Cell Wall Modification Based on Combination Reagents to Improve Dimensional Stability of Wood with High Efficiency.

Although γ-methacryloxypropyltrimethoxysilane (MPS) was proved to be an effective reagent for improving the dimensional stability of wood, a bottleneck in ASE value (around 50%) existed. The reason was that MPS with low polarity opened few hydrogen bonds in the amorphous region of cellulose, while these hydrogen bonds could be reopened by water. Therefore, citric acid (CA) is chosen to cooperate with MPS to further enhance the dimensional stability of wood. In this paper, MPS and CA were used to modify wood individually (MW and CW) or with different combinations, that is, one-step modification (M/CW) and two-step modification with MPS first (M-CW) or CA first (C-MW). CA and MPS concentrations were optimized at 5 wt%. The ASE value for M/CW was only 25.74% at a weight percent gain (WPG) of 6.43%, which was only 0.6 times to MW or 0.7 times to CW. For M-CW, the ASE value gradually decreased with the soaking cycles, from 65.64% at a WPG of 9.05% to 51.20%. The C-MW had the best dimensional stability, with the ASE value 75.35% at a WPG of 11.50%. Although it decreased during the first soaking cycle, it stabilized at 62.20% at last. SEM and EDS images showed that the polymer mainly distributed in cell walls and few in cell lumen in C-MW. Thus, the enhanced dimensional stability of C-MW could be explained by CA opening the hydrogen bonds in the amorphous region of cellulose first, which provided more binding sites for MPS.

Mechanically strong and biodegradable holocellulose films prepared from Camellia oleifera shells.

Bioplastic derived from renewable lignocellulosic biomass is an attractive alternative to petroleum-based plastics. Herein, Callmellia oleifera shells (COS), a unique byproduct from tea oil industry, were delignified and converted into high-performance bio-based films via a green citric acid treatment (15 %, 100 °C and 24 h), taking advantage of their high hemicellulose content. The structure-property relations of COS holocellulose (COSH) films were systematically analyzed considering different treatment conditions. The surface reactivity of COSH was improved via a partial hydrolysis route and strong hydrogen bonding formed between the holocellulose micro/nanofibrils. COSH films exhibited high mechanical strength, high optical transmittance, improved thermal stability, and biodegradability. A mechanical blending pretreatment of COSH, which disintegrated the COSH fibers before the citric acid reaction, further enhanced the tensile strength and Young's modulus of the films up to 123.48 and 5265.41 MPa, respectively. The films decomposed completely in soil, demonstrating an excellent balance between degradability and durability.

Heat Transfer Efficiency and pMDI Curing Behavior during Hot-Pressing Process of Tea Oil Camellia (Camellia Oleifera Abel.) Shell Particleboard.

The use of agricultural biomass composites as new construction and building materials has grown rapidly in recent decades. Considering that energy consumption is one of the most important factors in production, the aim of this work is to examine how heat transfer is affected at various ratios and combinations of three-layer tea oil camellia shell (TOCS) based particleboard with the purpose of creating a mat-forming structure, which has the best physical and mechanical properties for furniture and construction use in a dry environment and consumes the least amount of energy. Additionally, it investigated how raw materials type affects the curing process of polymeric methylene diisocyanate (pMDI) using differential scanning calorimetry (DSC). According to the obtained data, the centerline temperature could reach a maximum of 125 °C after 3 min regardless of the materials or combinations, while the pMDI curing time was 100-110 °C. The results demonstrated that efficient heat transfer could help resin polymerization and improve panel properties. The effect of raw materials on the curing behavior of resin indicated that TOCS particles somehow caused more heat reactions at the curing point. It appeared that particleboard with a ratio of 40% commercial wood particles in the surface layers and 50% TOCS particles (mesh size: -3 + 14) in the core layer with a modulus of rupture (MOR) of 11.29 N/mm2 and internal bonding (IB) of 0.78 N/mm2 has the best properties and met EN 312: 2010 standard requirements for particleboard P2.

Electrolyte Design Strategies for Non-Aqueous High-Voltage Potassium-Based Batteries.

