Different Plant Sporopollenin Exine Capsules and Their Multifunctional Usage

Sporopollenin exine capsules (SECs) are highly resistant to heat and various acids and bases. They are also cheap, highly porous, eco-friendly polymer biomaterials with stable microencapsulation capacity. Due to their strong and uniquely shaped exine layers, they can allow growth on metal oxide materials, as a biotemplate for use in different applications. In this study, first, a single SEC extraction method was applied to three different pollens from Pinus, Fraxinus excelsior, and Tilia. Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, and thermogravimetric/differential thermal analysis (TGA/DTA) measurements both before and after the extraction process were performed to observe changes in surface area, morphology, porous structure, and degradation properties. The protein content and removal were analyzed by elemental and spectrophotometric analyses. Then, SECs were loaded by passive and centrifuge loading for drug delivery, and the loading capacities were analyzed by Fourier transform infrared spectroscopy and spectrophotometry. The method was successful in opening the pores and maintaining the structural integrity of SECs. It was determined that the morphology and porosity affected the encapsulation efficiency. According to the loading capacities, Tilia SECs were the most efficient SECs for both loading methods. In addition, three different SECs were hydrothermally coated with cobalt and then heat-treated to obtain a metal oxide structure. A CO₃O₄ supercapacitor electrode constructed using CO₃O₄-F. excelsior SEC powder had the best surface area parameters. The electrode showed a maximum specific capacity of 473 F/g for over 3000 continuous cycles of galvanostatic charge-discharge (GCD).

Advances in the design and application of transition metal oxide-based supercapacitors

In the last years, supercapacitors (SCs) have been proposed as a promising alternative to cover the power density deficiency presented in batteries. Electrical double-layer SCs, pseudocapacitors, and hybrid supercapacitors (HSCs) have shown very attractive features such as high-power density, long cycle life, and tunable specific capacitance. The advances of these energy storage devices made by transition metal oxides (TMOs) and their production in pseudocapacitors and HSCs depend on chemical composition, crystalline structure, morphology, theoretical capacitance, and oxidation states. In this way, this critical review considers several metal oxides (RuO2, MnO2, V2O5, and Co3O4) and their different configurations with diverse carbon-based materials. Energy storage mechanisms and fundamental principles to understand the promising effect of metal oxides in SCs devices are thoroughly described. Special attention as regards to the energy storage mechanisms relative to the specific capacitance values is presented in the reviewed articles. This review envisages the TMO as a key component to obtain high specific capacitance SCs.

Hybrid supercapacitors using electrodes from fibers comprising polymer blend-metal oxide composites with polymethacrylic acid as chelating agent

Hybrid supercapacitors (SCs) made of carbon-metal oxide composites are devices which combine the advantages of electric double layer capacitors and pseudocapacitors viz high energy density, high power density and high cyclability. This is best achieved when the pseudocapacitive components are uniform in size and distribution on the conducting carbon support. Electrodes mats, fabricated from carbonized electrospun fibers generated from solutions of polyacrylonitrile (PAN) as the carbon source, cobalt (III) acetylacetonate as a metal oxide precursor, and polymethacrylic acid (PMAA) as a metal oxide precursor carrier were utilized in coin cell SCs. Fibers without the PMMA carrier were prepared for comparison. XRD and TGA showed conversion of the cobalt precursor to a mixture of cobalt and cobalt oxide (Co₃O₄). When the PMAA carrier was used, specific capacitance increased from 68 F g^-1in PAN-Co₃O₄to 125 F g^-1in PAN-PMAA-Co₃O₄. The addition of PMAA to the system results in better uniformity, accessibility and dispersion of metal and metal oxide particles. Due to the relatively low surface area of carbonized samples, Co₃O₄nanoparticles are the primary contributors to charge storage. The fabricated fibers show an energy density of 8.9 at 750 W kg^-1, which is twice that of the fibers made without PMAA.

Porous, flexible, and core-shell structured carbon nanofibers hybridized by tin oxide nanoparticles for efficient carbon dioxide capture

HYPOTHESIS

Carbon based nanofibrous materials are considered to be promising sorbents for the CO₂ capture and storage. However, the precise control of porous structure with flexibility still remains a challenging task. In this research, we report a simple strategy to develop tin oxide (SnO₂) embedded, flexible and highly porous core-shell structured carbon nanofibers (CNFs) derived from polyacrylonitrile (PAN)/polyvinylidene fluoride (PVDF) core-shell nanofibers.

EXPERIMENT

PAN/PVDF core-shell solutions were electrospun using co-axial electrospinning process. The as spun PAN core, and PVDF shell, with an appropriate amount of SnO₂, fibers were stabilized followed by carbonization to develop SnO₂ embedded highly porous and flexible core-shell structured CNFs.

