Synergistic Combination of Dual Clays in Multilayered Nanocomposites for Enhanced Flame Retardant Properties.

In an effort to reduce the flammability of synthetic polymeric materials such as cotton fabrics and polyurethane foam (PUF), hybrid nanocoatings are prepared by layer-by-layer assembly. Multilayered nanocomposites of a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA), are paired with two kinds of clay nanoplatelets, montmorillonite (MMT) and vermiculite (VMT). The physical properties such as thickness and mass and thermal behaviors in clay-based nanocoatings with and without incorporation of tris buffer are compared to assess the effectiveness of amine salts on flame retardant (FR) performances. A PDDA-tris/VMT-MMT system, in which tris buffer is introduced into the cationic PDDA aqueous solution, produces a thicker and heavier coating. Three different systems, including PDDA/MMT, PDDA/VMT-MMT, and PDDA-tris/VMT-MMT, result in conformal coating, retaining the weave structure of the fabrics after being exposed to a vertical and horizontal flame test, while the uncoated sample is completely burned out. The synergistic effects of dual clay-based hybrid nanocoatings are greatly improved by adding amine salts. Cone calorimetry reveals that the PDDA-tris/VMT-MMT-coated PUF eliminates a second peak heat release rate and significantly reduces other FR performances, compared to those obtained from the clay-based multilayer films with no amine salts added. Ten bilayers of PDDA-tris/VMT-MMT (≈250 nm thick) maintain the shape of foam after exposure to a butane torch flame for 12 s. As for practical use of these nanocomposites in real fire disasters, spray-assisted PDDA-tris/VMT-MMT multilayers on woods exhibit high resistance over flammability. Improved fire resistance in PDDA-tris/VMT-MMT is believed to be due to the enhanced char yield through the addition of tris buffer that promotes the deposition of more clay particles while retaining a highly ordered deposition of a densely packed nanobrick wall structure. This work demonstrates the ability to impart significant fire resistance to synthetic polymer materials in a fully renewable nanocoating that uses environmentally benign chemistry.

Upcycling Plastic Waste into High Value-Added Carbonaceous Materials.

Even though plastic improved the human standard of living, handling the plastic waste represents an enormous challenge. It takes more than 100 years to decompose discarded or buried waste plastics. Microplastics are one of the causes of significantly pervasive environmental pollutants. The incineration of plastic waste generates toxic gases, underscoring the need for new approaches, in contrast to conventional strategies that are required for recycling plastic waste. Therefore, several studies have attempted to upcycle plastic waste into high value-added products. Converting plastic waste into carbonaceous materials is an excellent upcycling technique due to their diverse practical applications. This review summarizes various studies dealing with the upcycling of plastic waste into carbonaceous products. Further, this review discusses the applications of carbonaceous products synthesized from plastic waste including carbon fibers, absorbents for water purification, and electrodes for energy storage. Based on the findings, future directions for effective upcycling of plastic waste into carbonaceous materials are suggested.

Understanding an Exceptionally Fast and Stable Li-Ion Charging of Highly Fluorinated Graphene with Fine-Controlled C-F Configuration.

Fluorine (F) atoms with the highest electronegativity and low polarizability can easily modify the surface and composition of carbon-based electrode materials. However, this is accompanied by complete irreversibility and uncontrolled reactivity, thus hindering their use in rechargeable electronic devices. Therefore, understanding the electrochemical effects of the C-F configuration might lead to achieving superior electrochemical properties. Here, we demonstrate that the fluorinated and simultaneously reduced graphene oxide (FrGO) was easily synthesized through direct gas fluorination. The as-prepared 11%-FrGO electrode exhibited a high capacity (1365 mAh g-1 at 0.1 A g-1), remarkable rate capability, and good stability (64% retention after 1000 cycles at 5 A g-1). Furthermore, the annealed FrGO (11%-FrGO(A)) electrode in which the C-F bond configurations were controlled by facile thermal treatment shows long-term stability (80% retention after 1000 cycles at 5 A g-1). Above a certain content, F atoms enhance Li-ion adsorption and electron transfer, accelerate Li-ion diffusion, and facilitate the formation of a solid electrolyte interphase layer. In particular, the C-F configuration plays a significant role in retaining the capacity under harsh recharging conditions. The results in this study could provide valuable insights into the field of rechargeable devices.

