Smart Thin Films




            Smart thin films are films with one or more special properties such as heating reflection film, self-cleaning film, pollutant treatment film, solar-cell thin film, electrochromic film, thermochromic film and so on. Titanium dioxide film (TiO2) is one of smart thin films that has special properties in heating reflection and self-cleaning when absorbed with UV irradiation. When TiO2 film exposes to UV irradiation, electrons will be activated and move from valence band to conduction band. As a result, electron (e-) and hole (h+) are generated and react with H2O and O2 to produce oxidizing agents which can destroy the pollutants. This reaction is known as “photocatalysis”. Even though, TiO2 is non toxic and highly reactive, the limitation of TiO2 film is that it must be used under UV irradiation. Several studied reported the methods to reduce band gap energy of TiO2 by doping various metals and non metals. Silver (Ag) is found to be a promising dopant for TiO2.  Ag/ TiO2 film exhibits good photocatalytic reactivity under visible light, which can be easily applied in indoor condition. Moreover, it was reported that Ag/ TiO2 film also provides antimicrobial function, especially for bacteria and fungi removal.

            Our current research focuses on the applications of Ag/ TiO2 film for indoor air treatment. The photocatalytic reactivity of Ag/ TiO2 film for BTEX removal is improved by incorporating with RH-MCM-41, called Ag/TiO2/MCM-41 smart film. Due to large surface area of RH-MCM-41 (>800 m2/g), the adsorbability of BTEX on Ag/ TiO2 film can be enhanced.  Overall removal efficiency can be improved 30-40% under visible light. Furthermore, the presence of silanol groups found in RH-MCM-41 brings about superhydrophilic property with water contact angle less than 10° during visible light. A very low contact angle (α) of water on surface film in the figure, meaning that the film surface has very high hydrophilicity or call as “super-hydrophilicity”. The super-hydrophilic property promotes photocatalytic degradation of airborne pollutant when irradiated with UV or even visible light. As a result, stain or soap scum can be easily removed from the surface. Ag/TiO2/MCM-41 smart film is now developed as a coating film on several substrates that commonly used in building such as glass, ceramic tile, PVC, PET, cotton fabric for the purposes of indoor air purification.