Reactivity differences of hydroxyl radicals and hydrated electrons in destructing azo dyes

Radiation induced degradation of dyes—An overview

“…Gamma radiolysis with UV-vis spectroscopy and gradient ion pair HPLC separation has been used to follow the degradation of Apollofix-Red SF-28(AR-28) dye and subsequent measurement of the degradation products [36]. The absorbance in the visible range was found to gradually decrease with increasing dose of irradiation, while at the same time there was a shift of the band to longer wavelengths supporting the idea of incorporation of an • OH group into the chromophoric part of the molecule.…”

“…The study was done in nitrogen saturated dye solution and has the findings have shown that the solvated electron produced as a result of water irradiation reacted with the dye molecule to cause its reduction. The reaction rate constant of Congo Red with e aq − was determined to In another study on Apollofix-Red SF-28 (AR-28) the reactions of hydrated electron e aq − and • OH radical were investigated separately and it was found that • OH radical preferentially reacted with the unsaturated bonds of the molecule [36]. Furthermore, the reactions of the • OH adduct radicals with the AR-28 molecules partly reformed the dye structure.…”

“…This effect is seen by numerous groups on various dyes [34][35][36][37][38]. At a higher radiation dose, more reactive species are generated in solution, which in turn are available to react with and degrade dye molecules.…”

“…The AOP technique has drawn considerable attention from various quarters of scientific community as it is easy to handle and produces significantly less residuals as compared to the classical approaches. Amongst the many techniques employed in the AOP approach are the UV photolytic technique [9][10][11][12], Fenton process [13][14][15][16][17][18], photo-Fenton process [19][20][21], ozonation process [22], sonolysis [23][24][25], photocatalytic approach [26][27][28][29][30], biodegradation [31][32][33] and the radiation induced degradation of dyes [34][35][36][37]. Furthermore, many workers have coupled the various AOP techniques to obtain significant improvement in their results [38][39][40][41][42][43].…”

Electrochemical discolouration and degradation of reactive dichlorotriazine dyes: reaction pathways

“…The • OH addition to the azo chromophoric group leads to the destruction of the extensive conjugation and the intensive absorption band in the visible range disappears. The addition of • OH radical to a triazine ring is less probable due to smaller reactivity of this ring with the radical and the fact that rate of this reaction is slow [36,37]. At the same time, the absorption bands in the wavelength range from 330 to 470 nm observed in the spectra recorded in the RR2 solution (Fig.…”