Next step in 2nd generation glucose biosensors: Ferrocene-loaded electrospun nanofibers

Glucose determination is one of the most common analyses in clinical chemistry. Employing biosensors for this purpose has become the method of choice for home use for diabetic patients. To limit the impact of dissolved O₂ concentration or possible interferences (known hindrances in the classical glucose detection approach), a variety of mediated pathways have been explored. Herein, an ingenious, facile and low-cost approach for immobilization of redox mediator within nanofibrous mats is presented. This '2^nd generation' biosensor is able to avoid common issues such as leaching or diffusion barriers whilst providing the necessary close contact between the enzyme and the redox shuttle, for enhancing the detection accuracy and accelerate the response. Polyacrylonitrile nanofibers loaded with carbon nanotubes and ferrocene (PAN/Fc/MWCNT-COOH NFs) have been successfully prepared and applied as biosensing matrices upon cross-linking of glucose oxidase (GOD). The morphology of the NFs was investigated by means of scanning electron microscopy (SEM-EDX) and correlated to the kinetics of mediated electron transfer and to the efficiency in glucose detection, which were evaluated through cyclic voltammetry (CV) and amperometric measurements. The content of Fc was varied from 0.5 to 5.0 wt%, with optimum biosensor performance at 1.0 wt% exhibiting a linear range up to 8.0 × 10^-3 M with sensitivity of ~27.1 mAM^-1 cm^-2 and 4.0 μM LOD. Excellent stability (RSD 2.68%) during 40 consecutive measurements along with insignificant interference and accurate recovery in real sample analysis (~100%) make for a very reliable sensor that can easily render itself to miniaturization and has the potential for a wide range of practical applications.

Swollen-layer constructed with polyamine on the surface of nano-polyacrylonitrile cloth used for extract uranium from seawater

In this study, a swelling layer was constructed on the surface of the nano-polyacrylonitrile (PAN) fiber fabric prepared by electrospinning to enrich uranium (U (VI)) adsorption from seawater. The constructed swelling layer composes of a polyethyleneimine (PEI) containing a huge amount of amino groups and imino groups with strong hydrophilicity. The molecular chain swelled in an aqueous solution by forming a swelling layer on the PAN surface. In addition, p-aminobenzenesulfonic acid (SA) was used as the side chain end group grafted on the PAN surface, the benzene ring as the side chain can hinder the rotation of the PEI chain, thereby increasing the rigidity. The increasing of the rigidity leads to stretch the conformation of the PEI molecular chain, increasing the probability of collision with U (VI), which is beneficial for adsorption. The adsorption capacity of the prepared adsorbent in the adsorption experiment reached 215.25 mg g^-1, and the adsorption capacity in the 8 ppm spiked simulated seawater reached 144.5 mg g^-1. The adsorption mechanism of U (VI) was analyzed by XPS. The sulfonic acid group in SA as the terminal group and amino group in the swelling layer formed a coordination structure with U (VI). The swelling layer constructed on the surface of polyacrylonitrile fibers is used to effectively extract uranium from seawater.

Fabrication and characterization of TiO2 and MWCNT coated electrospinning nanofibers for UV protection properties

This paper aimed to fabricate UV protective nanofibers by the use of specific nanoparticles. The DMF/TiO2 (Titanium dioxide), DMF/MWCNT (Multi-Walled Carbon Nano Tubes), and DMF/MWCNT+TiO2 (MWCNT: TiO2 mass ratio= 1:1) solutions were transferred into a syringe with a stainless steel needle with gauge 21. The electrospinning process was performed for 3 h at the optimized conditions. The surface morphology of nanofibers was characterized by field emission scanning electron microscopy (FESEM). Fourier transform infrared spectroscopy (FTIR) was utilized to characterize functional groups of oxidized MWCNTs and investigate the successful load of nanoparticles at the fiber surface. The UV protection property of nanofibers was investigated by measuring UV rays' transmittance through the composite web. The data of Spectroscopy was used to compute the UV protection factor (UPF). (1) The effect of CNT,TiO2, and CNT+TiO2 nanoparticles on ultraviolet protection property was analyzed separately and simultaneously. (2) The different concentrations of nanoparticles, including 1,5,10, & 15 wt%, were used to fabricate UV protective nanocomposites. (3) The electrospinning condition was optimized as a 15 cm distance between the needle tip and collector, 20 KV voltage, 250 RPM drum rotation, and 1.2 ml/h feeding rate to access the best nanofibers.

