Polyacrylonitrile Nanofibrous Membranes Research Articles

Fluorine-Free Hydrophobic Modification and Waterproof Breathable Properties of Electrospun Polyacrylonitrile Nanofibrous Membranes.

Waterproof breathable functional membranes have broad application prospects in the field of outdoors textiles. The fluorine-containing microporous membranes of the mainstream functional products easily cause harm to the environment, and thus, the fluorine-free environmental nanofibrous membranes are an important development direction for functional membranes. In this subject, the electrospun polyacrylonitrile nanofibrous membranes were first hydrophobically modified by amino functional modified polysiloxane (AMP), followed by in situ cross-linking modified with 4, 4'-methyl diphenylene diisocyanate (MDI). The fluorine-free modification by AMP altered the surface of the membranes from hydrophilic to hydrophobic, and greatly improved the waterproof properties with the hydrostatic pressure reaching to 87.6 kPa. In addition, the formation of bonding points and the in situ preparation of polyuria through the reaction between the isocyanate in MDI and the amino group in AMP, could improve the mechanical properties effectively. When using AMP with the concentration of 1 wt% and MDI with the concentration of 2 wt%, the relatively good comprehensive performance was obtained with good water resistance (93.8 kPa), modest vapor permeability (4.7 kg m-2 d-1) and air permeability (12.7 mm/s). Based on these testing data, the modified nanofibrous membranes had excellent waterproof and breathable properties, which has future potential in outdoor sports apparel.

Continuous coalescence and separation of oil-in-water emulsion via polyacrylonitrile nanofibrous membrane coalescer

Coalescence separation is an energy-efficient, physical separation method to enable the reuse of oil from oil-in-water (O/W) emulsions, which are widely found in industrial wastewater. However, traditional coalescers are generally ineffective in separating fine, emulsified oil droplets. Here, we applied the polyacrylonitrile (PAN) nanofibrous membrane possessing a three-dimensional network structure and high porosity to separate oil droplets smaller than 10 µm. We demonstrated that oil pieces floated on the surface of the discharged fluid. The continuous separation conducted under a flow rate of 40 mL/min was steady and with a separation ratio greater than 99.9% and a pressure drop of less than 25 kPa. In addition, an analysis of the amount of oil during the continuous operation indicated that the oil droplets did not form a cake layer, which would otherwise foul the membrane and hinder its long-term use. Moreover, the continuous separation of the surfactant-stabilized O/W emulsion with a SPAN20 concentration of 2 wt% in dodecane exhibited a high performance comparable to that of the surfactant-free emulsion. In conclusion, the PAN nanofibrous membrane exhibited excellent performances for the coalescence of fine oil droplets, demonstrating the industrial applicability of nanofibrous membranes for continuous O/W emulsion coalescence and separation.

A reusable nanofibrous air filter with anti-wetting microbead coating

Filtration technologies for fine dust particles have garnered attention as public awareness of air pollution has increased. In this study, we report a microbead-coated polyacrylonitrile nanofibrous membranes (MB-NFMs) filter, which is a reusable PAN nanofiber-based air filter with high dust-filtration efficiency. The MB-NFMs filter comprises a dual-layer structure composed of hydrophilic PAN nanofibers coated with hydrophobic microbeads to produce high filtration efficiency and water droplet cleaning ability. This membrane has water contact angles of approximately 144°, which allows water droplets to roll off its surface and carry captured dust particles with them. Furthermore, we discovered that the MB-NFMs filter has sufficient wetting resistance to maintain its hydrophobicity under raindrop impacts. The MB-NFMs filter had a removal efficiency of over 99.8% for PM2.5. Repetitive dust-filtration and water droplet-cleaning cycles were performed to evaluate the MB-NFMs filter's ability to clean water droplets. The filtration efficiency was higher than 99.8% throughout the tests, and the pressure drop was recovered by 99% after each cleaning cycle. The fabricated MB-NFMs filter is a viable solution for highly efficient and reusable dust-particle filtration. The MB-NFMs filter does not require periodic maintenance due to its water droplet cleaning ability, providing an economic advantage over conventional air filters.

