Polymeric Precursor Research Articles

Bulk and interface engineering with the combined addition of Na+ and E5+ (E = Nb5+, Ta5+) in the design of hematite photoanodes

In this letter, the synergistic effects of multiple element modification through a single polymeric precursor solution in hematite-based photoanodes using Na/Nb and Na/Ta as dopants are evaluated. Linear sweep voltammetry curves showed that the photoelectrochemical response was improved after Na/Nb (or Ta) addition. In both circumstances, an anodic shift (∼200 mV) in the onset potential was noticeable due to surface states created after Nb5+/Ta5+ segregation. The energetic loss caused by Nb (and Ta) segregation was partially restituted by NiFeOx addition due to the passivation of surface states, acting as recombination centers created by pentavalent modifiers. These combined modifications brought a three and four-fold increase for Na0.1HemNb1.5 NiFeOx and Na0.1HemTa1.0NiFeOx respectively. Charge carrier dynamics analysis studied by intensity modulated photocurrent spectroscopy revealed that the PEC enhancement in both systems is mainly associated with improved charge separation efficiency.

Synthetic Placement of Active Sites in MFI Zeolites for Selective Toluene Methylation to para-Xylene.

Brønsted acidic zeolites are ubiquitous catalysts in fuel and chemical production. Broadening the catalytic diversity of a given zeolite requires strategies to manipulate the acid site placement at framework positions within distinct microporous locations. Here, we combine experiment and theory to elucidate how intermolecular interactions between organic structure-directing agents (OSDAs) and framework Al centers influence the placement of H+ sites in distinct void environments of MFI zeolites and demonstrate the catalytic consequences of active site location on kinetically controlled (403 K) toluene methylation to xylene regioisomers. Kinetic measurements, interpreted using mechanism-derived rate expressions and transition state theory, alongside density functional theory (DFT) calculations show that larger intersection environments similarly stabilize all three xylene isomer transition states without altering well-established aromatic substitution patterns (ortho/para/meta ∼ 60%:30%:10%), while smaller channel environments preferentially destabilize transition states that form bulkier ortho- and meta-isomers, thereby resulting in high intrinsic para-xylene selectivity (∼80%). DFT calculations reveal that the flexibility of nonconventional OSDAs (e.g., 1,4-diazabicyclo[2.2.2]octane) to reorient within MFI intersections and their ability to hydrogen-bond to form protonated complexes favor the placement of Al in smaller channel environments compared to conventional quaternary OSDAs (e.g., tetra-n-propylammonium). These molecular-level insights establish a mechanistic link between OSDA structure, active site placement, and transition state stability in MFI zeolites and provide active site design strategies that are orthogonal to crystallite design approaches harnessing complex reaction-diffusion phenomena to enhance regioisomer selectivity in the industrial production of valuable polymer precursors.

Carbon Fibers Made from Cellulose Acetate as a Green Polymer Precursor

Carbon Fibers Made from Cellulose Acetate as a Green Polymer Precursor

Adsorption of Propane (C3H8) onto Microporous Activated Carbon Prepared from a Polymer Precursor

Adsorption of Propane (C3H8) onto Microporous Activated Carbon Prepared from a Polymer Precursor

Polyester networks based on Tulipalin A and ε‐caprolactone and activation of the Thioether groups by incorporation of trialkylsulfonium salts

