Optimization of Electron Transport Pathway: A Novel Strategy to Solve the Photocorrosion of Ag-Based Photocatalysts

Although Ag-containing photocatalysts exhibit excellent photocatalytic ability, they present great challenges owing to their photocorrosion and ease of reduction. Herein, an electron acceptor platform of Ag2O/La(OH)3/polyacrylonitrile (PAN) fiber was constructed using a heterojunction strategy and electrospinning technology to develop a novel photocatalytic membrane with a redesigned electron transport pathway. Computational and experimental results demonstrate that the optimized electron transport pathway included intercrystal electron transfer induced by the La-O bond between Ag2O and La(OH)3 as well as electron transfer between the catalyst crystal and electrophilic PAN membrane interface. In addition, the photocatalytic performance of the Ag2O/La(OH)3 membrane for tetracycline (TC) removal was still above 97% after five photocatalytic reaction cycles. Furthermore, the carrier life was greatly extended. Mechanistic study revealed that photogenerated holes on the Ag2O/La(OH)3 membrane were the main reactive species in TC degradation. Overall, this study proposes a novel electron transport pathway strategy that effectively solves the problems of photocatalyst photocorrosion and structural instability.

Utilizing Novel Lignocellulosic Material from Hart's-Tongue Fern (Asplenium scolopendrium) Leaves for Crystal Violet Adsorption: Characterization, Application, and Optimization

In this work, a new lignocellulosic adsorbent was obtained and tested for crystal violet dye removal from water. The material was obtained from hart's-tongue fern (Asplenium scolopendrium) leaves after minimal processing, without chemical or thermal treatment. The surface of the material was characterized using a variety of techniques, including FTIR, SEM, and color analysis. The effect of various factors on the adsorption capacity was then investigated and discussed. The kinetic and equilibrium studies showed that the general-order kinetic model and the Sips isotherm are the most suitable to describe the adsorption process. The equilibrium time was reached after 20 min and the maximum calculated value of the adsorption capacity was 224.2 (mg g-1). The determined values for the thermodynamic parameters indicated physical adsorption as the main mechanism involved in the process. The Taguchi method was used to optimize the adsorption conditions and identify the most influential controllable factor, which was pH. ANOVA (general linear model) was used to calculate the percentage contribution of each controllable factor to dye removal efficiency. Analysis of all the results shows that hart's-tongue fern (Asplenium scolopendrium) leaves are a very inexpensive, readily available, and effective adsorbent for removing crystal violet dye from aqueous solutions.

Electrospun Nanofibers from Waste Polyvinyl Chloride Loaded Silver and Titanium Dioxide for Water Treatment Applications

The electrospun nanofiber membrane from polyvinyl chloride (PVC) waste for water treatment applications has been successfully produced. The PVC precursor solution was prepared by dissolving the PVC waste in DMAc solvent, and a centrifuge was used to separate undissolved materials from the precursor solution. Ag and TiO₂ were added to the precursor solution before the electrospinning process. We studied the fabricated PVC membranes using SEM, EDS, XRF, XRD, and FTIR to study the fiber and membrane properties. The SEM images depicted that Ag and TiO₂ addition has changed the morphology and size of fibers. The EDS images and XRF spectra confirmed the presence of Ag and TiO₂ on the nanofiber membrane. The XRD spectra showed the amorphous structure of all membranes. The FTIR result indicated that the solvent completely evaporated throughout the spinning process. The fabricated PVC@Ag/TiO₂ nanofiber membrane showed the photocatalytic degradation of dyes under visible light. The filtration test on the membrane PVC and PVC@Ag/TiO₂ depicted that the presence of Ag and TiO₂ affected the flux and separation factor of the membrane.

Preparation of a Low-Protein-Fouling and High-Protein-Retention Membrane via Novel Pre-Hydrolysis Treatment of Polyacrylonitrile (PAN)

The attainment of high-protein-retention and low-protein-fouling membranes is crucial for industries that necessitate protein production or separation process. The present study aimed to develop a novel method for preparing polyacrylonitrile (PAN) membranes possessing a highly hydrophilic and negatively charged surface as well as interior structure. The method involved a pre-hydrolysis treatment during the preparation of the PAN dope solution, followed by phase inversion in an alkaline solution. Chemical and material characterization of the dopes and membranes uncovered that the cyclized PAN structure served as a reaction intermediate that facilitated strong hydrolysis effect during phase inversion and homogeneously formed carboxyl groups in the membrane's interior structure. The resulting membrane showed a highly hydrophilic surface with a contact angle of 12.4° and demonstrated less than 21% flux decay and more than 95% flux recovery during multi-cycle filtration of bovine serum albumin (BSA) solution, with a high protein rejection rate of 96%. This study offers a facile and effective alternative for preparing PAN membranes with enhanced antifouling and protein-retention properties.

