Mixture Of Polyacrylonitrile Research Articles

Chemical reaction and phase transformation mechanism of electrospun iron (III) acetylacetonate-polyacrylonitrile fibers during pre-oxidation process

Low-temperature pre-oxidation of electrospun metal-compound-incorporated carbon fibers can involve phase transitions and chemical reactions. However, their mechanics remain unclear. In this work, a mixture of polyacrylonitrile (PAN) and iron acetylacetonate is subjected to electrospinning followed by a pre-oxidation process at 230 °C, producing PAN fibers loaded with iron compounds. Our detailed investigations shed light on the mechanisms of phase transitions and associated chemical reactions during the pre-oxidation process. Our findings reveal that PAN undergoes cyclization during pre-oxidation, and that crystalline iron acetylacetonate within PAN fibers transforms into amorphous FeO and Fe2O3.

Conductive core/shell polymer nanofibres as anode materials for direct ethanol fuel cells

A conductive polymer-supported electrocatalyst in the form of fibrous mat has been developed that can be employed as a polymer-based electrode for direct ethanol fuel cells (DEFCs) with promoting effects to the state-of-the art Pd based catalysts. A series of conductive polyaniline (PANI)-containing polymer fibres-supported Pd electrocatalytic electrodes were successfully prepared and tested for the ethanol electro-oxidation reaction (EOR) in alkaline medium. The polymer support was a robust fibrous mat, where the fibres possessed a core-shell configuration. The core part was produced via electrospinning using a mixture of polyacrylonitrile (PAN) and 1-butyl-3-methylimidazolium chloride [BMIm]Cl ionic liquid (IL). The shell was a PANI layer deposited via the chemical polymerisation of aniline monomer. Pd was then electrodeposited on the fibres and the catalysts were tested for the EOR via cyclic voltammetry (CV) in a half-cell configuration and in a temperature range between 25 and 60 °C. The activity of the catalysts tested was measured in terms of activation energy and forward peak current density in the CV and compared to that of glassy carbon (GC)-supported Pd/PANI/PAN/IL fibrous catalysts. The polymer fibre-catalyst samples showed a higher active surface area and significantly lower activation energy than the GC-based ones. Even though the GC-supported catalysts showed a higher activity in terms of current, the Pd/(PAN/IL)-core/PANI-shell fibrous mats were active as well and, in some cases, demonstrated a promoting effect of PANI on Pd for EOR and a much better stability and robustness compared to the former. Furthermore, a series of promoting metals were investigated for these mats, such as Ag, Bi and Cu, with Ag and Bi demonstrating promoting effects compared to monometallic Pd/(PAN/IL)-core/PANI-shell mats in terms of both activation energy and peak current density. This work demonstrates a promising strategy in the arena of development of polymeric mats as anode electrodes for DEFCs, exploiting the benefits of PANI in terms of ease of synthesis, catalyst poisoning prevention, cost and promoting effects.

Effect of Acetone as Co-Solvent on Fabrication of Polyacrylonitrile Ultrafiltration Membranes by Non-Solvent Induced Phase Separation.

For the first time, the presence of acetone in the casting solutions of polyacrylonitrile (PAN) in dimethylsulfoxide or N-methyl-2-pyrrolidone was studied with regards to thermodynamical aspects of phase separation of polymeric solutions induced by contact with non-solvent (water), formation and performance of porous membranes of ultrafiltration range. The positions of the liquid equilibrium binodals on the phase diagrams of these three-component and pseudo-three-component mixtures were determined. For PAN-N-methyl-2-pyrrolidone-water glass transition curve on a ternary phase diagram was plotted experimentally for the first time. The real-time evolution of the structure of mixtures of PAN with solvents (co-solvents) upon contact with a non-solvent (water) has been studied. The thermodynamic analysis of the phase diagrams of these mixtures, together with optical data, made it possible to propose a mechanism of structure formation during non-solvent induced phase separation of different mixtures. The addition of acetone promotes the formation of a spongy layer on the membrane surface, which decreases the probability of defect formation on the membrane surface and keeps finger-like macrovoids from the underlying layers of the membrane. It was shown that the molecular weight cut-off (MWCO) of the membranes can be improved from 58 down to 1.8 kg/mol by changing the acetone content, while polymer concentration remained the same.