Electrospun polyacrylonitrile fibrous membrane for dust removal

Particulate matter (PM) pollution has become a serious threat to human health. Accordingly, an air filtration media that can efficiently remove particulate matter should be developed immediately. Nanofibrous membrane filter prepared by electrospinning technology has nanoscale diameter, high specific surface area, and relatively high porosity, which are suitable for dust removal. This paper explored the effects of electrospinning parameters on the microscopic morphology, fiber diameter, and pore size of polyacrylonitrile (PAN) nanofibrous membranes, including polymer solution concentration, applied voltage, and tip-to-collector distance. Thereafter, filtration efficiencies of electrospun PAN fibrous membrane and Polytetrafluoroethylene (PTFE), Cellulose acetate (CA), Nylon commercial filter were compared by removing smoke PMs. Results showed that fiber diameter and pore size increase with increasing concentration but decrease with increasing distance. With an increase in applied voltage, fiber diameter and pore size first decreased and increased thereafter. Lastly, filtration experimental results showed that filtration efficiency of electrospun PAN nanofibrous membranes was higher than that of those commercial filter membranes for ultra fine dust (0.3–0.5 μm).

Electrospun hierarchically channeled polyacrylonitrile nanofibrous membrane for wastewater recovery

With urgent demands on sustainable utilization of water resource, high-efficient, easy-to-use, and economic purification membrane for wastewater is highly desired. However, integration of micro/nanostructure into membrane through chemical routes inevitably requires tedious treatments and generate secondary pollution. Herein, an oily wastewater purifier with hierarchically porous channel structures is developed via water etching of sacrificial polyvinylpyrrolidone (PVP) cores within electrospun structured polyacrylonitrile (PAN) nanofibrous membrane. The PAN nanofibrous membrane possesses excellent hydrophilicity and underwater superoleophobicity, which is caused by a synergistic effect of hierarchical channel structures and abundant nanopores on nanofiber surface. The porous channel structures increase the gaps among the fibers, which generates a new permeation path, resulting in a significant increase of the water flux from 2275 to 6700 L/(m 2 ·h). The hierarchically constructed structures facilitate the emulsion demulsification, enabling high separation efficiency for various oil/water emulsions (>97%). This green manufacturing strategy provides a new path for developing next-generation wastewater purification membrane. • A hierarchically channeled PAN-based purifier is created via electrospinning and water etching. • The porous channel structures enable water storage and drainage for membrane. • The flux for pure water using the membrane is up to 6700 L/(m 2 ·h). • The membrane facilitates demulsification, reaching >97% separation efficiency for emulsions.

Light-activated antibacterial electrospun polyacrylonitrile-graphene quantum dot nanofibrous membranes

Polyacrylonitrile (PAN) nanofibrous membranes incorporating graphene quantum dots (GQD) as photoantibacterial additives were prepared by electrospinning. GQD encapsulation in the composite GQD-PAN membranes proved very stable, with negligible GQD leakage after 1 month immersed in neutral phosphate buffer solutions. A series of GQD-PAN membranes with different GQD content and electrospinning times were prepared to assess the influence of these parameters on the antibacterial activity of the membranes against Escherichia coli under visible light irradiation. Electrospinning time had a pronounced effect on membrane weight/thickness and nanofiber diameter, both parameters increasing with electrospinning time. Membranes with the optimal composition (1% wt. GQD and 1.5 h electrospinning time) showed excellent antibacterial activity against E. coli, with 99.9999% (6 logaritmic units) bacterial inactivation after 24 h illumination with visible light. Different bactericidal reactive oxygen species (ROS) were detected upon illumination of GQD solutions and GQD-PAN membranes, confirming photodynamic inactivation of the bacteria by GQD photosensitization. In terms of ROS production, GQD outperformed well-known photosensitizers crystal violet and toluidine blue O, both with long-established efficiency for photodynamic treatment of drug-resistant bacterial infections.

