Fabrication of novel MoOx / PVA hydrogel nanocomposite for photochromic smart window

Photochromic smart windows allow for simple manufacturing without the need for additional energy input for adaptive control of sunlight, which will have a huge impact on the comfort of daylight and the development of smart windows. Among them, although molybdenum-based materials have advantages such as low cost and stable coloring, the lack of fast transmission switching capability and liquid phase color changing environment limit its implementation in the field of smart windows. Here, we report a low-cost method to fabricate a novel photochromic hydrogel (MoOx/PVA) by combining molybdenum oxide nanosheets (MoOx, 2 ≤ x ≤ 3) with polyvinyl alcohol (PVA) gel. Under ultraviolet light (UV = 360–400 nm) irradiation, the hydrogel achieves rapid color change visible to the naked eye within 10 s, with an exponential decrease in transmittance, reversible switching of transparency between 70 % and 5 %, and retains about 95 % transmittance after 14 cycles. Due to the good biocompatibility of molybdenum oxide, hydrogel can also be used for personal wearable, which can achieve 1.4 °C of cooling when exposed to sunlight for 3 min. Moreover, the photochromic and recovery properties of the large-sized (29.7 cm × 21 cm) MoOx/PVA hydrogel demonstrate its broad prospects for production applications in smart windows. It is believed that this study will open new opportunities for both fabrication and application in photochromic smart windows and intelligent devices.