Fast response paper based visual color change gas sensor for efficient ammonia detection at room temperature.

We show that a cheap, disposable type rapid paper sensor (working at room temperature) can be made using perovskite halide CHNHPbI (MAPI) to detect presence of the toxic ammonia gas (NH)by just color change, where the black colored MAPI film (on the paper) changes to yellow color in presence of a very low concentration of NH gas. The sensor can detect presence of NH gas in open or closed atmosphere down to around 10 ppm with a response time of nearly 10 sec which decreases to few seconds when the concentration exceeds 20 ppm. The easy to fabricate sensor paper being a visual sensor does not need any other extra equipment for its operation. The sensor is not sensitive to moisture with RH upto 90% and does not also respond to gases like Methane (CH), Nitrous Oxide (NO), Carbon dioxide (CO) etc in the test chamber each up to a concentration of 500 ppm. Conversion/decomposition of MAPI to PbI on exposure to NH has been proposed as the mechanism of color change and the mechanism has been established using a collection of techniques like XRD, EDX, UV-Visible absorption and Photo Luminescence.