Color-Changing Microfiber-Based Multifunctional Window Screen for Capture and Visualized Monitoring of NH 3 .

Air pollution is one of the most serious issues affecting the world today. Instead of expensive and energy-intensive air-filtering devices, fiber-based transparent air filter coated on window screen is seen as one of the state-of-the-art filtration technology to combat the seriously growing problem, delivering the advantages of simplicity, convenience and high filtering efficiency. However, such window screen is currently limited to particulate matter (PM) filtration, and ineffective with other air pollutants. Here, we report the use of a newfangled type of color-changing fibers, porous Prussian blue analogues (CuHCF)/polymer composite microfibers, for transparent window screens towards air pollutant filtration. To increase pollution filtration, pores and dimples are purposely introduced to the fibers using binary solvent systems through a non-solvent induced phase separation mechanism. Such composite microfibers overcome some of the limitations of those previously used fibers, and could simultaneously capture PM2.5, PM10 and NH3 with high efficiency. More interestingly, a distinct color change is observed upon exposure to air pollutants in such window screens, which provides multifunctional capability of simultaneous pollutant capture and naked-eye screening of the pollutant amount. Specifically, in case of long-term exposure to low-concentration NH3, the symbol displayed in such window screen changes from yellow color to brown, and the coloration rate is directly controlled by NH3 concentration, which may serve as a careful reminder for those people who are repeatedly exposed to low-concentration ammonia gas (referred to as chronic poisoning). In contrast, after short-term exposure to a high concentration of ammonia gas, the yellow symbol immediately becomes blackened, which provides timely information about the risk of acute ammonia poisoning or even ammonia explosion. Further spectroscopic results show that the chromatic behaviors in response to different concentrations of NH3 are fundamentally different, which is related to the different locations of ammonia in the lattice of CuHCF, either in its interstitial sites or at the Fe(CN)6 vacancy sites, largely distinguished by the absence or presence of atmospheric moisture.