Manganese-cobalt geomimetic materials for supercapacitor electrode.

A manganese-cobalt asbolane material synthesized by low-temperature cationic exchange from birnessite in cobalt nitrate solution has been comprehensively characterized and tested for the first time as a massive (with high active mass loading) positive electrode material for to asymmetric aqueous supercapacitors. The structure of this Mn-rich material, which is homologous to the natural asbolanes well known by mineralogists, consists of MnO2-type slabs with partial substitution of Co3+ for Mn; the slabs alternate with Co(OH)2 islands located in the interlayer spacing. This structural arrangement was confirmed through in-depth electronic transmission microscopy analyses, which reveal two interlocking hexagonal sublattices with distinct a lattice-cell parameters but identical c parameters. The electrochemical performance of this geomimetic phase in alkaline electrolytes is highly promising, with specific capacitance of up to 180 F g-1 at moderate current densities and 94 F g-1 at 10 A g-1. Investigation into the charge storage mechanisms indicates effective synergy between the pseudocapacitive properties of the MnO2 slabs and the Co(OH)2 islands, in which protonic conduction is suspected to play a key role. Additionally, long-term cycling and calendar aging tests suggest that the interlayer cobalt gradually migrates to the metal oxide layer upon cycling while maintaining excellent energy storage performance. This study clearly underscores the value of exploring geomimetic minerals as potential electrode materials for energy storage applications.

Kraft Black Liquor as a Carbonaceous Source for the Generation of Porous Monolithic Materials and Applications toward Hydrogen Adsorption and Ultrastable Supercapacitors.

High internal phase emulsions (HIPEs) have templated self-standing porous carbonaceous materials (carboHIPEs) while employing Kraft Black Liquor, a paper milling industry byproduct, as a carbon precursor source. As such, the starting emulsion has been prepared through a laboratory-made homogenizer, while native materials have been characterized at various length scales either with Raman spectrometry, X-ray diffraction (XRD), mercury intrusion porosimetry, and nitrogen absorption. After thermal carbonization, specific surface areas ranging from ∼600 m2 g-1 to 1500 m2 g-1 have been reached while maintaining a monolithic character. Despite a poor graphitization yield, the carbonaceous materials offer good electronic transport properties, reaching 31 S m-1. When tested toward energy storage applications, the native unwashed materials revealed a hydrogen storage of 0.07 wt % at 40 bar and room temperature (RT), while hydrogen retention is reaching 0.37 wt % at 40 bar and RT for the washed sample. When employed as supercapacitor electrodes, these carbonaceous foams are able to deliver high capacities of ∼140 F/g at 1 A/g, thereby matching the ones obtained from a commercial carbon reference, while additionally providing a restored remnant capacity of 120 F/g at 2 A/g over 5000 cycle numbers.

Composite Mn-Co electrode materials for supercapacitors: why the precursor's morphology matters!

In the energy storage field, an electrode material must possess both good ionic and electronic conductivities to perform well, especially when high power is needed. In this context, the development of composite electrode materials combining an electrochemically active and good ionic conductor phase with an electronic conductor appears as a perfectly adapted approach to generate a synergetic effect and optimize the energy storage performance. In this work, three layered MnO2 phases with various morphologies (veils, nanoplatelets and microplatelets) were combined with electronic conductor cobalt oxyhydroxides with different platelet sizes (∼20 nm vs. 70 nm wide), to synthesize 6 different composites by exfoliation and restacking processes. The influence of precursors' morphology on the distribution of the Mn and Co objects within the composites was carefully investigated and correlated with the electrochemical performance of the final restacked material. Overall, the best performing restacked composite was obtained by combining MnO2 possessing a veil morphology with the smallest cobalt oxyhydroxide nanoplatelets, leading to the most homogeneous distribution of the Mn and Co objects at the nanoscale. More generally, the aim of this work is to understand how the size and morphology of the precursor building blocks influence their distribution homogeneity within the final composite and to find the most compatible building blocks to reach a homogeneous distribution at the nanoscale.

Design of Binary Nb2O5-SiO2 Self-Standing Monoliths Bearing Hierarchical Porosity and Their Efficient Friedel-Crafts Alkylation/Acylation Catalytic Properties.