Efficient Removal of Cs+ and Sr2+ Ions by Granulous (Me2NH2)4/3(Me3NH)2/3Sn3S7·1.25H2O/Polyacrylonitrile Composite

The need to effectively and selectively remove radioactive ¹³⁷Cs and ⁹⁰Sr from nuclear waste solutions persists to mitigate their environmental mobility and high radiotoxicity. Because it is difficult to effectively remove them from acidic environments that degrade most sorbents, new sorbent materials are highly desirable. Here, efficient removal of Cs⁺ and Sr²⁺ is achieved by the composite of layered tin sulfide (Me₂NH₂)_4/3(Me₃NH)_2/3Sn₃S₇·1.25H₂O (FJSM-SnS) and polyacrylonitrile (PAN) (FJSM-SnS/PAN). The granulous composite possesses regular particle morphology and good mechanical strength as an engineered form. It shows excellent acid-base and γ-irradiation resistance, high maximum adsorption capacities (q_m) of 296.12 and 62.88 mg/g for Cs⁺ and Sr²⁺ ions, respectively, and high selectivity even in the presence of excess Na⁺ ions or using lake water. Impressively, q_m^Cs of FJSM-SnS/PAN reaches 89.29 mg/g under even acidic conditions (pH = 2.5). The column loaded with FJSM-SnS/PAN granules exhibits high removal rates (R) toward low-concentration Cs⁺ and Sr²⁺ ions under both neutral and acidic conditions. Moreover, the composite can be recycled and reused with high R^Cs and R^Sr. This work highlights the great potential of metal sulfide ion-exchangers in engineered form for the efficient removal of Cs⁺ or Sr²⁺ ions, especially under acidic conditions, for radionuclide remediation.

Enhanced photocatalytic degradation of organic dyes by ultrasonic-assisted electrospray TiO2/graphene oxide on polyacrylonitrile/β-cyclodextrin nanofibrous membranes

Polyacrylonitrile (PAN)/β-cyclodextrin (β-CD) composite nanofibrous membranes immobilized with nano-titanium dioxide (TiO₂) and graphene oxide (GO) were prepared by electrospinning and ultrasonic-assisted electrospinning. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) confirmed that TiO₂ and GO were more evenly dispersed on the surface and inside of the nanofibers after 45 min of ultrasonic treatment. Adding TiO₂ and GO reduced the fiber diameter; the minimum fiber diameter was 84.66 ± 40.58 nm when the mass ratio of TiO₂-to-GO was 8:2 (PAN/β-CD nanofibrous membranes was 191.10 ± 45.66 nm). Using the anionic dye methyl orange (MO) and the cationic dye methylene blue (MB) as pollutant models, the photocatalytic activity of the nanofibrous membrane under natural sunlight was evaluated. It was found that PAN/β-CD/TiO₂/GO composite nanofibrous membrane with an 8:2 mass ratio of TiO₂-to-GO exhibited the best degradation efficiency for the dyes. The degradation efficiency for MB and MO were 93.52 ± 1.83% and 90.92 ± 1.52%, respectively. Meanwhile, the PAN/β-CD/TiO₂/GO composite nanofibrous membrane also displayed good antibacterial properties and the degradation efficiency for MB and MO remained above 80% after 3 cycles. In general, the PAN/β-CD/TiO₂/GO nanofibrous membrane is eco-friendly, reusable, and has great potential for the removal of dyes from industrial wastewaters.

Micro-patterned membranes prepared via modified phase inversion: Effect of modified interface on water fluxes and organic fouling

The introduction of patterns on a membrane-solute interface has been suggested as an effective method to tackle the reduced flux and fouling issues. Herein, the effectiveness of using spray-modified non-solvent induced phase separation (s-NIPS) to create a variety of micrometer-level structured interfaces is now studied. Circular, triangular and rectangular patterns with different dimensions were successfully created on polyacrylonitrile membranes. The rectangular pattern height was varied from 500 to 1500 µm, which resulted in a proportional increase in clean water permeance from 590 ± 47 L m^-2 h^-1 bar^-1 to 1345 ± 108 L m^-2 h^-1 bar^-1 respectively. This coincided with some BSA rejection loss for the highest patterns, indicating the fragile nature of these tall features. No significant rejection losses were found for the smaller pattern heights (145-250 µm) as compared to flat membranes, while fluxes more than doubled still. The critical pressure was also increased substantially for patterned membranes and showed a proportionality with the pattern height. These experimental findings were correlated with the reduced foulant adhesion due to a shear-induced slip boundary layer at the membrane-solution interface. Computational fluid dynamics simulations further showed higher shear stress values due to flow constriction within the membrane's valley regions. These findings indicate the high potential of s-NIPS patterned membranes in long-term industrial applications by requiring less membrane area for a given application and reducing cleaning interventions.

