Alexander E. Steinman

Boron nitride nanotube growth via boron oxide-assisted chemical vapor transport-deposition process using LiNO3 as a promoter

High-purity straight and discrete multiwalled boron nitride nanotubes (BNNTs) were grown via a boron oxide vapor reaction with ammonia using LiNO3 as a promoter. Only a trace amount of boron oxide was detected as an impurity in the BNNTs by energy-dispersive X-ray (EDX) and Raman spectroscopies. Boron oxide vapor was generated from a mixture of B, FeO, and MgO powders heated to 1,150 °C, and it was transported to the reaction zone by flowing ammonia. Lithium nitrate was applied to the upper side of a BN bar from a water solution. The bar was placed along a temperature gradient zone in a horizontal tubular furnace. BNNTs with average diameters of 30–50 nm were mostly observed in a temperature range of 1,280–1,320 °C. At higher temperatures, curled polycrystalline BN fibers appeared. Above 1,320 °C, the number of BNNTs drastically decreased, whereas the quantity and diameter of the fibers increased. The mechanism of BNNT and fiber growth is proposed and discussed.

BN nanoparticle/Ag hybrids with enhanced catalytic activity: theory and experiments

Hexagonal boron nitride nanoparticles (BNNPs) with different amounts of boron oxide on their surfaces were used as catalyst carriers. BNNPs/Ag nanohybrids were produced via ultraviolet (UV) decomposition of AgNO3 in a mixture of polyethylene glycol and BNNPs. High temperature (1600 °C, 1.5 h) vacuum annealing of BNNPs promoted small size (5–10 nm) Ag nanoparticle (AgNPs) formation on BN surfaces with narrow size distribution, whereas using BNNPs in their as-produced state resulted in large AgNPs with various sizes. An increase in the B2O3 content on the BNNPs surfaces (up to a certain point) during BNNP pre-annealing in air led to larger amounts of AgNPs on their surfaces. Experimental results were confirmed by theoretical calculations of the adhesion energy of the (111)Ag with (0001)h-BN and (100)B2O3 surfaces. In contrast to the nonwettability of the h-BN surface by AgNPs, silver bound well to B2O3 with the formation of a covalent bond at the interface. Excessive fraction of B2O3, however, was not beneficial in terms of obtaining the optimal contents of AgNPs. Results of catalytic activity tests demonstrated that BNNPs/Ag nanohybrids synthesized using BNNPs with an optimized amount of B2O3 possess significantly enhanced catalytic activity compared to BNNPs without or with excess amounts of oxide. Finally, the catalytic activity of nanohybrids was theoretically analyzed using density functional theory (DFT) calculations.

BN/Ag hybrid nanomaterials with petal-like surfaces as catalysts and antibacterial agents

BN/Ag hybrid nanomaterials (HNMs) and their possible applications as novel active catalysts and antibacterial agents are investigated. BN/Ag nanoparticle (NP) hybrids were fabricated using two methods: (i) chemical vapour deposition (CVD) of BN NPs in the presence of Ag vapours, and (ii) ultraviolet (UV) decomposition of AgNO3 in a suspension of BN NPs. The hybrid microstructures were studied by high-resolution transmission electron microscopy (HRTEM), high-angular dark field scanning TEM imaging paired with energy dispersion X-ray (EDX) mapping, X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (FTIR). They were also characterized in terms of thermal stability, Ag+ ion release, catalytic and antibacterial activities. The materials synthesized via UV decomposition of AgNO3 demonstrated a much better catalytic activity in comparison to those prepared using the CVD method. The best catalytic characteristics (100% methanol conversion at 350 °C) were achieved using the UV BN/Ag HNMs without preliminary annealing at 600 °C in an oxidizing atmosphere. Both types of the BN/Ag HNMs possess a profound antibacterial effect against Escherichia coli K-261 bacteria.