Selective CVD growth of boron nitride nanotubes via oxidation control of supported catalysts

Abstract

Carbon nanotubes (CNTs) have been successfully mass-produced via chemical vapor deposition (CVD) using supported catalysts, but boron nitride nanotube (BNNT) synthesis still relies on high-temperature processes, and research on supported catalyst-based CVD remains limited. In this study, we developed a tailored Ni–Pd (MgO) alloy-supported catalyst for BNNT synthesis, leveraging the high catalytic activities of Ni and Pd toward nitrogen and boron, respectively, as well as the low eutectic point of the alloy. By controlling the oxidation state of the MgO support, we demonstrated the selective synthesis of highly crystalline BNNTs and MgO-BN core/shell nanowires at a relatively low temperature of 1100 °C. Notably, MgO-BN core/shell nanowires, exceeding 50 μm in length, provide a practical alternative for large-scale BNNT production, as they can be converted into BNNTs via simple acid treatment and annealing. Transmission electron microscopy (TEM) and density functional theory (DFT) analyses revealed that BNNT tip growth is driven by the reduced eutectic point of the Ni–Pd catalyst, its quasi-liquid deformation, and catalyst lift-off induced by strong interactions with h-BN. This catalyst design and growth mechanism analysis present a crucial strategy for the low-temperature mass production of BNNTs and suggest the potential for further improving synthesis efficiency through the optimization of catalyst composition and reaction conditions.