The nanoparticles tin oxide (SnO₂) has been successfully synthesized via a sol-gel method. The as-prepared SnO₂ was characterized using thermogravimetric analysis coupled with mass spectroscopy, X-ray diffraction and scanning electron microscope. Batch experiments were carried out to study the adsorption kinetics of Congo red azo dye on SnO₂. The effect of varying parameters such as contact time, initial dye concentration and adsorbent dose on the adsorption process was investigated. The results showed that the SnO₂ catalysts has high crystallinity with tetragonal rutile structure and average particle size about 13–23 nm. The untreated sample SnO₂-80 exhibited high efficiency (84.41 %) after 60 min of exposure time, which was 2 times as much as that of SnO₂-450 sample. The adsorption process was found to be highly dye concentration and adsorbent dose dependent. Pseudo-second-order kinetic model gave the best fit, with highest correlation coefficients (R ² ≥ 0.99). Regarding the adsorption equilibrium, the experimental results suggest that the Langmuir model was applicable. The formation of hydrogen bond and the electrostatic interaction between the Sn²⁺ center and the electron rich nitrogen atoms of CR moiety were believed to be the main adsorption mechanism. These findings should be valuable for designing effectively adsorbent material and practical interest in terms of ecology and sustainable development.

Ca₃Co₄O_9+δ exhibits fast oxygen exchange kinetics rendering it a promising electrode for application as an air electrode in solid oxide cells.

Oxide diffusion was studied in two innovative SOFC cathode materials, Ba ₂ Co ₉ O ₁₄ and Ca ₃ Co ₄ O _9+δ derivatives. Although oxygen diffusion was confirmed in the promising material Ba ₂ Co ₉ O ₁₄ , it was not possible to derive accurate transport parameters because of an oxidation process at the sample surface which has still to be clarified. In contrast, oxygen diffusion in the well-known Ca ₃ Co ₄ O _9+δ thermoelectric material was improved when calcium was partly substituted with strontium, likely due to an increase of the volume of the rock salt layers in which the conduction process takes place. Although the diffusion coefficient remains low, interestingly, fast kinetics towards the oxygen molecule dissociation reaction were shown with surface exchange coefficients higher than those reported for the best cathode materials in the field. They increased with the strontium content; the Sr atoms potentially play a key role in the mechanism of oxygen molecule dissociation at the solid surface.