Alkylation of aromatic hydrocarbons is among the most industrially important reactions, employing acid catalysts such as AlCl3, H2SO4, HF, or H3PO4. However, these catalysts present severe drawbacks, such as low selectivity and high corrosiveness. Taking advantage of the intrinsic high acid strength and Lewis and Brønsted acidity of niobium oxide, we have designed the first series of Nb2O5-SiO2(HIPE) monolithic catalysts bearing multiscale porosity through the integration of a sol-gel process and the physical chemistry of complex fluids. The MUB-105 series offers efficient solvent-free heterogeneous catalysis toward Friedel-Crafts monoalkylation and -acylation reactions, where 100% conversion has been reached at 140 °C while cycling. Alkylation reactions employing the MUB-105(1) catalyst have a maximum turnover number (TON) of 104 and a turnover frequency (TOF) of 9 h-1, whereas for acylation, MUB-105(1) and MUB-105(2) yield maximum TON and TOF values of 107 and 11 h-1, respectively. Moreover, the catalysts are selective, producing equal amounts of ortho- and para-substituted alkylated products and greater than 90% of the para-substituted acylated product. The highest catalytic efficiencies are obtained for the MUB-105(1) catalyst, bearing the smallest Nb2O5 particle sizes, lowest Nb2O5 content, and the highest amorphous character. The catalysts presented here are in a monolithic self-standing state, offering easy handling, reusability, and separation from the final products.

Direct Triple Annulations: A Way to Design Large Triazastarphenes with Intertwined Hexagonal Packing.

A new straightforward synthetic strategy has been elaborated to achieve star-shaped triazatrinaphthylene and, for the first time, triazatrianthrylene derivatives. Their solution- and solid-state properties were thoroughly characterized by cyclic voltammetry, UV-vis absorption spectroscopy, X-ray diffraction, and density functional theory calculations. Original hexagonal molecular arrangements were found in the crystal phase, which opens a new pathway for designing materials with improved three-dimensional charge-transport properties.

Controlled Nanostructuration of Cobalt Oxyhydroxide Electrode Material for Hybrid Supercapacitors.

Nanostructuration is one of the most promising strategies to develop performant electrode materials for energy storage devices, such as hybrid supercapacitors. In this work, we studied the influence of precipitation medium and the use of a series of 1-alkyl-3-methylimidazolium bromide ionic liquids for the nanostructuration of ß(III) cobalt oxyhydroxides. Then, the effect of the nanostructuration and the impact of the different ionic liquids used during synthesis were investigated in terms of energy storage performances. First, we demonstrated that forward precipitation, in a cobalt-rich medium, leads to smaller particles with higher specific surface areas (SSA) and an enhanced mesoporosity. Introduction of ionic liquids (ILs) in the precipitation medium further strongly increased the specific surface area and the mesoporosity to achieve well-nanostructured materials with a very high SSA of 265 m2/g and porosity of 0.43 cm3/g. Additionally, we showed that ILs used as surfactant and template also functionalize the nanomaterial surface, leading to a beneficial synergy between the highly ionic conductive IL and the cobalt oxyhydroxide, which lowers the resistance charge transfer and improves the specific capacity. The nature of the ionic liquid had an important influence on the final electrochemical properties and the best performances were reached with the ionic liquid containing the longest alkyl chain.

pH-Mediated Colorimetric and Luminescent Sensing of Aqueous Nitrate Anions by a Platinum(II) Luminophore@Mesoporous Silica Composite.

Increased levels of nitrate (NO3-) in the environment can be detrimental to human health. Herein, we report a robust, cost-effective, and scalable, hybrid material-based colorimetric/luminescent sensor technology for rapid, selective, sensitive, and interference-free in situ NO3- detection. These hybrid materials are based on a square-planar platinum(II) salt [Pt(tpy)Cl]PF6 (tpy = 2,2';6',2″-terpyridine) supported on mesoporous silica. The platinum salt undergoes a vivid change in color and luminescence upon exposure to aqueous NO3- anions at pH ≤ 0 caused by substitution of the PF6- anions by aqueous NO3-. This change in photophysics of the platinum salt is induced by a rearrangement of its crystal lattice that leads to an extended Pt···Pt···Pt interaction, along with a concomitant change in its electronic structure. Furthermore, incorporating the material into mesoporous silica enhances the surface area and increases the detection sensitivity. A NO3- detection limit of 0.05 mM (3.1 ppm) is achieved, which is sufficiently lower than the ambient water quality limit of 0.16 mM (10 ppm) set by the United States Environmental Protection Agency. The colorimetric/luminescence of the hybrid material is highly selective to aqueous NO3- anions in the presence of other interfering anions, suggesting that this material is a promising candidate for the rapid NO3- detection and quantification in practical samples without separation, concentration, or other pretreatment steps.

