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The magnetic properties of spinel nanoparticles can be controlled by synthesizing particles of a specific shape and size. The synthesized nanorods, nanodots and cubic nanoparticles have different crystal planes selectively exposed on the surface. The surface effects on the static magnetic properties are well documented, while their influence on spin waves dispersion is still being debated. Our ability to manipulate spin waves using surface and defect engineering in magnetic nanoparticles is the key to designing magnonic devices. We synthesized cubic and spherical nanoparticles of a classical antiferromagnetic material Co3O4 to study the shape and size effects on their static and dynamic magnetic proprieties. Using a combination of experimental methods, we probed the magnetic and crystal structures of our samples and directly measured spin wave dispersions using inelastic neutron scattering. We found a weak, but unquestionable, increase in exchange interactions for the cubic nanoparticles as compared to spherical nanoparticle and bulk powder reference samples. Interestingly, the exchange interactions in spherical nanoparticles have bulk-like properties, despite a ferromagnetic contribution from canted surface spins.

Through glycerol electrooxidation, we demonstrate the viability of using a PdNi catalyst electrodeposited on Ni foam to facilitate industrially relevant rates of hydrogen generation while concurrently providing valuable organic chemicals as glycerol oxidation products. This electrocatalyst, in a solution of 2 M NaOH and 1 M glycerol at 80 °C, enabled current densities above 2000 mA cm−2 (in a voltammetric sweep) to be obtained in atmospheres of both air and N2. Repeated potential cycling under an aerated atmosphere to these exceptional current densities indicated a high stability of the catalyst. Through steady state polarisation curves, 1000 mA cm−2 was reached below an anodic potential of 0.8 V vs RHE. Chronoamperometry showed glycerate and lactate being the major oxidation products, with increased selectivity for lactate at the expense of glycerate in aerated systems. Aerated atmospheres were demonstrated to consistently increase the apparent Faradaic efficiency to >100%, as determined by the concentration of oxidation products in solution. The excellent performance of PdNi/Ni in aerated solutions suggests that O2 removal from the electrolyte is not needed for an industrial glycerol electrooxidation process, and that combining electrochemical and chemical glycerol oxidation, in the presence of dissolved O2, presents an important process advantage., QC 20230830

Glycerol electrolysis affords a green and energetically favorable route for the production of value-added chemicals at the anode and H2 production in parallel at the cathode. Here, a facile method for trapping Pt nanoparticles at oxygen vacancies of molybdenum oxide (MoOx) nanosheets, yielding a high-performance MoOx/Pt composite electrocatalyst for both the glycerol oxidation reaction (GOR) and the hydrogen evolution reaction (HER) in alkaline electrolytes, is reported. Combined electrochemical experiments and theoretical calculations reveal the important role of MoOx nanosheets for the adsorption of glycerol molecules in GOR and the dissociation of water molecules in HER, as well as the strong electronic interaction with Pt. The MoOx/Pt composite thus significantly enhances the specific mass activity of Pt and the kinetics for both reactions. With MoOx/Pt electrodes serving as both cathode and anode, two-electrode glycerol electrolysis is achieved at a cell voltage of 0.70 V to reach a current density of 10 mA cm−2, which is 0.90 V less than that required for water electrolysis.

Carboxylated cellulose nanofibers, prepared by TEMPO-mediated oxidation (TOCN), were processed into asymmetric mesoporous membranes using a facile paper-making approach and investigated as lithium ion battery separators. Membranes made of TOCN with sodium carboxylate groups (TOCN-COO-Na+) showed capacity fading after a few cycles of charging and discharging. On the other hand, its protonated counterpart (TOCN-COOH) showed highly improved electrochemical and cycling stability, displaying 94.5% of discharge capacity maintained after 100 cycles at 1 C rate of charging and discharging. The asymmetric surface porosity of the membranes must be considered when assembling a battery cell as it influences the rate capabilities of the battery. The wood-based TOCN-membranes have a good potential as an ecofriendly alternative to conventional fossil fuel-derived separators without adverse side effects.

TEMPO-oxidized cellulose nanofibrils (TOCN) are pH-responsive biopolymers which undergo sol-gel transition at acidic conditions (pH < 4) due to charge neutralization. Electronically conducting materials can be coated by such gels during aqueous electrolysis, when an electrochemical reaction generates a local pH decrease at the electrode surface. In this work, electro-precipitation of different TOCN gels has been performed on oxygen evolving anodes. We demonstrate that TOCN hydrogels can be electrochemically coated on the surface of any conductive material with even complex 3D shape. Further, not only TOCN but also micro- or nanosized particles containing TOCN composites can be coated on the electrode surface, and coatings containing multiple layers of different composites can be also produced. We demonstrate that this simple and facile electrocoating technique can be subject to various applications, such as coatings making electrodes selective for the hydrogen evolution reaction, as well as a new eco-friendly aqueous-based synthesis of Li-ion battery electrodes.