Long-term, synergistic and high-efficient antibacterial polyacrylonitrile nanofibrous membrane prepared by “one-pot” electrospinning process

Enhancing long-term antibacterial activity of membrane materials is an effective strategy to reduce biological contamination. Herein, we developed a long-term, synergistic antibacterial polyacrylonitrile (PAN) nanofiber membrane by a “one-pot” electrospinning process. In the reaction solution of PAN and N, N-dimethylformamide (DMF), silver-silicon dioxide nanoparticles (Ag@SiO2 NPs) are in-situ synthesized and stabilized using silane coupling agent; and [2-(methacryloyloxy)-ethyl] trimethylammonium chloride (MT) monomers are then in-situ cross-linked to obtain a polyquaternary ammonium salt (PMT). Subsequently, the casting solution is directly used to fabricate Ag@SiO2/PMT-PAN nanofibrous membrane (NFM) via electrospinning. The antibacterial activity, reusability, synergy effect and biological safety of the Ag@SiO2/PMT-PAN NFM are systematically investigated, and the synergistic antibacterial mechanism is also explored. Even at very low (0.3 wt%) content of silver, the Ag@SiO2/PMT-PAN NFM exhibits excellent antibacterial activity against E. coli (99%) and S. aureus (99%). Also, the antibacterial ability of the NFM remains the same level after three cycles of antibacterial processes with the efficient synergy effects of Ag@SiO2 and PMT components. When the Ag@SiO2/PMT-PAN contacts with bacteria, the PMT attracts and kills the bacteria through electrostatic action. The bacteria with damaged cell membranes are deposited on the nanofibrous membrane, which could greatly promote the release of Ag+ and further enhance the antibacterial activity. Moreover, L929 fibroblasts are co-cultured with the extract of 4 mg/mL Ag@SiO2/PMT-PAN for 5 days, which exhibits a low cytotoxicity with a cell proliferation ratio of 95%. This work opens new pathways for developing long-term effective and synergistic antibacterial nanofibrous membrane materials to prevent infections associated with biomedical equipment.

Polarity‐Dominated Stable N97 Respirators for Airborne Virus Capture Based on Nanofibrous Membranes

AbstractThe longevity and reusability of N95‐grade filtering facepiece respirators (N95 FFRs) are limited by consecutive donning and disinfection treatments. Herein, we developed stable N97 nanofibrous respirators based on chemically modified surface to enable remarkable filtration characteristics via polarity driven interaction. This was achieved by a thin‐film coated polyacrylonitrile nanofibrous membrane (TFPNM), giving an overall long‐lasting filtration performance with high quality factor at 0.42 Pa−1 (filtration efficiency: over 97 %; pressure drop: around 10 Pa), which is higher than that of the commercial N95 FFRs (0.10–0.41 Pa−1) tested with a flow rate of 5 L min−1 and the 0.26 μm NaCl aerosol. A coxsackie B4 virus filtration test demonstrated that TFPNM also had strong virus capture capacity of 97.67 %. As compared with N95 FFRs, the TFPNM was more resistant to a wider variety of disinfection protocols, and the overall filtration characteristics remained N97 standard.

Polarity-Dominated Stable N97 Respirators for Airborne Virus Capture Based on Nanofibrous Membranes.

The longevity and reusability of N95‐grade filtering facepiece respirators (N95 FFRs) are limited by consecutive donning and disinfection treatments. Herein, we developed stable N97 nanofibrous respirators based on chemically modified surface to enable remarkable filtration characteristics via polarity driven interaction. This was achieved by a thin‐film coated polyacrylonitrile nanofibrous membrane (TFPNM), giving an overall long‐lasting filtration performance with high quality factor at 0.42 Pa−1 (filtration efficiency: over 97 %; pressure drop: around 10 Pa), which is higher than that of the commercial N95 FFRs (0.10–0.41 Pa−1) tested with a flow rate of 5 L min−1 and the 0.26 μm NaCl aerosol. A coxsackie B4 virus filtration test demonstrated that TFPNM also had strong virus capture capacity of 97.67 %. As compared with N95 FFRs, the TFPNM was more resistant to a wider variety of disinfection protocols, and the overall filtration characteristics remained N97 standard.