Hydration and Thermal Response Kinetics of a Cross-Linked Thermoresponsive Copolymer Film on a Hydrophobic PAN Substrate Coating Probed by In Situ Neutron Reflectivity.

The hydration and thermal response kinetics of the cross-linked thermoresponsive copolymer poly((diethylene glycol monomethyl ether methacrylate)-co-poly(ethylene glycol) methyl ether methacrylate), abbreviated as P(MEO2MA-co-OEGMA300), thin film on a hydrophobic polyacrylonitrile (PAN) substrate coating, which resembles a synthetic fabric, is probed by in situ neutron reflectivity (NR). The PAN and monomer (MEO2MA and OEGMA300) solutions are sequentially spin-coated onto a silicon (Si) substrate. Afterward, plasma treatment is applied to realize the cross-linking of PAN and monomers. The as-prepared cross-linked P(MEO2MA-co-OEGMA300) film on the hydrophobic PAN substrate coating presents a two-layer structure: a substrate-near layer, which is a mixture of PAN and P(MEO2MA-co-OEGMA300), and a main layer, which is composed of pure hydrophilic P(MEO2MA-co-OEGMA300). During hydration in D2O vapor atmosphere, the hydrophobic PAN component prevents the formation of D2O enrichment in the substrate-near layer. However, an additional vapor-near layer is observed on top of the main layer, which is enriched with D2O. The hydration process is constrained by the cross-linking points in the film, inducing the relaxation time to be longer than that in a spin-coated P(MEO2MA-co-OEGMA300) film. Because the as-prepared cross-linked film presents a transition temperature (TT) at 38 °C, the hydrated film switches to the collapsed state when the temperature is increased from 23 to 50 °C. The response to a thermal stimulus is also slower due to the existence of the internal cross-linking points as compared to the spin-coated film. Interestingly, no reswelling is observed at the end of the thermal stimulus, which can be also attributed to the presence of internal cross-linking points.

High Concentration of Ti3C2Tx MXene in Organic Solvent

MXenes are currently one of the most widely studied two-dimensional materials due to their properties. However, obtaining highly dispersed MXene materials in organic solvent remains a significant challenge for current research. Here, we have developed a method called the tuned microenvironment method (TMM) to prepare a highly concentrated Ti3C2Tx organic solvent dispersion by tuning the microenvironment of Ti3C2Tx. The as-proposed TMM is a simple and efficient approach, as Ti3C2Tx can be dispersed in N,N-dimethylformamide and other solvents by stirring and shaking for a short time, without the need for a sonication step. The delaminated single-layer MXene yield can reach 90% or greater, and a large-scale synthesis has also been demonstrated with TMM by delaminating 30 g of multilayer Ti3C2Tx raw powder in a one-pot synthesis. The synthesized Ti3C2Tx nanosheets dispersed in an organic solvent possess a clean surface, uniform thickness, and large size. The Ti3C2Tx dispersed in an organic solvent exhibits excellent oxidation resistance even under aerobic conditions at room temperature. Through the experimental investigation, the successful preparation of a highly concentrated Ti3C2Tx organic solvent dispersion via TMM can be attributed to the following factors: (1) the intercalation of the cation can lead to the change in the hydrophobicity and surface functionalization of the material; (2) proper solvent properties are required in order to disperse MXene nanosheets well. To demonstrate the applicability of the highly concentrated Ti3C2Tx organic solvent dispersion, a composite fiber with excellent electrical conductivity is prepared via the wet-spinning of a Ti3C2Tx (dispersed in DMF) and polyacrylonitrile mixture. Finally, various types of MXenes, such as Nb2CTx, Nb4C3Tx, and Mo2Ti2C3Tx, can also be prepared as highly concentrated MXene organic solvent dispersions via TMM, which proves the universality of this method. Thus, it is expected that this work demonstrates promising potential in the research of the MXene material family.