AbstractLinear and star‐shaped poly(ε‐caprolactone‐co‐α‐methylene‐γ‐butyrolactone) P(CL‐co‐MBL) copolyesters with a pendant functional double bond of α‐methylene‐γ‐butyrolactone (MBL) comonomer were used as polymeric precursor for organo‐gels formation. Crosslinking was carried out by light‐initiated thia‐Michael reaction using 1,5‐pentanedithiol (PDT) and pentaerythritol tetrakis(3‐mercaptopropionate) (PETK). Double bond conversion and the content of free thiol groups in the obtained networks was followed and rationally estimated using confocal Raman spectroscopy. The gel content and the crosslinking density varied based on MBL comonomer and crosslinker content and were highest for slight thiol to double bond excess (SH/vinyl; 2/1 molar ratio) while decreasing with further thiol excess. These parameters were more pronounced by the replacement of linear PDT with the star‐shaped PETK crosslinker. The thermal and rheological properties investigation of the obtained materials was performed employing DSC, TGA and using frequency and temperature sweeps rheological measurements. Shear moduli in the range 0.14 up to 0.93 MPa were obtained due to different content of MBL in pre‐polymer and crosslinker in network formation. The strength was caused by the crystalline phase of the PCL segments up to a temperature of 50°C. Formed thioether bond within the network were not reversible up to 150°C as it was found based on temperature sweep rheology. Following, the activation and conversion of thioether bonds within the obtained materials into trialkylsulfonium salts was attained through the alkylation using butyl brosylate. The dynamic nature of the transalkylation at elevated temperature 150°C allowed network rearrangement, which was proved by stress relaxation experiment and investigation of the self‐healing capabilities.

Large-Area Fabrication of Porous Graphene Networks on Carbon Fabric via Millisecond Photothermal Processing of Polyaniline for Supercapacitors.

Supercapacitors demonstrate promising potential for flexible, multi-functional energy storage devices; however, their widespread adoption is confronted by fabrication challenges. To access a combination of desirable device qualities such as flexibility, lightweight, structural stability, and enhanced electrochemical performance, carbon fiber (CF) can be utilized as a current collector, alongside graphene as an electrochemically active material. Yet achieving a cost-effective, large-scale graphene production, particularly on CF, remains challenging. Here, a rapid (<1min) photothermal approach is developed for the large-scale production of graphene directly onto CF, utilizing polyaniline (PANI) as a polymer precursor. The in situ electropolymerization of PANI on CF facilitates its rapid synthesis on large areas, followed by conversion into graphene networks, enabling the binder-free fabrication of supercapacitor devices. These devices exhibit an areal capacitance of 180mFcm-2 (at 2mAcm-2 in 1mH2SO4), an order of magnitude higher than other fabric-based devices. Moreover, the devised photothermal strategy allows for one-step preparation of supercapacitor devices on areas exceeding 100cm-2, yielding an absolute areal capacitance of 4.5F. The proportional increase in capacitance with device area facilitates scaling and indicates the commercial viability of this approach for low-cost, energy-efficient, and high-throughput production of lightweight, high-performance graphene-based multi-functional supercapacitor devices.

Influence of solvent quality on the swelling and shear modulus of polymer gels chemically cross-linked in solution

The effect of temperature (T) is studied on the swelling of model poly(vinyl acetate) (PVAc) gels in isopropyl alcohol. The theta temperature Θ of these gels, at which the second osmotic virial coefficient A2 vanishes, is close to that of the corresponding high molecular mass polymer solution without cross-links so that solvent quality may be defined in the same way as the corresponding precursor polymer solution. We quantified the swelling and deswelling of PVAc gels relative to their size at the theta temperature, and also determined the effect of T on the shear modulus of these gels. It was found that both swelling and deswelling data could be reduced to a universal scaling equation of the same general form as derived from renormalization group (RG) theory for flexible linear polymer chains in solutions.Graphical abstractVariaton of the volumetric swelling factor as a function of the reduced temperature for PVAc gels swollen in isopropyl alcohol.

A backbone support structure and capillary effect-induced high-flux MOF-based mixed-matrix membrane for selective dye/salt separation

Metal-organic frameworks (MOFs) based mixed-matrix membranes (MMMs) exhibited an excellent promise for separating dye molecules and salt ions due to their permeability and selectability. However, controlling interfacial compatibility between the polymer and MOFs remained challenging, and MOF-based MMMs were poorly processable. Herein, the dual-bath coagulation method was developed to form the polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP) polymer precursor layer, which provided a skeleton support structure. Inspired by the capillary effect, the nanosheet copper-ZIFs were in situ grown in the skeleton support structure, forming capillary microporous channels. The formation of capillary microporous channels endowed the MOF-based MMMs with high permeability of water molecules. Interestingly, the MOF@PVDF/PVP membrane exhibited excellent water permeance (ca. 635.7 L·m−2·h−1·bar) and selectivity for dye/salt separation (dye removal approaching 100 %, salt removal < 10 %). Even for the cationic small-molecule dyes, the MMMs showed an outstanding rejection (e.g., 96.3 % for malachite green and 96.7 % for methylene blue). The water permeance of the MOF@PVDF/PVP membrane was much higher than that of most membranes with similar rejection rates for dyes. Besides, the antifouling and antibacterial properties confirm that the MMMs could maintain long-term stability in practical dyeing wastewater treatment. This study provides an efficient approach to preparing MOF-based MMMs with capillary and skeleton support structures, which exhibited superior performance and outstanding stability for water purification.

