase inversion of NCMs was accelerated with the addition of DCN, GO and GO@DCN nanomaterials, which lead to sequential increment in porosity, providing channels for water molecules. Besides, the Density Function Theory(DFT) calculations indicated a strong interaction between PVDF and GO@DCN, which also contributes to the rapid phase inversion of the PVDF/GO@DCN. Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory demonstrates that the attraction between PVDF/GO@DCN2.0 and Bovine Serum Albumin (BSA) is halved compared to PVDF and BSA, indicating superior antifouling ability. At the same time, the negative zeta potential of NCMs rose, which enhanced the repulsion between NCMs and the negatively charged BSA contaminants in water. Thus, in contrast to PVDF, the permeate flux of PVDF/GO@DCN2.0 increased from 161.6 Lm−2h−1 to 387.8 Lm−2h−1 and the rejection of BSA from 80.1% to 91.6%, respectively. The flux recovery ratio (FRR) of PVDF/GO@DCN2.0 improved 30.4%, and irreversible fouling decreased 29.6%. After five cleaning cycles, the NCM still maintained excellent stability.