Synthesis of Electrospun PAN/TiO2/Ag Nanofibers Membrane As Potential Air Filtration Media with Photocatalytic Activity

The PAN/TiO2/Ag nanofibers membrane for air filtration media was successfully synthesized with electrospinning method. The morphology, size, and element percentage of the nanofiber were characterized by a scanning electron microscopy-energy dispersive spectroscopy, while X-ray fluorescence and FTIR were used to observe the chemical composition. The water contact angle and UV-vis absorption were measured for physical properties. Performance for air filtration media was measured by pressure drop, efficiency, and quality factor test. TiO2 and Ag have been successfully deposited in nonuniform 570 nm PAN/TiO2/Ag nanofibers. The nanofiber membrane had hydrophilic surface after TiO2 and Ag addition with a water contact angle of 34.58°. UV-vis data showed the shifting of absorbance and band gap energy of nanofibers membrane to visible light from 3.8 to 1.8 eV. The 60 min spun PAN/TiO2/Ag nanofibers membrane had a 96.9% efficiency of PM2.5, comparable to results reported in previous studies. These properties were suitable to be applied on air filtration media with photocatalytic activity for self-cleaning performance.

Tailoring the Stabilization and Pyrolysis Processes of Carbon Molecular Sieve Membrane Derived from Polyacrylonitrile for Ethylene/Ethane Separation

For ethylene/ethane separation, a CMS (carbon molecular sieve) membrane was developed with a PAN (polyacrylonitrile) polymer precursor on an alumina support. To provide an excellent thermal property to PAN precursor prior to the pyrolysis, the stabilization as a pre-treatment process was carried out. Tuning the stabilization condition was very important to successfully preparing the CMS membrane derived from the PAN precursor. The stabilization and pyrolysis processes for the PAN precursor were finely tuned, and optimized in terms of stabilization temperature and time, as well as pyrolysis temperature, heating rate, and soaking time. The PAN stabilized at >250 °C showed improved thermal stability and carbon yield. The CMS membrane derived from stabilized PAN showed reasonable separation performance for ethylene permeance (0.71 GPU) and ethylene/ethane selectivity (7.62), respectively. Increasing the pyrolysis temperature and soaking time gave rise to an increase in the gas permeance, and a reduction in the membrane selectivity. This trend was opposite to that for the CMS membranes derived from other polymer precursors. The optimized separation performance (ethylene permeance of 2.97 GPU and ethylene/ethane selectivity of 7.25) could be achieved at the pyrolysis temperature of 650 °C with a soaking time of 1 h. The separation performance of the CMS membrane derived from the PAN precursor was comparable to that of other polymer precursors, and surpassed them regarding the upper bound trade off.

Solvation and Ion-Pairing Effects of Choline Acetate Electrolyte in Protic and Aprotic Solvents Studied by NMR Titrations

Choline-based electrolytes have been proposed as environmentally friendly and low-cost alternatives for secondary zinc air batteries. Choline acetate [Ch]+ [OAc]- in protic (D2 O) and aprotic (DMSO-d6 ) solvents has been studied by means of concentration-dependent 1 H NMR, viscosity, and density measurements. The viscosities have been calculated on the basis of the Jones-Dole equation and showed that the dominant contribution originates from short-range ion-solvent interactions. Site-specific association affinities were assigned from NMR chemical shift titrations. In DMSO-d6 , the hydroxyl group of choline was found to have the smallest dissociation constant followed by the methyl group of acetate. The corresponding Gibbs energies at low concentration were found to be in agreement with a solvent-separated ion pair (2SIP) configuration, whereas at concentrations above 300 mM, a solvent-shared ion pair (SIP) configuration was assigned. For [Ch]+ [OAc]- in D2 O, association effects were found to be weaker, attributed to the high dielectric constant of the solvent. On time scales on the order of 100 ms, NMR linewidth perturbations indicated a change in the local rotational dynamics of the ions, attributed to short-range cation-solvent interactions and not to solvent viscosity. At 184 mM, ∼ 40 % of the cations in DMSO-d6 and ∼ 10 % in D2 O were found to exhibit short-range interactions, as indicated by the linewidth perturbations. It was found that at about 300 mM, the ions in DMSO-d6 exhibit a transition from free to collective translational dynamics on time scales on the order of 400 ms. In DMSO-d6 , both ions were found to be almost equally solvated, whereas in D2 O solvation of acetate was stronger, as indicated by the obtained effective hydrodynamic radii. For [Ch]+ [OAc]- in DMSO-d6 , the results suggest a solvent-shared ion association with weak H-bonding interactions for concentrations between 0.3-1 M. Overall, the extent of ion association in solvents such as DMSO is not expected to significantly limit charge transport and hinder the performance of choline-based electrolytes.