Carbon nanofiber electrodes without commercial polymer precursors deliver superior electrochemical performance

Carbon nanofiber (CNF) electrodes are conductive and electrochemically stable, making excellent supercapacitor components. However, such fibers are commonly made from commercial polymer precursors, such as polyacrylonitrile (PAN), which are expensive to produce. Further, PAN carbon fibers are inert and lack porous surfaces, limiting their use as supercapacitor electrodes without further modification. We demonstrate the use of coal-derived polyurethane (CPU) in lieu of PAN, producing a cheap alternative precursor. Electrospinning and carbonization of this precursor produces porous fibers which are rich in nitrogen and oxygen species, creating an active surface facilitating fast faradaic reactions (FFRs). These electrodes offer superior electrochemical performance, with 604 F g−1 at 1 A g−1. After an initial activation period, this capacitance is stable over 10,000 cycles. In a symmetrical two electrode cell, this activated carbon offers superior rate performance and power-energy density trade-off compared to commercial and literature activated carbon electrodes with 20.9 Wh kg−1 energy density at a power density of 0.5 kW kg−1.

Correlation of the permeability and porosity development of carbon/carbon composites during pyrolysis

A cost-effective approach to manufacture Carbon/Carbon composites is to infiltrate carbon fiber preforms with a polymer precursor and pyrolyze it to form the carbon matrix. During pyrolysis, the microstructure changes due to decomposition reactions creating a high degree of porosity consisting of interconnected network of voids and cracks. To densify, the pyrolyzed composite is infiltrated with polymer precursor to fill the porous network. The cycle of pyrolysis followed by infiltration is repeated until the porosity is minimized and the desired density is achieved. The permeability, porosity and viscosity of the polymer govern the infusion pressure and time for the re-infiltration steps.In this work, the permeability of benzoxazine-based Carbon/Carbon composites was measured for different degradation levels with three distinctly different pyrolyzing schedules. The samples were characterized systematically at increasing pyrolyzing temperatures until full conversion of the precursor into carbon matrix was achieved. The porosity of the material was evaluated by X-ray micro-computed tomography and by pycnometry. The through the thickness permeability of the composite was measured via a pulse-decay experiment after each heating step in the pyrolysis cycle. In this experiment pressure decay with time is recorded as air is evacuated from the cavity through the connected pathways of the porous network within the sample. The experimental correlation between the permeability and interconnected porosity of the microstructure is established. It is shown that the pulse-decay test with air effectively characterizes the permeability of the pyrolyzed composite.

High conductivity poly(meta-terphenyl alkylene)s proton exchange membranes for high temperature fuel cell

Phosphoric acid (PA)-doped membranes are regarded as a promising candidate for high temperature proton exchange membranes (HT-PEMs), but the trade-off between mechanical property and conductivity is a major problem limiting their application. Here, two poly(meta-terphenyl alkylene)s (m-TPNs), namely m-TPN-MeIm and m-TPN-TMA, are synthesized by 1-methylimidazole (MeIm) and trimethylamine (TMA) reacting with precursor polymer, respectively. The influence of different cationic groups on the properties of m-TPNs HT-PEMs is investigated in detail. m-TPNs diminish plastication of PA molecules on the mechanical property by separating the adsorption sites for PA molecules from the polymer backbone through long alkyl side chains. As a result, both m-TPN-MeIm and m-TPN-TMA membranes exhibit good mechanical property. Besides, m-TPN-TMA/PA surpasses m-TPN-MeIm/PA in most of aspects owing to the higher ion exchange capacity (IEC) and more distinct microphase separation structure. Noticeably, the proton conductivity of m-TPN-TMA/PA is as high as 0.191 S cm−1 and exhibits excellent stability over a testing time of 100 h at 160 °C thanks to the remarkable acid uptake and microphase separation structure. The m-TPN-TMA/PA-based single cell produces an impressive peak power density of 552 mW cm−2 at 200 °C. Therefore, this work offers a viable alternative for structure design to mitigate the trade-off effect of PA-doped HT-PEMs.

