Construction of Nanofibrillar Networked Wood Aerogels Derived from Typical Softwood and Hardwood: A Comparative Study on the In Situ Formation Mechanism of Nanofibrillar Networks.

The construction of networks within natural wood (NW) lumens to produce porous wood aerogels (WAs) with fascinating characteristics of being lightweight, flexible, and porous is significant for the high value-added utilization of wood. Nonetheless, how wood species affect the structure and properties of WAs has not been comprehensively investigated. Herein, typical softwood of fir and hardwoods of poplar and balsa are employed to fabricate WAs with abundant nanofibrillar networks using the method of lignin removal and nanofibril's in situ regeneration. Benefiting from the avoidance of xylem ray restriction and the exposure of the cellulose framework, hardwood has a stronger tendency to form nanofibrillar networks compared to softwood. Specifically, a larger and more evenly distributed network structure is displayed in the lumens of balsa WAs (WA-3) with a low density (59 kg m-3), a high porosity (96%), and high compressive properties (strain = 40%; maximum stress = 0.42 MPa; height retention = 100%) because of the unique structure and properties of WA-3. Comparatively, the specific surface area (SSA) exhibits 25-, 27-, and 34-fold increments in the cases of fir WAs (WA-1), poplar WAs (WA-2), and WA-3. The formation of nanofibrillar networks depends on the low-density and thin cell walls of hardwood. This work offers a foundation for investigating the formation mechanisms of nanonetworks and for expanding the potential applications of WAs.

Rational Manipulation of Active CNT Encapsulated Fe Doped NiCoP Nanoparticles In Situ Grown in Hierarchically Carbonized Wood for High-Current-Density Water Splitting.

Precise morphology design and electronic structure regulation are critically significant to promote catalytic activity and stability for electrochemical hydrogen production at high current density. Herein, the carbon nanotube (CNT) encapsulated Fe-doped NiCoP nanoparticles is in-situ grown in hierarchical carbonized wood (NCF0.5 P@CNT/CW) for water splitting. Coupling merits of porous carbonized wood (CW) substrate, CNT encapsulating and Fe doping, the NCF0.5 P@CNT/CW features remarkable and durable electrocatalytic activity. The overpotentials of NCF0.5 P@CNT/CW at 50 mA cm-2 mV and 205 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and features high current density of 800 mA cm-2 within 300 mV for both OER and HER. Moreover, NCF0.5 P@CNT/CW displays outstanding overall water splitting performance (η50 = 1.62 V and η100 = 1.67 V), outperforming Pt/C║RuO2 (η50 = 1.74 V), and can achieve the current density of 700 mA cm-2 at a lower cell voltage of 1.78 V. Overpotential is only 4.0 % decay after 120 h measurement at 50 mA cm-2 . Density functional theory (DFT) calculations reveals Fe doping optimizes the binding energy and Gibbs free energy of intermediates, and regulates d-band center of NCF0.5 P@CNT/CW. Such synergistic strategy of morphology manipulation and electronic structure optimization provides a spark for developing effective and robust bifunctional catalysts.

Wood-inspired elastic and conductive cellulose aerogel with anisotropic tubular and multilayered structure for wearable pressure sensors and supercapacitors.

Cellulose nanofiber (CNF) aerogels hold considerable potential in wearable devices as pressure sensors and flexible electrochemical energy storage. However, the undirectional assembly of CNFs results in poor mechanical performance, which limits their application in structural engineering. In this study, we propose an anisotropic aerogel with both elastic and conductive properties inspired by the micro-nanostructure of natural wood. One-dimensional TEMPO cellulose nanofibers (TOCNF) were utilized as structural building blocks, while two-dimensional reduced graphene oxide (rGO) served as the electron transfer platform, owing to their high mechanical strength. The directionally aligned tubular structure composed of multilayered sheets was formed through rapid unidirectional freezing and subsequent steam heating reduction. These structures efficiently transferred stress throughout the porous skeleton, resulting in TOCNF-rGO aerogels with high compressibility and excellent fatigue resistance (2000 cycles at 60 % strain). The aerogel also exhibited high sensitivity, wide detection range, relatively fast response, and excellent compression cycle stability, making it suitable for accurately detecting various human biological and motion signals. Additionally, TOCNF-rGO can be assembled into a flexible all-solid-state symmetric supercapacitor that delivers excellent electrochemical performance. It is expected that this biomass-derived aerogel will be a versatile material for flexible electronic devices for energy conversion and storage.

