Enhanced performance of conductive polysulfone/MWCNT/PANI ultrafiltration membrane in an online fouling monitoring application

Lignin particles as green pore-forming agents for the fabrication of microporous polysulfone membranes

Templating polymeric membranes with micro-nano-scaled solid materials is an effective method to simultaneously improve the water flux and retention ratio. However, the fabrication of a green, recyclable, and size-controlled template material remains a challenge. Here, a new green pore-forming agent, lignin particles (LP), was developed to prepare porous polysulfone (PSF) membranes via the phase inversion technique. A series of LP have uniform sizes from ~200 nm to ~1800 nm. The performances of the templated PSF membranes cast at different sizes and contents of LP were examined for their surface and crosssection morphologies. The LP-templated PSF membranes displayed a remarkable enhancement in flux, porosity, and moisture content. Particularly, the PSF membranes cast with LP from ~200 to 1800 nm broke the traditional trade-off to a certain degree, which possessed stable retentions of bovine serum albumin (> 85 %) and significantly improved water flux (174.275 to 254.775 L m^-2 h^-1). In addition, the LP pore-forming agent is low-cost and environmentally friendly as it was prepared from industrial by-products and can be easily recycled. Overall, this study shows that lignin particles are green pore-forming agents that can be used for the fabrication of porous polymeric membranes with improved performance for water treatment.

A critical review on classifications, characteristics, and applications of electrically conductive membranes for toxic pollutant removal from water: Comparison between composite and inorganic electrically conductive membranes

Research efforts have recently been directed at developing electrically conductive membranes (EMs) for pressure-driven membrane separation processes to remove effectively the highly toxic pollutants from water. EMs serve as both the filter and the electrode during filtration. With the assistance of a power supply, EMs can considerably improve the toxic pollutant removal efficiency and even realize chemical degradation to reduce their toxicity. Organic-inorganic composite EMs and inorganic EMs show remarkable differences in characteristics, removal mechanisms, and application situations. Understanding their differences is highly important to guide the future design of EMs for specific pollutant removal from water. However, reviews concerning the differences between composite and inorganic EMs are still lacking. In this review, we summarize the classifications, fabrication techniques, and characteristics of composite and inorganic EMs. We also elaborate on the removal mechanisms and performances of EMs toward recalcitrant organic pollutants and toxic inorganic ions in water. The comparison between composite and inorganic EMs is emphasized particularly in terms of the membrane characteristics (pore size, permeability, and electrical conductivity), application situations, and underlying removal mechanisms. Finally, the energy consumption and durability of EMs are evaluated, and future perspectives are presented.

Development of High Flux Nanocomposite Polyphenylsulfone/Oxidized Multiwalled Carbon Nanotubes Membranes for Ultrafiltration Using the Systems with Critical Solution Temperatures

The study deals with the investigation of the effect of the modification of polyphenylsulfone (PPSU) flat sheet membranes for ultrafiltration using oxidized multiwalled carbon nanotubes (O-MWCNT) in order to enhance membrane permeability and antifouling performance. The effect of O-MWCNT loading to the PPSU-polyethylene glycol (PEG-20,000, M_n = 20,000 g·mol⁻¹)-polyvinylpyrrolidone (PVP K-30, M_n = 40,000 g·mol⁻¹)-N-methy-2-pyrrolidinone (NMP) colloid systems on the phase state and viscosity was studied. It was found that PPSU-PEG-20,000-PVP K-30-O-MWCNT-NMP colloid systems feature a gel point (T = 35–37 °C) and demixing temperature (T = 127–129 °C) at which two bulk phases are formed and a polymer system delaminates. According to the study of the phase state and viscosity of these colloid systems, a method for the preparation of high flux PPSU membranes is proposed which includes processing of the casting solution at the temperature higher than gel point (40 °C) and using a coagulation bath temperature lower than gel point (25 °C) or lower than demixing temperature (40 °C and 70 °C). Membrane structure, topology and hydrophilic-hydrophobic balance were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and water contact angle measurements. The effect of coagulation bath temperature and O-MWCNT concentration on the membrane separation and antifouling performance in ultrafiltration of human serum albumin and humic acids solutions was studied. It was found that the modification of PPSU ultrafiltration membranes by O-MWCNTs yielded the formation of a thinner selective layer and hydrophilization of the membrane surface (water contact angle decreased from 53–56° for the reference PPSU membrane down to 33° for the nanocomposite membrane with the addition of 0.19 wt.% O-MWCNT). These changes resulted in the increase in membrane flux (from 203–605 L·m⁻²·h⁻¹ at transmembrane pressure of 0.1 MPa for the reference membrane up to 512–983 L·m⁻²·h⁻¹ for nanocomposite membrane with the addition of 0.19 wt.% O-MWCNT depending on coagulation bath temperature) which significantly surpasses the performance of PPSU ultrafiltration membranes reported to date while maintaining a high level of human serum albumin rejection (83–92%). It was revealed that nanocomposite membrane demonstrated better antifouling performance (the flux recovery ratio increased from 47% for the reference PPSU membrane up to 62% for the nanocomposite membrane) and higher total organic carbon removal compared to the reference PPSU membrane in humic acids solution ultrafiltration.

