Abstract:Sodium azide(NaN3) is a white, odorless, tasteless, crystal or powder.It is highly toxic and a severe explosive risk if shocked or heated.It has been used for a wide variety of military, laboratory, medical and commercial purposes. Recently because of high demand for using sodium azide as an inflator propulsion in car airbag systems, annual manufacture of this product has increased dramatically.Sodium azide is highly water soluble with pKa of 4.6and when it mixed with water, it will change rapidly to a highly volatile irritant, hydroizoic acid (HN3). Sodium azide and hydrazoic acid are hazardous because they produce hypotension (low blood pressure) in laboratory animals and humans. In addition, they form strong complexes with hemoglobin and block oxygen transport to blood.According to United States Environmental Protection Agencymaximum allowable concentration for NaN3 in water is 0.15 mg/L[1].Because of its ready availability and high toxicity, determination of azide in the aqueous solutions becoming mandatory. Gold nanoparticles (AuNPs) have received considerable attention in different areas such as chemical and biological sensing, medical diagnostics and therapeutics and biological imaging, as these small particles exhibit a strong surface plasmon (SP) absorption band [2-3]. In this paper, we report A simple optical method for the sensing of Azide based on aggregation of gold nanoparticles (AuNPs)The Azide ions induces the aggregation of positively charged AuNPs, which results in a shift in the surface Plasmon band and a consequent color change of the AuNPs from red to blue. The color change was monitored using smartphone as the colorimeter and compared with UV-vis spectrophotometr. The aggregation was confirmed by transmission electron microscopic measurements. The degree of aggregation was found to be proportional to the concentration of the Azide concentration, allowing its quantitative detection. The change in the absorbance and color-value has been used to monitor the concentration of Azide. The electrostatic interaction between the negatively-charged Azide and the positively-charged gold nanoparticles leads to aggregation of gold nanoparticles and a color change from red to blue in solution, thus providing a simple and visual approach to colorimetric detection of Azide.

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