Enhanced adsorption and degradation of methylene blue over mixed niobium-cerium oxide - Unraveling the synergy between Nb and Ce in advanced oxidation processes.

Formation of reactive oxygen species (ROS) via HO activation is of vital importance in catalytic environmental chemistry, especially in degradation of organic pollutants. A new mixed niobium-cerium oxide (NbCeO) was tailored for this purpose. A thorough structural and chemical characterization of NbCeO along with CeO and NbO reference materials was carried out using TEM/STEM/EDS, SEM, XRD, XPS, EPR, UV-vis and N physisorption. The ability of the catalysts to activate HO towards ROS formation was assessed on the basis of EPR and Raman measurements. Catalytic activity of the oxides was evaluated in degradation of methylene blue (MB) as a model pollutant. Very high activity of NbCeO was attributed to the mixed redox-acidic nature of its surface, which originated from the synergy between Nb and Ce species. These two properties (redox activity and acidity) ensured convenient conditions for efficient activation of HO and degradation of MB. The activity of NbCeO in MB degradation was found 3 times higher than that of the commercial NbO CBMM catalyst and 240 times higher than that of CeO. The mechanism of the degradation reaction was found to be an adsorption-triggered process initiated by hydroxyl radicals, generated on the surface via the transformation of O/O.