Graphite-type activated carbon from coconut shell: a natural source for eco-friendly non-volatile storage devices.

Carbon from biomass as an active material for supercapacitor electrodes has attracted much interest due to its environmental soundness, abundance, and porous nature. In this context, activated carbon prepared from coconut shells via a simple activation process (water or steam as activation agents) was used as an active material in electrodes for eco-friendly supercapacitors. X-ray diffraction (XRD), Raman spectroscopy, conductivity, scanning electron microscopy (SEM), N2 sorption and thermogravimetry coupled to mass spectrometry (TGA-MS) studies revealed that activated carbon produced by this approach exhibit a graphitic phase, a high surface area, and large pore volume. The energy storage properties of activated carbon electrodes correlate with the morphological and structural properties of the precursor material. In particular, electrodes made of activated carbon exhibiting the largest Brunauer-Emmett-Teller (BET) surface area, i.e. 1998 m2 g-1, showed specific capacitance of 132.3 F g-1 in aqueous electrolyte (1.5 M H2SO4), using expanded graphite sheets as current collector substrates. Remarkably, this sample in a configuration with ionic liquid (1-methyl-1-propy-pyrrolizinium bis(fluorosulfonyl)mide) (MPPyFSI) as electrolyte and a polyethylene separator displayed an outstanding storage capability and energy-power handling capability of 219.4 F g-1 with a specific energy of 92.1 W h kg-1 and power density of 2046.9 W kg-1 at 1 A g-1 and maintains ultra-high values at 30 A g-1 indicating the ability for a broad potential of energy and power related applications. To the best of our knowledge, these values are the highest ever reported for ionic liquid-based supercapacitors with activated carbon obtained from the biomass of coconut shells.

Metal-organic magnets with large coercivity and ordering temperatures up to 242°C.

Magnets derived from inorganic materials (e.g., oxides, rare-earth-based, and intermetallic compounds) are key components of modern technological applications. Despite considerable success in a broad range of applications, these inorganic magnets suffer several drawbacks, including energetically expensive fabrication, limited availability of certain constituent elements, high density, and poor scope for chemical tunability. A promising design strategy for next-generation magnets relies on the versatile coordination chemistry of abundant metal ions and inexpensive organic ligands. Following this approach, we report the general, simple, and efficient synthesis of lightweight, molecule-based magnets by postsynthetic reduction of preassembled coordination networks that incorporate chromium metal ions and pyrazine building blocks. The resulting metal-organic ferrimagnets feature critical temperatures up to 242°C and a 7500-oersted room-temperature coercivity.

Silylation of bacterial cellulose to design membranes with intrinsic anti-bacterial properties.

In this work, we report a convenient method of grafting non-leachable bioactive amine functions onto the surface of bacterial cellulose (BC) nanofibrils, via a simple silylation treatment in water. Two different silylation protocols, involving different solvents and post-treatments were envisaged and compared, using 3-aminopropyl-trimethoxysilane (APS) and (2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPS) as silylating agents. In aqueous and controlled conditions, water-leaching resistant amino functions could be successfully introduced into BC, via a simple freeze-drying process. The silylated material remained highly porous, hygroscopic and displayed sufficient thermal stability to support the sterilization treatments generally required in medical applications. The impact of the silylation treatment on the intrinsic anti-bacterial properties of BC was investigated against the growth of Escherichia coli and Staphylococcus aureus. The results obtained after the in vitro studies revealed a significant growth reduction of S. aureus within the material.

Plasma-deposition of α-FeOOH particles on biochar using a gliding arc discharge in humid air: a green and sustainable route for producing oxidation catalysts.

