Titanate nanotubes were prepared by hydrothermal synthesis, followed by Titanate nanotubes were prepared by hydrothermal synthesis, followed by proton exchange, and calcined at 250°C for 2h. The properties of prepared nanotubes were investigated with field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), adsorption-desorption N 2 isotherms and UV-Vis diffuse reflectance spectroscopy (DRS). As-prepared sample displayed strongly aggregated nanotubes with crystal structure of H 2 Ti 2 O 5 ×H 2 O. Calcination yielded with loss of interlayer water and partial transformation of nanotubes to anatase phase. Adsorption and photocatalytic decomposition of methylene blue, used as a model pollutant, on as-prepared and calcined titanate nanotubes have been studied. It was established that calcination at 250°C for 2h improves the adsorption and photocatalytic properties of titanate nanotubes. It was shown that pseudo-second-order model was the most appropriate to describe adsorption of methylene blue on titanate nanotubes. Affinity toward methylene blue of 48.45mg g-1 and 95.24mg g-1 has been established for as-prepared and calcined titanate nanotubes, while equilibrium adsorption was attained in 120min. Adsorption process is controlled by intraparticle diffusion and surface sorption in both samples, but the contribution of surface sorption is greater for the calcined sample. The pseudo-first-order kinetic is an acceptable model for photocatalytic dye degradation process on titanate nanotubes. It was shown that the calcination slightly increased the photocatalytic activity of titanate nanotubes.
Hydrothermal synthesis of CeO2was optimized on two reactant concentrations and synthesis temperature and duration, in order to achieve material having the greatest specific surface area (SSA). Taguchi method of experimental design was employed in evaluation of the relative importance of synthesis parameters. CeO2nanoparticles were characterized using X-ray diffraction, nitrogen adsorption-desorption isotherms, and scanning electron microscopy. Optimum conditions for obtaining particles with greater SSA were calculated according to Taguchi’s model “the-higher-the-better.” Synthesis temperature was found to be the only parameter significant for enabling nanoparticles with greater SSA. Mesoporous nanocrystalline ceria with SSA as great as 226 m2 g−1was achieved, which is unprecedented for the hydrothermally synthesized ceria. The reason for this achievement was found in temperature dependence of the diffusion coefficient which, when low, favors nucleation yielding with fine particles, while when high it favors crystal growth and formation of one-dimensional structures. The occurrence of 1D-structure in sample exhibiting the smallest SSA was confirmed. Very fine crystallites with crystallite size as low as 5.9 nm have been obtained being roughly inverse proportional to SSA. Selected samples were tested as catalyst for soot oxidation. Catalyst morphology turned out to be decisive factor for catalytic activity.
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