Theophylline Molecular Imprinted Composite Membranes Prepared on a Ceramic Hollow Fiber Substrate

Theophylline (THO) molecular imprinted composite membranes (MIM) were successfully prepared by thermal-initiated free radical polymerization on the surface of α-Al₂O₃ ceramic microporous hollow fiber substrate membranes. Molecular imprinted polymerization layer was synthesized by taking theophylline as the template molecule, methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EDMA) as the cross-linker, and 2,2′-azobisisobutyronitrile (AIBN) as the free-radical initiator. After polymerization and the elution of the imprinted molecule, the <i>R</i>_max (the maximum pore size) upon the membrane surface decreased from 2.8 to 1.9 μm. The imprinted layer upon the ceramic membranes was investigated by scanning electron microscopy (SEM), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR). SEM micrographs showed a 1 μm thick composite membrane, and AFM showed different surface roughness. Moreover, the selectivity separation factor of theophylline (THO) to theobromine (TB) was determined as 2.63 in a mixed feed solution, thus suggesting that the imprinting process allowed for preferential permeance and affinity selectivity to THO

Preparation and Characterization of High-Performance Perfluorosulfonic Acid/SiO₂ Nanofibers with Catalytic Property via Electrospinning

Polymer nanofiber-supported perfluorosulfonic acid (PFSA)/SiO₂ catalysts are successfully fabricated by electrospinning method from polymer/nanoparticle suspensions. This kind of catalyst has a large number of active acid sites and high specific surface area up to 85.6 m²/g. Scanning electron microscope images reveal that the catalysts present high porosity and inner-connected porous structure which varies much with SiO₂ loading. Nitrogen adsorption–desorption measurements demonstrate a wide distribution of pore sizes inside the composites. Catalysts of different compositions are evaluated in esterification in a batch reactor under various conditions, and the results indicate that those of 20 wt % PFSA loading have the best activity of unit PFSA. Supporting PFSA by a nanofibrous matrix enhances liquid holdups inside the catalysts and offers accessibility of the acid sites, and therefore improves the activity of the catalysts. Moreover, these catalysts allow recovery at high percentages and regeneration with high activity

Processing–Structure–Property Correlations of Polyethersulfone/Perfluorosulfonic Acid Nanofibers Fabricated via Electrospinning from Polymer–Nanoparticle Suspensions

Polyethersulfone (PES)/perfluorosulfonic acid (PFSA) nanofiber membranes were successfully fabricated via electrospinning method from polymer solutions containing dispersed calcium carbonate (CaCO₃) nanoparticles. ATR-FTIR spectra indicated that the nanoparticles mainly existed on the external surface of the nanofibers and could be removed completely by acid treatment. Surface roughness of both the nanofibers and the nanofiber membranes increased with the CaCO₃ loading. Although FTIR spectra showed no special interaction between sulfonic acid (−SO₃) groups and CaCO₃ nanoparticles, XPS measurement demonstrated that the content of −SO₃ groups on external surface of the acid-treated nanofibers was enhanced by increasing CaCO₃ loading in solution. Besides, the acid-treated nanofiber membranes were performed in esterification reactions, and exhibited acceptable catalytic performance due to the activity of −SO₃H groups on the nanofiber surface. More importantly, this type of membrane was very easy to separate and recover, which made it a potential substitution for traditional liquid acid catalysts

Preparation and Characterization of Perfluorosulfonic Acid Nanofiber Membranes for Pervaporation-Assisted Esterification

Multilayer membranes were prepared by the combination of perfluorosulfonic acid/SiO₂ nanofibers and a poly­(vinyl alcohol) (PVA) pervaporation layer and were used to enhance the esterification of acetic acid (HAc) and ethanol (EtOH). The esterification–pervaporation experiments were carried out in a continuous membrane contactor. The effects of the temperature, the ratio of HAc to EtOH, and the ratio of membrane area to reaction volume were investigated. The results demonstrated that the membranes had good catalytic activities even at low temperature because of the nanofibrous structure of the catalysis layer. The conversion of HAc at 60 °C after 10 h was 10–15% more than the equilibrium conversion and by improved about 45% with respect to the equilibrium conversion after 55 h. The yield of EtAc was higher than 90%, which demonstrates that the difunctional membrane could enhance the esterification process greatly through the in situ removal of water

Facile Fabrication and Application of Superhydrophilic Stainless Steel Hollow Fiber Microfiltration Membranes