Based On Confined Polymerization: In Situ Synthesis of PANI/PEEK Composite Film in One-Step

Confined polymerization is an effective method for precise synthesis, which can further control the micro-nano structure inside the composite material. Polyaniline (PANI)-based composites are usually prepared by blending and original growth methods. However, due to the strong rigidity and hydrogen bonding of PANI, the content of PANI composites is low and easy to agglomerate. Here, based on confined polymerization, it is reported that polyaniline /polyether ether ketone (PANI/PEEK) film with high PANI content is synthesized in situ by a one-step method. The micro-nano structure of the two polymers in the confined space is further explored and it is found that PANI grows in the free volume of the PEEK chain, making the arrangement of the PEEK chain more orderly. Under the best experimental conditions, the prepared 16 µm-PANI/PEEK film has a dielectric constant of 205.4 (dielectric loss 0.401), the 75 µm-PANI/PEEK film has a conductivity of 3.01×10-4 S m-1 . The prepared PANI/PEEK composite film can be further used as electronic packaging materials, conductive materials, and other fields, which has potential application prospects in anti-static, electromagnetic shielding materials, corrosion resistance, and other fields.

Zwitterionic Polysulfone Copolymer/Polysulfone Blended Ultrafiltration Membranes with Excellent Thermostability and Antifouling Properties

Membrane fouling has been one of the most important challenges in membrane separation operations. In this study, we report a facile strategy to prepare antifouling polysulfone (PSf) UF membranes by blending amphiphilic zwitterion polysulfone-co-sulfobetaine polysulfone (PSf-co-SBPSf) copolymer. The copolymer chemical structure was characterized by ¹HNMR spectroscopy. The PSf/PSf-co-SBPSf blend membranes with various zwitterionic SBPSf segment contents exhibited better surface hydrophilicity and excellent antifouling ability compared to PSf and PSf/PEG membranes. The significant increase of both porosity and water permeance indicates that the PSf-co-SBPSf has a pore-forming effect. The pure water flux and flux recovery ratio of the PSf/PSf-co-SBPSf blend membranes were both remarked to improve 286.43 L/m²h and 92.26%, while bovine serum albumin (BSA) rejection remained at a high level (97.66%). More importantly, the water flux and BSA rejection see minimal variance after heat treatment, indicating excellent thermostability. Overall, the PSf/PSf-co-SBPSf blend membranes achieved a comprehensive performance of sustainable hydrophilic, high permeation flux, and remarkable antifouling ability, thus becoming a promising candidate in high-temperature separation application.

Green Synthesis of Silver Nanoparticles as an Effective Antibiofouling Material for Polyvinylidene Fluoride (PVDF) Ultrafiltration Membrane

Silver nanoparticles (AgNPs) were successfully synthesized using the aqueous extract of the Paronychia argentea Lam (P. argentea) wild plant. The results showed that the conversion of Ag⁺ to Ag⁰ nanoparticles ratio reached 96.5% as determined by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), with a negative zeta potential (ζ) of −21.3 ± 7.68 mV of AgNPs expected to improve the stability of synthesized AgNPs. AgNP antibacterial activity has been examined against Streptococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria. The minimum inhibition concentration (MIC) was 4.9 µL/mL for both E. coli and S. aureus bacteria, while the minimum bactericidal concentrations (MBC) were 19.9 µL/mL and 4.9 µL/mL for S. aureus and E. coli, respectively. The synthesized AgNPs were incorporated in ultrafiltration polyvinylidene Fluoride (PVDF) membranes and showed remarkable antibiofouling behavior against both bacterial strains. The membranes were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and X-ray diffraction (XRD). The contact angle and porosity of the membrane were also determined. The efficiency of the membranes regarding rejection rate was assessed using bovine serum albumin (BSA). It was found in the flux experiments that membranes BSA rejection was 99.4% and 98.7% with and without AgNPs, respectively.

Water purification performance enhancement of PVC ultrafiltration membrane modified with tourmaline particles

In this study, a novel PVC/tourmaline ultrafiltration membrane was fabricated by phase inversion method in order to improve anti-fouling performance and water quality. FESEM was used to examine the changes in the morphology of pure PVC and PVC/tourmaline hybrid membranes. The introduction of tourmaline resulted in the increase of porosity and mean pore size. EDX images indicated that tourmaline particles were homogeneously dispersed in the membranes when the amount were less than 1.0 wt%. The hybrid membranes exhibited lower contact angle (78.7°) and higher water flux (121.3 L/m2 h) than the pure PVC membrane. The anti-fouling performance of the membranes were studied by filtration of BSA solution. The results demonstrated that the hybrid membrane with 1.0 wt% tourmaline particles exhibited the best anti-fouling performance and the highest BSA rejection. In addition, the pH and conductivity of the filtered water were measured by pH meter and electrical conductivity meter. And the results showed that the quality of the filtered water was improved after treating through the hybrid membranes.

