나노섬유와 pH 지시약을 이용한 색변환 환경센서

Abstract

Colorimetric sensors were investigated to achieve a low-cost warning device for harmful gases such as formaldehyde, acetic acid, hydrochloric acid and ammonia. The detection relies on color-changing property of pH indicator dyes impregnated on a solid membrane substrate. In the case of formaldehyde detection, sulfuric acid is produced through selective reactions between hydroxylamine sulfate and HCHO, and then results in colorimetric response through the acid-base reaction with dye molecules. An optimized HCHO detection was observed in sensors prepared by using bromophenol blue (BPB) dye and nylon sheet. An initial color of green was changed to yellow when exposed to gaseous formaldehyde. The color change was recorded using an office scanner and further analyzed in term of RGB distance for quantifying sensor’s response. The optimized formaldehyde sensor exhibited a recognizable colorimetric response even at 50 ppb, being lower than WHO’s standard of 80 ppb. In addition, the sensor was found to have quite good selectivity in HCHO detection under the presence of common volatile organic compounds. On the other hand, volatile acidic compounds (HCl and acetic acid) and basic ammonia gas were well detected by chemically-modified PAN nanofiber mats using metacresol purple (m-CP) and bromocresol green (BCG), respectively. Color changes could be interpreted with acid-base reactions between indicator dyes and analyte molecules. Obtained limit-of-detection values were lower than the PEL concentrations (10 ppm for AcOH, 5 ppm for HCl, and 50 ppm for NH3) suggested by OSHA. Furthermore, the detection sensitivity was found to be modulated with controlling the pH value of a dye solution through the addition of KOH or HCl.