Controllable synthesis of boron nitride nanotubes (BNNTs) remains challenging due to the difficulty of stabilizing reactive boron species and regulating their conversion pathways during high-temperature reactions. In this study, lithium carbonate (Li2CO3) is employed as a controlled Li–O releasing precursor, which decomposes in situ to promote the formation of lithium borate–rich Li–B–O liquid phases. These lithium borates act as the true reactive species that activate boron and facilitate vapor–liquid–solid (VLS) growth of BNNTs. The effects of reaction temperature and Li2CO3/B molar ratio on the morphology, structure, and purity of BNNTs were systematically investigated. An optimal Li2CO3/B ratio of 0.06 produced uniform, high-purity BNNTs, whereas insufficient or excessive Li2CO3 led to incomplete nitridation or the formation of Li–B–O byproducts. Structural analyses─including FT-IR, XRD, Raman spectroscopy, and XPS─reveal that the optimized conditions suppress defect formation and enhance B–N coordination, yielding BNNTs with well-defined tubular architecture. A refined VLS growth mechanism is proposed, in which the size, shape, and spatial distribution of Li-containing liquid droplets govern BNNT diameter, crystallinity, and nucleation density. This work establishes a mechanistic framework for Li2CO3-assisted BNNT synthesis, clarifying the precursor role of Li2CO3 in generating active lithium borate species, and provides a controllable strategy for achieving BNNTs with uniform morphology and well-defined crystalline structures through liquid-phase-mediated growth.
Huang et al. (Tue,) studied this question.