High-voltage potassium-based batteries are promising alternatives for lithium-ion batteries as next-generation energy storage devices. The stability and reversibility of such systems depend largely on the properties of the corresponding electrolytes. This review first presents major challenges for high-voltage electrolytes, such as electrolyte decomposition, parasitic side reactions, and current collector corrosion. Then, the state-of-the-art modification strategies for traditional ester and ether-based organic electrolytes are scrutinized and discussed, including high concentration, localized high concentration/weakly solvating strategy, multi-ion strategy, and addition of high-voltage additives. Besides, research advances of other promising electrolyte systems, such as potassium-based ionic liquids and solid-state-electrolytes are also summarized. Finally, prospective future research directions are proposed to further enhance the oxidative stability and non-corrosiveness of electrolytes for high-voltage potassium batteries.

Hexamethyldisilazane-Mediated Amidination of Sulfonamides and Amines with Formamides.

Hexamethyldisilazane was reacted with formamides to generate N,N-disubstituent formimidamide, after which a reaction with sulfonamides was induced to form sulfonylformamidines. This protocol can be applied for arylformamidine formation in which anilines are used as substrates under optimized conditions. The advantages of this method are high efficiency, structural diversity in products with good yields, and applicability in large-scale operations.

Facile synthesis of nanocellulose-based Cu2O/Ag heterostructure as a surface-enhanced Raman scattering substrate for trace dye detection.

Semiconductor metal-oxide/metal heterostructures with synergetic properties have potential applications in photocatalysis and optical sensors. Here, Cu2O sub-micro cubes were synthesized under environmentally benign conditions using 2, 2, 6, 6-tetramethylpyperdine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils as a reducing and stabilizing agent. Then the surface of the Cu2O cubes was decorated with silver nanoparticles (AgNPs) by a substitution reaction. The Cu2O/Ag heterostructures within the cellulose nanofibrils (CNFs) network were employed as a promising surface-enhanced Raman scattering (SERS) assay for efficient sensing of methylene blue (MB), reaching a maximum enhancement factor (EF) of 4.0 × 104. Their SERS intensities depended on the coverage density of AgNPs and the wavelength of the excitation laser. The excellent SERS performance may result from the charge transfer between Ag and Cu2O molecules and the strong electromagnetic field at the interface. The CNF-Cu2O/Ag substrates were capable of detecting MB dye down to 10-8 M level with a relative standard deviation of 10-15%, demonstrating great sensitivity and reproducibility.

Rational Design of Cellulose Nanofibrils Separator for Sodium-Ion Batteries.

Cellulose nanofibrils (CNF) with high thermal stability and excellent electrolyte wettability attracted tremendous attention as a promising separator for the emerging sodium-ion batteries. The pore structure of the separator plays a vital role in electrochemical performance. CNF separators are assembled using the bottom-up approach in this study, and the pore structure is carefully controlled through film-forming techniques. The acid-treated separators prepared from the solvent exchange and freeze-drying demonstrated an optimal pore structure with a high electrolyte uptake rate (978.8%) and Na+ transference number (0.88). Consequently, the obtained separator showed a reversible specific capacity of 320 mAh/g and enhanced cycling performance at high rates compared to the commercial glass fiber separator (290 mAh/g). The results highlight that CNF separators with an optimized pore structure are advisable for sodium-ion batteries.

Resistance to Growth of Molds for Wood Modified with Hydrophobic Hybrid Silica Gel Containing Copper Amine Complexes.

Complexation copper with amine provides an effective strategy for fixation copper in wood, while hydrophobic modification improves the dimensional stability of wood. Thus, a combination of complexation and hydrophobization is expected to enhance the efficiency of copper-based biocides. In this study, hydrophobic hybrid silica gel containing copper amine complexes (MACu) was prepared through an in situ sol-gel process in wood using methyltriethoxysilane (MTES), 3-amino-propyltriethoxysilane (APTES), and copper chloride. The resistance to growth of molds for MACu modified wood (Populus tomentosa) was measured according to ASTM D3273-16. A leaching resistance test was carried out in accordance with AWPA E11-16. The results showed that only Aspergillus niger covered the surface of untreated wood blocks and no mold grew on the MACu surface even after the leaching test. MACu xerogel and MACu wood were further characterized by SEM-EDS, FTIR, and XPS. A possible schematic diagram of the reaction mechanism was proposed to explain the high-efficiency anti-mold performance of MACu wood.