In Situ Ion‐Conducting Protective Layer Strategy to Stable Lithium Metal Anode for All‐Solid‐State Sulfide‐Based Lithium Metal Batteries

AbstractLithium metal is well known to be one of the most promising anodes for all‐solid‐state batteries, due to its ultrahigh capacity (3860 mAh g−1) and the extremely low standard negative electrochemical potential (−3.04 V). However, direct and confined contact of lithium metal with solid‐state electrolytes is still a great obstacle for excellent battery performance, which induces poor interfacial compatibility to further lead to weak lithium ion transport and dendrite formation. In this work, a well‐lithium‐ion‐conducting protective interfacial layer in all‐solid‐state‐Li6PS5Cl‐based lithium metal batteries is in situ established on the surface of polished Li through spin‐coating technique with a mixture of polyacrylonitrile (PAN) and fluoroethylene (FEC) carbonate. Interestingly, it is found there is synergistic effect between PAN and FEC via a solution‐based route. The artificial protective layer (LiPFG) consisting of organic matrix embedded with inorganic Li3N and LiF on the surface of Li regulates the uniform lithium deposition and enhances interface stability and compatibility. Specifically, a high reversible discharge capacity of 125.7 mAh g−1 at 0.1C and a lifetime of over 80 cycles can be achieved for LiZrO3@LiCoO2/Li6PS5Cl/LiPFG@Li full cells. This work inspires ideas for in situ construction of well‐lithium‐ion‐conducting artificial layer by a feasible spin‐coating technique for all solid state lithium metal batteries.

Effect of different phenylsilane contents on the electrochemical behavior of cyclodextrin/phenylsilane-W. dela Cruzderived carbon nanofiber composites

Highly porous carbon nanofiber composites (PPSCD) are prepared through one-step electrospinning using a mixture of polyacrylonitrile (PAN), phenylsilane (PS), and α-cyclodextrin (CD) in a carbonization process without any additional physical/chemical activation step. Their capacitive performance is well optimized by adjusting the PS concentration. The PS concentration of 3 wt% in a PAN and CD polymer solution provides a large specific surface area of 563 m2g−1, which is advantageous for double layer capacitance for charge storage and rapid ion transport in charge–discharge processes. The PPSCD electrode shows a maximum specific capacitance (189 Fg−1 at a current density of 1 mAcm−2) and high energy density (22–15 Whkg−1 at power densities ranging from 400 to 10,000 Wkg−1) in a 6 M KOH aqueous solution.

Hydrophilic/Hydrophobic Property Changes on Polyacrylonitrile/Cellulose Acetate Nanofiber Membrane

Nanofibers membrane are potential material for water filtration, and surface properties of the membrane are an important factor to avoid fouling on the membrane surface. The combination of filter material is known to influence the membrane surface properties. We investigated the mixture of polyacrylonitrile (PAN) and cellulose acetate (CA) on the nanofiber membrane by electrospinning. This blend was dissolved in dimethylformamide as feed polymer in electrospinning technique. We prepared the ratio of PAN to CA were 0:10, 4:6, 5:5, 6:4, and 10:0 in 8 wt%. All the membranes formed fiber, except 0:10 which only created a thin layer from the sprays. Contact angle measurements related to membrane surface properties were measured and resulted in 128o, 126o, and 125o for 4:6, 5:5 dan 6:4 membranes, respectively. This results indicated that all PAN/CA membranes had hydrophobic properties. The hydrophobic property was also observed by Fourier transform infrared (FTIR) spectroscopy, a sharp peak of-CH3 appeared. It is interesting while mixing two hydrophilic polymers we obtain a hydrophobic membrane.

Electrospun Coal Liquefaction Residues/Polyacrylonitrile Composite Carbon Nanofiber Nonwoven Fabrics as High-Performance Electrodes for Lithium/Potassium Batteries

Coal liquefaction residues (CLRs)-based nanofiber nonwoven fabrics are fabricated by electrospinning using the mixture of polyacrylonitrile and preasphaltene (toluene insoluble-tetrahydrofuran solu...

