Developing a Novel Continuous Flow Process Using Hydrazine to Synthesize VO2 Nanoparticles for Thermochromic Films

Thermochromic materials can selectively block solar infrared (IR) radiation, allowing for “smart” window films to improve insulation and reduce energy usage in buildings. Vanadium dioxide (VO₂) nanoparticles have been the primary focus of thermochromic research for several decades, yet three fundamental issues are major barriers to widespread adoption:

1. Current processes require batch reactors that take several hours to produce particles.

2. VO₂ particles must be in a pure “M-phase” crystalline structure to be thermochromic, which can be difficult to achieve with faster processes.

3. VO₂ particles should be as small as possible (<30 nm) to produce effective films.

This project aims to solve these scalability and film effectiveness issues by developing a novel continuous flow process for synthesizing ultra-small M-phase VO₂ particles using hydrazine monohydrate (N₂H₄•H₂O). Vanadium oxide (V₂O₅) was reduced by N₂H₄•H₂O to form a precursor solution of V⁴⁺ ions, which was subsequently nucleated via a continuous flow hydrothermal reactor. By varying several parameters—such as component ratios, precursor flow rates, and reactor temperatures—and using DLS, TEM, SEM, and XRD instruments to determine particle size, morphology, and phase, optimal parameters were obtained. Precursor synthesis time was reduced 20-fold, pure M-phase VO₂ particles were consistently produced, and particles under 60 nm were synthesized. Future optimization with capping agents and sodium hydroxide will likely yield smaller particles. This project has introduced a novel methodology for VO₂ nanoparticle synthesis that demonstrates great promise in mass-producing thermochromic materials.