Polyacrylonitrile Solution Research Articles

Tailoring the phase evolution of molybdenum-based nanocrystals in carbon nanofibers for enhanced performance of lithium-ion batteries

The design and development of flexible and free-standing molybdenum (Mo)-based composite nanomaterials have aroused intensive attention in the fields of electrocatalysis, energy storage, and wearable electronics. In this study, novel nanocomposite membranes constructed with Mo-based compound nanocrystals loaded carbon nanofibers (CNFs) were successfully generated by a combination of electrospinning molybdenum acetylacetone-contained polyacrylonitrile (PAN) solution and subsequent annealing process from 580 to 900 ºC. The relationship and mechanisms between the generation of different types of Mo-based nanocrystals and the annealing temperature were systematically explored. It was found that MoO2 nanocrystals were formed when the annealing temperature was 580 °C. With the temperature increasing, Mo2N nanocrystals began to form due to the reaction between the formed MoO2 and the N atoms in the PAN macromolecules. At higher temperature like 669 °C, Mo2C nanocrystals started to form due to the reaction between Mo2N and C atoms in the carbonized PAN macromolecules, and single-phase Mo2C nanocrystals were produced in CNFs at 900 ºC. Then, a series of flexible CNF-based nanocomposite membranes embedded with various different types of Mo-based compound nanocrystals were generated by effectively controlling the annealing temperature, which were all utilized as anodes for the construction of lithium-ion batteries. Electrochemical measurements showed that the anode materials annealed at 600 oC possessed the highest specific capacity, which were due to the high theoretical specific capacity of MoO2 and significantly improved conductivity of Mo2N. Moreover, all the as-developed electrodes exhibited excellent cycling stability during the charge-discharge process. The present study provides a facile and broadly-applicable routine to tailor the component, structure, and electrochemical properties of Mo-based nanocrystals in CNFs, which finds huge application potential in the fields of various flexible electrochemical devices.

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.

Silica-Filled Polyacrylonitrile Solutions: Rheology, Morphology, Coagulation, and Fiber Spinning.

The fumed silica influence on the morphology, coagulation processes, and rheological properties of suspensions in dimethyl sulfoxide (DMSO) and polyacrylonitrile (PAN)-DMSO solutions has been studied for the production of composite films and fibers. It has been shown that silica-DMSO concentrated suspensions (24 wt%) form a weak gel with a yield point of about 200 Pa. At concentrations of ~5 wt% and above the dispersions, depending on the shear stress, are pseudoplastic or dilatant liquids. It has been found that the silica addition method into a PAN solution has a significant impact on the aggregates dispersibility and the rheological behavior of the obtained systems. A thixotropy appearance and a sharp increase in the relaxation time were observed for PAN solutions at a SiO2 content of more than 3-5 wt%, which indicates the formation of structures with a gel-like rheological behavior. Upon reaching the critical stress their destruction takes place and the system starts to behave like a viscoelastic liquid. Two spinning methods have been used for preparing fibers: standard wet and mechanotropic. By the mechanotropic method it is possible to achieve a higher draw ratio at spinning and to obtain fibers with better mechanical properties. It is possible to spin fibers from PAN solutions containing up to 15 wt% of silica per polymer with a tensile strength up to 600 MPa.

Effect of swelling and deswelling on the elasticity of polyacrylonitrile gels prepared by freezing and thawing techniques

. The repeating cycle of freezing and thawing brings about a physical gelation for the solutions of polyacrylonitrile (PAN) in N, N-dimethylacetamide (DMA) for appropriate concentrations. It was revealed from wide-angle-X-ray diffraction that the PAN molecules were “cross-linked” by the crystallization to form a network through the freezing and thawing steps. The profiles of small-angle-X-ray scattering for the gels showed the excess scattering from the network structure formed through gelation, which could not be observed for the pure PAN solution. A reversible swelling and shrinking were observable for the PAN gel as a function of the relative content of DMA and benzene by varying the mixing ratio. The degree of swelling measured by weight, for the swollen and shrunk gels, was in a range from 0.7 to 8. A scaling relation appeared for the gel swelling between the PAN volume fraction (ϕ) and the shear moduli (G) which was measured by tensile and indentation tests, as G = G s ×(ϕ)s; G s= 1200kPa and s = 2.26 ± 0.23. A discussion is given on the value of the scaling exponent, s, on the basis of the conformation of flexible chain molecules in solution and the analogy in the microscopic and macroscopic properties between semidilute polymer solutions and gels.