Osteogenic differentiation of mesenchymal stem cells on the bimodal polymer polyurethane/polyacrylonitrile containing cellulose phosphate nanowhisker

Polycaprolactone diol is the cornerstone, equipped with polyacrylonitrile and cellulose nanowhiskers (CNWs), of biocompatible and biodegradable polyurethanes (PUs). The solvent casting/particulate leaching technique was employed to contracting foam scaffolds with bimodal sizes from the combination of polyurethane/polyacrylonitrile/cellulose nanowhisker nanocomposites. Sugar and sodium chloride are components used as porogens to develop the leaching method and fabricate the 3D scaffolds. Incorporation of different percentages of cellulose nanowhisker leads to the various efficient structures with biodegradability and biocompatibility properties. All nanocomposites scaffolds, as revealed by MTT assay using mesenchymal stem cell (MSC) lines, were non-cytotoxic. PU/PAN/CNW foam scaffolds were used for osteogenic differentiation of human mesenchymal stem cells (hMSCs). Based on the results, PU/PAN/CNW nanocomposites could not only support osteogenic differentiation but can also enhance the proliferation of hMSCs in three-dimensional synthetic extracellular matrix.

Surface functionalization of recycled polyacrylonitrile fibers with ethylenediamine for highly effective adsorption of Hg(II) from contaminated waters

In this research, recycled polyacrylonitrile fibers (PANFs) acquired from the textile recycling process were amino-functionalized in one simple step by means of ethylenediamine (EDA). The amino-functionalized polyacrylonitrile fibers (AF-PANFs) were utilized for adsorption of Hg(II) ions from aquatic media. Temperature and contact time during the synthesis were optimized by the Central Composite Design (CCD) method. FE-SEM, EDS, BET, and FT-IR analysis, and pH_ZPC measurement were conducted to characterize the features of the AF-PANFs. The average diameter of raw fiber was 20 μm, which increased 20 percent after functionalizing. The impact of independent parameters on the adsorption process was investigated using the Box-Behnken Design (BBD) method during the batch experiments. The column tests were conducted in a semi-continuous system with the removal efficiency of over 99% for various initial concentrations after specific cycles. Freundlich, Langmuir, UT, Redlich-Peterson, and Temkin isotherm models were employed to analyze the relation between the final concentration of Hg(II) (C_o) and the equilibrium adsorption capacity (q_e) of the AF-PANFs. According to the isotherm models and experimental results, the maximum q_e of the AF-PANFs was 1116 mg g^-1 at initial Hg(II) concentration of 850 mg L^-1, contact time of 120 min, solution pH of 6, and at 40 °C. Kinetic and thermodynamic studies illustrated the approximate equilibrium time and endothermicity or exothermicity of the process. Regeneration of the AF-PANFs was accomplished for seven times without efficiency drop. The superb performance of the AF-PANFs in the presence of co-existing ions did not decline.

Anchoring ZIF-67 particles on amidoximerized polyacrylonitrile fibers for radionuclide sequestration in wastewater and seawater

Capturing uranium (U(VI)) ions from wastewater and seawater is highly attractive for the environment and clean energy with the increasing deficiency of land sources. Howbeit, the massive volume of water and the ultralow concentration of U(VI) pose a substantial challenge to the industrial application. Accordingly, we have synthesized a novel organic-inorganic hybrid adsorbent through in-situ growing MOF particles on electrospun polyacrylonitrile fibers (PAN) followed by modifing with amidoxime groups to form amidoximed PAN/ZIF-67 (AOPAN/ZIF) hybrid fibers. In such fibers, the N atoms from imidazole and amidoxime can improve the adsorption performance synergistically in a wide pH range, which is favorable for capturing U(VI) under nuclear wastewater and seawater. As a result, the AOPAN/ZIF fibers exhibit high adsorption amount of 498.4 mg g^-1 in U(VI) contaminated aqueous solution at pH 4. Furthermore, the adsorption amount of U(VI) reached 2.03 mg g^-1 in natural seawater after 36 d, which implies that the AOPAN/ZIF fibers may promote the development of U(VI) recovery.

