Photochemical Synthesis of Ultrafine Cubic Boron Nitride Nanoparticles under Ambient Conditions

Self-assembled Cubic Boron Nitride Nanodots

One of the low-dimensional Boron Nitride (BN) forms, namely, cubic-BN (c-BN) nanodots (NDs), offers a variety of novel opportunities in battery, biology, deep ultraviolet light emitting diodes, sensors, filters, and other optoelectronic applications. To date, the attempts towards producing c-BN NDs were mainly performed under extreme high-temperature/high-pressure conditions and resulted in c-BN NDs with micrometer sizes, mixture of different BN phases, and containing process-related impurities/contaminants. To enhance device performance for those applications by taking advantage of size effect, pure, sub-100 nm c-BN NDs are necessary. In this paper, we report self-assembled growth of c-BN NDs on cobalt and nickel substrates by plasma-assisted molecular beam epitaxy. It is found that the nucleation, formation, and morphological properties of c-BN NDs can be closely correlated with the nature of substrate including catalysis effect, lattice-mismatch-induced strain, and roughness, and growth conditions, in particular, growth time and growth temperature. The mean lateral size of c-BN NDs on cobalt scales from 175 nm to 77 nm with the growth time. The growth mechanism of c-BN NDs on metal substrates is concluded to be Volmer-Weber (VW) mode. A simplified two-dimensional numerical modeling shows that the elastic strain energy plays a key role in determining the total formation energy of c-BN NDs on metals.

Tailoring Transition-Metal Hydroxides and Oxides by Photon-Induced Reactions

Controlled synthesis of transition-metal hydroxides and oxides with earth-abundant elements have attracted significant interest because of their wide applications, for example as battery electrode materials or electrocatalysts for fuel generation. Here, we report the tuning of the structure of transition-metal hydroxides and oxides by controlling chemical reactions using an unfocused laser to irradiate the precursor solution. A Nd:YAG laser with wavelengths of 532 nm or 1064 nm was used. The Ni²⁺ , Mn²⁺ , and Co²⁺ ion-containing aqueous solution undergoes photo-induced reactions and produces hollow metal-oxide nanospheres (Ni_0.18 Mn_0.45 Co_0.37 O_x ) or core-shell metal hydroxide nanoflowers ([Ni_0.15 Mn_0.15 Co_0.7 (OH)₂ ](NO₃ )_0.2 ⋅H₂ O), depending on the laser wavelengths. We propose two reaction pathways, either by photo-induced redox reaction or hydrolysis reaction, which are responsible for the formation of distinct nanostructures. The study of photon-induced materials growth shines light on the rational design of complex nanostructures with advanced functionalities.

Precise casting of biomorphic La0.9K0.1CoO3 catalysts derived from pinewood for diesel soot combustion

A biomorphic perovskite-type oxide, possessing a large surface area, was successfully fabricated using pinewood as a template. The porous structure prompted catalytic activity towards soot combustion under low temperature.