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Stephanie E. Atkinson, Ciera E. Cipriani, Nelson R. Vinueza and Melissa A. Pasquinelli, Textile Engineering, Chemistry and Science, NC State University, 1020 Main Campus Dr, Raleigh, NC 27606
Azo compounds possess the structure R-N=N-R’ and are commonly used in the textile industry. Previous studies have shown that azo dyes generally break down at their azo bonds by photodegradation forming toxic aromatic compounds. However, our results from high-resolution mass spectrometry (MS) and molecular modeling of the dye Disperse Red 1, Disperse Orange 3 and Disperse Orange 37 indicated that the major photodegradation products were not based on the azo bond breaking, but rather breakage within the dye’s arylamine group. The photodegradation mechanism proposed previously for disperse dyes was investigated using density functional theory (DFT) calculations. The reactivities of these dyes for both the ground and excited states, and for the cis-to-trans transition were determined. A trend was seen in the reactivity of the studied azo dyes, in which the trans isomers were generally most susceptible to radical attack at their amino end groups, while the cis isomers were more reactive at their azo bonds. Previously, it had not been studied how these dyes would change their photodegradation mechanism when putting into solution instead of on fabric as in solution it could simulate wastewater. From the analyses of ethyl acetate solution-dyed with DR1 and photodegraded for different time intervals, a general photodegradation pathway was solidified for DR1 and correlated with previous results with poly(ethylene terephthalate) dyed fabric as well as correlating with molecular modeling results. The molecular structure of the terminal groups and pendant side chains, reduction of the azo bonds, and conformation were determined as main factors that change the reactivity of the azo center, ethyl, and hydroxyethyl groups. Thus, modifying the molecular structure and the medium in which azo dyes are found may allow for control of the location and mechanism of photodegradation, so that fewer harmful aromatic compounds are released into the environment.
Presenter: Stephanie Atkinson
Institution: NC State University
Type: Poster
Subject: Chemistry
Status: Approved
