A Facile Design of Colourimetric Polyurethane Nanofibrous Sensor Containing Natural Indicator Dye for Detecting Ammonia Vapour

Chemicals and industrial gases endanger both human health and the environment. The inhalation of colourless ammonia gas (NH3) can cause organ damage or even death in humans. Colourimetric materials are becoming more popular in the search for smart textiles for both fashion and specific occupational applications. Colourimetric textile sensors based on indicator dyes could be very useful for detecting strong gaseous conditions and monitoring gas leaks. In this study, black carrot extract (BCE) as a natural indicator dye and polyurethane (PU) polymer were used to develop a colourimetric sensor by electrospinning. The properties of the BCE/PU nanofibrous mats were characterized by the Fourier transform infrared spectrum (FTIR) and a scanning electron microscope (SEM). The BCE caused a change in the morphology of the PU nanofibrous mat. To evaluate the colour shift due to NH3 vapour, the BCE/PU nanofibrous mats were photographed by a camera, and software was used to obtain the quantitative colour data (CIE L*a*b). The BCE/PU nanofibrous exhibited a remarkable colour change from pink–red to green–blue under NH3 vapour conditions with a fast response time (≤30 s). These findings showed that colourimetric nanofibrous textile sensors could be a promising in situ material in protective clothing that changes colour when exposed to harmful gases.

Synthesis and characterization of polypyrrole/molybdenum oxide composite for ammonia vapour sensing at room temperature

In this study, polypyrrole (PPy) and polypyrrole/molybdenum oxide composite (PPy/MoO3) were synthesized by the chemical oxidative method in an aqueous medium, using anhydrous ferric chloride (FeCl3) as an oxidant. The successful preparation of materials was confirmed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmittance electron microscopy (TEM). PPy and PPy/MoO3 were converted into pellets which were used as the sensor. A four-in-line probe device was used for studying DC electrical conductivity–based ammonia vapour–sensing properties at three different ammonia concentrations, that is, 1 M, 0.5 M and 0.1 M. The PPy/MoO3 sensor showed much-improved sensing performance than the PPy sensor in terms of % sensing response and reversibility. PPy/MoO3 sensor showed excellent selectivity for ammonia vapours against various VOCs. The % sensing response of PPy/MoO3 sensor towards ammonia was found to be 2.19, 2.50, 3.16, 3.87, 4.1, 5.15, 6.19, 6.55 and 7.77 times greater than ethanol, methanol, acetone, acetaldehyde, formaldehyde, toluene, benzene, chloroform and n-hexane, respectively. In the end, a sensing mechanism was also proposed, which is based on rapid adsorption–desorption of ammonia molecules on the PPy/MoO3 sensor’s surface.

Poly(n-vinylpyrrolidone-co-acrylonitrile-co-methacrylic acid)–graphene quantum dot conjugate: synthesis and characterization for sensing ammonia vapour

We report the biosynthesis of Graphene QDs and their composite with poly(n-vinylpyrrolidone-co-acrylonitrile-co-methacrylic acid) for efficient detection of ammonia with a detection limit of 0.232 ppm using a fabricated portable electronic device.

Two-step crystal–crystal phase transformation of N-salicylidene-p-aminobenzoic acid by gas–solid reaction with aqua–ammonia vapour

Crystal–crystal phase transformation by external stimuli has attracted significant attention for application in switchable materials, which can change their structures and properties. Herein, it is revealed that N-salicylidene-p-aminobenzoic acid crystals undergo a two-step crystal–crystal phase transformation through a gas–solid reaction with aqua–ammonia vapour. The photochromic behaviour of the crystals switched from nonphotochromic to photochromic and back to nonphotochromic via a phase transformation. The two-step phase transformation and photochromic behaviour change were characterized and correlated by X-ray crystal structure analysis, UV–Vis spectroscopy, differential scanning calorimetry and scanning electron microscopy. This article is the first report to capture the stepwise structural change in the gas–solid (acid–base) reaction of ammonia with benzoic acid derivatives.