Hybrid Carbon Nano-Fibers with Improved Oxidation Resistance

Hybrid Carbon-Silicon Carbide (C-SiC) nano-fibers were fabricated while using a mixture of polyacrylonitrile (PAN) and silicon (Si) nanoparticles as precursors. The microstructure of the material was examined using X-ray diffraction and Raman spectroscopy as a function of processing temperature and holding time. A complete transformation of Si to SiC occurred at 1250 °C. However, for heat treatments below 1000 °C, three distinct phases, including Si, C, and SiC were present. The effect of microstructural changes, due to the heat treatment, on oxidation resistance was determined using thermogravimetric analysis (TGA). Furthermore, the char yield showed exponential growth with increasing the carbonization temperature from 850 °C to 1250 °C. The holding times at higher temperatures showed a significant increase in thermal properties because of SiC grain growth. At longer holding times, the SiC phase has the function of bothcoating and reinforcing phase. Such structural changes were related to fibers mechanical properties. The tensile strength was the highest for fiber carbonized fibers at 850 °C, while the modulus increased monotonically with increasing carbonization temperature.

Thermoelectric properties of electrospun carbon nanofibres derived from lignin

Developing sustainable and efficient thermoelectric materials is a challenge because the most common thermoelectric materials are based on rare elements such as bismuth and telluride. In this context, we have produced bio-based carbon nanofibres (CNFs) derived from mixtures of polyacrylonitrile and lignin using electrospinning. The addition of lignin (up to 70%) reduces the diameter of CNFs from 450 nm to 250 nm, increases sample flexibility, and promotes inter-fibre fusion. The crystalline structure of the CNFs was analysed by Raman spectroscopy. The electrical conductivity and the Seebeck coefficient were evaluated as function of the lignin content in the precursor and carbonised equivalents. Finally, a conversion of p-type to n-type semiconducting behaviour was achieved with a hydrazine vapour treatment. We observe a maximum p-type power factor of 9.27 μW cm−1 K−2 for CNFs carbonised at 900 °C with 70% lignin which is a 34.5-fold increase to the CNFs with 0% lignin. For the hydrazine treated samples, we observe a maximum n-type power factor of 10.2 μW cm−1 K−2 for the CNFs produced in the same way which is an 11.0-fold increase to the hydrazine-treated CNFs with 0% lignin.

Electrospun N-doped porous carbon nanofiber webs as anodes for lithium-ion batteries

Nitrogen-doped porous carbon nanofiber webs (NPCNFs) were prepared from mixtures of polyacrylonitrile and melamine byelectrospinning, followed by oxidative stabilization, carbonization and steam activation. The NPCNFs are free-standing,exhibit an interconnected non-woven nanofibrous morphology and a well-developed microporous structure, and can be used directly as anodes for lithium ion batteries without adding binder or conductive filler. The NPCNF from the mixture with a melamine/polyacrylonitrile mass ratio of 1:3 has a high specific capacity of 856 mAh·g-1 and a satisfactory rate capability. These intriguing characteristics make the NPCNFs promising anode candidates for high-performance lithium ion batteries.

Optimization of rotating-jet electrospinning process using response surface methodology

Rotating-jet electrospinning method is one of the efficient techniques for producing aligned nanofibers. This paper reports an accurate investigation on the influence of collector diameter (CD), voltage, polymer concentration (PC), and insulator length (IL) of spinneret on the degree of fiber alignment (DFA), production rate of fiber, and fiber diameter. The polymer solution was a mixture of polyacrylonitrile and N,N-dimethylformamide. The ranges of independent variables were 20–50 cm for CD, 10–22 kV for voltage, 13–19 wt% for PC, and 0.5–3 cm for IL. To minimize the number of required experiments for a complete evaluation, response surface methodology (RSM) and central composite rotatable design were applied by means of Expert Design Software. After defining the upper and lower bounds of the above independent variables in the software, 30 unique experiments were delivered. The recommended operating conditions by the software were exactly applied in the laboratory and the corresponding values for the DFA, production rate, and fiber diameter were measured. The nanofiber morphology was examined by scanning electron microscopy (SEM). By applying the least-squares method in the DX7.0.0 software, well-fitting polynomial correlations to the experimental results were obtained, and using these correlations, the influence of independent variables and responses was comprehensively studied. Finally, the best values of independent variables for optimizing the responses were determined using RSM.