Animal Silk-Derived Amorphous Carbon Fibers for Electricity Generation and Solar Steam Evaporation

Animal silk-derived carbon materials are of interest to various applications, such as smart cloth and wearable sensors. However, it remains a challenge to massively transform silks into continuous carbon fibers. In this work, carbon fibers based on two kinds of animal silks, i.e., Bombyx mori (B. mori) silk and Antheraea pernyi (A. pernyi) silk, are prepared by using a large-scale-capable one-step heating process without any additives or activation process. These carbon fibers and yarns are electroconductive and mechanically robust. To expand the application of these carbonized silks, we further weaved them with cotton yarns to obtain composite fabrics with different textures and evaluated their performance for solar steam evaporation. Our results confirmed that the advantages of these composite fabrics in light absorption, large surface area, and hierarchical liquid transport channels allowed them to be used as a solar steam generation for desalination and sewage treatment. In addition, we reported that these conductive carbon fibers could be assembled into fluidic nanogenerators to generate electricity from the water flow. This work is expected to guide a large-scale preparation and use of animal silk-derived amorphous carbon fibers.

Electrospun Polyacrylonitrile/Clinoptilolite Coating for SPME of PAHs from Water Samples

Electrospun polyacrylonitrile/clinoptilolite (PAN/CP) nanofibers were used to extract polycyclic aromatic hydrocarbons (PAHs) (acenaphthene, acenaphthylene, naphthalene, and phenanthrene) from water samples by solid-phase microextraction (SPME). The target PAHs was detected and quantified by gas chromatography equipped with a flame ionization detector. The PAN/CP fibrous coating with uniform morphology and without beads was electrospun after optimizing the electrospinning parameters by the Taguchi method. Thermogravimetric analysis of PAN/CP nanofibers indicated that the nanofibers are thermally stable up to 357°C. The effective parameters that affect the extraction by SPME were optimized using the response surface methodology based on the central composite design. The limits of detection and limits of quantification by the proposed method were 0.10-0.32 and 0.45-1.12 ng mL-1, respectively. The relative standard deviations were below 12%. The method was assessed for extracting PAHs from real samples including agricultural water, rainwater and spring water. The obtained relative recoveries were higher than 86%.

Introduction of a Methodology to Enhance the Stabilization Process of PAN Fibers by Modeling and Advanced Characterization

A methodology for designing the oxidative stabilization process of polyacrylonitrile (PAN) fibers is examined. In its core, this methodology is based on a model that describes the characteristic fiber length variation during thermal processing, through the de-convolution of three main contributors (i.e., entropic and chemical shrinkage and creep elongation). The model demonstrated an additional advantage of offering further insight into the physical and chemical phenomena taking place during the treatment. Validation of PAN-model prediction performance for different processing parameters was achieved as demonstrated by Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). Τensile testing revealed the effect of processing parameters on fiber quality, while model prediction demonstrated that ladder polymer formation is accelerated at temperatures over 200 °C. Additionally, according the DSC and FTIR measurements predictions from the application of the model during stabilization seem to be more precise at high-temperature stabilization stages. It was shown that mechanical properties could be enhanced preferably by including a treatment step below 200 °C, before the initiation of cyclization reactions. Further confirmation was provided via Raman spectroscopy, which demonstrated that graphitic like planes are formed upon stabilization above 200 °C, and thus multistage stabilization is required to optimize synthesis of carbon fibers. Optical Microscopy proved that isothermal stabilization treatment did not severely alter the cross section geometry of PAN fiber monofilaments.