Highly N-doped and flexible carbon nanofiber membrane as cathode host for Li-Se batteries

Se as an active material attracts tremendous attention because of its high volumetric capacity and better conductivity than S for rechargeable batteries. Herein, a carbon nanofiber membrane (PM-CNF) is designed and prepared as free-standing Se host by electrospinning the solution of polyacrylonitrile (PAN) and poly(styrenesulfonic acid)-melamine salt, followed by carbonization and activation process. PM-CNF shows super flexibility and high N-doping level of 8.92 % (pyrrolic-N: 2.15 % and pyridinic-N: 3.07 %), which is beneficial for ions diffusion and electrons transformation. The free-standing PM-CNF/Se cathode delivers a high reversible capacity of 570 mAh g−1 at 0.5 C, superior rate capacity of 375 mAh g−1 at 8 C, and stabile cycling over 1800 cycles. The excellent electrochemical performance can be ascribed to high Li-ion diffusion coefficient (2.99 × 10−9 cm2 s−1) and capacitance-contributed ratio (77.1 % at 0.1 mV s−1). The analysis of the charge/discharge process reveals that no polyselenide intermediates are observed during the first cycling process and thus the inhibited shuttle effect of polyselenides over cycling, which primarily contributes to the long cycling stability.

The dual effects of non-solvent on the sol-gel transition of polyacrylonitrile solution: The promotion in thermodynamics and hindrance in kinetics

The effects of non-solvent on the sol-gel transition of polyacrylonitrile (PAN) solution were investigated in thermodynamics and kinetics by the means of rheology method. The facilitating effects of non-solvent in thermodynamics was illustrated by the variety of viscoelasticity and gel transition temperature (Tgel). With the addition of non-solvent, the mobility of PAN molecular chains are limited due to its increased entanglement. As a result, the PAN solution with higher non-solvent content has lower conformation entropy to satisfy the occurrence of sol-gel transition at higher temperature. It means that less thermodynamic driving is demanded. The kinetical characteristics of PAN solution with different non-solvent content in sol-gel transition process were also discussed. The kinetic hindrance of non-solvent was proved by the gradually stronger time-dependence of loss tangent with the addition of non-solvent during sol-gel transition. This apparent extending of relaxation time is resulted from the more restriction of the mobility of PAN molecules. The gelation activation energy (Egel) was calculated according to Ozawa method. The results also indicated that the activity of PAN molecules in this transition became weaken with the addition of non-solvent since a relative tight connection between PAN molecules was there. Therefore, the formation of physical junction points for sol-gel transition was hindered due to the decreasing of the mobility of self-adjustment for PAN molecules. This is the fundamental reason for the kinetic hindrance role of non-solvent.

Rheology and molecular interactions in polyacrylonitrile solutions: Role of a solvent

We examined the rheological properties of polyacrylonitrile (PAN) solutions in seven solvents over a wide range of shear rates. These solutions were characterized using the Hansen solubility parameter. The viscosity of these dilute solutions was primarily determined by this parameter. However, above the crossover point (at c[η] > 0.7) not only viscosity but also nature of the solvents was found to be an important factor. At high polymer concentrations, certain solutions showed gelation tendency.This study aims to determine a correlation between the rheological properties of the solutions and the affinity of the solvent with PAN. These correlations are present for an intrinsic viscosity (or the Huggins constant), a second virial coefficient, and solubility parameter. However, in certain cases, experimental points do not correspond to general dependence. This is also observed for these solutions when presenting the data of viscoelastic measurements in G′–G″ coordinates: certain points deviate from the general dependence.A detailed infrared spectroscopy analysis has been used for examining these experimental results. It has been shown the water presence in the solvents and polymer solutions even than anhydrous solvents were used. Water presence tend to a solvent–water associate formation in the solutions. The solubility of PAN in these solvents and the gelation tendency depends on the polymer concentration, in addition to the structure and stability of the polymer–water associates. The experimental results obtained and the reported correlation made it possible to develop a subsequence of solvents used as per their affinity with PAN. The charactristics of dilute solutions were compared with the rheological properties of moderately concentrated solution.

