Photocatalytic dye degradation, self-cleaning, and chromogenic properties of VO2 thin films for eco-friendly smart window application

Vanadium dioxide (VO 2 ) thin film is a promising energy-efficient material owing to its reversible metal to insulator transition (MIT) property. Prepared thin films evinced both thermochromic and photochromic properties. Thermochromic property of VO 2 thin film with a thickness of 300 nm showed a low transition temperature (54 °C) compared to 400 (64 °C) and 500 (73 °C) nm thickness. This clearly shows that the monoclinic structure (Insulating state) of VO 2 thin films is converted to tetragonal rutile structure (metallic state) above 54 °C owing to its MIT property. The reversible MIT property was also clearly seen when the films were cooled from 100 to 30 °C. Also VO 2 films exhibited metamaterial property in a small region of temperature. The photochromic property of 300 nm film exhibited higher transmittance of about 51% and decreased to 11% after 60 min of exposure to sunlight. After 72 h of bleaching it was seen that the transmittance increased to 49% proving a good quality of reversible photochromic property. The developed thin films showed a magnificent amount of hydrophilicity (low water contact angle of 12°) and also displayed photocatalytic degradation against methylene blue dye (about 55% under sunlight irradiation for 120 min). The attained properties of the thin film can be used for the development of environmentally friendly smart window applications.