Impact of Alternative Stabilization Strategies for the Production of PAN-Based Carbon Fibers with High Performance

The aim of this work is to review a possible correlation of composition, thermal processing, and recent alternative stabilization technologies to the mechanical properties. The chemical microstructure of polyacrylonitrile (PAN) is discussed in detail to understand the influence in thermomechanical properties during stabilization by observing transformation from thermoplastic to ladder polymer. In addition, relevant literature data are used to understand the comonomer composition effect on mechanical properties. Technologies of direct fiber heating by irradiation have been recently involved and hold promise to enhance performance, reduce processing time and energy consumption. Carbon fiber manufacturing can provide benefits by using higher comonomer ratios, similar to textile grade or melt-spun PAN, in order to cut costs derived from an acrylonitrile precursor, without suffering in regard to mechanical properties. Energy intensive processes of stabilization and carbonization remain a challenging field of research in order to reduce both environmental impact and cost of the wide commercialization of carbon fibers (CFs) to enable their broad application.

Preparation of a novel nitrogen-containing graphitic mesoporous carbon for the removal of acid red 88

A novel nitrogen-containing graphitic mesoporous carbon was prepared through MnO-templated method using polyacrylonitrile (PAN) as both carbon and nitrogen sources, and MnCO₃ as both template and catalyst precursors. The effects of preparation conditions on the physicochemical properties of obtained samples were systematically investigated. The results showed that as the decrease of the weight ratios of PAN and MnO (2:1-1:4), the increase of carbonization temperature (700-900 °C) and pre-oxidation temperature (180-200 °C), the samples had higher specific surface area, mesopores volume and ratios, up to 507 m²/g, 0.824 cm³/g and 96.83%, respectively. Moreover, the prepared samples presented relatively high graphitic degree and nitrogen contents (~2.21%). The adsorption capacity for acid red 88 (AR88) was as high as 309 mg/g, which were dramatically affected by the mesoporous properties and C- and N-containing groups on the surface of prepared carbon. The rich graphic carbon and pyridine-N in mesoporous carbon generated π-π dispersion and electrostatic interaction with AR88, respectively, which jointly were responsible for the adsorption process. The results of the isotherm and kinetic studies indicated that the AR88 adsorption on mesoporous carbon could be well depicted using Langmuir model and pseudo-2^nd-order model.

Thermal Analysis and Crystal Structure of Poly(Acrylonitrile-Co-Itaconic Acid) Copolymers Synthesized in Water

The composition and structure of polyacrylonitrile (PAN) precursors play an important role during thermal stabilization, which influences the properties of the resulting carbon fibers. In this paper, PAN homopolymer and PAN-itaconic (IA) copolymers with different IA contents were synthesized by aqueous phase precipitation polymerization. The effects of IA content on the structure and thermal properties were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The morphology of PAN polymers showed that the average size of the PAN particles increased with the increase of IA content in the feed. The content of the IA comonomer on the copolymers was quantitatively characterized by the relative absorbance intensity (A₁₇₃₅/A₂₂₄₃) in FTIR spectrum. With the increase of IA content in the feed, PAN-IA copolymers exhibited lower degree of crystallinity and crystal size than the control PAN homopolymer. The results from DSC curves indicated that PAN-IA1.0 copolymers had lower initial exothermic temperature (192.4 °C) and velocity of evolving heat (6.33 J g⁻¹ °C⁻¹) in comparison with PAN homopolymer (T_i = 238.1 °C and ΔH/ΔT = 34.6 J g⁻¹ °C⁻¹) in an air atmosphere. TGA results suggested that PAN-IA1.0 copolymers had higher thermal stability than PAN homopolymer, which can form a ladder structure easier during thermal processing. Therefore, PAN-IA1.0 copolymers would be a suitable candidate for preparing high performance PAN based carbon fibers.

Structural Transformation of Polyacrylonitrile (PAN) Fibers during Rapid Thermal Pretreatment in Nitrogen Atmosphere

The modification before the stabilization process could tune the exothermic behavior and the structural evolution of PAN fibers during stabilization. In this study, we demonstrate that a rapid thermal pretreatment in nitrogen can effectively mitigate the exothermic behavior of PAN fibers, such as decreasing the initial temperature, broadening the exothermal peak, and decreasing the nominal heat release during heating the fibers in air. The color of fibers has shown gradual changes from white to light yellow, yellow and brown during thermal pretreatment in nitrogen with the increase of pretreating temperature and time. The differential scanning calorimetry (DSC), Fourier Transform Infrared Spectrometer (FTIR), X-ray diffraction (XRD), and Thermogravimetric Analysis (TG) characterization have been applied to analyze the thermal properties, chemical and physical structural difference between PAN, and thermally pretreated PAN fibers. The thermal pretreatment of PAN fibers in nitrogen could induce cyclization, dehydrogenation, and cross-linking reactions, in which the cyclization play an important role on improving the cyclization index of stabilized PAN fibers. Meanwhile, the pretreatment can result in noticeable changes of the aggregation structure of PAN fibers, as indicated by the increase of crystallinity and crystalline size. These structural modifications can benefit the main cyclization reaction during stabilization and enhance the carbon yield in resultant carbon fibers. The rapid thermal pretreatment in nitrogen could increase efficiency of modification on PAN fibers, and that could save much time and energy. It is beneficial to manufacture low-cost carbon fibers and to spread the applications of carbon fibers.

