A new smart window is designed to control the transmittance of sunlight, heats the interiors of buildings by converting solar radiation into heat, and virtually eliminates E. coli bacteria living on the glass.
The researchers, led by Yan-Yan Song at Northeastern University in Shenyang, China, and Xing-Hua Xia at Nanjing University in Nanjing, China, have published a paper on the new sterile smart window in a recent issue of ACS Nano in July 2018. These sterile smart windows have applications in airplanes, hospitals, public transportation, and others. According to the research team, integration of various functions into single smart window is challenging, as each function requires different material composition.
For instance, one of the most widely used materials for smart windows that control visible light transmission is WO3 (tungsten trioxide). As an electro chromic material, WO3 can reversibly change its optical transmittance in response to electrochemical charging and discharging. Furthermore, smart windows converting near-infrared solar radiation into heat typically involve metal nanoparticles. Also, a wide range of materials have antimicrobial properties, most notably copper. As a part of the new study, the researchers designed an electrochromic-photothermal film composed of 3D WO3 in a honeycomb-like structure embedded with gold nanoparticles and nanorods. While the WO3 controls the amount of visible light that passes through the window, the gold nanostructures convert incoming sunlight into thermal energy for heating the building interior.
The team demonstrated various properties, which included change of color from transparent to pitch black within minutes. Furthermore, it was examined that near-infrared laser increases the temperature of the window by 24 °C in five minutes. For examining antimicrobial properties, the glass was treated with E. coli and irradiated with a near-infrared laser, which showed that bactericidal effect was strongest when the window was in its dark state, in which it could eliminate virtually all of the bacteria.