FINDINGS

The optimized CNFs membrane shows a prominent CO₂ capture capacity of 2.6 mmol g^-1 at room temperature, excellent CO₂ selectivity than N₂, and a remarkable cyclic stability. After 20 adsorption-desorption cycles, the CO₂ capture capacity retains >95% of the preliminary value showing the long-term stability and practical worth of the final product. The loading of SnO₂ nanoparticles in the carbon matrix not only enhanced the thermal stability of the precursor nanofibers, their surface characteristics, and porous structure to capture CO₂ molecules, but also improves the flexibility of the CNFs by serving as a plasticizer for single-fiber-crack connection. Meaningfully, the flexible SnO₂ embedded core-shell CNFs with excellent structural stability can prevail the limitations of annihilation and collapse of structures for conventional adsorbents, which makes them strongly useful and applicable. This research introduces a new route to produce highly porous and flexible materials as solid adsorbents for CO₂ capture.

Co3O4/carbon composite nanofibrous membrane enabled high-efficiency electromagnetic wave absorption

Electromagnetic (EM) wave absorbing materials have been fabricated from diverse materials such as conductive polymers, carbon based nanostructures and magnetic metal oxides. Nevertheless, it has remained a great challenge to develop lightweight and high-efficiency EM wave absorbing materials with a broad frequency range. Herein, we report a scalable strategy to create Co₃O₄/carbon composite nanofibrous membrane by electrospinning technique followed by stabilization and carbonization processes. An optimal reflection loss (R_L) value of 36.27 dB is reached at 13.76 GHz for a layer of 2 mm thickness. RL exceeding −20 dB can be realized in any interval within the 4.5–14.4 GHz range by selecting a proper thickness of the absorbing layer between 1 and 5 mm. The Co₃O₄/carbon composite nanofibrous membrane could be well served as promising and attractive candidates for lightweight and enhanced EM wave absorbing materials. This presented research provides an innovative and effective approach to design the novel EM wave absorbing material in a broad frequency range for practical applications.

Flexible Fe3O4@Carbon Nanofibers Hierarchically Assembled with MnO2 Particles for High-Performance Supercapacitor Electrodes

Increasing use of wearable electronic devices have resulted in enhanced demand for highly flexible supercapacitor electrodes with superior electrochemical performance. In this study, flexible composite membranes with electrosprayed MnO₂ particles uniformly anchored on Fe₃O₄ doped electrospun carbon nanofibers (Fe₃O₄@CNF_Mn) have been prepared as flexible electrodes for high-performance supercapacitors. The interconnected porous beaded structure ensures free movement of electrolyte within the composite membranes, therefore, the developed supercapacitor electrodes not only offer high specific capacitance of ~306 F/g, but also exhibit good capacitance retention of ~85% after 2000 cycles, which certify that the synthesized electrodes offer high and stable electrochemical performance. Additionally, the supercapacitors fabricated from our developed electrodes well maintain their performance under flexural stress and exhibit a very minute change in specific capacitance even up to 180° bending angle. The developed electrode fabrication strategy integrating electrospinning and electrospray techniques paves new insights into the development of potential functional nanofibrous materials for light weight and flexible wearable supercapacitors.

Transition Metal Ions Enable the Transition from Electrospun Prolamin Protein Fibers to Nitrogen-Doped Freestanding Carbon Films for Flexible Supercapacitors

Flexible carbon ultrafine fibers are highly desirable in energy storage and conversion devices. Our previous finding showed that electrospun hordein/zein fibers stabilized by Ca²⁺ were successfully transferred into nitrogen-doped carbon ultrafine fibers for supercapacitors. However, their relatively brittle nature needed to be improved. Inspired by this stabilizing effect of Ca²⁺, in this work, four transition metal divalent cations were used to assist the formation of flexible hordein/zein-derived carbon ultrafine fibers. Without alteration of the electrospinnability, adequate amounts of zinc acetate and cobalt acetate supported the fibrous structure during pyrolysis. This resulted in flexible freestanding carbon films consisting of well-defined fibers with nitrogen-doped graphitic layers and hierarchical pores. These carbon films were easily cut into small square pieces and directly applied as working electrode in the three-electrode testing system without the need for polymer binders or conducting agents. Notably, the hz-Zn0.3-p electrode, synthesized with 0.3 mol/L Zn²⁺ and post-acid treatment, exhibited a specific capacitance of 393 F/g (at 1 A/g), a large rate capability (72.3% remained at 20 A/g), and a capacitance retention of ∼98% after 2000 charging-discharging cycles at 10 A/g. These superior electrochemical properties were attributed to the synergistic effects of the well-developed graphitic layers induced by Zn²⁺, the nitrogen-decorated carbon structure, and the interconnected channels generated by HCl treatment. This research advances potential applications for prolamin proteins as nitrogen-containing raw materials in developing carbon structures for high-performance supercapacitors.

A nanocrystalline Co3O4@polypyrrole/MWCNT hybrid nanocomposite for high performance electrochemical supercapacitors

In this study, a ternary hybrid nanocomposite of Co₃O₄@polypyrrole/MWCNT was prepared via oxidative polymerization of pyrrole monomer and a hybrid composite by a hydrothermal process.