Samuel Bernard

Novel monolith-type boron nitride hierarchical foams obtained through integrative chemistry

A novel class of monolith-type boron nitride hierarchical foams has been prepared through an integrative chemistry-based synthetic path. These materials contain interconnected pores in the nanometre to the micrometre range with high porosity (∼75 vol%), a specific surface area up to 300 m2 g−1 and a resistance toward mechanical stress making them suitable for innovative applications.

A Review on the Preparation of Borazine-Derived Boron Nitride Nanoparticles and Nanopolyhedrons by Spray-Pyrolysis and Annealing Process

Boron nitride (BN) nanostructures (= nanoBN) are structural analogues of carbon nanostructures but display different materials chemistry and physics, leading to a wide variety of structural, thermal, electronic, and optical applications. Proper synthesis routes and advanced structural design are among the great challenges for preparing nanoBN with such properties. This review provides an insight into the preparation and characterization of zero dimensional (OD) nanoBN including nanoparticles and nanopolyhedrons from borazine, an economically competitive and attractive (from a technical point of view) molecule, beginning with a concise introduction to hexagonal BN, followed by an overview on the past and current state of research on nanoparticles. Thus, a review of the spray-pyrolysis of borazine to form BN nanoparticles is firstly presented. The use of BN nanoparticles as precursors of BN nanopolyhedrons is then detailed. Applications and research perspectives for these OD nanoBN are discussed in the conclusion.

High-yield synthesis of hollow boron nitride nano-polyhedrons

Hollow boron nitride nano-polyhedrons have been successfully prepared by annealing of boron nitride nanoparticles in a nitrogen atmosphere at 1800 °C without a catalyst. In our two-step process, we demonstrated that these boron nitride nanoparticles prepared by spray-pyrolysis of borazine are key precursors to grow these architectures. The samples were carefully analyzed using electron microscopies and Energy-Dispersive X-ray spectroscopy analysis. Based on such characterization tools, the growth mechanism of these architectures has been discussed and detailed. It is noteworthy that these nanostructures are generated via a solid-state transformation in relatively high yields without a metal catalyst and might open new opportunities in exploring chemical and physical properties.

In Situ Controlled Growth of Titanium Nitride in Amorphous Silicon Nitride: A General Route Toward Bulk Nitride Nanocomposites with Very High Hardness

Bulk nanocomposites possessing very high hardness in which TiN nanocrystallites are homogeneously embedded in an amorphous Si3N4 matrix are produced from perhydropolysilazane and tetrakisdimethylaminotitanium. That is, a low-molecular-weight TiN molecule is mixed in controlled molar ratio with a polymeric Si3N4 precursor; further processing, including ammonolysis, warm pressing, and controlled nanocrystal growth, yields nanocomposites with the desired properties.

Hollow core@mesoporous shell boron nitride nanopolyhedron-confined ammonia borane: a pure B–N–H composite for chemical hydrogen storage

Ammonia borane-derived boron nitride nanopolyhedra with a hollow core@mesoporous shell structure displaying a specific surface area of 200.5 m2 g−1, a total pore volume of 0.287 cm3 g−1 and a bimodal pore size distribution were successfully prepared and used as nanoscaffolds to improve the dehydrogenation properties of ammonia borane by an exclusive nanoconfinement effect.

Silicon–boron–carbon–nitrogen monoliths with high, interconnected and hierarchical porosity

Silicon–boron–carbon–nitrogen (Si–B–C–N) monoliths with high, interconnected and hierarchical porosity have been prepared by spark plasma sintering (SPS) of ordered mesoporous powders with a P6mm hexagonal symmetry at low temperature without any sintering additives. The ordered mesoporous Si–B–C–N powders derived from boron-modified polycarbosilazanes displayed a mesopore population centred on 4.6 nm, a total pore volume of 0.78 cm3 g−1 and a specific surface area of 544 m2 g−1. They have been partially sintered in the temperature range 800–1000 °C under nitrogen to lead to robust meso-/macroporous Si–B–C–N monoliths with surface areas of 123–171 m2 g−1, mesopore diameters centred on 6.2–6.5 nm and total pore volumes varying from 0.25 to 0.35 cm3 g−1 measured by nitrogen adsorption experiments. As-obtained crack-free Si–B–C–N monoliths displayed porosities from 59 to 69% and a relatively large pore size distribution as determined by helium pycnometry and confirmed by mercury porosimetry. TEM observations and low angle X-ray diffraction (LA-XRD) confirmed the formation of monoliths that maintained a mesoporosity organization in comparison to starting powders while SEM experiments showed a microstructure in which necks are formed around the area of contact between particles. With a thermal stability extending up to 1400 °C in flowing nitrogen and a heat conductivity of 0.647 W m−1 K−1 for the most porous component, these new materials display the necessary intrinsic properties required as porous supports working in a harsh environment.