Synthetic polymers blend used in the production of high activated carbon for pesticides removals from liquid phase

ABSTRACT For the activated carbon (AC) production, we used the most common industrial and consumer solid waste, namely polyethyleneterephthalate (PET), alone or blended with other synthetic polymer such polyacrylonitrile (PAN). By mixing PET, with PAN, an improvement in the yield of the AC production was found and the basic character and some textural and chemical properties were enhanced. The PET–PAN mixture was subjected to carbonisation, with a pyrolysis yield of 31.9%, between that obtained with PET (16.9%) or PAN (42.6%) separately. The AC revealed a high surface area (1400, 1230 and 1117 m2 g−1) and pore volume (0.46, 0.56 and 0.50 cm3 g−1), respectively, for PET, PAN and PET–PAN precursors. Selected ACs were successfully tested for 4-chloro-2-methylphenoxyacetic acid (MCPA) and diuron removal from the liquid phase, showing a higher adsorption capacity (1.7 and 1.2 mmol g−1, respectively, for MCPA and diuron) and good fits with the Langmuir (PET) and Freundlich equation (PAN and PET–PAN blend). With MCPA, the controlling factor to the adsorption capacity was the porous volume and the average pore size. Concerning diuron, the adsorption was controlled essentially by the external diffusion. A remarkable result is the use of different synthetic polymers wastes, as precursors for the production of carbon materials, with high potential application on the pesticides removals from the liquid phase.

Evaluation of in vivo solid phase microextraction for minimally invasive analysis of nonvolatile phytochemicals in Amazonian plants

IntroductionAlthough solid phase microextraction (SPME) has been used extensively for fingerprinting volatile compounds emitted by plants, there are very few such reports for direct insertion SPME. In this research, direct contact of SPME probes with the interstitial fluid of plants was investigated as a method for phytochemical analysis. ObjectiveMedicinal plants from the Amazon have been the source of numerous drugs used in western medicine. However, a large number of species used in traditional medicine have not been characterized chemically, partly due to the difficulty of field work. In this project, the phytochemical composition of plants from several genera was fingerprinted by combining convenient field sampling by solid phase microextraction (SPME) with laboratory analysis by LC-MS. The new method was compared with classical sampling followed by liquid extraction (LE). MethodologySPME probes were prepared by coating stainless steel wires with a mixture of polyacrylonitrile and either RP-amide or HS-F5 silica particles. Sampling was performed by inserting the microextraction probes into various tissues of living plants in their natural environment. After in vivo extraction, the probes were sealed under vacuum and refrigerated until analyzed. The probes were desorbed in mobile phase and analyzed on a Waters Acquity UPLC with triple quadrupole mass spectrometer in positive ion mode. ResultsTwenty Amazonian plant species were sampled and unique metabolomic fingerprints were obtained. In addition, quantitative analysis was performed for previously identified compounds in three species. Comparison of the fingerprints obtained by in vivo SPME with those obtained by LE showed that 27% of the chromatographic features were unique to SPME, 57% were unique to LE, and 16% were common to both methods. ConclusionIn vivo SPME caused minimal damage to the plants, was much faster than traditional liquid extraction, and provided unique fingerprints for all investigated plants. SPME revealed unique chromatographic features, undetected by traditional extraction, although it produced only half as many peaks as ethanol extraction.

Fabrication of polyacrylonitrile/lignin-based carbon nanofibers for high-power lithium ion battery anodes

Low-cost carbon nanofibers are fabricated from lignin, the second most abundant raw material in wood after cellulose and polyacrylonitrile mixture as a carbon precursor by electrospinning, followed by suitable heat treatments. As the lignin content in the precursor increases, the carbon nanofibers become thinner, as seen from scanning electron microscopy images. However, their carbon structure and electrochemical performance are found to be very similar, even though surface functional groups on carbon nanofibers are slightly different from each other. For example, in the initial charge (lithium insertion) and discharge (lithium deinsertion) process, the reversible specific capacities of the various carbon nanofibers come from different precursor ratios of lignin and polyacrylonitrile are similar. Even at a fast (7 min) charge and discharge condition, the carbon nanofibers prepared from the lignin-containing precursors show a discharge capacity of 150 mAh g−1. The lignin-based carbon nanofibers thus show promise for use in high-power lithium ion battery anodes with low price.