Lateral Size Effect of Graphene Oxide on Its Surface-Enhanced Raman Scattering Property.

The lateral size effect of graphene oxide (GO) on surfaced-enhanced Raman scattering (SERS) property is systematically investigated by using size-fractionalized GO. For the size fractionalization without changes of chemical structure, large-sized GO (LGO) and small-sized GO (SGO) are separated from the as-synthesized GO (AGO) by centrifugation and membrane filtration, respectively. The size-fractionalized GO sheets are immobilized on a solid substrate for the parallel comparison of their SERS property. As a result, we find that LGO shows considerably higher SERS property than SGO for typical Raman probes such as rhodamine 6G and crystal violet. Furthermore, the lateral size effect of GO derivatives is consistently observed when they are hybridized with plasmonic silver nanoparticles. These results indicate that LGO is superior to AGO and SGO as a SERS platform, and it is also quantitatively confirmed by calculating their enhancement factor.

Fabrication of Poly(ethylene terephthalate) Fiber@Microporous Organic Polymer with Amino Groups@Cu Films for Flexible and Metal-Economical Electromagnetic Interference Shielding Materials.

Flexible and metal-economical electromagnetic interference (EMI) shielding films were fabricated based on microporous organic polymer (MOP) chemistry. MOP with amino groups (MOP-A) could be introduced to the surface of poly(ethylene terephthalate) (PET) fibers. Due to the microporosity and amino groups of MOP-A, Ag+ could be easily incorporated into PET@MOP-A. Through Ag-catalyzed electroless Cu deposition, PET@MOP-A@Cu films were fabricated. The morphological and chemical structures of the PET@MOP-A@Cu were characterized by scanning electron microscopy, X-ray diffraction studies, and X-ray photoelectron spectroscopy. Among the films, the PET@MOP-A@Cu-40 with 41 wt % Cu (a thickness of 0.64 µm) showed excellent EMI shielding performance with 64.3-73.8 dB against an EM of 8-12 GHz. Moreover, it showed retention of the original EMI shielding performance against 1000 bending (R = 5 mm) tests.

High-toughness natural polymer nonwoven preforms inspired by silkworm cocoon structure.

As the interest in environmentally friendly materials and concerns regarding depletion of petroleum resources has increased, the research on natural polymers is being actively pursued. Among the various materials based on natural polymeric resources, the interest in using natural fibers in bio-composites has grown due to their lightweight, non-toxicity, low cost, and abundance. However, the lack of interfacial adhesion between filaments and poor water resistance make the use of natural fiber-based polymer composites less attractive. To overcome these drawbacks, formaldehyde-based synthetic binders have been used. However, this requires an additional synthesis of the binder, and potential toxicity problems exist. In this work, robust and rigid natural polymer nonwoven preforms were prepared by mixing jute fibers with silk sericin (SS). SS was employed as a natural facile binder and the strong binding between jute fibers and SS resulted in remarkable enhancements in tensile strength, elongation, and toughness, which increased up to 539.1, 385.7, and 1943.8%, respectively, compared with the pristine jute nonwoven. In addition, the dense and rigid structure obtained through SS coating ensured the structural stability of the nonwoven preforms in moisture environments. Silkworm cocoon-structured natural polymer nonwoven preforms with excellent mechanical strength and higher physical stability may have more potential utilization in the composite material fields.

Pyrolytic Carbon Nanosheets for Ultrafast and Ultrastable Sodium-Ion Storage.

