Ceramic metal oxides with Ni2+ active phase for the fast degradation of Orange II dye under dark ambiance

Ceramic metal oxides based on calcium strontium nickel (CSN) were synthesized via a combined EDTA-citric acid complexation method and evaluated using Orange II (OH) as the model pollutant under dark conditions, without adding any extemal stimulants. The CSN catalyst was characterized by a very fast reaction reaching 97% OH degradation within 5 min. The surface of CSN metal oxides proved to be very active toward the breakdown of the -N=N- azo bond of OII. A second electron generating pathway was found as Ni2+ phase in the CSN catalyst oxidized to Ni3+ for the spent catalyst. Both electron generating pathways resulted in the formation of hydroxyl radicals (OH.) as determined using radical quenchers. Hydroxyl radicals were responsible for the formation of several intermediate products. The Ni2+ phase was very active contrary to the Ni3+ phase which could not degrade OH. The fast degradation kinetics of OII using CSN in dark at room temperature was attributed to the double electron generation pathways.