Engineering Pseudomonas putida KT2440 for Dipicolinate Production via the Entner-Doudoroff Pathway.

Dipicolinic acid (DPA), a cyclic diacid, has garnered significant interest due to its potential applications in antimicrobial agents, antioxidants, chelating reagents, and polymer precursors. However, its natural bioproduction is limited since DPA is only accumulated in Bacillus and Clostridium species during sporulation. Thus, heterologous production by engineered strains is of paramount importance for developing a sustainable biological route for DPA production. Pseudomonas putida KT2440 has emerged as a promising host for the production of various chemicals thanks to its robustness, metabolic versatility, and genetic tractability. The dominant Entner-Doudoroff (ED) pathway for glucose metabolism in this strain offers an ideal route for DPA production due to the advantage of NADPH generation and the naturally balanced flux between glyceraldehyde-3-phosphate and pyruvate, which are both precursors for DPA synthesis. In this study, DPA production via the ED pathway was in silico designed in P. putida KT2440. The systematically engineered strain produced dipicolinate with a titer of 11.72 g/L from glucose in a 5 L fermentor. This approach not only provides a sustainable green route for DPA production but also expands our understanding of the metabolic potential of the ED pathway in P. putida KT2440.

Improved relaxor ferroelectrics and energy storage performance of polycrystalline Ba0.95Sr0.05Ti2O5 ceramics modified with La dopants

Lead-free relaxor ferroelectrics are useful in energy storage applications. In particular, BaTi2O5-based dielectric materials may have great potential for such applications. In this study, polycrystalline Ba0.95Sr0.05Ti2O5-xLa (BST2-xLa) ceramics were synthesized using a standard solid-state reaction method with as-prepared nanoparticles prepared via a modified Pechini polymeric precursor method. The structural and electrical properties of the BST2-xLa ceramics were systematically investigated using a series of measurements. The phase analysis results confirm that La3+ is a donor dopant that replaced Ba2+ sites in the structure, which results in a decrease in oxygen vacancies to maintain charge neutrality. The intrinsic electronic conduction mechanism for electrical conductivity was evaluated from the fitted activation energy based on the Arrhenius equation. The relaxor ferroelectric behaviour and energy storage density and efficiency are improved by the addition of a small amount of lanthanum (<3.6 mol%) because of the charge and ionic radius mismatch in the structure. These results suggest that lanthanum can effectively optimise the relaxor ferroelectrics of BST2-xLa ceramics, which have promising potential as energy storage materials.

Dual reconfigurable network from a semi-crystalline functional polyolefin

A statistical copolymer p(E-co-GMA) of ethylene and glycidyle methacrylate (4.5 wt%) is considered as a starting point towards semicrystalline networks with exchangeable links. Application of the binomial law to size exclusion chromatographic data suggests that chains deprived of reactive comonomers would represent less than 6 wt% of the total, allowing to expect the formation of high gel-content networks. Experimentally, up to 98 wt% gel is obtained upon modification with 3,3′-dithiopropionic acid (DTPA). The crosslinking reaction can be performed in the molten state through a 2-steps procedure: 1°) x mol. of a commercial grade p(E-co-GMA), y mol. of DTPA and z mol. of triazabicyclodecene (TBD) are sheared in a twin-screw compounder at 115 °C, a temperature right above the melting point of the polymer precursor, without triggerring the epoxy-acid addition; 2°) the thermolatent reactive blend thereby obtained is then crosslinked at 170 °C. Samples with x = 1, y = 1 to 4 and z = 0 to 0.8 were thus prepared and evaluated. The presence of TBD accelerates disulfide exchange reaction, possibly by involvement of the thiolate anion whereas it decelerates the epoxy-acid addition. The final networks present several characteristic properties of vitrimers such as insolubility in xylene above the melting point, thermo-activated stress relaxation and creep. Particular shape memory regimes, related to the semicrystalline vitrimer character and the high insoluble fraction are demonstrated. Eventually, production scale-up using continuous reactive extrusion is evaluated.