Dialysis/adsorption bifunctional thin-film nanofibrous composite membrane for creatinine clearance in portable artificial kidney

In this study, we proposed a facile strategy for the lightweight design for portable artificial kidney by using a novel dialysis/adsorption bifunctional thin-film nanofibrous composite (TFNC) membrane, which consisting of polyvinyl alcohol (PVA) hydrogel as a separation layer and polyacrylonitrile (PAN) nanofibrous membrane with UiO-66-(COOH)2 nanoparticles as a porous affinity substrate were developed to effectively remove creatinine and substantially reduce the volume of dialysate in dialysis process simultaneously. Here, as-synthesized UiO-66-(COOH)2 nanoparticles were strung through PAN nanofibers using colloid-electrospinning technique to prepare necklace-like nanofibrous affinity membrane for creatinine adsorption. The obtained PAN/UiO-66-(COOH)2 nanofibrous membrane (PAN-U) with optimum UiO-66-(COOH)2 loading (60 wt%) exhibited encouraging maximum adsorption capacities (54 mg/g) based on Langmuir isotherm models and pseudo-second-order kinetic models. In addition, the simulated dialysis results demonstrated that 62.8% of creatinine were eliminated and over 98% of bovine serum albumin (BSA) were rejected. Furthermore, the PVA/PAN-U TFNC membrane not only improved the clearance of creatinine in simulated blood, but also efficiently maintained the concentration of creatinine in simulated dialysate at a very low level compared to the pure PVA/PAN TFNC membrane. More importantly, the usage of dialysate in volume for PVA/PAN-U TFNC membranes in dialysis was only one tenth of that for PVA/PAN TFNC membranes but with very comparable dialysis performance. Therefore, the introduction of adsorption function in TFNC hemodialysis membrane may facilitate the development of the lightweight of portable artificial kidney.

Photocatalytic GO/M88A “interceptor plate” assembled nanofibrous membrane with photo-Fenton self-cleaning performance for oil/water emulsion separation

Developing the high-efficient and robust antifouling membranes for oily emulsions to achieve the purpose of prolonging the service life of the membrane shows great demand because of the restriction of hydration anti-fouling mechanism strategy to against pollution. Herein, a hydrophilic photo-Fenton-like catalyst – GO/Fe-MOF assembled stabilized polyacrylonitrile (SPAN) nanofibrous membrane with underwater superoleophobicity, robust mechanical strength and photo-Fenton self-cleaning performance was firstly designed and fabricated via ultrasonic assistance, mussel-inspired fixation and low temperature hydrothermal synthesis methods. In this work, benefiting by the regulable amounts of GO nanosheets on the SPAN@GO/M88A membrane surface, the obtained membrane possessed sub-micrometer skin layer, which guarantees the balance of fast permeation flux (920–7083 ± 47 L m−2 h−1) and separation efficiency (>99.2%) for diesel/water emulsion with small emulsified oils. Moreover, introduced hydrophilic Metal-organic frame nanoparticles (MIL-88A (Fe)) into modified membrane endowed underwater anti-oil-fouling and photo-Fenton catalytic degradation performance for organic contaminants. Meanwhile, the charged GO/M88A heterostructure can assist to achieve demulsification for separation of surfactant-stabilized emulsions by strong electrostatic force. More importantly, attached and irremovable contaminants on the membrane can be quickly removed by photo-Fenton self-cleaning method, and achieved over 96% of recovery flux recovery ratio, which effectively prolonged the service life of the membrane. We believe the newly designed SPAN@GO/M88A membrane with hydration antifouling and photo-Fenton self-cleaning properties can stimulate more studies on revivable separation membranes for multifunctional applications.