One-pot synthesis of sodium lauryl sulfate-loaded polyacrylonitrile solid-phase extractor for investigating the adsorption behavior of radioactive strontium(II) from aqueous solutions

Sodium lauryl sulfate-loaded polyacrylonitrile (SLSLPAN) was synthesized in the present investigation using an in-situ one step process through gamma radiation-induced polymerization. The structure, composition, surface area and pore size and volume of the employed adsorbent were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption-desorption measurements. Adsorption of radioactive strontium(II) onto SLSLPAN was studied in the pH range 3-13. Batch kinetic data showed that the equilibrium was attained at 840 min and the pseudo-first-order was the best kinetic model for describing the kinetic data of the present adsorption process. The diffusion of strontium(II) into SLSLPAN was deeply studied using four diffusion models, namely, Bangham, Boyd, Weber-Morris and Mathewas-Weber models. Two-parameter (Freundlich, Langmuir and Temkin) and three-parameter (Redlich-Peterson, Toth and Generalized) isotherm models were used to analyze the adsorption equilibrium data of strontium(II) onto SLSLPAN. The maximum adsorption capacity calculated by the Generalized isotherm model is found to be 0.391 mmol strontium(II) per gram of SLSLPAN. The estimated mean free energy (E = 2.151 kJ/mol) indicated that strontium(II) radionuclides were physically adsorbed onto SLSLPAN. The value of enthalpy change (ΔH^o = 35.325 kJ/mol) and those of free energy change (ΔG^o = -15.278, -16.948, -18.619 and -20.288 at 303, 313, 323 and 333 K, respectively) confirmed that adsorption of strontium(II) radionuclides on SLSLPAN was endothermic and spontaneous process.

Construction of gel-like swollen-layer on Polyacrylonitrile Surface and Its Swelling Behavior and Uranium Adsorption Properties

In this study, a hyperbranched chelated hydrophilic swollen-layer was constructed on the surface of polyacrylonitrile (PAN) fiber with amino trimethylene phosphoric acid (ATMP) as a terminal group, which applied as an adsorbent for seawater uranium U(VI) extraction. This shows that U(VI) enter the gel-like swollen-layer to form a more complex body structure. The molecular chain conformational extension in the swollen-layer reduces the resistance of the uranyl ion to enter the swollen-layer, which is conducive to the adsorption behavior. The adsorption performance on the U(VI) by the adsorption experiment were found to be consistent with the Langmuir isotherm adsorption model and the pseudo-second-order kinetics, indicating that the adsorption of U(VI) by this material is uniform single-layer chemical adsorption. Ion competition experiments and cyclic adsorption experiments verify the practical application potential of the materials. In the dynamic simulation of seawater adsorption experiments, the adsorption capacity of the adsorbent reached 7.4 mg/g. Studies on the adsorption mechanism have found that a large number of hydroxyl groups in the swollen-layer and ATMP as an end machine have a chelation effect on U(VI).

Adsorption of antimonite and antimonate from aqueous solution using modified polyacrylonitrile with an ultrahigh percentage of amidoxime groups

Porous modified polyacrylonitrile (PAN) with an ultrahigh percentage of amidoxime groups (UAPAN) was synthesized for the first time and used to adsorb antimonite (Sb(III)) and antimonate (Sb(V)) from aqueous solution. Fourier transform infrared (FT-IR), Zeta potential, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) were adopted to characterize UAPAN and explore adsorption mechanism. Moreover, batch experiments were performed to investigate the influence of various adsorption parameters, including initial pH, contact time, temperature, coexisting ions and reusability on adsorption capacities. Results showed that the maximum adsorption capacities for Sb(III) and Sb(V) were 125.4 and 177.3 mg g^-1, respectively, which were much higher than those of other adsorbents reported in literature. The adsorption thermodynamics was evaluated, indicating the spontaneous and endothermic adsorption. The adsorption isotherm was suitable to be modeled by Langmuir isotherm (R² > 0.96). Results of FT-IR, Zeta potential and XPS indicated that adsorption was involved with electric charge attraction and ligand exchange. DFT further explained that better adsorption of Sb(V) on UAPAN than that of Sb(III) was caused by the higher adsorption energy, more favorable bond lengths and atom charge density. Accordingly, UAPAN is expected to be a compelling candidate for antimony decontamination from aqueous environment.