In this paper, we use dynamic light scattering in polarized and depolarized modes to determine the translational and rotational diffusion coefficients of concentrated rodlike cellulose nanocrystals in aqueous suspension. Within the range of studied concentrations (1-5 wt %), the suspension starts a phase transition from an isotropic to an anisotropic state as shown by polarized light microscopy and viscosity measurements. Small-angle neutron scattering measurements also confirmed the start of cellulose nanocrystal alignment and a decreasing distance between the cellulose nanocrystals with increasing concentration. As expected, rotational and translational diffusion coefficients generally decreased with increasing concentration. However, the translational parallel diffusion coefficient was found to show a local maximum at the onset of the isotropic-to-nematic phase transition. This is attributed to the increased available space for rods to move along their longitudinal axis upon alignment. This increased parallel diffusion coefficient thus confirms the general idea that rodlike particles gain translational entropy upon alignment while paying the price for losing rotational degrees of freedom. Once the concentration increases further, diffusion becomes more hindered even in the aligned regions due to a reduction in the rod separation distance. This leads once again to a decrease in translational diffusion coefficients. Furthermore, the relaxation rate for fast mode translational diffusion (parallel to the long particle axis) exhibited two regimes of relaxation behavior at concentrations where significant alignment of the rods is measured. We attribute this unusual dispersive behavior to two length scales: one linked to the particle length (at large wavevector q) and the other to a twist fluctuation correlation length (at low wavevector q) along the cellulose nanocrystal rods that is of a larger length when compared to the actual length of rods and could be linked to t

The gene CCT67099 from Fusarium fujikuroi was shown to encode a novel enzyme from the Lytic Polysaccharide Monooxygenase (LPMO) Family AA11. The gene was expressed and a truncated version of the enzyme, designated as FfAA11, was purified from the periplasmic space of Escherichia coli cells at high yield. FfAA11 exhibited oxidative activity against α- and β-chitins, as well as lobster shells. Under optimised conditions, FfAA11 introduced 35 nmol of carboxylate (COO−) moieties per milligram of α-chitin. These carboxylate groups were introduced onto the chitin surface under mild enzymatic oxidation conditions in an aqueous solution without changes to the crystallinity of the chitin fibres. FfAA11 was also combined with a simple and environmentally friendly chemical method that transforms recalcitrant chitins into desirable functionalised (nano)materials. The use of ethyl(hydroxyimino)cyanoacetate (Oxyma)-assisted click chemistry allowed the rapid modification of the surface of FfAA11-oxidized chitins, with a fluorescent probe, a peptide, and gold nanoparticles. The chemical steps performed, including the FfAA11 oxidase treatment and surface chemical modification, were achieved without the production of any toxic by-products or waste organic solvents. This approach represents a novel method for the greener production of chitin-based biomaterials., QC 20180521

Assembly of bio-based nano-sized particles into complex architectures and morphologies is an area of fundamental interest and technical importance. We have investigated the assembly of sulfonated cellulose nanocrystals (CNC) dispersed in a shrinking levitating aqueous drop using time-resolved small angle X-ray scattering (SAXS). Analysis of the scaling of the particle separation distance (d) with particle concentration (c) was used to follow the transition of CNC dispersions from an isotropic state at 1-2 vol% to a compressed nematic state at particle concentrations above 30 vol%. Comparison with SAXS measurements on CNC dispersions at near equilibrium conditions shows that evaporation-induced assembly of CNC in large levitating drops is comparable to bulk systems. Colloidal states with d vs. c scalings intermediate between isotropic dispersions and unidirectional compression of the nematic structure could be related to the biphasic region and gelation of CNC. Nanoscale structural information of CNC assembly up to very high particle concentrations can help to fabricate nanocellulose-based materials by evaporative methods.

Understanding the assembly of nanoparticles into superlattices with well-defined morphology and structure is technologically important but challenging as it requires novel combinations of in-situ methods with suitable spatial and temporal resolution. In this study, we have followed evaporation-induced assembly during drop casting of superparamagnetic, oleate-capped gamma-Fe2O3 nanospheres dispersed in toluene in real time with Grazing Incidence Small Angle X-ray Scattering (GISAXS) in combination with droplet height measurements and direct observation of the dispersion. The scattering data was evaluated with a novel method that yielded time-dependent information of the relative ratio of ordered (coherent) and disordered particles (incoherent scattering intensities), superlattice tilt angles, lattice constants, and lattice constant distributions. We find that the onset of superlattice growth in the drying drop is associated with the movement of a drying front across the surface of the droplet. We couple the rapid formation of large, highly ordered superlattices to the capillary-induced fluid flow. Further evaporation of interstitital solvent results in a slow contraction of the superlattice. The distribution of lattice parameters and tilt angles was significantly larger for superlattices prepared by fast evaporation compared to slow evaporation of the solvent.

Silicon is a good alternative to conventional graphite anode but it has bad cycling and rate performance. To overcome these severe problems, extensively interconnected silicon nanoparticles using carbon network derived from ultrathin cellulose nanofibers were synthesized. Ultrathin cellulose nanofibers, an abundant and sustainable material, entangle each silicon nanoparticle and become extensively interconnected carbon network after pyrolysis. This wide range interconnection provides an efficient electron path by decreasing the likelihood that electrons experience contact resistivity and also suppresses the volume expansion of silicon during lithiation. In addition, Ultrathin cellulose nanofibers are carboxylated and therefore adhesive to silicon nanoparticles through hydrogen bonding. This property makes ultrathin cellulose the perfect carbon source when making silicon composites. As a consequence, it exhibits 808 mAh g(-1) of the reversible capacity after 500 cycles at high current density of 2 A g(-1) with a coulombic efficiency of 99.8%. Even at high current density of 8 A g(-1), it shows a high reversible discharge capacity of 464 mAh g(-1). Moreover, extensively interconnected carbon network prevents the formation of a brittle electrode with a water-based binder. Therefore, this remarkable material has a huge potential for LIBs applications.

The physicochemical properties used in numerous advanced nanostructured devices are directly controlled by the oxidation states of their constituents. In this work we combine electron energy-loss spectroscopy, blind source separation, and computed tomography to reconstruct in three dimensions the distribution of Fe2+ and Fe3+ ions in a FeO/Fe3O4 core/shell cube-shaped nanoparticle with nanometric resolution. The results highlight the sharpness of the interface between both oxides and provide an average shell thickness, core volume, and average cube edge length measurements in agreement with the magnetic characterization of the sample.

QC 20170421