Hexagonal boron nitrite (hBN) is an attractive material for many applications such as in electronics as a complement to graphene, in anti-oxidation coatings, light emitters, etc. However, the synthesis of high-quality hBN at cost-effective conditions is still a great challenge. Thus, this work reports on the synthesis of large-area and crystalline hBN nanosheets via the modified polymer derived ceramics (PDCs) process. The addition of both the BaF2 and Li3N, as melting-point reduction and crystallization agents, respectively, led to the production of hBN powders with excellent physicochemical properties at relatively low temperatures and atmospheric pressure conditions. For instance, XRD, Raman, and XPS data revealed improved crystallinity and quality at a decreased formation temperature of 1200 °C upon the addition of 5 wt% of BaF2. Moreover, morphological determination illustrated the formation of multi-layered nanocrystalline and well-defined shaped hBN powders with crystal sizes of 2.74–8.41 ± 0.71 µm in diameter. Despite the compromised thermal stability, as shown by the ease of oxidation at high temperatures, this work paves way for the production of large-scale and high-quality hBN crystals at a relatively low temperature and atmospheric pressure conditions.

Hexagonal boron nitride (h-BN) is nowadays an increasingly attractive material, especially for two-dimensional material applications, due to its intrisic properties. However, its properties are highly dependent on the used synthesis approach. The polymer derived ceramics (PDCs) route allows elaboration of h-BN with tailored textural and structural properties. Here, we demonstrate the interest of the PDCs pathway for the synthesis of h-BN. Growth of h-BN single crystals with crystal sizes of a few microns at relatively low temperature and atmospheric pressure is successfully achieved from borazine precursor using PDCs. The crystallization is improved by additivation of 5 wt% of Li3N to the pre-ceramic polymer. Furthermore, by coupling PDCs with gas pressure sintering, starting from the same pre-ceramic polymer and 25 wt% of Li3N, the crystal size is enlarged up to hundreds of microns. The fabricated single crystals of pure h-BN can then be exfoliated into h-BN nanosheets. Finally, by combining PDCs with atomic layer deposition, functional BN nano-/hetero-structures are successfully synthesized from highly structured sensitive templates, making this ALD process a promising alternative for fabricating functional BN nanostructures.

The development of porous films presenting accessible high specific surface area is important to design new adsorbents, sensors or catalyst supports. Here, we describe a simple method to prepare a foam silica coating by using an evaporation induced emulsification method assisted by calcium chloride. An alcoholic silica sol containing calcium chloride and a poly(ethylene oxide) containing polymer is deposited on a substrate by dip-coating. The alcohol evaporation induces a phase separation between a silica-rich phase and a calciumrich one. The droplets size increases via a coalescence process until the sol gelation, which determines the final pore size comprised between 100 nm and 3 µm. Thermal analysis and droplet evaporation monitoring both confirm that the solvent departure is delayed by the presence of calcium chloride into the sol. Influence of the polymer nature on the porosity is discussed. Using a block copolymer such as the Pluronic F-127, which strongly stabilizes the emulsion, allows to reach a low pore size (400 nm) while on the opposite, we propose to use a short poly(ethylene glycol) (PEG) such as the PEG-400, which weakly stabilizes it, leading 2 to larger pores (2-3 microns). Moreover, we show that adding a zirconium salt (ZrOCl 2 .8H 2 O) into the silica sol speeds up the condensation step of the silica network and leads to the decreasing in the pore size.