Superhydrophobized Polyacrylonitrile/Hierarchicall-FeOOH Nanofibrous Membrane for High-salinity Water Treatment in Membrane Distillation

Water flux and hydrophobic durability play important roles in membrane distillation(MD) applications. Compared with the method of adsorbing nanoparticles by electrostatic adsorption, the surface roughness constructed by chemical bonding is more conducive to the performance of membrane. This paper reports a facile approach to fabricating superhydrophobic fluoroalkyl silane/polydimethylsiloxane@FeOOH@stabilized polyacrylonitrile(FAS/PDMS@FeOOH@SPAN) nanofibrous membrane(NFM) with outstanding hierarchical structures, aiming to achieve efficient and stable performance in MD. Electrospun polyacrylonitrile(PAN) membrane after peroxidation was chosen as the base membrane, followed by in-situ synthesis of iron oxyhydroxide and liquid-phase silanization. We tested the characteristics of FAS/PDMS@FeOOH@SPAN NFM in each preparation stage and its performance in direct contact membrane distillation(DCMD). The chemical bond between iron oxyhydroxide and the membrane is stronger, making the rough structure steady and dense. The FAS/PDMS@FeOOH@SPAN NFM exhibited a water contact angle of 155.4° and excellent hydrophobicity towards different pollutants. Besides, it showed satisfied properties with a water flux of 24.7 L·m−2·h−1, a high salts rejection of ca. 100% and an extended-term stability in DCMD using hypersaline water(10%, mass ratio). It is believed that this novel study proposes a universal and efficient method to fabricate a superhydrophobic surface and has great potential for high-salinity wastewater treatment in MD.

Diffusion of Protein Molecules through Microporous Nanofibrous Polyacrylonitrile Membranes.

Porous nanofibrous membranes have ultrahigh specific surface areas and could be broadly employed in protein purification, enzyme immobilization, and biosensors with enhanced selectivity, sensitivity, and efficiency. However, large biomolecules, such as proteins, have hindered diffusion behavior in the micro-porous media, significantly reducing the benefits provided by the nanofibrous membranes. The study of protein diffusion in polyacrylonitrile (PAN) nanofibrous membranes produced under varied humidity and polymer concentration of electrospinning revealed that heterogeneous structures of the nanofibrous membranes possess much smaller effective pore sizes than the measured pore sizes, which significantly affects the diffusion of large molecules through the system though sizes of proteins and pH conditions also have great impacts. Only when the measured membrane pore size is at least 1000 times higher than the protein size, the diffusion behavior of the protein is predictable in the system. The results provide insights into the design and applications of proper nanofibrous materials for improved applications in protein purification and immobilizations.

A novel carboxylated polyacrylonitrile nanofibrous membrane with high adsorption capacity for fluoride removal from water

To deal with the drinking water safety caused by fluoride, a novel carboxylated polyacrylonitrile nanofibrous membrane (C-PAN NFM) is designed and fabricated massively for the first time by adopting synchronously biaxial stretching and carboxylation. The C-PAN NFM is composed of the layered stack structure by cross-linked nanofibers. Due to its high specific surface area, excellent hydrophilicity, a large amount of carboxyl and amine groups, C-PAN NFM owns high fluoride adsorption capacity and outstanding selectivity. Both the carboxylation and acid treatment of C-PAN NFM improved the fluoride adsorption capacity remarkably. Specifically, C-PAN NFM shows excellent reusability without secondary pollution. The fluoride adsorption behavior of C-PAN NFM is dominated by chemical adsorption, and the adsorption mechanism is mainly driven by hydrogen bonding and ion exchange. The mass-produced C-PAN NFM is a novel polyacrylonitrile-based porous membrane that shows a great application potential for fluoride removal with good efficiency and recyclability.

Hydrophilic Surface-Modified PAN Nanofibrous Membranes for Efficient Oil-Water Emulsion Separation.