A facile access to N-sulfonylthioimidates and their use for the transformation to 3,4-dihydroquinazolines.

N-Sulfonylthioimidates can be efficiently synthesized through one-pot three-component coupling of terminal alkynes, sulfonyl azides, and thiols by using a copper(i) catalyst in the presence of 4-dimethylaminopyridine. The proposed reaction is characterized by mild reaction conditions and tolerance of diverse functional groups. Additionally, the crucial pharmacophore of 3,4-dihydroquinazolines was synthesized using a one-pot synthetic strategy from N-sulfonylthioimidates.

Facile access to N-formyl imide as an N-formylating agent for the direct synthesis of N-formamides, benzimidazoles and quinazolinones.

N-Formamide synthesis using N-formyl imide with primary and secondary amines with catalytic amounts of p-toluenesulfonic acid monohydrate (TsOH·H2O) is described. This reaction is performed in water without the use of surfactants. Moreover, N-formyl imide is efficiently synthesized using acylamidines with TsOH·H2O in water. In addition, N-formyl imide was successfully used as a carbonyl source in the synthesis of benzimidazole and quinazolinone derivatives. Notable features of N-formylation of amines by using N-formyl imide include operational simplicity, oxidant- and metal-free conditions, structurally diverse products, and easy applicability to gram-scale operation.

The underestimated charge storage capability of carbon cathodes for advanced alkali metal-ion capacitors.

Li-ion capacitors (LICs) are emerging as complementary energy storage devices to Li-ion batteries to satisfy some specific applications where high power density and long cycle life are required. Due to the wide usage of LICs, LICs with promising energy density are urgently needed; however, at this stage, the achievement of this type of LICs is the main challenge. In this study, we increased the energy density of LICs via both material optimization and charge storage mechanism exploration. Moreover, porous carbon with a high surface area of over 2800 m2 g-1 was fabricated from alkali lignin via a traditional KOH activation method assisted by self-activation. A wide voltage window of 1.0-4.8 V was applied where the synergistic storage of anions and cations was achieved. This shows that a deep discharge down to 1.0 V is necessary for the complete desorption of anions, which also triggers the adsorption of cations (Li+), resulting in increased capacity. However, a compromise must be made in the energy efficiency due to intensified battery polarization upon deep discharging. Furthermore, considering the natural abundance of sodium and potassium over lithium, Na- and K-ion capacitors have been investigated for sustainable development using the as-prepared carbon materials.

Hybrid Aqueous/Organic Electrolytes Enable the High-Performance Zn-Ion Batteries.

Rechargeable aqueous zinc ion batteries (ZIBs) are considered as one of the most promising systems for large-scale energy storage due to their merits of low cost, environmental friendliness, and high safety. The utilization of aqueous electrolyte also brings about some problems such as low energy density, fast self-discharge, and capacity fading associated with the dissolution of metals in water. To combat the issues, we utilize a freestanding vanadium oxide hydrate/carbon nanotube (V2O5·nH2O/CNT) film as the cathode and probe the performance in aqueous/organic hybrid electrolytes. The corresponding structural and morphological evolution of both V2O5·nH2O/CNT cathode and Zn anode in different electrolytes is explored. The integrity of electrodes and the suppression of zinc dendrites during cycles are largely improved in the hybrid electrolytes. Accordingly, the battery in hybrid electrolyte exhibits high capacities of 549 mAh g-1 at 0.5 A g-1 after 100 cycles and 282 mAh g-1 at 4 A g-1 after 1000 cycles, demonstrating an excellent energy density of 102 Wh kg-1 at a high power of 1500 W kg-1 based on the cathode.

Recycling polyethylene terephthalate wastes as short fibers in Strain-Hardening Cementitious Composites (SHCC).

