Flexible colorimetric sensor for ammonia detection based on polyurethane and bromocresol green

Abstract Ammonia (NH 3 ) is a highly toxic, colorless gas with the potential to cause severe health damage and even fatality. This study aims to develop an inexpensive, flexible, and reversible colorimetric thin film based on thermoplastic polyurethane (TPU), poly (vinyl alcohol) (PVOH) and bromocresol green (BCG) as a colorimetric gas sensor reagent. The fabrication of the sensor films process involves a two-step procedure consisting of melt compounding and compression molding on a laboratory scale. Optimization of the materials composition of the sensor film revealed the optimal concentrations of 0.5 wt% of BCG and 1 wt% of PVOH in the TPU matrix. A visible transition from yellow-orange to green upon exposure to gaseous and liquid ammonia was attributed to the deprotonation of BCG by ammonia nitrogen atom. Furthermore, the sensor exhibited an efficient gas detection limit of 25 ppm and good reversibility for at least 10 exposure cycles. Additionally, the sensor exhibits outstanding selectivity in detecting ammonia over various basic solutions. This study also demonstrates the feasibility of using the proposed system for industrial-scale production as exemplified by the fabrication of filament by continuous extrusion process. The colorimetric filament with diameter of 0.8 mm was successfully weaved onto different cotton fabrics to show their applicability as smart ammonia textile sensors. Graphical abstract