Silicon nanocrystals-embedded carbon nanofibers from hybrid polyacrylonitrile – TEOS precursor as high-performance lithium-ion battery anodes

The high capacity of silicon (Si) for lithium incorporation makes it a promising anode material for lithium-ion batteries; however, pulverization of Si due to huge volume changes during lithiation/delithiation leads to significant capacity loss during cycling. To address challenges in low cyclability, nanostructured Si in carbon nanocomposites offers an attractive solution. In this study, we report an efficient method for the synthesis of a nanocomposite containing Si nanoparticles homogeneously embedded in an electrically conductive carbon nanofiber (CNF) network. Electrospinning of polyacrylonitrile (PAN) solution containing hydrolyzed tetraethyoxysilane (TEOS), as a Si precursor, and subsequent carbonization of hybrid nanofibers yielded a composite of SiO2 ultrafine nano-domains in the carbon network (C-SiO2). Low temperature molten salt-assisted aluminothermic reduction of C-SiO2 nanofibers allowed us to produce a C-Si/SiOx nanocomposite without forming detrimental SiC, which is thermodynamically favorable at high temperatures in a system with a high interfacial surface area between the carbon and SiO2 phases. The nanocomposite C-Si/SiOx anodes showed a reversible capacity of 860 mAh g−1 at a current rate of 200 mA g−1, retaining a capacity of 680 mAh g−1 after 100 cycles. In addition, the nanocomposite anodes delivered a reversible capacity of 569 mAh g−1 at a current rate of 400 mA g−1 while maintaining 95% of maximum capacity after subsequent 100 cycles. This study demonstrates the capability of designing nanocomposite anodes from reaction precursors combined with low-temperature aluminothermic reduction to produce a capacity-retaining anode composite of Si nanocrystals uniformly dispersed in the carbon matrix.

Fabrication of Polyacrylonitrile UF Membranes by VIPS Method with Acetone as Co-Solvent.

For the first time, a systematic study was carried out of the replacement of the low-volatility solvents N-methyl-2-pyrrolidone (NMP) or dimethylsulfoxide (DMSO) with the high-volatility solvent acetone in the casting solution of polyacrylonitrile (PAN). The effect of acetone’s presence in the casting solution on the performance of ultrafiltration membranes fabricated via vapor-induced phase separation (VIPS) was investigated. It was possible to replace 40% of NMP and 50% of DMSO with acetone, which resulted in the reduction of the casting solution viscosity from 70.6 down to 41.3 Pa∙s (20% PAN, NMP), and from 68.3 down to 20.6 Pa∙s (20% PAN, DMSO). It was found that 20 min of exposure to water vapor (relative humidity—85%) was sufficient to govern the phase separation, which was mainly induced by the water vapor. Regardless of the casting solution composition (15 or 20% PAN; DMSO or NMP), all membranes formed via VIPS possessed a sponge-like porous structure. The addition of acetone to the casting solution allowed the reduction of the transport pore size from 35–48 down to 8.5–25.6, depending on the casting solution composition. By varying the acetone content at constant polymer concentration, it was possible to decrease the molecular weight cut-off (MWCO) from 69 to 10 kg/mol. Membranes prepared from 20% PAN solution in an acetone/DMSO mixture had the lowest MWCO of 10 kg/mol with a water permeance of 5.1 L/(m2·h·bar).