As an important portion of the total plastic waste bulk but lack of reuse and recycling, the enormous amounts of polyethylene terephthalate (PET) solid wastes have led to serious environmental issues. This study explores the feasibility of recycling PET solid wastes as short fibers in Strain-Hardening Cementitious Composites (SHCCs), which exhibit strain-hardening and multiple cracking under tension, and therefore have clear advantages over conventional concrete for many construction applications. Based on micromechanical modeling, fiber dispersion and alkali resistance, the size of recycled PET fibers was first determined. Then the hydrophobic PET surface was treated with NaOH solution followed by a silane coupling agent to achieve the dual purpose of improving the fiber/matrix interfacial frictional bond (from 0.64 MPa to 0.80 MPa) and enhancing the alkali resistance for applications in alkaline cementitious environment. With surface treatment, recycling PET wastes as fibers in SHCCs is a promising approach to significantly reduce the material cost of SHCCs while disposing hazardous PET wastes in construction industry.

Graphene Oxide Papers Simultaneously Doped with Mg(2+) and Cl(-) for Exceptional Mechanical, Electrical, and Dielectric Properties.

This paper reports simultaneous modification of graphene oxide (GO) papers by functionalization with MgCl2. The Mg(2+) ions enhance both the interlayer cross-links and lateral bridging between the edges of adjacent GO sheets by forming Mg-O bonds. The improved load transfer between the GO sheets gives rise to a maximum of 200 and 400% increases in Young's modulus and tensile strength of GO papers. The intercalation of chlorine between the GO layers alters the properties of GO papers in two ways by forming ionic Cl(-) and covalent C-Cl bonds. The p-doping effect arising from Cl contributes to large enhancements in electrical conductivities of GO papers, with a remarkable 2500-fold surge in the through-thickness direction. The layered structure and the anisotropic electrical conductivities of reduced GO papers naturally create numerous nanocapacitors that lead to charge accumulation based on the Maxwell-Wagner (MW) polarization. The combined effect of much promoted dipolar polarizations due to Mg-O, C-Cl, and Cl(-) species results in an exceptionally high dielectric constant greater than 60 000 and a dielectric loss of 3 at 1 kHz by doping with 2 mM MgCl2. The excellent mechanical and electrical properties along with unique dielectric performance shown by the modified GO and rGO papers open new avenues for niche applications, such as electromagnetic interference shielding materials.

Graphene aerogel/epoxy composites with exceptional anisotropic structure and properties.

3D interconnected graphene aerogels (GAs) are prepared through one-step chemical reduction and rational assembly of graphene oxide (GO) sheets, so that the difficulties to uniformly disperse the individual graphene sheets in the polymer matrixes are avoided. Apart from ultralow density, high porosity, high electrical conductivity, and excellent compressibility, the resulting GAs possess a cellular architecture with a high degree of alignment when the graphene content is above a threshold, ∼0.5 wt %. The composites prepared by infiltrating GA with epoxy resin present excellent electrical conductivities, together with high mechanical properties and fracture toughness. The unusual anisotropic structure gives rise to ∼67% and ∼113% higher electrical conductivity and fracture toughness of the composites, respectively, in the alignment direction than that transverse to it.

Exceptional electrical conductivity and fracture resistance of 3D interconnected graphene foam/epoxy composites.

Cellular-structured graphene foam (GF)/epoxy composites are prepared based on a three-step fabrication process involving infiltration of epoxy into the porous GF. The three-dimensional (3D) GF is grown on a Ni foam template via chemical vapor deposition. The 3D interconnected graphene network serves as fast channels for charge carriers, giving rise to a remarkable electrical conductivity of the composite, 3 S/cm, with only 0.2 wt % GF. The corresponding flexural modulus and strength increase by 53 and 38%, respectively, whereas the glass transition temperature increases by a notable 31 °C, compared to the solid neat epoxy. The GF/epoxy composites with 0.1 wt % GF also deliver an excellent fracture toughness of 1.78 MPa·m(1/2), 34 and 70% enhancements against their "porous" epoxy and solid epoxy counterparts, respectively. These observations signify the unrivalled effectiveness of 3D GF relative to 1D carbon nanotubes or 2D functionalized graphene sheets as reinforcement for polymer composites without issues of nanofiller dispersion and functionalization prior to incorporation into the polymer.