Facile architecture of highly effective nanofibrous membrane adsorbent via electrospun followed by hydrothermal carbonization for potential application in dye removal from water

Rapid removal of toxic dye pollutants in water by conventional materials is ineffective and expensive that warrants the necessity for the architecture of hybrid nanofibrous membrane through layer by layer deposition using electrospinning method. In order to achieve this, here we demonstrated the electrospun fabrication of graphene/ferrocene intercalated polyacrylonitrile nanofibrous (GFPN) membrane through hydrothermal carbonization (HTC) method and studied its potential adsorption properties for the removal of environmental pollutants. An aqueous dispersion of graphene/ferrocene (1 mg/mL) stabilized by the polymeric backbone was prepared by the solvent homogenization method and electrospun to yield nanofibrous membrane and further characterized by several analytical and spectroscopic techniques. Raman and XPS investigations corroborated the intercalation of graphene/Fe decorated onto the nanofibrous network. Adsorption experiments found that the GFPN membrane achieved more than 90% removal of anionic Congo red (CR) dye within 30 min in the aqueous phase irrespective of the concentration and takes some additional time for attaining the equilibrium. The longevity and stability of the membrane was studied by conducting successive adsorption-desorption cycles for the regeneration of its adsorption properties. The de-coloration mechanism was comprehensively investigated through the mathematical approaches using the kinetic and intraparticle diffusion studies and confirmed with the experimental findings through IR and XPS spectroscopic techniques. In a nutshell, this work focuses on the fabrication of hybrid nanofibrous membrane and studied its adsorption properties through varying concentrations of dye (20 to 150 mg/L). Moreover, this work extensively explored the mechanism associated with the adsorption process and specifically emphasize the existence of combined phenomena during the process, i.e., anion-cation interactions, hydrogen bonding, and successive stages of intraparticle diffusion through the comparative elucidation of both theoretical and experimental approaches.

Polyacrylonitrile nanofibrous mat from electrospinning: Born with potential anti-fungal functionality

Electrospun nanofibers have been found in many applications such as air/water filtration, performance apparel, drug delivery, and scaffold for tissue engineering and started to be integrated in commercial products, which leads to their exposure to environment. Electrospun nanofibrous material is a relatively new material to microorganism in nature and little is known about the biological implication of interactions between electrospun nanofibrous mats and cellular fungal cells. Herein the interaction between electrospun polyacrylonitrile (ESPAN) nanofibrous mat and representative non-pathogenic/pathogenic cellular yeasts (Saccharomyces cerevisiae and Candida albicans) was investigated. It is demonstrated for the first time that when these cellular yeasts, species of the kingdom fungi, were exposed to ESPAN nanofibrous mat, they exhibited lower growth rate, radical change to morphology, and reduced viability without presence of any chemical antifungal agent. These responses were distinct from the cellular interactions with other forms of PAN materials (e.g. solid film or microfibrous mat). Exploration of mechanism indicated that the interaction between yeast cell and electrospun nanofibrous mat is a complex phenomenon in which both nanofibrous morphology and fiber surface composition/property play significant roles. The inherent anti-yeast and potential anti-fungal functionality of ESPAN nanofibrous mat may make an immediate impact on environmental microorganism and could also benefit the next-generation material design to control microbial growth through solely physical contact.

Flexible and Washable CNT-Embedded PAN Nonwoven Fabrics for Solar-Enabled Evaporation and Desalination of Seawater

Nanostructured photothermal membranes hold great potential for solar-driven seawater desalination; however, their pragmatic applications are often limited by substantial salt accumulation. To solve this issue, we have designed and prepared flexible and washable carbon-nanotube-embedded polyacrylonitrile nonwoven fabrics by a simple electrospinning route. The wet fabric exhibits a strong photoabsorption in a wide spectral range (350-2500 nm), and it has a photoabsorption efficiency of 90.8%. When coated onto a polystyrene foam, the fabric shows a high seawater evaporation rate of 1.44 kg m^-2 h^-1 under simulated sunlight irradiation (1.0 kW m^-2). With a high concentration of simulated seawater as the model, the accumulation of solid salts can be clearly observed on the surface of the fabric, resulting in a severe decay of the evaporation rate. These salts can be effortlessly washed away from the fabric through a plain handwashing process. The washing process has a negligible influence on the morphology, photoabsorption, and evaporation performance of the fabric, demonstrating good durability. More importantly, a larger fabric can easily be fabricated, and the combination of washable fabrics with various parallel PS foams can facilitate the construction of large-scale outdoor evaporation devices, conferring the great potential for efficient desalination of seawater under natural sunlight.