Wet-Spun Side-by-Side Electrically Conductive Composite Fibers

Electrically conductive fibers play an important role in smart electronic textiles to connect the key components of a smart system, convey energy, and sometimes serve as a sensor. Polymers for traditional fibers are insulating. Incorporating conductive fillers to produce blend fibers is a common method to produce conductive flexible fibers. In the filler/polymer blend system, increasing the filler load enhances fiber conductivity but that adversely affects fiber processability and deteriorates the fiber mechanical performance. In this study, an innovative wet spinning technique was used to manufacture heterostructured polyacrylonitrile (PAN) and polyaniline (PANI) conductive fibers. A PAN/PANI blend solution was co-spun with a neat PAN solution to produce side-by-side (SBS) fibers. The results showed that, by employing the SBS technique, PAN/PANI solutions of high PANI load that were not spinnable by themselves could be co-spun into SBS fibers with neat PAN. The SBS fibers maintained a similar level of conductivity to the fibers produced from the PAN/PANI blend solution only, although the overall PANI load in the SBS fiber was much lower. Additionally, the SBS fibers exhibited superior mechanical performance with the neat PAN serving as a substrate. The study demonstrated a manufacturing technique to produce conductive polymer composite fibers for e-textiles.

Eco-friendly WBF/PAN nanofiber composite membrane for efficient separation various surfactant-stabilized oil-in-water emulsions

The development of superhydrophilic and underwater superoleophobic membranes has brought promising prospect for solving severe environmental pollution caused by oily wastewater. However, most of such membranes cannot be widely used in practical oily wastewater treatment due to their harmfulness to environment and expensive price. Herein, an eco-friendly and economical nanofiber composite membrane was designed and fabricated by electrospinning strategy. The mixed solutions of waste bamboo fiber (WBF) and polyacrylonitrile (PAN) particles were electrospun on stainless steel mesh. It was found that the WBF/PAN nanofiber composite membrane possessed excellent underwater superoleophobic performance and ultralow oil adhesion ability. Particularly, the as-prepared membrane can selectively separate water from various surfactant-stabilized oil-in-water emulsions including high viscosity crude oil-in-water emulsions with high separation efficiency (> 99.3%) driven by only gravity. Furthermore, the WBF/PAN membrane maintained exceptional underwater superoleophobicity in the harsh environments (3.5 wt % NaCl, 0.1 M HCl, 0.1 M NaOH) even after being immersed into a corrosive solution for 24 h. Meanwhile, the membrane also showed excellent chemical stability after 10 separation cycles and robust mechanical stability after 50 times of abrasion test. More importantly, the eco-friendly and low-cost WBF/PAN nanofiber composite membrane conforms to the environmental protection concept of waste recycling and green sustainable development, which would be a competitive alternative for crude oil leakage and oily wastewater purification.

Mercapto-decorated Zn-based metal-organic framework embedded nanofibrous membrane for oxo-anions treatment in aqueous solution

Metal-organic frameworks (MOFs) and nanofibrous MOF-embedded membranes (NMOM) have drawn significant attention in recent times towards wastewater treatment. We report the fabrication of nanofibrous membrane (NMOM) embedded with a newly designed and developed Zn(II)-MOF {[Zn(L)(dmbpy)]n using ligands 1-(4-carboxyphenyl)-5-mercapto-1H-tetrazole (L) and 5,5′-dimethyl-2,2′-bipyridine (dmbpy)} bearing free mercapto and methyl groups on its surface. While the methyl group introduces hydrophobicity to the MOF, resulting in its good water stability, the free peripheral mercapto-functionality acts as interacting site for the foreign substrates. The NMOM was prepared by mixing Zn-MOF into a polyacrylonitrile (PAN) solution and extruding composite nanofibre via electrospinning technique. Both, Zn-MOF and Zn-MOF-based NMOM were used as selective adsorbents for the treatment of oxo-anion contaminated water. With these adsorbents, the selective adsorption, as well as separation of permanganate (MnO4−) ions from the mixture of permanganate (MnO4−) and dichromate (Cr2O72−), was achieved. The synthesized Zn-MOF was also utilized for the photocatalytic reduction of Cr(VI) to less toxic Cr(III) ions under UV light irradiation with good efficiency. The double faceted nature of Zn-MOF was further explored in a one-pot sequential selective adsorption of MnO4− ions from an aqueous mixture of both MnO4− and Cr2O72−, followed by photocatalytic reduction of Cr2O72− ions. Further, the developed NMOM was examined for a large-scale adsorption process. The pristine Zn-MOF showed a maximum adsorption capacity of 937.32 mg/g for the adsorption of MnO4− ions, whereas NMOM showed a higher adsorption capacity of 1077.56 mg/g. The enhanced hydrophobicity and surface area can be attributed to the increased adsorption capacity of the membrane. Thus, induced hydrophobicity of the membrane coupled with hydrolytic stable Zn-MOF showcases the potential of NMOM in treatment of oxo-anion contaminated wastewater.