Approaching well-dispersed MoS2 assisted with cellulose nanofiber for highly durable hydrogen evolution reaction.

The agglomeration and low conductivity of molybdenum disulfide (MoS2) electrocatalysts restrict the presentation of its real intrinsic reaction activity, which leads to challenges for the high-performance hydrogen evolution reaction (HER). Herein, a well-dispersed and superhydrophilic/superaerophobic MoS2 catalyst with uniform three-dimensional conductive networks have been prepared assisted with cellulose nanofiber (CNF) and carboxylated multi-walled carbon nanotubes (cMWCNT). The resulted CNF/cMWCNT/MoS2 catalysts present a superhydrophilic/superaerophobic state with contact angles for water and bubble of 0° and 154.1° respectively. This structure effectively disperses MoS2 nanoparticles through uniform embeddedness and promotes gas-liquid mass transfer via wettability. Benefiting from these optimizations, the CNF/cMWCNT/MoS2 exhibits better HER performance and a low overpotential (154 mV @ 10 mA/cm2). Encourangingly, CNF/cMWCNT/MoS2 catalysts have a slight decay of 6.99 % at 10 mA/cm2 after 100 h, while the cMWCNT/MoS2 shows a decay of 35.83 %. This approach using natural CNF for well-dispersed catalysts provides a potential for high-performance HER electrode design.

Numerical modelling of magnetic characteristics of ferrite core taking account of both eddy current and displacement current.

In the magnetic field analysis of magnetic devices using a ferrite core, such as a pulse transformer, the frequency-domain analysis is often carried out using the measured complex permeability under different frequency range. However, the nonlinear magnetic characteristics cannot be considered in the frequency-domain analysis because of the harmonics caused by it cannot be represented. The nonlinear magnetic characteristics can be considered in the time-domain analysis, but suitable constant conductivity and permittivity taking account of the microstructure of ferrite core, which can represent the measured complex permeability under different frequencies, needs to be investigated for the time-domain analysis. In this paper, the effective permeability of a toroidal ferrite core is tried to be demonstrated by using the linear ac steady state magnetic field analysis taking account eddy currents and displacement currents. It is shown that the measured permeability can be realized roughly by using the modified constant conductivity and permittivity. The nonlinear time-domain magnetic field analysis can be carried out using the modified constant conductivity and permittivity obtained from this paper.

Cr-Doped FeNi-P Nanoparticles Encapsulated into N-Doped Carbon Nanotube as a Robust Bifunctional Catalyst for Efficient Overall Water Splitting.

Exploring high-efficiency, stable, and cost-effective bifunctional electrocatalysts for overall water splitting is greatly desirable and challenging. Herein, a newly designed hybrid catalyst with Cr-doped FeNi-P nanoparticles encapsulated into N-doped carbon nanotubes (Cr-doped FeNi-P/NCN) with unprecedented electrocatalytic activity is developed by a simple one-step heating treatment. The as-synthesized Cr-doped FeNi-P/NCN with moderate Cr doping exhibits admirable oxygen evolution reaction and hydrogen evolution reaction activities with overpotentials of 240 and 190 mV to reach a current density of 10 mA cm-2 in 1 m KOH solution. When used in overall water splitting as a bifunctional catalyst, it needs only 1.50 V to give a current density of 10 mA cm-2 , which is superior to its typically integrated Pt/C and RuO2 counterparts (1.54 V @ 10 mA cm-2 ). Density functional theory calculation confirms that Cr doping into a FeNi-host can effectively alter the relative Gibbs adsorption energy and reduces the theoretical overpotential. Additionally, the synergetic effects between Cr-doped FeNi-P nanoparticles and NCNs are regarded as significant contributors to accelerate charge transfer and promote electrocatalytic activity in hybrid catalysts.

Erratum to "Numerical modelling of magnetic characteristics of ferrite core taking account of both eddy current and displacement current" [Heliyon Volume 5, Issue 8, August 2019, e02229].

[This corrects the article DOI: 10.1016/j.heliyon.2019.e02229.].

Cellulose Nanofibrils Aerogel Cross-Linked by Poly(vinyl alcohol) and Acrylic Acid for Efficient and Recycled Adsorption with Heavy Metal Ions.

