High-throughput Screening of Vanadium (IV) Oxide via Continuous Hydrothermal Flow Synthesis Reactor

The synthesis of inorganic nanoparticles using continuous hydrothermal flow synthesis (CHFS) reactor systems is an up-and-coming process to manufacture high-quality nanomaterials with singular control of the experimental parameters on the scale of seconds as opposed to hours. VO2-based systems manufactured using an autoclave reactor lack scalability, and current commercial products feature particle sizes too large for feasible application. In this paper, the detailed implementation of a CHFS system that can operate at and above supercritical water conditions (22.06 MPa at 374˚C) is described. Control over the CHFS system’s temperature, flow rate, and precursor concentration parameters allowed the tunability of size, crystallinity, and shape of VO2 nanoparticles to be investigated across seven studies. The resulting VO2 nanoparticles were characterized for size, shape, morphology, and crystallinity using dynamic light scattering (DLS), scanning electron microscopy (SEM), and x-ray diffraction (XRD). This investigation resulted in new operating procedures that enable the synthesis of high-quality, uniform, spherical, and pure M-phase VO2 nanoparticles under 50 nm in diameter in the residence time of a few seconds. Additionally, the procedure described in this paper is performed in a single step, thus eliminating the tedious post-annealing process.