In order to protect the environment, it is important that oily industrial wastewater is degreased before discharging. Membrane filtration is generally preferred for separation of oily wastewater as it does not require any specialised chemical knowledge, and also for its ease of processing, energy efficiency and low maintenance costs. In the present work, hybrid polyacrylonitrile (PAN) nanofibrous membranes were developed for oily wastewater filtration. Membrane surface modification changed nitrile groups on the surface into carboxylic groups, which improve membrane wettability. Subsequently, TiO2 nanoparticles were grafted onto the modified membranes to increase flux and permeability. Following alkaline treatment (NaOH, KOH) of the hydrolysed PAN nanofibres, membrane water permeability increased two- to eight-fold, while TiO2 grafted membrane permeability increase two- to thirteen-fold, compared to unmodified membranes. TiO2 grafted membranes also displayed amphiphilic properties and a decrease in water contact angle from 78.86° to 0°. Our results indicate that modified PAN nanofibrous membranes represent a promising alternative for oily wastewater filtration.

Evaluation of Fe₃O₄/PAN Magnetic Nanofibrous Membrane for Heat Generation and Magnetic Actuation

Nanofibers are being widely applied in biomedicine, especially in tissue engineering given their porosity. We developed magnetic nanofibrous membranes aiming to devise new applications that use their thermal properties and mobility for actively targeted hyperthermia and microrobots. We fabricated Fe3O4 (iron oxide)/PAN (polyacrylonitrile) nanofibrous membranes and verified the properties of corresponding nanoparticles/fiber composites. Fe3O4 is a material with superparamagnetic properties under a critical size and can be controlled by a magnetic field and heated up by a high frequency alternating magnetic field. The Fe3O4/PAN nanofibers in this study were prepared at concentration of 20, 25, and 30 wt% by dispersing Fe3O4 nanoparticles of 20 nm in a PAN solution. At a nanoparticle concentration of 30wt%, the magnetic membrane generated heat up to 49.9°C in a magnetic field of 15.57kA/m and a driving frequency of 205.9 kHz during 600 s. In addition, we investigated the performance for steering and active locomotion (robotic control) of a magnetic nanofibrous membrane with 3 mm in diameter by using magnetic force control. The ranges (0.08~.014 mT/mm) of fiend gradient provided an average movement speed of 2.15 mm/s with accurate steering. The robotic control ability of the proposed magnetic nanofibrous membrane seems promising for increasing the diversity of biomedical applications for magnetic nanofibers as microrobot.

Development of Sunlight-Driven Reduced Graphene Oxide (rGO)/CeO₂-CuO Nanofibrous Photocatalyst for Efficient Removal of Organic Dyes.

A hybrid nanofibrous membrane photocatalysts was developed through electrospinningcarbonization method. In this work, the hybrid membrane with p-n hetero-structure consisting of CeO₂ and CuO metal-oxide nanoparticles was prepared by a hierarchical and facile approach through electrospun technique and stabilized by hydrothermal process. The obtained heterogeneous photocatalyst membrane was studied for its catalytic properties by performing several experiments using test solutions of anionic Congo red (CR) and cationic methylene blue (MB) dyes, respectively. The as-prepared Graphene-CeO₂/CuO intercalated polyacrylonitrile nanofibrous (GCPNs) membrane is characterized by using various analytical techniques and its photocatalytic degradation properties was studied by conducting batch studies and validated using the kinetics models. Furthermore, the functional group transformation, electronic transition state, binding energy values and chemical oxidation state of the GCPNs membrane before and after degradation was investigated by spectroscopic studies. The optical properties of the GCPNs membrane was further analysed by UV-VIS diffuse reflectance spectroscopy (DRS). Also, the enhanced photo-degradation behaviour of the p-n hetero-structure due to the suppression of the recombination rate of the photogenerated electron-hole pairs was confirmed by photoluminescence studies (PL). These investigations implied that the developed photocatalyst GCPN membrane follows the pseudo first-order kinetics having higher reaction rate constant. Comprehensively, the GCPN has varying dye removal capacity of 90-98% for Congo red and 30-90% for Methylene blue in which the photocatalytic degradation capacity increases with increase in dye concentration and time. The reusability studies supported the sustainability and durability of the photocatalytic membrane for longer lifetime and practical value. Henceforth, nanotechnology-based cutting-edge technology offers novel hybrid nanomaterials having excellent properties that are pre-requisite for the development of sunlight mediated nano-photocatalytic reactors in the commercial applications.

