David Portehault

Porous boron nitride nanosheets for effective water cleaning

Effective removal of oils, organic solvents and dyes from water is of significant, global importance for environmental and water source protection. Advanced sorbent materials with excellent sorption capacity need to be developed. Here we report porous boron nitride nanosheets with very high specific surface area that exhibit excellent sorption performances for a wide range of oils, solvents and dyes. The nanostructured material absorbs up to 33 times its own weight in oils and organic solvents while repelling water. The saturated boron nitride nanosheets can be readily cleaned for reuse by burning or heating in air because of their strong resistance to oxidation. This easy recyclability further demonstrates the potential of porous boron nitride nanosheets for water purification and treatment.

Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives

and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Boron Carbon Nitride Nanostructures from Salt Melts: Tunable Water-Soluble Phosphors

A simple, high yield, chemical process is developed to fabricate layered h-BN nanosheets and BCNO nanoparticles with a diameter of ca. 5 nm at 700 °C. The use of the eutectic LiCl/KCl salt melt medium enhances the kinetics of the reaction between sodium borohydride and urea or guanidine as well as the dispersion of the nanoparticles in water. The carbon content can be tuned from 0 to 50 mol % by adjusting the reactant ratio, thus providing precise control of the light emission of the particles in the range 440-528 nm while reaching a quantum yield of 26%. Because of their green synthesis, low toxicity, small size, and stability against aggregation in water, the as-obtained photoluminescent BCNO nanoparticles show promise for diagnostics and optoelectronics.

A Core–Corona Hierarchical Manganese Oxide and its Formation by an Aqueous Soft Chemistry Mechanism

One of the main challenges that still needs to be overcome in the design of nanotextured materials is the synthesis of uniform complex architectures. Indeed, many properties are known to be greatly modified by the size and shape of nanostructures. Other than size and shape tailoring, however, control of the ordering between nanostructures and the resulting texture is still difficult. Synthetic routes that make use of organic solvents and templates (i.e., surfactants) often require subsequent purification procedures which significantly increase production costs. The development of environmentally friendly, low-cost, and template-free synthetic methods that produce complex architectures is therefore key to enhancing both the control of the properties and the viability of such materials. In this context, porous manganese oxide materials are attracting great interest due to their applicability in domains such as ion-exchange, catalysis, and energy storage in Li batteries and supercapacitors. Indeed, layered birnessitelike manganese oxides (LMO) are particularly relevant due to their lamellar structure, which contain layers of MnO6 octahedra between which different species can be intercalated (see Figure S1 in the Supporting Information). However, the design of ordered LMO architectures remains a significant challenge as their synthesis usually takes place in an aqueous medium by sol–gel or precipitation methods, both of which result in fast and uncontrolled solid growth that hinders the synthesis of well-ordered nanostructures. Herein we present a low-temperature aqueous precipitation of potassium-intercalated LMO with a peculiar hierarchical core–corona architecture in the absence of both a template and an organic medium. Particle formation takes place in an easy “one-pot” process involving two distinct precipitation kinetic stages. The synthesis of similar inorganic/ inorganic core–corona morphologies generally requires two steps for core formation and shell growth, and there are very few reports concerning one-pot procedures that lead to fully inorganic core–shell particles. Furthermore, these methods are generally limited to metal–oxide structures. The approach presented herein, which uses in situ seeding to control the solid growth, significantly broadens the range of strategies available for the elaboration of hierarchical inorganic structures and can be extended to the design of new functional nanostructured materials, by taking advantage of the unique oxide properties, in areas such as catalysis, energy harnessing, and information storage. The synthesis of birnessite (see the Experimental Section and the Supporting Information) is based on the redox reaction between MnSO4 and an excess of KMnO4 [4f, 5b] (total Mn concentration of 0.2 molL ) in water according to Equation (1). Mixing the acidic (pH 2) solutions of the

Structural and morphological control of manganese oxide nanoparticles upon soft aqueous precipitation through MnO4−/Mn2+ reaction

A low-temperature (60 or 95 °C) “one-pot” procedure for the aqueous precipitation of manganese oxide nanoparticles is developed through the MnO4−/Mn2+ reaction. Characterization of the particles is carried out using elemental analysis, mean oxidation state determination, powder XRD, FESEM, TEM and electron diffraction. Many synthesis parameters are investigated, such as acidity, reactant ratio, concentration and nature of the counter-cation, temperature and aging time. Speciation diagrams are drawn for the synthesis of five different pure phases (spinel-type Mn3O4, layered birnessite-type δ-MnO2, tunnel-based frameworks cryptomelane-type α-MnO2, γ-MnO2 and pyrolusite β-MnO2). The influence of synthetic parameters is rationalized and reaction pathways toward various structures and morphologies are discussed.

