Free-Radical-Induced Oxidation and Reduction of 1-Arylazo-2-naphthol Dyes: A Radiation Chemical Study

Sulfite activation by cobaltosic oxide nanohydrangeas for tetracycline degradation: Performance, degradation pathways and mechanism

Sulfite has been used as a classic reductant for the dehalogenation and reduction of organic compounds for a long time, it is recently deemed as a promising alternative (for persulfate) to generate sulfate radical for wastewater treatment due to its low price and eco-toxicity. In contrast with the enormous work developed in the field of tetracycline (TC) degradation via PMS activization, sulfite activization could play a important role in TC degradation but there is only very few available reports in this area. Herein, the novel and efficient CoNHs nanocatalyst is designed and developed, via immobilization of hydrangea-shaped Co₃O₄ nanoparticles onto graphitic carbon nanosheet (GCN), for the degradation of tetracycline via sulfite activation. The detailed characterizations have confirmed that CoNHs possesses a nanohydrangea-shaped structure with high microporosity. The comparison with other supports (such as CeO₂ and MoS₂), CoNHs provides the highest degradation efficiency in TC degradation, due to the synergistic effect between Co₃O₄ and GCN. Free radical quenching experiments and EPR analysis confirm that SO₄•^- and O₂•^- are major reactive oxygen species in the CoNHs/sulfite system. This work could provide a simple, economical and durable cobalt-based catalyst for organic wastewater treatment via sulfite activation.

Role of surfactant derived intermediates in the efficacy and mechanism for radiation chemical degradation of a hydrophobic azo dye, 1-phenylazo-2-naphthol

A combined methodology involving gamma and pulse radiolysis, product analysis and toxicity studies has been adopted to comprehend the degradation process of a model hydrophobic azo dye, 1-phenylazo-2-naphthol, emphasizing the role of the surfactant, which is an integral part of textile waste. Two new and important findings are underlined in this article. The first is the direct attestation of the hydrazyl radical-parent adduct, formed in the reaction of the dye with e(-)aq followed by protonation and subsequent addition to the unreacted dye molecule. This has been confirmed from concentration dependent studies. Secondly, we have clearly shown that in the reaction of hydroxyl radical with the dye in Triton X-100 media, the initially produced TX radicals cause reductive degradation of the dye. Identification and detailed analysis of HPLC and GCMS data reveals that similar products are formed in both the reactions of e(-)aq and OH radicals. Moreover, the cytotoxicity of 10(-4)moldm(-3) dye was found to be reduced significantly after irradiation. Thus, the present study not only depicts new pathways for the degradation of hydrophobic azo dye, but also demonstrates the role of a surfactant in the entire process.

Photocatalytic decolorization of soluble dyes by a bis-ions coexistence system of NH4(+) and NO3(-) with high photoreduction ability

In this paper, we found that the acidic and basic dyes were easily decolorized by a bis-ions coexistence system of NH(4)(+) and NO(3)(-) under UV light irradiation. The coexistence of NH(4)(+) and NO(3)(-) is a necessary condition for the photocatalytic decolorization of soluble dyes. The photocatalytic decolorization of methyl orange (MO) and methylene blue (MB) follows the first order rate kinetics. The location of an absorption peak in the visible region is blue-shifted with the increase in the illumination time. It is proposed that the photocatalytic decolorization of soluble dyes in the bis-ions coexistence system of NH(4)(+) and NO(3)(-) is a photoreduction reaction, in which the ammonium nitrate acts as a photocatalyst. The chromophore of acidic and basic dyes reacts with hydrogen and then results in their rapid decolorization.

Ultrasonic irradiation-induced degradation of low-concentration bisphenol A in aqueous solution

The treatment of bisphenol A (BPA)-contaminated water has attracted great interest recently. In this contribution, ultrasound (US) was applied to remove low-concentration BPA in aqueous solution at the frequency of 20 kHz, and the effects of ultrasonic intensity and ozone on BPA removal were evaluated for the first time. Considering the coexistence of halomethanes and BPA in chlorinated drinking water, BPA was degraded under US in the presence of CCl(4). In addition, the main intermediates resulting from BPA ultrasonic degradation were identified by gas chromatography-mass spectrometry. On the basis of these studies, OH radical induced oxidation was identified as the major destruction pathway during BPA sonolysis.

Degradation of aryl-azo-naphthol dyes by ultrasound, ozone and their combination: effect of alpha-substituents

Lab-scale degradation of azo dyes with ultrasound (300 kHz), ozone and both was investigated using an aryl-azo-naphthol dye-C.I. Acid Orange 8. It was found that in all schemes color decay was faster than UV absorbance, and the rates followed pseudo-first-order kinetics except for the decay of UV-254 band by ozone. Sonication alone was sufficient for decolorization, but not for UV absorption abatement or mineralization. Ozonation was more effective than ultrasound in bleaching, but not as much for the mineralization of the dye. Combined operation of ultrasound and ozone improved the rate of bleaching and UV absorption decay and remarkably enhanced the mineralization of the dye. This was attributed to increased mass transfer of ozone in solution and its decomposition in the gas phase to yield hydroxyl radicals and other oxidative species. The effect of alpha-methyl substituent at the aryl carbon of the dye was found to decelerate the rate of degradation as a result of weakened intramolecular hydrogen bonding.

Experimental and Computational Studies of Structure and Bonding in Parent and Reduced Forms of the Azo Dye Orange II

The structure and bonding of the azo dye Orange II (Acid Orange 7) in parent and reduced forms have been studied using NMR, infrared, Raman, UV-visible, and electron paramagnetic resonance (EPR) spectroscopy, allied with density functional theory (DFT) calculations on three hydrazone models (no sulfonate, anionic sulfonate, and protonated sulfonate) and one azo model (protonated sulfonate). The calculated structures of the three hydrazone models are similar to each other and that of the model without a sulfonate group (Solvent Yellow 14) closely matches its reported crystal structure. The 1H and 13C NMR resonances of Orange II, assigned directly from 1D and 2D experimental data, indicate that it is present as > or = 95% hydrazone in aqueous solution, and as a ca. 70:30 hydrazone:azo mixture in dimethyl sulfoxide at 300 K. Overall, the experimental data from Orange II are matched well by calculations on the hydrazone model with a protonated sulfonate group; the IR, Raman, and UV-visible spectra of Orange II are assigned to specific vibrational modes and electronic transitions calculated for this model. The EPR spectrum obtained on one-electron reduction of Orange II by the 2-hydroxy-2-propyl radical (*CMe2OH) at pH 4 is attributed to the hydrazyl radical produced on protonation of the radical anion. Calculations on reduced forms of the model dyes support this assignment, with electron spin density on the two nitrogen atoms and the naphthyl ring; in addition, they provide estimates of the structures, vibrational spectra, and electronic transitions of the radicals.