High molecular weight improves microstructure and mechanical properties of polyacrylonitrile based carbon fibre precursor

This work presents the influence of polyacrylonitrile (PAN) molecular weight (MW) on the microstructure and macrostructure of PAN based carbon fibre precursor while fixing the PAN solution viscosity to achieve identical spinning. The impact of molecular weight on macrostructure was reported by cross sectional shape, fibre density, shear viscosity, mechanical properties and microstructure evolution was reported by void size, shape, and crystallinity. The study was carried out in the PAN MW range between 141 and 503 Kgmol-1. The PAN fibre strength improvement of 5–9 cNdtex−1 with increasing PAN MW is caused by the drop in PAN fibril size from 24 nm at 141 Kgmol-1 to 18 nm at 503 Kgmol-1. The improvement in PAN fibre density from 1.14 to 1.18 gcm−3 with increasing PAN MW is caused by the improved microstructure alignment from 15o to 8o and is the driving force for increased mechanical modulus from 115 to 150 cNdtex−1.

Flexible and freestanding manganese/iron oxide carbon nanofibers for supercapacitor electrodes

In this study, freestanding carbon nanofibers embedded with bimetallic manganese-iron oxide are fabricated for flexible supercapacitor applications via electrospinning. A polyacrylonitrile solution is used as the carbon source, and poly(methyl methacrylate) functions as a sacrificial template to produce microporous carbon nanofibers. The concentrations of manganese acetate and iron acetylacetonate are varied to determine the fabrication conditions for maximal electrochemical performance. The optimized supercapacitor cell exhibits a capacitance of 467 F g−1 at a current density of 1 A g−1 and a capacitance retention of 94% at the end of N = 10,000 cycles. The higher mechanical durability of the electrode is confirmed by the absence of electrochemical deterioration at the end of performing 500 bending cycles. Overall, the sample comprising carbon nanofibers, in which the optimal amount of manganese-iron oxide is embedded, has the required pseudocapacitive characteristics and is an interesting choice for high-energy-storage supercapacitor electrodes.

Synthesis of 1D Bi2O3 nanostructures from hybrid electrospun fibrous mats and their morphology, structure, optical and electrical properties

The aim of this study was to produce Bi2O3 nanowires using a combination of sol–gel process and electrospinning methods and a solution based on a 13% solution of polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF) containing 1.5 g of bismuth (III) nitrate pentahydrate (Bi(NO3)3·5H2O). The obtained fibrous composite mats were dried at room temperature for 24 h followed by the calcination process in air at two different temperatures of 400 °C and 600 °C. Analysis of the morphology of the fabricated Bi2O3 nanomaterials based on TEM images showed that the obtained ceramic structures could be classified as one-dimensional Bi2O3 nanostructures, with the sizes of the presented structures being 260 nm, 125 nm and 200 nm for diameter, and 5.5μm , 2 μm and 2.125 μm for length, respectively. Moreover, further analysis of the morphology of the obtained Bi2O3 nanostructures with the use of SEM showed that their diameters ranged from 150 to 500 nm when a calcination temperature of 400 °C was employed, while Bi2O3 nanowires with diameters ranging from 150 to 450 nm were obtained at 600 °C. To analyse the chemical composition and oscillatory transitions of atoms vibrating between the oscillatory levels in the molecules of the produced 1D nanostructures, and to determine the functional groups existing therein, EDX and FTIR were used. Transmission peaks in FTIR spectra recorded for wave numbers in the range of 400–4000 cm-1 were due to the presence of vibrations in Bi–O bonds, which correspond to the structure of Bi2O3. In addition, a detailed analysis of optical constants of one-dimensional Bi2O3 nanostructures fabricated using a combination of sol–gel process, electrospinning and calcination methods has been presented in this paper for the first time. Optical studies based on the recorded UV–Vis spectra showed that the obtained Bi2O3 nanowires were characterized by sharp absorption edges of radiation in the near-ultraviolet range, with sharp absorption edges falling at wavelengths of 400 nm, regardless of the applied temperature during the calcination process. The study of optical constants showed that the Bi2O3 nanostructures exhibited refractive indices of 2.62 and 2.53 at temperatures of 400 °C and 600 °C, respectively, while dielectric constants were 6.87 and 6.42, respectively. The final stage of the study was the determination of the width of energy gaps of the produced bismuth oxide nanostructures, which were found to be 3.19 and 2.97 eV, respectively. The presented results of morphology and optical properties of the obtained one-dimensional Bi2O3 semiconductor nanostructures indicate a potential possibility to apply this type of materials for the production of a new generation of dye-sensitized photovoltaic cells (DSSCs).