Centimeter-scale giant spherulites in mixtures of polar polymers and crystallizable diluents: Morphology, structure, formation and application

A series of giant spherulites at centimetre scale were effectively constructed from the mixtures of polyacrylonitrile (PAN)/dimethyl sulfone (DMSO2), although neither PAN nor DMSO2 itself forms spherical morphology during crystallization. A detailed investigation was carried out on the morphology, microstructure, and formation mechanism by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray diffraction, polarized FTIR spectroscopy, and differential scanning calorimetry. These giant spherulites constituted of PAN phase and DMSO2 crystals alternately distributed in divergent patterns. The fast crystallization of DMSO2 dominates the large growth rate and the macroscopic size, while PAN composes the skeleton of the giant spherulites. The cooperative deposition of PAN beside DMSO2 crystals originates from dipole–dipole interaction between the nitrile groups of PAN and the sulfone groups of DMSO2, accounting for the branching and splaying in the giant spherulites. These macroscopic morphologies were universally observed in other mixtures of PAN/dimethyl sulfoxide, PAN/maleic anhydride, poly(vinylidene fluoride)/DMSO2, and cellulose acetate/DMSO2. We propose that the giant spherulites can be formed by introducing suitable diluent crystallization and appropriate polymer–diluent interaction. Furthermore, this spherulitic pattern has been used as a template to direct the oriented growth of calcium carbonate based on the molecular orientation in the giant spherulite.

Kinetics and equilibrium study of phenol adsorption on nitrogen-enriched activated carbons

The influence of an enhanced amount of nitrogen functionalities in activated carbon (AC) upon the adsorption of phenol from water was studied. The ACs were prepared from polyacrylonitrile (PAN) and a mixture of PAN and coal-tar pitch (CTP) by a process of carbonization followed by activation with steam. Because AC produced from a mixture of polyethylene terephthalate (PET) and CTP (1:1w/w) has a high capacity to adsorb phenol, it was used as a reference of AC without nitrogen functionalities at the surface. All the ACs were characterized by similar porous textures but different nitrogen contents, in the range of 0.75–7.42wt%. These features imply differences in the basicity of the carbon surface. The contribution of pyridinic nitrogen amounted to 26–34% of the total nitrogen content in the nitrogen-enriched ACs (N-ACs). The phenol adsorption measurements were carried out in static conditions at ambient temperature. The pseudo-second order kinetics and Langmuir models were found to fit the experimental data very well. For N-ACs the adsorption was characterized by a very high affinity of phenol towards the carbon surface. However, an enhanced nitrogen content improved the adsorption capacity of the AC only slightly. The adsorption of phenol occurred mainly in micropores smaller than 1.4nm, where the pore filling mechanism prevails. The contribution of pyridinic nitrogen to phenol adsorption in wider micropores is discussed in details.

Cobalt and tin oxalates and PAN mixture as a new electrode material for lithium ion batteries

A mixture between cobalt oxalate, tin oxalate and dispersed polyacrylonitrile (PAN) molecules has been used as a new electrode active material for lithium ion batteries. The electrode shows good capacity retention in the case that the imposed potential limit is below 2.0 V. The mechanism of the reaction with lithium was studied by using XRD and 119Sn Mössbauer spectroscopy. The electrode materials become irreversibly amorphous at the beginning of the reaction, when tin oxalate is decomposed and Sn(IV) is detected. Then, the metallic ions are reduced and amorphous tin–cobalt phases are formed. Finally, previously unknown LiCoSn phases are reversibly formed near 0.0 V. The oxalate groups and the PAN form an electrochemically inert matrix. Due to the matrix, the aggregation of the amorphous particles into crystalline particles upon cycling is avoided. The extraction of lithium at the potential values near 2.0 V yields to tin–oxygen interactions and this feature disturbs the matrix and yields to capacity fade.

Electric Conductivity and Thermorheology Properties of Polyacrylonitrile/Nylon6 Composites Filled with Carbon Black

The electric conductive polymer composites, which were made of carbon black particles through dispersing in mixtures of polyacrylonitrile (PAN)/nylon6 (PA6), were prepared in a Haake Thermo-mixer. The morphology, conductivity, thermorheology properties and their relationships were studied. Microphase separations and partial miscibility were confirmed when a small mass of PAN was introduced into PA6/CB composites. A part of CB particles could be attracted by PAN, and transferred to the interface of PA6 and PAN, leading to an increase of electric conductivity. Results also indicated that the introduction of PAN in the PA6/CB composite improved its elastic modulus as well as the thermal stability of its electric conductivity.