Making fibers from cellulose derivatives by pressurized gyration and electrospinning

Cellulose derivatives are obtained from renewable sources, making them an environmentally friendly option in many industrial applications. Manufacturing fine cellulose fibers is confronted with multifaceted challenges due to cellulose's intricate nature, such as its highly organized structure and hydrogen bonding chain. In this study, for the first time, fibers in the nanometer to micrometer scale diameter from cellulose derivatives were successfully produced without the assistance of polymer precursors using the pressurized gyration (PG) technique. The cellulose derivatives investigated in this work were ethyl cellulose (EC) and cellulose acetate (CA), representing the ether and ester cellulose derivatives, respectively. Electrospinning (ES) technique was also used to compare the fibers produced by this technique with those produced by PG. Both PG and nozzle-PG succeeded in producing EC-based fibers with diameters ranging from 488 to 825 nm, with a higher production rate than ES. In contrast, ES succeeded in producing bead-free fibers from EC and CA with a wide range of solvent systems and concentrations. Scanning electron microscopy was used to analyze the fiber morphology, diameter distribution, and alignment. Additionally, Fourier transform infrared spectroscopy, x-ray diffraction, and differential scanning calorimetry were used to compare the physicochemical nature of the fibers produced by PG and ES. These tests revealed that the fibers produced from the two spinning methods had identical physicochemical structures and properties. With further research and development efforts, PG has the potential to be a promising technique for producing cellulose derivative-based fibers with a high production rate, which could be employed for applications in drug delivery, tissue engineering, and wound dressing.

Preparation of Hirudin-Loaded Chitosan/Polycaprolactone Bowl-Shaped Particles and an Application for a Drug Delivery System

Atherosclerosis, a disease that mainly affects human blood vessels, can cause various cerebral ischaemic diseases such as coronary heart disease and peripheral arterial disease. However, conventional drugs for the treatment of atherosclerosis have the disadvantages of low bioavailability and high toxicity. Bowl-shaped particles not only have the excellent properties of traditional spherical particles, such as improved drug distribution, increased drug absorption, reduced drug toxicity and side effects, but also are easier to circulate in the blood for a long time, have reduced immune rejection and have a larger specific surface area. Chitosan/polycaprolactone bowl-shaped particles were prepared via electrostatic spraying, and the effects of precursor solution concentration and polymer ratio on particle morphology were investigated. Chitosan/polycaprolactone composite bowl-shaped particles containing hirudin were prepared under optimal parameters for sustained anticoagulation. The anticoagulant molecules of hirudin could be continuously released from the composite scaffold as the bowl particles degraded. The biocompatibility and haemocompatibility of the composite particles were assessed using mouse glial cells and rabbit blood, and the results showed that the cell viability of the drug-loaded particles was overall above 90% and the haemolysis rate was below 2%. By controlling the release rate of hirudin, bowl-shaped particles can achieve a long-term anticoagulant drug delivery system and have wider application potential as a novel blood contact material.

Hybrid HfC‐SiCN matrix for improved oxidation resistance of carbon fiber–reinforced mini‐composites