Facile General Route toward Tunable Magneli Nanostructures and Their Use As Thermoelectric Metal Oxide/Carbon Nanocomposites

Engineering nanoscale interfaces is a requisite for harnessing electrical and thermal transports within nanostructured materials, especially those destined for thermoelectric applications requiring an unusual combination of low thermal conductivity and electrical resistivity. Nanocomposites open up possibilities in this area, but are still bound to a very narrow range of materials. Here, we report a new approach combining the sol-gel process toward hybrid materials with spark plasma sintering (SPS) to yield functional nanocomposites based on substoichiometric titanium oxides Ti(n)O(2n-1), so-called Magnéli phases. The potential of this new approach is demonstrated by three results. First, multiple Ti(n)O(2n-1) compounds (n = 3, 4, 5, 6, 8) are obtained for the first time as sole nano-Magnéli crystalline phases with controlled specific surface areas from 55 to 300 m(2)·g(-1), classified as potential thermoelectric n-type metal oxides and paving the way toward advanced systems for energy-harvesting devices and optoelectronics. Second, this work combines the use of sol-gel and SPS processes to yield percolated nanocomposites based on metal oxide nanoparticles embedded in a carbon matrix with low electrical resistivity (2 × 10(-4) Ω·m for a Ti(4)O(7) compound) and reduced thermal conductivity (1 W·m(-1)·K(-1)) with respect to bulk phases. Finally, the discovered materials are reliable with thermoelectric figures of merit (ZT = 0.08) relatively high for n-type Ti-O-based systems and metal oxides. Thereby this study represents a proof of concept for the development of promising, cheaper, and more efficient thermoelectric conversion devices.

Chromium nitride and carbide nanofibers: from composites to mesostructures

This work describes an easy two-step approach for metal nitride/carbide nanocomposite ceramic nanofibers via heat treatment of electrospun precursor fibers. Possibilities to tune their composition, carbon scaffold organization and texture depend on the calcination temperature, and yield two different types of fiber structures. Fiber mats with various morphologies were obtained from polyacrylonitrile–chromium chloride precursor electrospun fibers, while well defined rod-like fiber non-woven mats were obtained when a methylated polyurea was used as an additive to the previous system. It was observed that the use of a two component organic system, involving a fiber stabilizing polymeric template (PAN) and a specific nitrogen/carbon donor (PUF), enables to maintain the morphology of the initial fibers during heat treatment and prevents the system from forming sintered membranes at high humidity conditions. The chromium content found for PAN-free and PAN-containing was 9 and 12 wt%, respectively. Moreover, thermal treatment at temperatures higher than 1000 °C led to graphitization of the carbon subphase of both series. Nitrogen sorption studies revealed that the graphitization process increases the specific surface area of the fibers, which possess a pore system with a wide diameter distribution and inkbottle-shaped pores. Conductivity studies revealed that the fiber systems are suitable for electrochemical applications.

Selective heterogeneous oriented attachment of manganese oxide nanorods in water: toward 3D nanoarchitectures

MnOOH and MnO2 polymorphs are synthesized using a reaction between Mn2+and MnO4− in water at low temperature (95 °C). Nanoparticles are characterized using powder XRD, TEM and electron diffraction. Depending on the acidity of the aging medium, γ-MnO2 compounds are shown to be obtained as nanorods (final pH = 2.0) or hollow nanocones (3.6 ≤ final pH ≤ 4.5). The external faces of the cones originate from heterogeneous oriented attachment of α-MnOOH nanorods on early cones. The selective attachment between (−110)γ–MnO2 and (101)α–MnOOH faces is discussed by taking into account the surface charge of the primary particles and the reactivity of the Mn–OHx surface groups. This study underlines the role of the electrostatic repulsions and the surface reactivity in the oriented attachment mechanism in water for oxides.

Original Electrospun Core Shell Nanostructured Magneli Titanium Oxide Fibers and their Electrical Properties

A combination of sol-gel chemistry and the electrospinning process leads to unprecedented versatility in the design of nano-Magnéli phases. Adjusting experimental levers provides an efficient route for tuning the composition, the crystal structure, and the nano- and microstructure of titanium sub-oxides, thus paving the way to functional membranes and tissues.

High and Stable Ionic Conductivity in 2D Nanofluidic Ion Channels between Boron Nitride Layers

Achieving a high rate of ionic transport through porous membranes and ionic channels is important in numerous applications ranging from energy storage to water desalination, but it still remains a challenge. Herein we show that ions can quickly pass through interlayer spaces in hydrated boron nitride (BN) membranes. Measurements of surface-charge governed ionic currents between BN nanosheets in a variety of salt solutions (KCl, NaCl and CaCl2) at low salt concentrations (<10-4 M) showed several orders of magnitude higher ionic conductivity compared to that of the bulk solution. Moreover, due to the outstanding chemical and thermal stability of BN, the ionic conduits remain fully functional at temperatures up to 90 °C. The BN conduits can operate in acidic and basic environments and do not degrade after immersing in solutions with extreme pH (pH ∼ 0 or 14) for 1 week. Those excellent properties make the BN ionic conduits attractive for applications in nanofluidic devices and membrane separation.