Non-thermal atmospheric plasma of the gliding arc type was used as a tool for goethite-on-biochar hybrid material preparation. Biochars were first prepared by carbonizing raffia bamboo (the leafstalk of raffia palm) pith at 300 °C (BC3), 500 °C (BC5) and 700 °C (BC7). A suspension of each biochar in Fe2+ aqueous solution was then exposed to a plasma discharge burning in humid air. α-FeOOH particles were thus formed and spontaneously deposited on the biochar surface. In order to investigate the effect of plasma species on the support during goethite deposition, biochars were also treated with plasma in the absence of Fe2+ ions and then characterized. Results revealed a substantial hydroxylation and slight N-doping of biochar after plasma treatment. The prepared composite materials were tested in oxidative degradation of nitroresorcinol. The catalytic performances were in the order Fe-BC3 < Fe-BC7 < Fe-BC5 according to the abatement efficiency and half-time values obtained for each catalyst. This study establishes that waste biomass and atmospheric air can be simultaneously valorised for green production of heterogeneous catalysts.

Ionic liquids to monitor the nano-structuration and the surface functionalization of material electrodes: a proof of concept applied to cobalt oxyhydroxide.

This paper reports on an innovative and efficient approach based on the use of ionic liquids to govern the nano-structuration of HCoO2, in order to optimize the porosity and enhance the ionic diffusion through the electrode materials. In this work, we show that (1-pentyl-3-methyl-imidazolium bromide (PMIMBr) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4)) ionic liquids (ILs) used as templates during the synthesis orientate the nanoparticle aggregation which leads to increase of the porosity and the average pore size of the electrode material. It is also demonstrated that the ILs are strongly bonded to the HCoO2 surface, leading to surface functionalized HCoO2 materials, also called nanohybrids. This surface tailoring stabilizes the material upon cycling and shifts the oxidation potential linked to the Co(iii)/Co(iv) redox couple to lower voltage in an alkaline 5 M KOH electrolyte. The surface and porosity optimizations facilitate the ionic diffusion through the material, improve the electron transfer ability within the electrode and lead to greatly enhanced specific capacity in both alkaline 5 M-KOH and neutral 0.5 M-K2SO4 aqueous electrolytes (66.7 mA h g-1 and 47.5 mA h g-1 respectively for HCoO2-PMIMBr and HCoO2-EMIMBF4 compared to 18.1 mA h g-1 for bare HCoO2 in 5 M-KOH at 1 A g-1).

Preparation of Polyester PolyMIPEs by Polycondensation of Low-Molecular Weight Polyol and Divinyl Ester Using Microwave Activation.

Several stable non-aqueous apolar-in-polar medium internal phase emulsions (MIPEs) containing divinyl adipate and pentaerythritol in the continuous phase are formulated by varying the nature of the hydrocarbon. Polycondensation is then conducted either under conventional heating or microwave irradiation after addition of a commercially available organocatalyst. Solvent elimination and drying lead to the corresponding polyester polyMIPEs. A tremendous morphological difference between materials is observed according to the heating method employed. The particular efficiency of microwave activation in the polycondensation of the continuous phase of a non-aqueous emulsion is discussed.

Finely Tuned SnO2 Nanoparticles for Efficient Detection of Reducing and Oxidizing Gases: The Influence of Alkali Metal Cation on Gas-Sensing Properties.

Tin dioxide (SnO2) nanoparticles were straightforwardly synthesized using an easily scaled-up liquid route that involves the hydrothermal treatment, either under acidic or basic conditions, of a commercial tin dioxide particle suspension including potassium counterions. After further thermal post-treatment, the nanomaterials have been thoroughly characterized by Fourier transform infrared and Raman spectroscopy, powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and nitrogen sorption porosimetry. Varying pH conditions and temperature of the thermal treatment provided cassiterite SnO2 nanoparticles with crystallite sizes ranging from 7.3 to 9.7 nm and Brunauer-Emmett-Teller surface areas ranging from 61 to 106 m2·g-1, acidic conditions favoring potassium cation removal. Upon exposure to a reducing gas (H2, CO, and volatile organic compounds such as ethanol and acetone) or oxidizing gas (NO2), layers of these SnO2 nanoparticles led to highly sensitive, reversible, and reproducible responses. The sensing results were discussed in regard to the crystallite size, specific area, valence band energy, Debye length, and chemical composition. Results highlight the impact of the counterion residuals, which affect the gas-sensing performance to an extent much higher than that of size and surface area effects. Tin dioxide nanoparticles prepared under acidic conditions and calcined in air showed the best sensing performances because of lower amount of potassium cations and higher crystallinity, despite the lower surface area.