Jingwei Hou

Surface zwitterionic functionalized graphene oxide for a novel loose nanofiltration membrane

Surface zwitterionization of graphene oxide (GO) was firstly conducted by grafting poly(sulfobetaine methacrylate) (PSBMA) onto the GO surface via reverse atom transfer radical polymerization (RATRP). Then, a novel type of GO-PSBMA/polyethersulfone (PES) loose nanofiltration membrane (NFM) was constructed by mixing with modified GO composites via phase inversion. FTIR, XRD, TEM, XPS and TGA were applied to analyze the chemical composition and morphology, confirming a favorable synthesis of GO-PSBMA composites. Besides, the effect of the embedded GO-PSBMA nanoplates on the morphology and overall performance of the hybrid membranes was systematically investigated based on the SEM images, water contact angle, zeta potential, and fouling parameters. It was found that the water flux of the hybrid membrane was greatly enhanced from 6.44 L m−2 h−1 bar−1 to 11.98 L m−2 h−1 bar−1 when the GO-PSBMA content increased from 0 to 0.22 wt%. The antifouling tests revealed that the GO-PSBMA embedded membranes had an excellent antifouling performance: a high flux recovery ratio (ca. 94.4%) and a low total flux decline ratio (ca. 0.18). Additionally, the hybrid membranes exhibited a distinct advance in the mechanical strength due to the addition of highly rigid GO. Notably, compared with unmodified membranes, the hybrid membranes had a higher retention of Reactive Black 5 (99.2%) and Reactive Red 49 (97.2%), and a lower rejection of bivalent salts (10% for Na2SO4) at an operational pressure of 0.4 MPa, rendering the membranes promising for dye/salt fractionation.

Janus Membranes: Exploring Duality for Advanced Separation

Janus membranes are an emerging class of materials having opposing properties at an interface. This structure results in selective and often novel transport characteristics. In this Minireview, a definition of the Janus membrane, beyond merely asymmetric materials, is introduced and common fabrication strategies are outlined. Also presented are current and potential applications in directional transport, switchable permeation, and performance optimization with detailed mechanisms.

Formation of Ultrathin, Continuous Metal–Organic Framework Membranes on Flexible Polymer Substrates

Metal-organic framework (MOF) materials have an enormous potential in separation applications, but to realize their potential as semipermeable membranes they need to be assembled into thin continuous macroscopic films for fabrication into devices. By using a facile immersion technique, we prepared ultrathin, continuous zeolitic imidazolate framework (ZIF-8) membranes on titania-functionalized porous polymeric supports. The coherent ZIF-8 layer was surprisingly flexible and adhered well to the support, and the composite membrane could sustain bending and elongation. The membranes exhibited molecular sieving behavior, close to the theoretical permeability of ZIF-8, with hydrogen permeance up to 201×10(-7)  mol m(-2)  s(-1)  Pa(-1) and an ideal H2 /CO2 selectivity of 7:1. This approach offers significant opportunities to exploit the unique properties of MOFs in the fabrication of separation and sensing devices.

Surface and interface engineering for organic–inorganic composite membranes

Organic–inorganic composite (OIC) membranes have received great attention over the past decades due to their enhanced performances in many applications. It is well known that surfaces and interfaces play crucial roles in the fabrication and application of the OIC membranes. In this review, we summarize the typical processes used to fabricate the OIC membranes and categorize these membranes as either mixed matrix OIC membranes or interfacial composite OIC membranes, and primarily focus on how the organic–inorganic interfaces influence the membrane formation process and its final structure. Then we reveal how the membrane surfaces and organic–inorganic interfaces in the membrane affect the final performance in certain applications. Through this review, we wish to provide a comprehensive guide to membrane fabrication and regulation, as well as a better understanding of the structure–performance relationships in OIC membranes.

Long-lasting antibacterial behavior of a novel mixed matrix water purification membrane

Membrane fouling by microbial and organic components is considered as the “Achilles heel” of membrane processes as it not only reduces the membrane performance but also leads to membrane biodegradation. In this work, a novel high flux, antibacterial and antifouling ultrafiltration membrane was fabricated by blending the silver nanoparticles (AgNPs)–halloysite nanotubes (HNTs)–reduced graphene oxide (rGO) nanocomposite (AgNPs–HNTs–rGO) into a polyethersulfone (PES) membrane matrix. HNTs were applied to expand the interlayer space between neighboring rGO sheets and eliminate the leaching on AgNPs. The hybrid membranes had higher hydrophilicity, surface smoothness and higher water permeation flux when compared with the pure PES membrane. Both dynamic and static BSA adsorption tests revealed improved antifouling behavior of the hybrid membrane. In addition, the incorporated AgNPs were evenly attached onto the rGO support with an average size of 10 nm, which ensured its good antibacterial performance: the hybrid membrane had an ideal bacteriostasis rate against Escherichia coli (E. coli) even after six months of storage.

Graphene-based antimicrobial polymeric membranes: a review

Biofouling is an inevitable obstacle that impairs the overall performance of polymeric membranes, including selectivity, permeability, and long-term stability. With an increase of various biocides being utilized to inhibit biofilm formation, the enhancement of bacterial resistance against traditional bactericides is increasingly becoming an extra challenge in the development of antimicrobial membranes. Graphene-based nanomaterials are emerging as a new class of strong antibacterial agents due to their oxygen-containing functional groups, sharp edges of the one-atom-thick laminar structure, and synergistic effect with other biocides. They have been successfully employed not only to confer favorable antibacterial abilities, but also to impart superior separation properties to polymeric membranes. However, the exact bactericidal mechanism of graphene remains unclear. This review aims to examine the synthesis methods and antimicrobial behavior of graphene-based materials, offering an insight into how the nanocomposites influence their antimicrobial abilities. Most importantly, the use of graphene-based nanomaterials in the design and development of antimicrobial membranes is highlighted.

