Making Thermochromic VO2 Nanoparticles for Smart Window Application

Nanoparticles have many applications due to their outstanding characteristics and performances. However, the large-scale manufacturing of high-quality nanoparticles with controlled geometries and physical properties is a non-trivial task. Recently, it has been discovered that VO2 nanoparticulate films can double the solar infrared heat modulation and transmittance efficiency of visible light when compared to those of their bulk film counterparts, making them promising next-generation thermochromic materials for high performance smart windows. Current manufacturing methods, typically using an autoclave reactor, prevent large-scale production due to low conversion efficiency, poor control of product quality and safety, and extremely slow process (on the order of days). Modern green chemistry processes provide fundamental enhancements of such manufacturing through the use of (1) high temperature to exponentially accelerate chemical reactions, and thus drastically shorten the synthesis time; (2) more powerful energy supply approaches (e.g., microwave, ultrasound, micro-reactor) to intensify transfer process and thus boost reaction conversion and product selectivity; as well as (3) simple and scalable manufacturing techniques that enable quick and economically marketable products. This presentation will introduce the “smart windows” concept, followed by our development of continuous flow hydrothermal synthesis using a microscale flow reactor.

The experimental demonstration will be presented to show it is feasible to continuously synthesize VO2 (M-phase) micro- and/or nanoparticles in a single step within a significantly reduced period of synthesis time by using our novel processing technology. Li will explain the influence that in-situ surface modifications of the nucleated particles using surfactants has had on the particle carry-out with the effluent. In addition, ongoing activities related to the material scale-up and commercialization will also be briefly discussed. Finally, Li will give a perspective on applying our process to preparation of other advanced nanomaterials. Through this work, Li seeks to develop nano-material processing techniques to support advanced manufacturing of not only smart building materials, but also a spectrum of other advanced micro- and nanoscale powder materials that are becoming increasingly necessary and important as raw materials in additive manufacturing (3D printing) of metallic and metal oxide devices.