Time Dependent Structure and Property Evolution in Fibres during Continuous Carbon Fibre Manufacturing

Here we report on how residence time influences the evolution of the structure and properties through each stage of the carbon fibre manufacturing process. The chemical structural transformations and density variations in stabilized fibres were monitored by Fourier Transform Infrared Spectroscopy and density column studies. The microstructural evolution and property variation in subsequent carbon fibres were studied by X-ray diffraction and monofilament tensile testing methods, which indicated that the fibres thermally stabilized at longer residence times showed higher degrees of structural conversion and attained higher densities. Overall, the density of stabilized fibres was maintained in the optimal range of 1.33 to 1.37 g/cm³. Interestingly, carbon fibres manufactured from higher density stabilized fibres possessed lower apparent crystallite size (1.599 nm). Moreover, the tensile strength of carbon fibres obtained from stabilized fibres at the high end of the observed range (density: 1.37 g/cm³) was at least 20% higher than the carbon fibres manufactured from low density (1.33 g/cm³) stabilized fibres. Conversely, the tensile modulus of carbon fibres produced from low density stabilized fibres was at least 17 GPa higher than those from high density stabilized fibres. Finally, it was shown that there is potential to customize the required properties of resultant carbon fibres suiting specific applications via careful control of residence time during the stabilization stage.

One-Way Water Transport Fabrics Based on Roughness Gradient Structure with No Low Surface Energy Substances

Despite great recent progress in one-way water transport (OWT) fabrics, the development of these fabrics based on roughness gradient without low surface energy materials has yet to be achieved. In this work, we prepared OWT fabrics using five polymers with hydrophobic or hydrophilic groups by constructing a roughness gradient structure along the fabric thickness. Electrospraying was used to deposit a rough layer on fabric's single side. The surface energy gradient change across the fabric thickness derived from roughness gradient structure played a major part in determining the OWT performance. With the roughness gradient structure, even polymers with hydrophilic groups, such as polyacrylonitrile and polyamide 6, could become OWT fabrics. Besides, the layer deposited on the surface of the fabric showed no effects on the air permeability of the fabric. These novel results provided an opportunity for more polymers, especially for hydrophilic polymers, to be used to prepare OWT fabrics by designing a roughness gradient along the thickness of the fabric. The method would be applied in designing of OWT fabrics with high performance.

Tuning Transpiration by Interfacial Solar Absorber-Leaf Engineering

Plant transpiration, a process of water movement through a plant and its evaporation from aerial parts especially leaves, consumes a large component of the total continental precipitation (≈48%) and significantly influences global water distribution and climate. To date, various chemical and/or biological explorations have been made to tune the transpiration but with uncertain environmental risks. In recent years, interfacial solar steam/vapor generation is attracting a lot of attention for achieving high energy transfer efficiency. Various optical and thermal designs at the solar absorber-water interface for potential applications in water purification, seawater desalination, and power generation appear. In this work, the concept of interfacial solar vapor generation is extended to tunable plant transpiration by showing for the first time that the transpiration efficiency can also be enhanced or suppressed through engineering the solar absorber-leaf interface. By tuning the solar absorption of membrane in direct touch with green leaf, surface temperature of green leaf will change accordingly because of photothermal effect, thus the transpiration efficiency as well as temperature and relative humidity in the surrounding environment will be tuned. This tunable transpiration by interfacial absorber-leaf engineering can open an alternative avenue to regulate local atmospheric temperature, humidity, and eventually hydrologic cycle.

Poly(acrylonitrile-co-2-methylenesuccinamic acid) as a potential carbon fiber precursor: preparation and stabilization

A bifunctional comonomer was synthesized to prepare polyacrylonitrile-co-(2-methylenesuccinamic acid) copolymer, which can improve the stabilization of polyacrylonitrile as carbon fiber precursor.