AbstractHafnium carbide (HfC) is an ultrahigh‐temperature ceramic with high melting point, chemical stability, hardness, and wear resistance. However, its low fracture toughness and poor thermal shock resistance limit its structural applications in extreme environments. In this study, co‐curing of liquid precursors was carried out prior to complete pyrolysis of individual polymeric precursors. First, HfC preceramic polymer precursor was cured, followed by silicon carbonitride (SiCN) precursor curing on a 2D carbon fiber (CF) cloth using the drop‐coating process. The infiltrated CFs were pyrolyzed at 800°C to achieve CF/HfC‐SiCN ceramic mini‐composites. The cross‐linked precursor‐to‐ceramic yield was observed to be as high as 65% when the procedure was carried out in an inert environment. Although stable up to 1200°C, CF/HfC‐SiCN samples demonstrated susceptibility to oxidation at 1500°C in ambient air. The oxidation of HfC in the presence of SiC leads to the formation of a hafnium‐containing silicate (HfxSiyOz) along with hafnia (HfO2). This compound of silicate and hafnia limits oxygen diffusion better than SiO2 and HfO2 individually. The incorporation of SiCN in HfC ceramic led to improved phase stability compared to a neat HfC system. The results of this study also show that the use of liquid‐phase precursors for HfC and SiCN in the polymer‐infiltrated pyrolysis method is a promising approach to fabricating high‐temperature structural ceramic matrix composites with good oxidation resistance.

Formation mechanism of (Ti, Zr, Hf)C medium-entropy carbide derived from polymer precursors and its modification on the ablative mechanism of C/C-SiC composites

Medium-entropy carbide (MEC) of (Ti, Zr, Hf)C was synthesized and its modification on the ablative mechanism of C/C-SiC composites was investigated. After 60 s oxyacetylene flame test, the mass and linear ablation rates were 1.43 mg/s and 11.1 μm/s, respectively. The evolution of ceramics oxide scale dominated the anti-ablation process, which transfers from (Ti, Zr, Hf)xCyOz, (Ti, Zr, Hf)xSiyOz to (Ti, Zr, Hf)O2, (Zr, Hf)TiO4. With further evaporation of SiO2, the generated (Ti, Zr, Hf)O2 skeleton and the residual liquid oxides ((Zr, Hf)TiO4 and (Zr, Hf)SiO4) can block the oxygen channel and further reduce oxidation of the inner matrix.

Ionic Liquid Modified Polymer Gel for Arsenic Speciation.

A new ionic liquid modified polymer gel containing methylimidazolium groups (poly(MIA)) is proposed as a sorbent for the separation and enrichment of trace inorganic and organic arsenic species in surface waters. The poly(MIA) was synthesized by chemical modification of polymeric precursor using post-polymerization modification of poly(glycidyl methacrylate-co-trimethylolpropane trimethacrylate). The composition, structure, morphology, and surface properties of the prepared particles were characterized using elemental analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption-desorption measurements. Optimization experiments showed that at pH 8, monomethylarsonic acid (MMAs), dimethylarsinic acid (DMAs), and As(V) were completely retained on the poly(MIA), while the sorption of As(III) was insignificant. The desorption experiments revealed that due to the weaker binding of organic arsenic species, selective elution with 1 mol/L acetic acid for MMAs + DMAs, followed by elution with 2 mol/L hydrochloric acid for As(V), ensured their quantitative separation. The adsorption kinetic and mechanism were defined. The analytical procedure for As(III), As(V), MMAs, and DMAs determination in surface waters was developed and validated through the analysis of certified reference material.

Fe-doped N/S-rich carbon catalyst derived from porphyrine-ferrocene conjugated microporous polymer for bifunctional electrocatalysis and zinc-air batteries

Facile fabrication of non-noble electrocatalysis with precisely tunned active centers for oxygen reduction reaction (ORR) and zinc–air batteries (ZABs) are intriguing yet still challenging. Herein, an iron porphyrin-ferrocene conjugated microporous polymer (FeCMP) with isolated Fe centers was used as precursor to fabricate Fe-Nx electrocatalyst. Innovatively, NaSCN as both an active site protectant and a heteroatomic dopant was introduced. Subsequent carbonization at 800℃ for FeCMP mixed with NaSCN resulted in the formation of highly isolated Fe with S- and N-doped porous carbon (FeSNC800), which acts as a bifunctional catalyst with good ORR (E1/2 = 0.88 V) and OER (oxygen evolution reaction, η10 = 0.34 V) performance. The assembled Zinc-air battery possesses 118 mW cm−2 of power density and is stable over 300 cycles. This work highlights the strength of rational designed polymer precursor and heteroatom doping in controlled pyrolysis of platinum group-free electrocatalysts.