Highly aligned graphene/polymer nanocomposites with excellent dielectric properties for high-performance electromagnetic interference shielding.

Nanocomposites that contain reinforcements with preferred orientation have attracted significant attention because of their promising applications in a wide range of multifunctional fields. Many efforts have recently been focused on developing facile methods for preparing aligned graphene sheets in solvents and polymers because of their fascinating properties including liquid crystallinity and highly anisotropic characteristics. Self-aligned in situ reduced graphene oxide (rGO)/polymer nanocomposites are prepared using an all aqueous casting method. A remarkably low percolation threshold of 0.12 vol% is achieved in the rGO/epoxy system owing to the uniformly dispersed, monolayer graphene sheets with extremely high aspect ratios (>30000). The self-alignment into a layered structure at above a critical filler content induces a unique anisotropy in electrical and mechanical properties due to the preferential formation of conductive and reinforcing networks along the alignment direction. Accompanied by the anisotropic electrical conductivities are exceptionally high dielectric constants of over 14000 with 3 wt% of rGO at 1 kHz due to the charge accumulation at the highly-aligned conductive filler/insulating polymer interface according to the Maxwell-Wagner-Sillars polarization principle. The highly dielectric rGO/epoxy nanocomposites with the engineered structure and properties present high performance electromagnetic interference shielding with a remarkable shilding efficiency of 38 dB.

Fabrication of highly-aligned, conductive, and strong graphene papers using ultralarge graphene oxide sheets.

This study demonstrates that large-size graphene oxide (GO) sheets can impart a tremendous positive impact on self-alignment, electrical conductivity, and mechanical properties of graphene papers. There is a remarkable, more than 3-fold improvement in electrical conductivity of the papers made from ultralarge GO sheets (with an average area of 272.2 µm(2)) compared to that of the small GO counterpart (with an average area of 1.1 µm(2)). The corresponding improvements in Young's modulus and tensile strength are equally notable, namely 320% and 280%, respectively. These improvements of bulk properties due to the large GO sheets are correlated to multiscale elemental and structural characteristics of GO sheets, such as the content of carboxyl groups on the GO edge, C/O ratio and Raman D/G-band intensity ratio of GO on the molecular-scale, and the degree of dispersion and stacking behavior of GO sheets on the microscale. The graphene papers made from larger GO sheets exhibit a closer-stacked structure and better alignment as confirmed by the fast Fourier transform analysis, to the benefits of their electrical conductivity and mechanical properties. The molecular dynamics simulation further elucidates that the enhanced intersheet interactions between large GO sheets play a key role in improving the Young's modulus of GO papers. The implication is that the said properties can be further improved by enhancing the intersheet stress transfer and electrical conduction especially through the thickness direction.

Transparent conductive films consisting of ultralarge graphene sheets produced by Langmuir-Blodgett assembly.

Monolayer graphene oxide (GO) sheets with sizes ranging from a few to ∼200 µm are synthesized based on a chemical method and are sorted out to obtain four different grades having uniform sizes. Transparent conductive films are produced using the ultralarge graphene oxide (UL-GO) sheets that are deposited layer-by-layer on a substrate using the Langmuir-Blodgett (LB) assembly technique. The density and degree of wrinkling of the UL-GO monolayers are turned from dilute, close-packed flat UL-GO to graphene oxide wrinkles (GOWs) and concentrated graphene oxide wrinkles (CGOWs) by varying the LB processing conditions. The method demonstrated here opens up a new avenue for high-yield fabrication of GOWs or CGOWs that are considered promising materials for hydrogen storage, supercapacitors, and nanomechanical devices. The films produced from UL-GO sheets with a close-packed flat structure exhibit exceptionally high electrical conductivity and transparency after thermal reduction and chemical doping treatments. A remarkable sheet resistance of ∼500 Ω/sq at 90% transparency is obtained, which outperforms the graphene films grown on a Ni substrate by chemical vapor deposition. The technique used in this work to produce transparent conductive UL-GO thin films is facile, inexpensive, and tunable for mass production.