Magnetic nanoparticle - indium phthalocyanine conjugate embedded in electrospun fiber for photodynamic antimicrobial chemotherapy and photodegradation of methyl red

ClIn(III) octacarboxy phthalocyanine (ClInOCPc) when alone or conjugated to magnetic nanoparticles (MNP-ClInOCPc) was employed for both photodynamic antimicrobial chemotherapy of an unknown water sample and Staphylococcus aureus, and for photo-degradation of methyl red (MR). The singlet oxygen quantum yields (Φ_Δ) in water using ClInOCPc and MNP-ClInOCPc embedded in polyacrylonitrile (PAN) electrospun fibers were 0.36 and 0.22, respectively. When in solution, MNP-ClInOCPc gave 90.6% photoinactivation of microbes in a water sample from the stream and of ClInOCPc resulted in 84.8 % photoinactivation. When embedded to the polymer, there was 48.0% clearance for ClInOCPc and 63.7% clearance for MNP-ClInOCPc for the microbes in the water sample from the stream. For the photo-degradation of MR, the rate of degradation increased with decrease of the MR concentration with the MNP-ClInOCPc having the fastest rate.

Membrane layers intensifying quorum quenching alginate cores and its potential for membrane biofouling control

Quorum quenching (QQ) has been proved to be an efficient method to mitigate biofouling in membrane bioreactors (MBRs). In this paper, in order to enhance practicability of QQ microcapsules, we prepared three types microcapsules with same alginate cores (SAs). The microcapsules with polyacrylonitrile (PAN) layer showed excellent performance in preventing cell leakage from the microcapsules, increasing service life and improving mechanical strength. And confocal laser scanning microscopy images demonstrated that there were very little dead bacteria in the microcapsules with both chitosan and PAN layer than microcapsules with only PAN layer because chitosan layer can protect bacteria entrapped in cores from the hurt caused by poisonous PAN solution. At the same time, the microcapsules with PAN layer presented more efficient anti-biofouling ability in the physical washing test. At last, the bacterial microcapsules coated with both chitosan and PAN layer showed an obvious biofouling mitigation during the MBRs operation.

Degradation of methyl orange on Fe/Ag nanoparticles immobilized on polyacrylonitrile nanofibers using EDTA chelating agents

Bimetallic nanoparticles are effective for the removal of organic pollutants from environmental water samples through catalytic degradation reactions. Hence, this work reports on the preparation of Fe/Ag bimetallic nanoparticles immobilized on electrospun polyacrylonitrile nanofibers (PAN NFs) pre-functionalized with EDTA and ethylenediamine (EDA) chelating agents. Characterization techniques included attenuated total reflectance coupled to Fourier transform infrared spectrometer (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The liquid chromatography coupled to a mass spectrometer (HPLC-MS) was used to investigate the degradation by-products. The impregnation of EDTA-EDA chelating agents imparted changes on the pristine PAN NFs as evidenced by increased nanofiber's average diameter and surface chemistry. The zero valent Fe and Ag NPs were successfully immobilized on PAN NFs and their catalytic activity was tested for the degradation of azo dyes. Results showed efficient decolourization of methyl orange dye molecules from synthetic water samples after four (4) cycles of reuse (e.g. >96% removal efficiency). The hydrogenation of methyl orange was found to be the removal mechanism due to the presence of hydrogenated methyl orange by-products in the treated water samples. Therefore, the fabricated nanocomposites exhibit potential application for the remediation of textile wastewater.

Nanocrystalline cellulose as a reinforcing agent for electrospun polyacrylonitrile (PAN) nanofibers

OBJECTIVES

Nanocrystalline cellulose (NCC) is a sustainable material with excellent mechanical properties and can potentially be used as a reinforcement agent. The objective of this work was to test the effects of NCC incorporation on the mechanical properties of electrospun polyacrylonitrile (PAN) nanofibers.

METHODS

Eleven percent in weight of PAN (molecular weight 150 kD) in a dimethylformamide (DMF) solution was electrospun at 14.6 kV. Nonfunctionalized NCC was added to the solution at 1%, 2%, or 3 wt% (NCC/PAN). Suspensions were mixed and sonicated for 2 h before spinning. Strips (5 × 0.5 cm) were cut from the spun mat, parallel and perpendicular to the rotational direction of the fiber collection drum. Tensile tests were performed, and ultimate tensile strength (UTS), yield strength (YS; 0.3%), elastic modulus (E), and elongation at maximum stress (EMS, %) were calculated from stress-strain plots. Data were analyzed by multiple t tests and one-way ANOVA (α = 0.05).