Fabrication of metal-organic framework-based nanofibrous separator via one-pot electrospinning strategy

Metal-organic framework (MOF)/polymer composites have attracted extensive attention in the recent years. However, it still remains challenging to efficiently and effectively fabricate these composite materials. In this study, we propose a facile one-pot electrospinning strategy for preparation of HKUST-1/polyacrylonitrile (PAN) nanofibrous membranes from a homogeneous stock solution containing HKUST-1 precursors and PAN. MOF crystallization and polymer solidification occur simultaneously during the electrospinning process, thus avoiding the issues of aggregation and troublesome multistep fabrication of the conventional approach. The obtained HKUST-1/PAN electrospun membranes show uniform MOF distribution throughout the nanofibers and yield good mechanical properties. The membranes are used as separators in Li-metal full batteries under harsh testing conditions, using an ultrathin Li-metal anode, a high mass loading cathode, and the HKUST-1/PAN nanofibrous separator. The results demonstrate significantly improved cycling performance (capacity retention of 83.1% after 200 cycles) under a low negative to positive capacity ratio (N/P ratio of 1.86). The improvement can be attributed to an enhanced wettability of the separator towards electrolyte stemmed from the nanofibrous structure, and a uniform lithium ion flux stabilized by the open metal sites of uniformly distributed HKUST-1 particles in the membrane during cycling.

Enhancing immobilization of Aspergillus oryzae ST11 lipase on polyacrylonitrile nanofibrous membrane by bovine serum albumin and its application for biodiesel production

The partially purified lipase from Aspergillus oryzae ST11 was immobilized on the surface-modified electrospun polyacrylonitrile (PAN) nanofibrous membrane. The effects of time and concentrations of glutaraldehyde and bovine serum albumin (BSA) were studied. The immobilized lipase reached the maximum activity at 180 min with the recovered activity of 44.2% (0.22 U/mg-support) in the absence of BSA. After adding 6 mg/mL BSA and 40 mM glutaraldehyde gave the recovered activity at 86.9% (0.43 U/mg-support). It showed the highest stability at pH 7.5 but the soluble lipase was at pH 7.0. In addition, the immobilized lipase was more stable at pH 4.0 and 9.0. The immobilized lipase preserved 56% activity at 70 °C but the soluble lipase had 34% activity. It conserved 86% activity while the soluble lipase had 18% activity after 13 days of storage at 4 °C. The operating parameters such as biocatalyst concentration, water content, and the molar ratio of methanol and palm oil were optimized for biodiesel production. The highest biodiesel conversion (95%) was obtained with the immobilized lipase 15% (w/w), 40% (w/w) 50 mM Tris-HCl buffer pH 7.0 and methanol/palm oil (3.5:1.0). This immobilized lipase could be reused with 82.9% conversion after 10 cycles of batch production.

Novel gelatin/polyacrylonitrile thin film nanofibrous composite membranes with high filtration performance

High performance thin film nanofibrous composite (TFNC) membrane consisting of a thin gelatin (GE) selective skin layer and a polyacrylonitrile (PAN) nanofibrous substrate was fabricated in this work. Ultrathin GE nanofibers were electrospun and deposited onto the PAN nanofibrous supporting membranes and followed by moistening treatment and hot-pressing treatment. The moistened electrospun GE nanofibers would be melted and pressed into an integrated selective skin layer on the porous PAN nanofibrous membranes. The treated GE/PAN double-layer membranes were then chemically cross-linked by glutaraldehyde (GA). The depositing time of GE nanofibers was optimized to achieve a thin and integrated GE separating layer. The optimized GE/PAN TFNC membrane exhibited high flux (182.1 L m−2 h−1) and rejection (98.3%) in BSA test at 0.3 MPa. In addition, the GE/PAN composite membrane possessed great mechanical stabilities.