Author: Challapalli Phaneendranath
Formaldehyde is commonly caused indoor air pollution. It is widely used as a base chemical material to manufacture building materials and numerous household products in many industrial processes with approximately ten megatons produced per year. Formaldehyde as a possible carcinogen was qualified in 1980 when the carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure was reported. The World Health Organization (WHO) has set a standard for safe exposure of 80 ppb averaged over 30 min.
The availability of highly efficient sensors for the detection of formaldehyde continues to be a significant scientific challenge due to its possible threat to public health. Owing to the exciting optical and structural properties, nanostructure materials have evoked much interest as attractive media for sensors. Colorimetric sensor strips for the detection of formaldehyde are based on nylon 6 nano fiber net (NFN) platform, which impregnated with the processing solution containing hydroxylamine sulfate, Methyl Yellow, glycerin, and methanol. When the sensor strip are exposed to formaldehyde, the Methyl Yellow on the tape reacted with sulfuric acid produced by the reaction of hydroxylamine sulfate with formaldehyde to produce a yellow-to-red color change. Fabrication of the Methyl Yellow-impregnated nylon 6 colorimetric NFN membranes Fabrication of the Methyl Yellow-impregnated nylon 6 colorimetric NFN membranes.
The white nylon 6 NFN membranes were collected on the surface of a grounded aluminum foil (tip to collector distance was 15 cm) and dried at room temperature under vacuum for 1 h. The obtained membranes were cut into 15 mm×15 mm square strips and fixed on the side glass, and then immersed into a processing solution for 1 min.
When the sensor strip was exposed to formaldehyde, the Methyl Yellow on the tape reacted with sulfuric acid produced by the reaction of hydroxylamine sulfate with formaldehyde to produce a yellow-to-red color change as (Fig 4). The reaction of this method is represented by: 2HCHO+(NH2OH)2·H2SO4→2H2CNOH+H2SO4+2H2O. The Nylon NFN based sensor is a simple and cheap method with relatively high resolution for determination of formaldehyde concentration in the air.