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The catalytic degradation of hazardous organic contaminants in industrial wastewater is a promising technology. Reactions of tartrazine, the synthetic yellow azo dye, with Oxone® in the presence of catalyst in strong acidic condition (pH 2), were detected by using UV–Vis spectroscopy. In order to extend the applicability profile of Co-supported Al-pillared montmorillonite catalyst an investigation of Oxone® induced reactions were performed in extreme acidic environment. The products of the reactions were identified by liquid chromatography–mass spectrometry (LC-MS). Along with the catalytic decomposition of tartrazine induced by radical attack (confirmed as unique reaction path under neutral and alkaline conditions), the formation of tartrazine derivatives by reaction of nucleophilic addition was also detected. The presence of derivatives under acidic conditions slowed down the hydrolysis of tartrazine diazo bond in comparison to the reactions in neutral environment. Nevertheless, the reaction in acidic conditions (pH 2) is faster than the one conducted in alkaline conditions (pH 11). Theoretical calculations were used to complete and clarify the mechanisms of tartrazine derivatization and degradation, as well as to predict the UV–Vis spectra of compounds which could serve as predictors of certain reaction phases. ECOSAR program, used to estimate toxicological profile of compounds to aquatic animals, indicated an increase in the harmfulness of the compounds identified by LC-MS as degradation products from the reaction conducted for 240min. It could be concluded that an intensification of the process parameters (higher concentration of Oxone®, higher catalyst loading, increased reaction time, etc.) is needed in order to obtain only biodegradable products. [Display omitted] • Degradation of tartrazine was investigated in the presence of Oxone®. • Co2+ impregnated pillared clay was tested as catalyst for degradation of tartrazine. • Mechanism of the reaction in an extremely acidic environment was clarified. • Toxicological profile of products to aquatic organisms was evaluated. • Degradation capacity and exquisite applicability in wide range of pH was proven. [ABSTRACT FROM AUTHOR]

Porous cobalt-doped alumina catalysts were synthetized using the sol-gel method. The synthesized materials were calcined at 500 °C, 1000 °C and 1100 °C and denoted as CoA-500, CoA-1000 and CoA-1100, respectively. Catalysts were characterized using XRPD, H 2 -TPR and low temperature N 2 physisorption techniques. Applied techniques showed that the annealing temperature affects the structural and textural properties of the catalysts. The synthesized catalysts were investigated in the degradation of tartrazine in the presence of Oxone®. The influence of the mass of catalyst, reaction time, reaction temperature and initial pH were investigated. The temperature increase was beneficial for the dye degradation rate. CoA-500 was proved to be the most efficient among the investigated catalysts. The reaction followed the pseudo-first order kinetics for all investigated temperatures for all three catalysts. All cobalt-doped alumina catalysts were found to be efficient in the Oxone® induced catalytic degradation of tartrazine with CoA-500 showing the best performance. [Display omitted] • Porous Co-doped alumina powders were synthetized using the sol-gel method. • Materials were calcined at T = 500, 1000 and 1100 °C (CoA-T). • Novel utilisation of CoA-T as catalysts for Oxone activated dye degradation. • Annealing temperatures affected textural properties and catalytic performance. • CoA-T were found to be very fast and efficient catalysts in investigated process. [ABSTRACT FROM AUTHOR]

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 SO 4 ˙ˉ 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. [Display omitted] • Co2+ impregnated pillared clay was tested as catalyst in presence of SO 4 ˙ˉ radical. • Uv–Vis spectroscopy, GC-MS and DFT calculations were used to determine pH influence. • Predictors of mechanisms of pH dependent tartrazine degradation were established. • Besides main reaction pH dependent different competitive paths were proposed. • H atom bonded to diazo group is essential for radical cleavage of diazo compounds. [ABSTRACT FROM AUTHOR]

• Co2+ doped Al 2 O 3 coatings were formed by plasma electrolytic oxidation (PEO). • Cobalt content of coatings increased in agreement with Co2+ content of PEO solutions. • Cobalt in coatings significantly improved catalytic activity in the Oxone® based AOP. • The Co2+ doped Al 2 O 3 coatings exhibited good stability in the investigated reaction. The aim of this work is to examine the possibility of the formation of cobalt doped Al 2 O 3 coatings on aluminum substrate by plasma electrolytic oxidation process (PEO) and application of the obtained material as catalyst in the sulfate radical (SO 4 −) based advanced oxidation process (SR-AOP). The morphology and elemental composition, of the coatings were characterized using Scanning Electron Microscopy. The obtained material was tested as catalyst in SR-AOP in the degradation of model dye (tartrazine) in aqueous solution. Potassium peroxymonosulfate (Oxone®) was used as the source of radicals. The catalytic role of cobalt in tartrazine decolorization was tested in the catalytic system consisting of PEO cobalt doped Al 2 O 3 coated Al plates and Oxone®. It was found that the addition of cobalt precursor into PEO electrolyte solution significantly improved the catalytic properties of obtained coatings with respect to cobalt-free Al 2 O 3 coating and Oxone®. The influence of cobalt content in the supporting electrolyte during PEO process on the catalytic activity of the coatings, as well as Oxone® dosages in SR-AOP, were examined. [ABSTRACT FROM AUTHOR]