Na-ion cointercalation in the graphite host structure in a glyme-based electrolyte represents a new possibility for using carbon-based materials (CMs) as anodes for Na-ion storage. However, local microstructures and nanoscale morphological features in CMs affect their electrochemical performances; they require intensive studies to achieve high levels of Na-ion storage performances. Here, pyrolytic carbon nanosheets (PCNs) composed of multitudinous graphitic nanocrystals are prepared from renewable bioresources by heating. In particular, PCN-2800 prepared by heating at 2800 °C has a distinctive sp2 carbon bonding nature, crystalline domain size of ≈44.2 Å, and high electrical conductivity of ≈320 S cm-1 , presenting significantly high rate capability at 600 C (60 A g-1 ) and stable cycling behaviors over 40 000 cycles as an anode for Na-ion storage. The results of this study show the unusual graphitization behaviors of a char-type carbon precursor and exceptionally high rate and cycling performances of the resulting graphitic material, PCN-2800, even surpassing those of supercapacitors.

Ultra strong pyroprotein fibres with long-range ordering.

Silks are protein-based natural structured materials with an unusual combination of high strength and elongation. Their unique microstructural features composed of hard ß-sheet crystals aligned within a soft amorphous region lead to the robust properties of silks. Herein we report a large enhancement in the intrinsic properties of silk through the transformation of the basic building blocks into a poly-hexagonal carbon structure by a simple heat treatment with axial stretching. The carbon clusters originating from the ß-sheet retain the preferred orientation along the fibre axis, resulting in a long-range-ordered graphitic structure by increasing heat-treatment temperatures and leading improvements in mechanical properties with a maximum strength and modulus up to ∼2.6 and ∼470 GPa, respectively, almost four and thirty times surpassing those of raw silk. Moreover, the formation of sp 2 carbon configurations induce a significant change in the electrical properties (e.g. an electrical conductivity up to 4.37 × 103 S cm-1).The mechanical properties of silk are determined by tight stacks of sheet-like peptide crystals distributed in amorphous regions. Here, the authors heat and stretch silk fibres to align these crystal into a long range ordered carbon structure and dramatically enhance the silk strength.

Long-Lasting Nb2O5-Based Nanocomposite Materials for Li-Ion Storage.

Advanced nanostructured hybrid materials can help us overcome the electrochemical performance limitations of current energy storage devices. In this study, three-dimensional porous carbon nanowebs (3D-CNWs) with numerous included orthorhombic Nb2O5 (T-Nb2O5) nanoparticles were fabricated using a microbe-derived nanostructure. The 3D-CNW/T-Nb2O5 nanocomposites showed an exceptionally stable long-term cycling performance over 70 000 cycles, a high reversible capacity of ∼125 mA h g-1, and fast Li-ion storage kinetics in a coin-type two-electrode system using Li metal. In addition, energy storage devices based on the above nanocomposites achieved a high specific energy of ∼80 W h kg-1 together with a high specific power of ∼5300 W kg-1 and outstanding cycling performance with ∼80% capacitance retention after 35 000 cycles.

Pyroprotein-Based Electronic Textiles with High Stability.

Thermally reducible pyroprotein-based electronic textiles (e-textiles) are fabricated using graphene oxide and a pyroprotein such as cocoon silk and spider web without any chemical agents. The electrical conductivity of the e-textile is 11.63 S cm-1 , which is maintained even in bending, washing, and temperature variation.

Sodium-Ion Storage in Pyroprotein-Based Carbon Nanoplates.

Pyroprotein-based carbon nanoplates are fabricated from self-assembled silk proteins as a versatile platform to examine sodium-ion storage characteristics in various carbon environments. It is found that, depending on the local carbon structure, sodium ions are stored via chemi-/physisorption, insertion, or nanoclustering of metallic sodium.

Carbonization of a stable ß-sheet-rich silk protein into a pseudographitic pyroprotein.