Cellulose nanofibrils (CNFs), disintegrated from natural fibers, are promising alternatives in wastewater purification for the porous structure and numerous hydroxyls. The pristine CNFs aerogel has limited mechanical strength and are vulnerable to collapse when exposed to water. In this work, eco-friendly and recycled CNFs aerogel adsorbents were successfully prepared using cellulose nanofibrils (CNFs), which cross-linked by poly(vinyl alcohol) (PVA) and acrylic acid (AA). The combination of PVA and AA endowed CNFs aerogel strong three-dimensional porous structure and desirable adsorption properties. The heavy metal ions were adsorbed on the CNFs-PVA-AA (CPA) adsorbents efficiently and the maximum adsorption capacities for Cu2+ and Pb2+ approached 30.0 mg/g and 131.5 mg/g, respectively. The CPA adsorbent also showed excellent reusability and their adsorption capacities maintained 89% and 88% for Cu2+ and Pb2+ after 5 repeated uses. The adsorption of these heavy metal ions were confirmed to follow pseudo-second-order kinetic and Langmuir isotherm model. The functions of C ═ O and -OH were the major adsorption sites. Chemical adsorption combined with the porous physical adsorption made the CPA to be excellent adsorbent for the removal of heavy metal ions in wastewater.

A green route to prepare fluorescent and absorbent nano-hybrid hydrogel for water detection.

An environment-friendly fluorescent nano-hybrid hydrogel has been synthesized successfully, from cellulose nanocrystal (CNC), acrylic acid (AA) and phosphorescent Eu2+/Dy3+ doped SrAl2O4 via free radical polymerization. The hydrogel network matrix fixed Eu2+/Dy3+ doped SrAl2O4 nanoparticles by polymer chains with coordinate bonds that prevented particles from aggregating and quenching in water. The fluorescent nano-hybrid hydrogel exhibited extremely high water absorption of which the swelling ratio in distilled water and NaCl salt solution were respectively of 323.35 g/g and 32.65 g/g. Furthermore, the hydrogel displayed excellent water retention property that can keep half of the moisture even exposed to 80 °C for 210 min. Besides, the hydrogel had bright green fluorescence under the sunlight or ultraviolet excitation, and the fluorescence intensity was up to 125477 after swelling 50 times in water. The time-resolved photoluminescence (TRPL) afterglow decay examination showed that the fluorescent emission persisted for 4 h after hydrogels excited at 368 nm wavelength UV-light for 10 min. The fluorescence intensity behaved significant linear relationship with the swelling ratio. As a result, these hydrogels were considered as promising candidates for the preparation of stable and sensitive sensor materials in green water detection.

Preparation of highly charged cellulose nanofibrils using high-pressure homogenization coupled with strong acid hydrolysis pretreatments.

Cellulose nanofibrils (CNFs) are attracting much attention for the advantages of excellent mechanical strength, good optical transparency, and high surface area. An eco-friendly and energy-saving method was created in this work to produce highly negative charged CNFs using high-pressure mechanical defibrillation coupled with strong acid hydrolysis pretreatments. The morphological development, zeta potential, crystal structure, chemical composition and thermal degradation behavior of the resultant materials were evaluated by transmission electron microscopy (TEM), zeta potential analysis, X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), and thermogravimetric analysis (TGA). These CNFs were fully separated, surface-charged, and highly entangled. They showed a large fiber aspect ratio compared to traditional cellulose nanocrystrals that are produced by strong acid hydrolysis. Compared to hydrochloric acid hydrolysis, the CNFs produced by sulfuric acid pretreatments were completely defibrillated and presented stable suspensions (or gels) even at low fiber content. On the other hand, CNFs pretreated by hydrochloric acid hydrolysis trended to aggregate because of the absence of surface charge. The crystallinity index (CI) of CNFs decreased because of mechanical defibrillation, and then increased dramatically with increased sulfuric acid concentration and reaction time. FTIR analysis showed that the C-O-SO3 group was introduced on the surfaces of CNFs during sulfuric acid hydrolysis. These sulfate groups accelerated the thermal degradation of CNFs, which occurred at lower temperature than wood pulp, indicating that the thermal stability of sulfuric acid hydrolyzed CNFs was decreased. The temperature of the maximum decomposition rate (Tmax) and the maximum weight-loss rates (MWLRmax) were much lower than for wood pulp because of the retardant effect of sulfuric acid during the combustion of CNFs. By contrast, the CNFs treated with hydrochloric acid had better thermal stability, because no functional groups were introduced on the surface.