Combinatorial Atmospheric Pressure Chemical Vapor Deposition of Graded TiO2–VO2 Mixed-Phase Composites and Their Dual Functional Property as Self-Cleaning and Photochromic Window Coatings

A combinatorial film with a phase gradient from V:TiO2 (V: Ti ≥ 0.08), through a range of TiO2–VO2 composites, to a vanadium-rich composite (V: Ti = 1.81) was grown by combinatorial atmospheric pressure chemical vapor deposition (cAPCVD). The film was grown from the reaction of TiCl4, VCl4, ethyl acetate (EtAc), and H2O at 550 °C on glass. The gradient in gas mixtures across the reactor induced compositional film growth, producing a single film with numerous phases and compositions at different positions. Seventeen unique positions distributed evenly along a central horizontal strip were investigated. The physical properties were characterized by wavelength dispersive X-ray (WDX) analysis, X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and UV–visible spectroscopy. The functional properties examined included the degree of photoinduced hydrophilicity (PIH), UVC-photocatalysis, and thermochromism. Superhydrophilic contact angles could be achieved at all positions, even within a highly VO2-rich composite (V: Ti = 1.81). A maximum level of UVC photocatalysis was observed at a position bordering the solubility limit of V:TiO2 (V: Ti ≈ 0.21) and fragmentation into a mixed-phase composite. Within the mixed-phase TiO2: VO2 composition region (V: Ti = 1.09 to 1.81) a decrease in the semiconductor-to-metal transition temperature of VO2 from 68 to 51 °C was observed.