Silk proteins are of great interest to the scientific community owing to their unique mechanical properties and interesting biological functionality. In addition, the silk proteins are not burned out following heating, rather they are transformed into a carbonaceous solid, pyroprotein; several studies have identified potential carbon precursors for state-of-the-art technologies. However, no mechanism for the carbonization of proteins has yet been reported. Here we examine the structural and chemical changes of silk proteins systematically at temperatures above the onset of thermal degradation. We find that the ß-sheet structure is transformed into an sp(2)-hybridized carbon hexagonal structure by simple heating to 350 °C. The pseudographitic crystalline layers grew to form highly ordered graphitic structures following further heating to 2,800 °C. Our results provide a mechanism for the thermal transition of the protein and demonstrate a potential strategy for designing pyroproteins using a clean system with a catalyst-free aqueous wet process for in vivo applications.

Nylon 610/graphene oxide composites prepared by in-situ interfacial polymerization.

Nylon 610/nylon 610-grafted graphene oxide (nylon 610/GO-g-nylon 610) composites were fabricated using acyl chloride-functionalized graphene oxide by in-situ interfacial polymerization. GO-g-nylon 610 was synthesized by the condensation reaction between the acyl chloride groups of GO and the amino groups at the nylon 610 chains during the in-situ polymerization. Nylon 610/GO composites without grafting nylon 610 onto GO were also prepared to investigate the influence of grafting nylon 610 on the interfacial adhesion between GO and the nylon 610 matrix. The thermal properties of the nylon 610/GO-g-nylon 610 composites were enhanced with increasing GO-g-nylon 610 content in the nylon 610 matrix. The degradation temperature and thermal conductivity of the nylon 610/GO-g-nylon 610-10 composite were increased to 72.2 °C and 36.9%, respectively, compared with those of pure nylon 610. The crystallinity of the nylon 610/GO-g-nylon 610-10 composite was significantly lower than that of pure nylon 610 due to the hindered mobility of the nylon 610 chains by the strong interfacial adhesion between the GO-g-nylon 610 and the nylon 610 matrix.

Silver nanowire catalysts on carbon nanotubes-incorporated bacterial cellulose membrane electrodes for oxygen reduction reaction.

Silver nanowires have unique electrical, thermal and optical properties, which support their potential application in numerous fields including catalysis, electronics, optoelectronics, sensing, and surface-enhanced spectroscopy. Especially, their application such as catalysts for alkaline fuel cells (AFCs) have attracted much interest because of their superior electrical conductivity over that of any metal and their lower cost compared to Pt. In this study, multiwalled carbon nanotubes (MWCNTs)-incorporated bacterial cellulose (BC) membrane electrode with silver nanowire catalyst was prepared. First, acid-treated MWCNTs were incorporated into BC membranes and then freeze-dried after solvent exchange to tert-butanol in order to maintain the 3D-network macroporous structure. Second, silver nanowires synthesized by polyol process were introduced onto the surface of the MWCNTs-incorporated BC membrane through easy vacuum filtration. Finally, thermal treatment was carried out to confirm the effect of the PVP on the silver nanowire catalysts toward oxygen reduction reaction. The electrode with thermally treated silver nanowire had great electrocatalytic activity compared with non-treated one. These results suggest that the MWCNTs-incorporated BC electrode with silver nanowire catalysts after thermal treatment could be potentially used in cathodes of AFCs.

Microporous carbon nanoplates from regenerated silk proteins for supercapacitors.

Novel carbon-based microporous nanoplates containing numerous heteroatoms (H-CMNs) are fabricated from regenerated silk fibroin by the carbonization and activation of KOH. The H-CMNs exhibit superior electrochemical performance, displaying a specific capacitance of 264 F/g in aqueous electrolytes, a specific energy of 133 Wh/kg, a specific power of 217 kW/kg, and a stable cycle life over 10000 cycles.

Improved thermal properties of graphene oxide-incorporated poly(methyl methacrylate) microspheres.

