Research PaperDegradation of azo dye Orange II under dark ambient conditions by calcium strontium copper perovskite

- CSC perovskite degraded Orange II under dark conditions without peroxides or ozone.
- Fast kinetics under dark conditions up to 80% of AO7 degraded within 10 min.
- CSC proved to be effective for breaking NN bonds and generating electrons.
- Electrons reacted with oxygen on the CSC surface and produced radicals.
- Radicals partially degraded by-products.

This work investigates the effect of calcium strontium copper (CSC) based catalysts for the degradation of an azo dye orange II (OII) under dark conditions without the addition of peroxides or ozone. CSC were synthesized via a combined EDTA-citric acid complexation method. The resultant catalyst was composed of perovskite and metal oxide phases, however, the perovskite phase was the most active for degradation of OII. The content of Ca and Sr in the A-site of the perovskite structure was varied whilst the B-site was Cu rich. CSC compounds with higher Ca content in the A-site were slightly more effective at degrading OII. The degradation kinetics under dark conditions was fast with up to 80% of OII being degraded within 10 min. TOC results showed that the degradation was only partial as more than 60% of the organic carbon remained in the solution, supported by the formation of by-products determined by HPLC. The remainder of the carbon were found to be adsorbed on the surface of the spent CSC catalyst, as by-products of the reaction and OII molecules. The CSC catalyst proved to be effective for breaking NN bonds from solutions containing low (10 ppm) to high (100 ppm) OII concentrations. This reaction produced electrons which generated radical species, including hydroxyl radicals as confirmed by 2-propanol, which further degraded OII and its by-products.

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