RESULTS

Among all groups, samples with 3 wt % NCC loading had significantly superior mechanical properties. The fiber mats showed anisotropic behavior.

CONCLUSIONS

Regardless of concentration, the addition of NCC resulted in increased UTS, E, and YS of the nanofibers.

Highly efficient immobilization of NZVI onto bio-inspired reagents functionalized polyacrylonitrile membrane for Cr(VI) reduction

To provide superior substrates and determine the specific species of immobilized nano zero-valent iron (NZVI) system, polyacrylonitrile (PAN) membrane was functionalized by bio-inspired polydopamine (PDA) and poly(_l-DOPA) (PDOPA) for efficient immobilization of NZVI. The synthesized composites were denoted as PAN/PDA-NZVI (PPN) and PAN/PDOPA-NZVI (PON), respectively. Analyses of XRD, SEM/EDS and XPS show that the aggregation and release of iron nanoparticles had been successfully controlled by improving membrane hydrophilcity and iron-chelating capacity via the graft of functionalized groups (i.e. OH and COOH) of PDA and PDOPA on PAN membrane. Both PPN and PON composites exhibited superior reactivity for Cr(VI) removal (Cr(VI) removal efficiency and reaction rate were 2.21-2.22 and 9.90-10.14 times higher than that of bare NZVI, respectively). The stability and recyclability of PPN and PON composites could be maintained over repeated cycles. Further analyses indicate that PON is more capable for Cr(VI) elimination than PPN due to the proprietary carboxyl of _l-DOPA. With the addition of 1,10-phenanthroline, membrane-chelated Fe(II) was determined to be the major species in Cr(VI) removal system, accounting for 56.9% and 53.8% with regard to PPN and PON composites, and Fe⁰ was responsible for the reduction of residual Cr(VI). Analyse of reacted composites revealed that Cr(VI) was completely converted into Cr(III), followed by formation of dominant Cr(III)/Fe(III) (oxy)hydroxides and partial desorption from NZVI reactive sites. This study suggested that both synthesized PPN and PON composites have potentials for Cr(VI)-contaminated wastewater treatment.

Preparation of immobilized lipase by modified polyacrylonitrile hollow membrane using nitrile-click chemistry

The application of immobilized lipase in the enzymatic production of biodiesel has shown numerous advantages. In this study, surface of Polyacrylonitrile (PAN) hollow membrane was first modified using nitrile-click chemistry in order to fit for interaction with enzyme proteins. Then sodium alginate (SA) was introduced and the membrane was post-treated by CaCl₂. When the prepared PAN-PEI-SA-CaCl₂ was used for lipase immobilization, the protein loading was 36.90 mg/g, and the enzyme activity reached up to 54.47 U/g, which was 2.5 times as much as that of Novozym® 435. As a result, the constructed immobilized lipase obtained a maximum biodiesel yield of 78.5%, which was 2.4 times that of the Novozym® 435 in transesterification reactions. Moreover, the biodiesel yield decreased by only 11% after the immobilized enzyme was continuously used for 20 times. This study exhibits that this technic has broad application prospects in the field of conversion of biomass resources.

Application of activated carbon-decorated polyacrylonitrile nanofibers as an adsorbent in dispersive solid-phase extraction of fluoroquinolones from wastewater

A cheap and simple sample preparation method, consisting of a dispersive solid-phase method and an adsorbent, activated carbon decorated PAN nanofibers, was employed and used for the extraction of antibiotics (ciprofloxacin, danofloxacin, and enrofloxacin) in wastewater. Electrospun PAN nanofibers that were decorated with activated carbon produced from waste tires were used as the solid phase and the antibiotics analyzed by using high-performance liquid chromatography. Parameters such as pH, mass of adsorbent (MA), extraction volume (EV), and extraction time (ET) were optimized owing to their potential effect on the extraction of antibiotics from water. The recovery of all antibiotics was satisfactory, in the range of 90%–99%. The limits of detection and quantification were 0.05, 0.11, 0.20, and 0.53, 1.21, 2.17 µg/L, respectively. The precision was determined from the repeatability and reproducibility and expressed as the intra-day (n = 20) and inter-day (n = 5) precision. The intra-day and inter-day precision was reported in terms of the percentage relative standard deviation, which was 3% and 4%, respectively. The adsorption capacity of the activated carbon-decorated PAN nanofibers was satisfactory, and the reusability of the adsorbent was impressive when reused ten times. The accuracy of the dispersive solid phase extraction (DSPE) was validated by spike recovery tests; the results proved the reliability and efficiency of adsorbing antibiotics from wastewater. Finally, the proposed method was applied to wastewater samples collected from a wastewater treatment plant, which included influent, secondary, and effluent wastewater.