Graphene, a single layer of carbon atoms in a two-dimensional lattice, has attracted considerable attention owing to its unique physical, chemical and mechanical properties. In particular, because of its excellent thermal properties such as high thermal conductivity and good thermal stability, graphene has been regarded as a one of the promising candidates for the reinforcing fillers on the polymer composites field. In this study, we prepared the poly(methyl methacrylate) (PMMA)/graphene oxide (GO) nanocomposite by a simple solution mixing process, and examined the thermal reinforcing effects of GO on a PMMA matrix. Using thermogravimetric analysis, differential scanning calorimeter, and thermal conductivity meter, we investigated the effects of GO on the thermal properties of PMMA/GO nanocomposites. With 3 wt% of GO loading, the glass transition temperature (Tg) of the PMMA/GO nanocomposite were increased by more than 7 degrees C and the thermal conductivity of which also improved 1.8 times compared to pure PMMA.

Bacterial cellulose nanocrystals-embedded silk nanofibers.

Nanofibrous Bacterial cellulose nanocrystals (BCNs)-embedded silk fibroin were successfully fabricated using electrospinning. The morphology, structure and mechanical properties of the silk fibroin nanofibers were investigated at various BCNs concentrations from 0 to 7 wt%. SEM, TEM and XRD analyses were conducted to confirm the incorporation of the BCNs in the electrospun silk fibroin nanofibers. The average diameter of the silk fibroin/BCNs nanofibers increased from 230 to 430 nm according to the increasing of the BCNs ratio due to the rising solute content. The FT-IR spectra confirmed the conformational transition of the silk fibroin, from a random coil to a beta-sheet structure, which shows the enhanced mechanical properties of silk fibroin based nanofibers even with small amounts of the BCNs. Moreover, it was observed that the Young's modulus of the silk fibroin/BCNs nanofibers unexpectedly increased with the formation of BCNs with a percolation structure at a concentration between 3 and 5 wt%.

Silk fibroin particles as templates for mineralization of calcium-deficient hydroxyapatite.

Silk fibroin particles prepared by phase separation with polyethylene oxide were coated with calcium-deficient hydroxyapatite (CDHA) crystals under various pH conditions. For different pH values, the growth and the morphology of CDHA crystals on the surface of silk fibroin particles were investigated in detail by zeta potential analysis, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction techniques. Negative charges formed by deprotonation of the functional groups on the surface of silk fibroin particles at high pH lead to an increase of binding affinity between the calcium ions of the CDHA crystals and the functional groups of the silk fibroin particles. Consequently, the generation of many CDHA crystals was promoted to deposit on the surface of silk fibroin particles at a high pH value.

Controlling microstructure of three-dimensional scaffolds from regenerated silk fibroin by adjusting pH.

For tissue engineering, it is very important to design and control the pore architecture of three-dimensional (3D) polymeric scaffolds, which plays an important role in directing tissue formation and function. In this study, 3D porous silk fibroin scaffolds produced using a freeze drying technique were prepared at pHs ranging from 5 to 9. The effects of pH on the pore microstructure of the silk fibroin scaffold were examined by rheometry, FESEM and FTIR. Different pore structures were formed according to the pH of silk fibroin because silk fibroin exhibits water-like behavior under basic conditions and gel-like behavior under acidic conditions.

Flexible bio-composites based on silks and celluloses.

Biomaterials have attracted worldwide attention due to the concerns regarding health and the environment. Silk, a natural protein produced by several species of insects, has been examined as a potential material for applications in many biotechnological and biomedical fields. However, regenerated silk fibroin has poor ductility and mechanical properties. Therefore, in this study, silk fibroin-cellulose composite films were prepared in an aqueous system to increase the ductility of regenerated silk fibroin. The morphology of the silk fibroin-cellulose composite film was observed by field emission scanning electron microscopy. The structure of the silk fibroin-cellulose composite films was examined by Fourier transform-infrared spectroscopy. The flexibility was analyzed using a bending test.