Highly sensitive photochromic aerogel sensor for acidic gas detection based on SP/WPU/CNF composite materials

Gas sensors are crucial in various applications such as environmental monitoring, industrial safety, and air quality control. However, many of these sensors still encounter significant challenges, including complex fabrication processes, low sensitivity, and poor stability. This study presents the development of a novel photochromic sensor using spiropyran (SP), waterborne polyurethane (WPU), and cellulose nanofiber (CNF) aerogel, aiming to overcome these challenges and provide highly sensitive detection of acidic gases. Under ultraviolet (UV) irradiation, the SP component in the aerogel isomerizes to its open-ring merocyanine (MC) form, which is further protonated to protonated merocyanine (MCH) in the presence of acid vapors. Systematic testing reveals that the SP/WPU/CNF aerogel sensor exhibits a rapid response time of 20 s under UV light irradiation and retains 75 % of its photoresponsivity after 20 cycles, demonstrating excellent durability. Additionally, the sensor exhibits a response time of 20 s to acidic gases, with a color change from purple to yellow when exposed to HCl gas at concentrations as low as 1 ppm. After undergoing five protonation and recovery cycles, the sensor maintains a certain level of acid responsiveness. These exceptional properties highlight the potential of the SP/WPU/CNF aerogel-based sensor to be a highly sensitive, efficient, and stable solution for acidic gas detection.