A novel approach in revealing mechanisms and particular step predictors of pH dependent tartrazine catalytic degradation in presence of Oxone®.

The degradation of tartrazine in the presence of cobalt activated Oxone® (potassium peroxymonosulfate) was investigated at different initial pH values. Aluminum pillared clay had the role of a support for catalytically active cobalt oxide species. The degradation of tartrazine and the formation of a mixture of degradation products were monitored using the Ultraviolet-Visible (UV-Vis) spectroscopy and gas chromatography-mass spectrometry (GC-MS). The exact qualitative composition of this mixture and the determination of the most probable mechanism of degradation (the primary goal) were obtained using GC-MS. Besides, the main reaction pathway (reaction with SO4˙- radical anion) and secondary pathways were proposed depending on the pH value. At pH = 6 the reaction with HO˙ radical was proposed. At pH = 11 decarboxilation was suggested as the first step of the secondary proposed reaction pathway. The combination of results acquired from the deconvolution of UV-Vis spectra and the theoretical UV-Vis spectra of degradation products, whose occurrence was predicted by quantum-chemical calculations, was proven to be beneficial for the identification of tartrazine degradation products and for defining UV-Vis predictors of particular degradation steps. An additional contribution of this paper, from the reactivity aspect, was the establishment of the critical structural demand for the radical degradation of any diazo compound. The existence of a hydrogen atom bound to a diazo group was found to be the essential prerequisite for the radical cleavage of diazo compounds.

Differently shaped nanocrystalline (Fe, Y)3O4 and its adsorption efficiency toward inorganic arsenic species.

Herein we report effects of partial substitution of Fe3+ by Y3+ in magnetite (Fe3O4) on morphology and inorganic arsenic species adsorption efficiency of the Fe3-x Y x O4 nanoparticles formed. The series of Fe3-x Y x O4 (x = 0.00, 0.042 and 0.084, labeled as Y00, Y05 and Y10, respectively) was synthesized using co-precipitation followed by microwave-hydrothermal treatment (MW) at 200 °C. With increase of yttrium content (x value), both the morphological inhomogeneity of the samples and the fraction of spinel nanorods as compared to spinel pseudospherical particles increased. By both transmission electron microscopy and x-ray powder diffraction analyses, it was determined that the direction of growth of the spinel nanorods is along the [110] crystallographic direction. The Fe3-x Y x O4 affinities of adsorption toward the inorganic arsenic species, As(III) (arsenite, AsO3 3-) and As(V) (arsenate, AsO4 3-), were investigated. Increased Y3+ content related to changes in sample morphology was followed by a decrease of As(III) removal efficiency and vice versa for As(V). The increase in Y3+ content, in addition to increasing the adsorption capacity for As(V), significantly expanded the optimum pH range for the maximum removal and decreased the contact time for necessary 50% removal (t 1/2) of As(V) (Y00: pH 2-3, t 1/2 = 3.12 min; Y05: pH 2-6, t 1/2 = 2.12 min and Y10: pH 2-10, t 1/2 = 1.12 min). The results point to incorporation of Y3+ in the crystal lattice of magnetite, inducing nanorod spinel structure formation with significant changes in sorption properties important for the removal of inorganic arsenic from waters.

Influence of process parameters on the photodegradation of synthesized azo pyridone dye in TiO2 water suspension under simulated sunlight.

Photocatalytic degradation of synthesized azo pyridone dye (5-(4-sulpho phenylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone), in aqueous solutions by simulated sunlight in the presence of commercial TiO(2), Aeroxide P25, was studied. The reaction kinetics analysis showed that photodegradation exhibits pseudo first-order kinetics according to Langmuir-Hinshelwood model. The effects of various process parameters on the photocatalytic degradation were investigated. The optimal catalyst content and pH were determined. A decrease in the reaction rate was observed upon the increase of the initial dye concentration. Degradation of the dye was enhanced by hydrogen peroxide, but it was inhibited by ethanol. The influence of temperature was studied, and the energy of activation was determined. According to total organic carbon (TOC) analysis, 54% of TOC remained when 100% of the dye was decolorized. Although the intermediates were not determined in this study, the TOC results clearly indicate their presence during the reaction. In addition, photocatalytic degradation of simulated dyehouse effluents, containing tested azo pyridone dye and associated auxiliary chemicals was investigated.