Synthesizing Boron Nitride Quantum Dots in Microdroplets

We demonstrate that water microdroplets create a highly reactive interfacial environment that enables the rapid, room-temperature synthesis of boron nitride quantum dots (BNQDs). Using a borane ammonia complex (BH₃NH₃) and a boric acid-ammonia system as precursors, we obtain green- and blue-emissive BNQDs, respectively, under ambient conditions. Mass spectrometry reveals a dehydrogenative cyclization pathway for BH₃NH₃, delineates the size distribution of B_xN_y clusters, and reveals reaction kinetics accelerated by 6 orders of magnitude relative to conventional bulk hydrothermal synthesis. Hydroxyl radicals (OH^•), generated from interfacial water and entrained oxygen, act as key oxidants driving stepwise dehydrogenation of BH₃NH₃. For the boric acid-ammonia system, the dehydration and deamination process is accelerated on the air-water interface. In a spraying-recirculating microdroplet reactor, milligram-scale quantities of BNQDs with an average diameter of ∼8.5 nm are produced within 1 h, establishing a green, bottom-up route for nanomaterial synthesis by exploiting the intrinsic reactivity of water microdroplets.