Sulfonic acid-functionalized spiropyran colorimetric gas-sensitive aerogel for real-time visual ammonia sensing

Abstract

With the increasing demand for ammonia (NH₃) detection in environmental monitoring, industrial safety, and food freshness assessment, developing portable, cost-effective, and highly sensitive NH₃ sensors remains a challenge. This study presents a smart colorimetric aerogel based on sulfonated spirocyclic pyran (SC-MPC aerogel) for real-time, highly sensitive, and visual NH₃ detection. The aerogel exhibits significant color changes due to proton transfer reactions triggered by NH₃ exposure and can recover to its initial state under acidic conditions. Experimental results demonstrate that the aerogel has a rapid response time of just 8 s, a detection limit as low as 1.79 ppm, and excellent repeatability with over 40 cycles of use. Additionally, it shows a high selectivity for NH₃, with a linear response range from 3 to 150 ppm, and exhibits exceptional stability under variations in humidity and temperature. Density functional theory (DFT) calculations further confirm the proton transfer mechanism involved in the NH₃ sensing process. This aerogel demonstrates broad application potential, particularly in seafood freshness detection, while also holding promise for use in environmental monitoring and industrial safety, providing a cost-effective and highly sensitive solution for ammonia detection.