Recent Progress in One- and Two-Dimensional Nanomaterial-Based Electro-Responsive Membranes: Versatile and Smart Applications from Fouling Mitigation to Tuning Mass Transport

Membrane technologies are playing an ever-important role in the field of water treatment since water reuse and desalination were put in place as alternative water resources to alleviate the global water crisis. Recently, membranes are becoming more versatile and powerful with upgraded electroconductive capabilities, owing to the development of novel materials (e.g., carbon nanotubes and graphene) with dual properties for assembling into membranes and exerting electrochemical activities. Novel nanomaterial-based electrically responsive membranes have been employed with promising results for mitigating membrane fouling, enhancing membrane separation performance and self-cleaning ability, controlling membrane wettability, etc. In this article, recent progress in novel-nanomaterial-based electrically responsive membranes for application in the field of water purification are provided. Thereafter, several critical drawbacks and future outlooks are discussed.

A Conductive Microfiltration Membrane for In Situ Fouling Detection: Proof-of-Concept Using Model Wine Solutions

Cross-flow microfiltration, using a microporous membrane, is a well-established technique for wine clarification in oenology because of its cost-effectiveness and high-throughput. However, membrane fouling remains a significant issue for wine filtration in high-throughput systems. Herein, an approach for in situ real-time monitoring of fouling in filtration systems using a conductive filtration membrane and a model fluid for filtration is reported. The membrane is fabricated by embedding poly(3,4-ethylenedioxythiophene) into an electrospun sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene microporous membrane, producing a conductive microfiltration membrane. Measurement of the resistance of the conductive membrane during filtration with the fouling solutions containing pectin, as one of the major foulants in unfiltered wine and pre-fermentation grape juice, shows a time- and concentration-dependent response. This work opens a door to new methodology for in situ monitoring of fouling processes in wine and juice filtration systems.

Multifunctional PVDF/CNT/GO mixed matrix membranes for ultrafiltration and fouling detection

Membrane fouling can be effectively addressed by modifying the membrane to realize anti-fouling capability together with real-time fouling detection. Here, we present the synthesis and water treatment testing of a promising candidate for this application, a composite membrane of polyvinylidene fluoride (PVDF) and functionalized carbon nano-materials prepared by a facile phase inversion method. The synergistic effect of oxidized multi-walled carbon nanotubes (OMWCNTs) and graphene oxide (GO) enabled better surface pore structures, higher surface roughness, hydrophilicity, and better antifouling property as compared with that of pristine PVDF membranes. The PVDF/OMWCNT/GO mixed matrix membranes (MMMs) achieved a high water flux of 125.6 L m^-2 h^-1 with high pollutant rejection rate, and their electrical conductivity of 2.11 × 10^-4 S cm^-1 at 100 kHz was sensitive to the amount of pollutant uptake. By using hybrid MMMs, we demonstrate simultaneous pollutant filtering and uptake monitoring, which is an important step in revolutionizing the water treatment industry.

Removal of model dyes on charged UF membranes: Experiment and simulation

Charged ultrafiltration (UF) membranes can repel electrically charged molecules that are smaller than the size of the membrane pores and display high rejection of solutes, high flux, and low operation pressures compared to uncharged UF, nanofiltration (NF) and reverse osmosis (RO). Here, a charged UF membrane composite (PANI/PVDF) was prepared and regulated via electrochemically reversible control in portions of amine/imine functional groups of PANI. As a result, the permeability and rejection ratios of CR^2- on charged PANI/PVDF, with PVDF as a control, increased from 19.6 to a maximum of 183.3 L m^-2 h^-1 bar^-1 and from 3.4% to 74%, which expands the trade-off confine benefited from surface potential change from -12.21 mV to -25.26 mV, furtherly, the rejection ratio of CR^2- on PANI/PVDF reached up to 93% via the electrochemical regulation. Finally, a fixed-charge model was built that well describes the steric and electric repulsion effects on membrane performance and the important roles of the electrochemically controllable surface charge. Moreover, the contour map of rejection ratios containing the ratio of molecular size vs the average pore size of the membrane (r/R = 0.2-1.0) and the zeta potential (-10 to -60 mV) were taken into account, which can be used to visually understand the rejection performance of membranes. This model is also appropriate for varying molecular sizes and for molecules with different charges. Our work opens a new horizon for the design of electrochemically controllable charged membranes to remove charged compounds.

Fabrication of Concentric Carbon Nanotube Rings and Their Application on Regulating Cell Growth

The carbon nanotube (CNT) pattern plays an important role in various electronic devices and biological fields for its superior conductivity and biocompatibility. Herein, we fabricated regularly arranged concentric multiwalled carbon nanotube (MWCNT) rings in a Petri dish by evaporation-driven self-assembly technology. By adjusting the dispersion ratio, heating temperature, and solution volume, various MWCNT rings with different shapes and morphologies were obtained. The variation law of ring radius, formation range, and ring numbers was processed with statistical analysis. With fine adjustment of parameters, the control of desired MWCNT rings can be achieved for further scientific researches. By culturing L929 cells with these rings, oriented cell growth along the rings was achieved, which is of significance for cell regulation, tissue repairing, and related biological applications.