2.2.2. Functionalization of Whatman Paper for Acetaldehyde Vapor Detection

The colorimetric detection of gaseous C2H4O was obtained by coating a Whatman filter paper with thin methyl red film. methyl red and methyl red sodium salt was dissolved in a solvent constituted by CH3OH, water and C3H8O3 (1 mM). The red-orange solution was stirred for approximately 1 h. NaOH (8 mM) was added to the solution and stirred at room temperature for 1 h. The yellow-colored solution obtained was translocated in a petri dish where a piece of Whatman filter paper was immersed for 1 h. After this time, the paper was dried at room temperature overnight. The filter paper sheet was then cut into small round disks (diameter of approximately 2 cm) and successively exposed to different concentrations of C2H4O. After 5 min, the color appeared on the paper. The schematic representation of this procedure is represented in Figure 1b.