Superhydrophilic stainless steel hollow fiber microfiltration membranes (SSHF-MFs) were developed through a facile dip-coating method, followed by sintering at a low temperature of 500 °C. A novel mediating additive was explored to mediate the coating suspensions. The additive, which could form hydrogen bonds with TiO₂ agglomerations, facilitated the formation of a continuous TiO₂ layer on the rough surface of stainless steel hollow fibers (SSHFs). The fabricated SSHF-MFs exhibited superhydrophilic and underwater superoleophobicity wettability, which enabled SSHF-MFs to be applied to antifouling fields. The fouling resistance of SSHF-MFs for oil/water emulsion, cake layer foulant (sodium alginate, SA), and adhesive foulant (bovine serum albumin, BSA) were investigated systematically. SSHF-MFs exhibited superior antifouling properties and high rejections of 99% and 90% for oil/water emulsion and SA foulant solution, respectively. For the adhesive BSA solution, SSHF-MFs still showed good antifouling property after washing with a dilute alkaline solution and superior separation performance (90%). Meanwhile, SSHF-MFs exhibited an excellent separation performance for polystyrene microspheres (100 nm) with a rejection of 100%. In conclusion, SSHF-MFs showed great potential, not only in traditional microfiltration fields, such as solid–liquid separation, but also in the antifouling field, such as oil/water separation. The facile fabrication conditions and superior wettability further improved the sustainability of SSHF-MFs in practical applications

FAS Grafted Electrospun Poly(vinyl alcohol) Nanofiber Membranes with Robust Superhydrophobicity for Membrane Distillation

This study develops a novel type of electrospun nanofiber membranes (ENMs) with high permeability and robust superhydrophobicity for membrane distillation (MD) process by mimicking the unique unitary microstructures of ramee leaves. The superhydrophobic ENMs were fabricated by the eletrospinning of poly­(vinyl alcohol) (PVA), followed by chemical cross-linking with glutaraldehyde and surface modification via low surface energy fluoroalkylsilane (FAS). The resultant FAS grafted PVA (F-PVA) nanofiber membranes were endowed with self-cleaning properties with water contact angles of 158° and sliding angles of 4° via the modification process, while retaining their high porosities and interconnected open structures. For the first time, the robust superhydrophobicity of the ENMs for MD was confirmed by testing the F-PVA nanofiber membranes under violent ultrasonic treatment and harsh chemical conditions. Furthermore, vacuum membrane distillation experiments illustrated that the F-PVA membranes presented a high and stable permeate flux of 25.2 kg/m²h, 70% higher than those of the commercial PTFE membranes, with satisfied permeate conductivity (<5 μm/cm) during a continuous test of 16 h (3.5 wt % NaCl as the feed solution, and feed temperature and permeate pressure were set as 333 K and 9 kPa, respectively), suggesting their great potentials in myriad MD processes such as high salinity water desalination and volatile organiccompounds removal

Interfacial Polymerization with Electrosprayed Microdroplets: Toward Controllable and Ultrathin Polyamide Membranes

Commercial polyamide membranes for seawater desalination and water purification have low water permeability because of their relatively thick rejection layers. We report a novel interfacial polymerization method for synthesizing ultrathin polyamide layers with a precisely controllable thickness. Monomer solutions of <i>m</i>-phenylenediamine and trimesoyl chloride were electrosprayed into fine microdroplets. The polymerization reaction between microdroplets of different monomers leads to a fine and controllable amount of deposition. We fabricated smooth polyamide layers from 4 nm to several tens of nanometers in thickness, with a growth rate of approximately 1 nm/min. Our study provides a new dimension for the rational design and preparation of ultrathin polyamide membranes with tunable separation properties

Nanofoaming of Polyamide Desalination Membranes To Tune Permeability and Selectivity

Recent studies have documented the existence of discrete voids in the thin polyamide selective layer of composite reverse osmosis membranes. Here we present compelling evidence that these nanovoids are formed by nanosized gas bubbles generated during the interfacial polymerization process. Different strategies were used to enhance or eliminate these nanobubbles in the thin polyamide film layer to tune its morphology and separation properties. Nanobubbles can endow the membrane with a foamed structure within the polyamide rejection layer that is approximately 100 nm in thickness. Simple nanofoaming methods, such as bicarbonate addition and ultrasound application, can result in a remarkable improvement in both membrane water permeability and salt rejection, thus overcoming the long-standing permeability–selectivity trade-off of desalination membranes