Designing a novel 3D nanofibrous scaffold based on nanoalloy AuAg NPs (AuAg@ PAN NFs) for osteogenic differentiation of human adipose derived mesenchymal stem cells (hADMSCs)

The present study applied a new strategy to modify the surface properties of a polymeric matrix with the aim of forming an osteogenic scaffold with a stable structure and better osteo-inductive potential. To this purpose, we applied appropriate electrospinning conditions to design the nanofibrous scaffold of AuAg@ polyacrylonitrile (P) nanofibers (AAP NFs), based on incorporation of the AuAg nanoparticles (AA NPs) which were prepared by ultrasound irradiation, with an electrospinning solution of polyacrylonitrile. This study has combined structural properties (crystalline, morphology, roughness) and surficial properties (mechanical and wettability) of fibrous samples, in order to elucidate the role of surface modification and formation of a stable fibrous scaffold in osteogenic differentiation. The XRD and FT-IR findings showed that the all crystalline properties of hexagonal system and the intensity of related IR-bands were changed. This modification caused the removal a smooth outer fiber layer of the P NFs and the creation of chunky shapes of AA NPs on the surface of the corresponding fibrous sample, which were confirmed by enhancing Ra values. The nanofibrous scaffold with 2% AA NPs disclosed the best mechanical performance and wettability. Finally, we showed that AAP NFs, not only improved cell adhesion, but also induced osteogenic differentiation of human adipose derived mesenchymal stem cells(hADMSCs) more efficiently than P NFs and tissue culture plates (TCPs).

The effect of liquid crystalline graphene oxide compared with non-liquid crystalline graphene oxide on the rheological properties of polyacrylonitrile solution

Abstract In this article, polyacrylonitrile (PAN) and two kinds of graphene oxide (GO) with different structural properties are blended in dimethyl sulfoxide (DMSO) according to a certain ratio to prepare stable-spinning solution. One kind of GO is purchased, and we call it GO1. The other is a kind of self-made GO with liquid crystal property in solution, which is called GO2. The effects of two kinds of GO on the rheological properties of PAN/GO spinning solution (15 wt%) were studied. The results show that the viscous activation energy of the liquid crystal GO2/PAN blend solution is significantly higher than that of the nonliquid crystal GO1/PAN blend solution. Moreover, the liquid crystal system is more obviously affected by temperature. The structural viscosity index of the liquid crystalline GO2/PAN solution is obviously lower than that of the GO1/PAN solution. It indicates that the existence of liquid crystallinity is beneficial to the spinning of the solution. In the low-frequency region, the addition of GO1 makes the solution more elastic, and the addition of GO2 makes the solution more viscous.

