Thermocatalytic Performance of LaCo1-xNixO3-delta Perovskites in the Degradation of Rhodamine B

Perovskite-type LaCo1-xNixO3-delta (x = 0, 0.2, 0.4, 0.6, and 0.8) powders were synthesized by solution combustion synthesis. The crystal structure, morphology, texture, and surface were characterized by X-ray powder diffraction combined with Rietveld refinement, scanning electron microscopy, N-2-adsorption, X-ray photoelectron spectroscopy, and zeta-potential analysis. The thermocatalytic properties of the perovskites were investigated by UV-Vis spectroscopy through degradation of rhodamine B in the temperature range 25-60 degrees C. For the first time, this perovskite system was proven to catalyze the degradation of a water pollutant, as the degradation of rhodamine B occurred within 60 min at 25 degrees C. It was found that undoped LaCoO3-delta is the fastest to degrade rhodamine B, despite exhibiting the largest energy band gap (1.90 eV) and very small surface area (3.31 m(2) g(-1)). Among the Ni-doped samples, the catalytic performance is balanced between two main contrasting factors, the positive effect of the increase in the surface area (maximum of 12.87 m(2) g(-1) for 80 mol% Ni) and the negative effect of the Co(III) stabilization in the structure (78% in LaCoO3 and 89-90% in the Ni-containing ones). Thus, the Co(II)/Co(III) redox couple is the key parameter in the dark ambient degradation of rhodamine B using cobaltite perovskites.