Performance comparison of hematite (α-Fe2O3)-polymer composite and core-shell nanofibers as point-of-use filtration platforms for metal sequestration

Point-of-use water treatment technologies can help mitigate risks from drinking water contamination, particularly for metals (and metalloids) that originate in distribution systems (e.g., chromium, lead, copper) or are naturally occurring in private groundwater wells (e.g., arsenic). Here, composite nanofibers of polyacrylonitrile (PAN) with embedded hematite (α-Fe₂O₃) nanoparticles were synthesized via a single-pot electrospinning synthesis. A core-shell nanofiber composite was also prepared through the subsequent hydrothermal growth of α-Fe₂O₃ nanostructures on embedded hematite composites. Properties of embedded hematite composites were controlled using electrospinning synthesis variables (e.g., size and loading of embedded α-Fe₂O₃ nanoparticles), whereas core-shell composites were also tailored via hydrothermal treatment conditions (e.g., soluble iron concentration and duration). Although uptake of Cu(II), Pb(II), Cr(VI), and As(V) was largely independent of the core-shell variables explored, metal uptake on embedded nanofibers increased with α-Fe₂O₃ loading. Both materials exhibited maximum surface-area-normalized sorption capacities that were comparable to α-Fe₂O₃ nanoparticle dispersions and exceeded that of a commercial iron oxide based sorbent. Further, both types of composite exhibited strong performance across a range of environmentally relevant pH values (6.0-8.0). Notably, core-shell structures, with a majority of surface accessible α-Fe₂O₃, performed far better than embedded composites in kinetically limited flow through systems than was anticipated from their relative performance in equilibrium batch systems. Core-shell nanofiber filters also retained much of the durability and flexibility exhibited by embedded nanofibers. Additional tests with authentic groundwater samples demonstrated the ability of the core-shell nanofiber filters to remove simultaneously both As and suspended solids, illustrating their promise as a nano-enabled technology for point-of-use water treatment.

Fabrication of a loose nanofiltration candidate from Polyacrylonitrile/Graphene oxide hybrid membrane via thermally induced phase separation

It is still a challenge to design and fabricate a robust nanoporous membrane in large scale and of fundamental importance for practical application. Here, a robust three/two-dimensional polyacrylonitrile/graphene oxide (PAN/GO) homogeneous nanoporous membrane is fabricated in large scale via thermally induced phase separation method, which guarantees the membrane with high mechanical strength and selective separation properties. Differing from conventional nanofiltration (NF) membrane with high rejection to both salt and dye, the resulting hybrid membrane is relative loose, which shows outstanding performances, i.e. high dye rejection and low salt rejection, high permeability and antifouling properties, acting as a promising candidate for dye/salt fractionation. The incorporation of 0.2 wt% GO endows membrane with excellent performance, where high tensile strength, high water permeability (33 L⋅ m^-2⋅ h^-1⋅ bar^-1), selectivity (100% to methyl blue, 99.8% to acid red 18, 26.7% to magnesium sulfate and 10.9% to sodium chloride and flux recovery ratio of 84.4%) are perfectly balanced. Its homogeneous structure and high strength guarantee long term use without the peeling of thin active layer as encountered by conventional NF membranes. The successful fabrication of such a hybrid membrane provides an attractive opportunity for loose NF membrane preparation with performance enhancement in a feasible way for practical application.

The preparation of carboxylic-functional carbon-based nanofibers for the removal of cationic pollutants

A simple route is presented to fabricate carboxylic-functional carbon-coated polyacrylonitrile nanofibers (oPAN@C) through preoxidation and hydrothermal carbonization. PAN fibers were firstly preoxidized to form aromatic ladder structure with the resistance to hydrothermal condition, in which more carboxyl groups were introduced on the fiber surface at the present of chitosan and citric acid. The oPAN@C composites exhibit a high adsorption capacity towards methylene blue (MB) and lead ion (Pb²⁺). The adsorption data matched the pseudo-second-order kinetic model and Langmuir model well with the maximum adsorption capacity (153.37 and 143.27 mg g^-1) for methylene blue and Pb²⁺, respectively. Moreover, oPAN@C could be regenerated easily by hydrochloric acid, and still remained high removal efficiency after 5 cycles. Therefore, oPAN@C fibers should have potential application in sewage treatment.