Monodisperse platinum nanoparticles supported on highly ordered mesoporous silicon nitride nanoblocks: superior catalytic activity for hydrogen generation from sodium borohydride

Late transition metal have attracted considerable interest for catalytic applications. Their immobilization over supports with tailored porosity is advantageous for nanosizing metal particles and avoiding their agglomeration which is known to bring a serious issue to the catalytic performance. Herein, ordered mesoporous silicon nitride (Si3N4) nanoblocks with hexagonal symmetry of the pores, high specific surface areas (772.4 m2 g−1) and pore volume (1.19 cm3 g−1) are synthesized by nanocasting using perhydropolysilazane as precursor. Then, Si3N4 nanoblocks are used as supports to synthesize platinum nanoparticles (Pt NPs) by precursor wet impregnation. Detailed characterizations by TEM show that monodispersed spherical Pt NPs with a 6.77 nm diameter are successfully loaded over nanoblocks to generate nanocatalysts. The latter are subsequently used for the catalytic hydrolysis of sodium borohydride (NaBH4). A hydrogen generation rate of 13.54 L min−1 gPt−1 is measured. It is notably higher than the catalytic hydrolysis using Pt/CMK-3 nanocatalysts (2.58 L min−1 gPt−1) most probably due to the textural properties of the Si3N4 supports associated with the intrinsic properties of Si3N4. This leads to an attractive nanocatalyst in pursuit of practical implementation of B-/N-based chemical hydrides as a hydrogen source for fuel cell application.

Ordered mesoporous polymer-derived ceramics and their processing into hierarchically porous boron nitride and silicoboron carbonitride monoliths

Inorganic porous materials are widely used in a number of applications, where there is a need to produce materials with a controlled and/or multiscale porosity. In this category, periodic mesoporous boron- and silicon-based non-oxide ceramic frameworks with P6mm hexagonal symmetry attract increasing interest due to their unique properties, functionalities and potential applications. These materials are prepared by a hard-templating route (= nanocasting) using ordered mesoporous templates including silica (SBA-15) and carbon (CMK-3). In the first part of this perspective, the synthesis approach of ordered mesoporous boron nitride (BN) and silicoboron carbonitride (Si–B–C–N) is emphatically described including precursor selection and synthesis, nanocasting process, pyrolysis and template removal. In order to satisfy the requirement for practical applications, the second part of this perspective describes how a convenient powder processing approach that adopts the flexibility of powder-based processes (spark plasma sintering (SPS)) has been employed to produce without the use of any sintering additives mechanically stable, hierarchically porous BN and Si–B–C–N monoliths from ordered mesoporous powders.

Micro-/Mesoporous Platinum-SiCN Nanocomposite Catalysts (Pt@SiCN): From Design to Catalytic Applications.

The synthesis, characterization, and catalytic studies of platinum (Pt) nanoparticles (NPs) supported by a polymer-derived SiCN matrix are reported. In the first step and under mild conditions (110u2009°C), a block copolymer (BCP) based on hydroxyl-group-terminated linear polyethylene (PEOH) and a commercially available polysilazane (PSZ: HTT 1800) were synthesized. Afterwards, the BCP was microphase separated, modified with an aminopyridinato (Ap) ligand-stabilized Pt complex, and cross-linked. The green bodies thus obtained were pyrolyzed at 1000u2009°C under nitrogen and provided porous Pt@SiCN nanocomposite via decomposition of the PEOH block while Pt nanoparticles grew in situ within the SiCN matrix. Powder X-ray diffraction (PXRD) studies confirmed the presence of the cubic Pt phase in the amorphous SiCN matrix whereas transmission electron microscopy (TEM) measurements revealed homogeneously distributed Pt nanoparticles in the size of 0.9 to 1.9u2005nm. N2 sorption studies indicated the presence of micro- and mesopores. Pt@SiCN appears to be an active and robust catalyst in the hydrolysis of sodium borohydride under harsh conditions.

Nanocomposites through the Chemistry of Single-Source Precursors: Understanding the Role of Chemistry behind the Design of Monolith-Type Nanostructured Titanium Nitride/Silicon Nitride

Monolith-type titanium nitride/silicon nitride nanocomposites, denoted as TiN/Si3 N4 , have been prepared by a reaction of polysilazanes with a titanium amide precursor, warm pressing of the resultant polytitanosilazanes, and subsequent pyrolysis of the green bodies at 1400u2009°C. Initially, a series of polytitanosilazanes was synthesized and the role of the chemistry behind their synthesis was studied in detail by using solid-state NMR spectroscopy, elemental analysis, and molecular-weight measurements. The intimate relationship between the chemistry and the processability of these precursors is discussed. Polytitanosilazanes display the appropriate requirements for facile processing in solution and as a melt, but they must be treated with liquid ammonia to be adapted for solid-state processing, that is, warm-pressing, to design dense and mechanically stable structures after pyrolysis. We provide a comprehensive mechanistic study of the nanocomposite conversion based on solid-state NMR spectroscopy coupled with thermogravimetric experiments. HRTEM images coupled with XRD and Raman spectroscopy confirmed the unique nanostructural features of the nanocomposites, which appear to be a result of the molecular origin of the materials. The as-obtained samples are composed of an amorphous Si3 N4 matrix, in which TiN nanocrystals are homogeneously formed in situ in the matrix during the process. The hardness and Young moduli were measured and are discussed.