Zeolitic imidazolate framework (ZIF-8)/polyacrylonitrile derived millimeter-sized hierarchical porous carbon beads for peroxymonosulfate catalysis

Well dispersed nanocatalysts on porous substrate with macroscopic morphology are highly desired for the application of heterogeneous catalysis. Traditional fabrication process suffers from multiple steps for controlling the structure on nanocatalysts and matrix or both. Herein, we report a facile strategy for the synthesis of millimeter-sized hierarchical porous carbon beads (HPCBs) which containing well dispersed hollow-nano carbon boxes for peroxymonosulfate catalysis. Specially, the precursors of HPCBs were prepared by phase inversion method, which involving introduction of zeolitic imidazolate framework (ZIF-8) nanocubes into polyacrylonitrile (PAN) solutions followed by solidification of the mixture. After pyrolysis, nitrogen doped and hierarchical porous HPCBs with diameter of about 1.2 mm were obtained. The merits of our synthesis strategy lie in that synchronizes the hollow microstructure evolution with the shaping of ZIF-8 nanocubes into millimeter scale beads. Attribute to its special structure feature and the appropriate chemical composition, the resultant millimeter-sized HPCBs exhibit enhanced catalytic performance by activation of peroxymonosulfate (PMS) for tetracycline degradation. The degradation efficiency of TC is up to 85.1% within 120 min, which is 18% higher than that of ZIF8-Solid/PAN carbon bead (SPCBs). In addition, the possible decomposition pathways, main reactive oxygen species, and reasonable enhanced mechanism for the HPCBs/PMS system are systematically investigated by quenching experiments, electron paramagnetic resonance (EPR) and liquid chromatography-mass spectrometry (LC-MS). This work addresses the issue of easy aggregation and recycling of carbon materials in industrial productions and extends the prospects of carbon materials in engineering applications.

Effect of magnetic lens on the electrospinning whipping instability, fiber diameter and its distribution

Electrospinning is an efficient and straightforward method for producing thin fibers from various materials. Although such thin fibers have diverse potential applications, the remaining problems with electrospinning are the whipping instability (also known as bending instability) of electrically charged liquid jets of polymer nanofibers and uneven fiber diameter distribution. In this study, we report a novel magnetic lens electrospinning system and discuss the principle of reducing the fiber diameter and width of the whipping circle in this electrospinning process. The effects of three types of electrospinning devices, needle-to-plate, needle-exciting coil-to-plate, and needle-magnetic lens-to-plate types, were studied through numerical simulation to analyze the electrospinning fiber collection state. For the 12 wt% polyacrylonitrile solution, when the applied voltage was 14–20 kV, the feed rate was 0.4–0.7 ml/h, and the current applied to the excitation coil or magnetic lens was 1 A, the experimental results demonstrated that, compared with needle-to-plate-type and needle-exciting coil-to-plate-type electrospinning, needle-magnetic lens-to-plate-type electrospinning produced smaller whipping circles with thinner and more uniform fibers.

Production of fibers based on polyacrylonitrile with magnetite nanoparticles

The paper presents the results of experiments on the production of composite fibers based on polyacrylonitrile (PAN) and magnetite. For this, magnetite nanoparticles were synthesized by the method of chemical condensation from iron (III) chloride solutions with a concentration of 0.32 mol/l and iron sulfate with a concentration of 0.2 mol/l by gradually adding a 25 % aqueous ammonia solution. It was shown that a simple deposition method can be used to synthesize homogeneous nanoparticles of Fe3O4 magnetite with a particle size of 8–25 nm. This is confirmed by the results of X-ray phase analysis and transmission electron microscopy. Magnetite nanoparticles were then used to obtain PAN/Fe3O4 composite fibers by adding magnetite in a 7 wt.% PAN solution in dimethylformamide. Fibers were obtained from the PAN/Fe3O4 suspension in dimethylformamide by electrospinning. Scanning electron microscopy showed that magnetite nanoparticles are uniformly distributed throughout the fiber surface, and the fiber size is 288–658 nm. The comparison of PAN fibers without the magnetite additive and PAN/Fe3O4 fibers showed that the addition of magnetite leads to a decrease in the fiber diameter at the same polymer concentrations and electrospinning conditions. XRD and elemental analysis of PAN/Fe3O4 fibers showed that magnetite particles in the fibers did not change their chemical composition and represent single-phase magnetite in a polymer matrix. The results obtained in the studies showed the possibility of obtaining composite fibers based on magnetite by the electrospinning method. Resulting composite fibers may be useful in practical scientific and engineering applications.