Hybrid membrane with TiO2 based bio-catalytic nanoparticle suspension system for the degradation of bisphenol-A

The removal of micropollutant in wastewater treatment has become a key environmental challenge for many industrialized countries. One approach is to use enzymes such as laccase for the degradation of micropollutants such as bisphenol-A. In this work, laccase was covalently immobilized on APTES modified TiO2 nanoparticles, and the effects of particle modification on the bio-catalytic performance were examined and optimized. These bio-catalytic particles were then suspended in a hybrid membrane reactor for BPA removal with good BPA degradation efficiency observed. Substantial improvement in laccase stability was achieved in the hybrid system compared with free laccase under simulated harsh industrial wastewater treatment conditions (such as a wide range of pH and presence of inhibitors). Kinetic study provided insight of the effect of immobilization on the bio-degradation reaction.

Elevated Performance of Thin Film Nanocomposite Membranes Enabled by Modified Hydrophilic MOFs for Nanofiltration

Metal-organic frameworks (MOFs) are studied for the design of advanced nanocomposite membranes, primarily due to their ultrahigh surface area, regular and highly tunable pore structures, and favorable polymer affinity. However, the development of engineered MOF-based membranes for water treatment lags behind. Here, thin-film nanocomposite (TFN) membranes containing poly(sodium 4-styrenesulfonate) (PSS) modified ZIF-8 (mZIF) in a polyamide (PA) layer were constructed via a facile interfacial polymerization (IP) method. The modified hydrophilic mZIF nanoparticles were evenly dispersed into an aqueous solution comprising piperazine (PIP) monomers, followed by polymerizing with trimesoyl chloride (TMC) to form a composite PA film. FT-IR spectroscopy and XPS analyses confirm the presence of mZIF nanoparticles on the top layer of the membranes. SEM and AFM images evince a retiform morphology of the TFN-mZIF membrane surface, which is intimately linked to the hydrophilicity and adsorption capacity of mZIF nanoparticles. Furthermore, the effect of different ZIF-8 loadings on the overall membrane performance was studied. Introducing the hydrophilizing mZIF nanoparticles not only furnishes the PA layer with a better surface hydrophilicity and more negative charge but also more than doubles the original water permeability, while maintaining a high retention of Na2SO4. The ultrahigh retentions of reactive dyes (e.g., reactive black 5 and reactive blue 2, >99.0%) for mZIF-functionalized PA membranes ensure their superior nanofiltration performance. This facile, cost-effective strategy will provide a useful guideline to integrate with other modified hydrophilic MOFs to design nanofiltration for water treatment.

Biocatalytic Janus membranes for CO2 removal utilizing carbonic anhydrase

A novel hydrophilic–superhydrophobic biocatalytic membrane was developed for CO2 capture with a gas–liquid membrane contactor. This “Janus” membrane contains a layer of hydrophilic carbon nanotubes (CNTs) coated on a fluorosilane treated superhydrophobic membrane support. Carbonic anhydrase (CA) was then immobilized on the hydrophilic CNT side, which was located at the CO2–solvent interface within a gas–liquid membrane contactor, whilst the superhydrophobic porous side of the membrane was oriented towards the gas phase. This “Janus” configuration ensured that the immobilized CA remained hydrated, and minimized the CO2 diffusion length in the solvent. The CNT coating layer showed good integrity and adhesion to the membrane, and the effect of superhydrophobic treatment on the porous structure of the membrane was negligible. The p-NPA assay results revealed that up to 30% CA activity was retained after immobilization. Further, the CO2 hydration test confirmed that the immobilized CA possessed significantly improved catalytic efficiency when compared with the equal amount of free CA. Effective regeneration of the enzyme coating was demonstrated over five cycles. The novel “Janus” membrane developed in this study exhibits great potential to be used as an immobilization support for a wide variety of enzymes not only CA for CO2 capture but also other types of enzymes in different applications.

Preparation of titania based biocatalytic nanoparticles and membranes for CO2 conversion

A biomimetic route for CO2 conversion catalyzed by carbonic anhydrase (CA) is an attractive option for carbon capture and storage due to the high efficiency and specificity of CA in CO2 hydration. The preparation of TiO2 based biocatalytic nanoparticles and membranes via CA immobilization facilitates the reuse of the enzyme and could be potentially integrated in a gas–liquid membrane contactor for highly efficient CO2 capture. In this work, different immobilization protocols were compared based on CA loading, activity and stability. For biocatalytic nanoparticles, over 80% activity recovery corresponding to 163 mg g−1 support was achieved. Repeated reuse and recovery of the biocatalytic nanoparticles over twenty cycles showed only modest loss in activity. For the biocatalytic membranes, the nanostructure of the titania coating and the pH values during immobilization were examined to optimize the biocatalytic performance. Biocatalytic membranes prepared at pH 6 with two cycles of sol–gel coating were able to immobilize a 700 μg CA per cm2 nominal membrane area. The CO2 hydration efficiency of the biocatalytic nanoparticles and membranes was examined, and only marginal loss of catalytic efficiency was observed when compared with their free CA counterpart, indicating good potential for application of such biocatalytic nanoparticles and membranes for CO2 conversion.