RESUMO
The photocatalytic efficiency of some semiconductors depends mainly on their morphological, optical, and structural properties, which can be modified by varying the calcination temperature. In order to evaluate how these properties change, as a function of temperature in a AA'BB'O3 perovskite material, La0.9Sr0.1Fe0.8Co0.2O3±Î´ (LSFC) was synthesized by the Pechini method and calcined at different temperatures (600 °C, 700 °C, 800 °C, and 900 °C). All the samples were characterized structurally, morphologically, and optically by XRD, SEM, and UV-Vis spectroscopy. Additionally, specific surface area and pore size distribution were calculated by BET and BHJ methods. LSFC was evaluated as photocatalyst material, estimating the degradation of reactive black 5 (RB5), employing as irradiation source UV light and sunlight. The obtained results display a clear tendency between the photoactivity and the heat treatment: degradation percentage decreases as the calcination temperature increases mainly due to the crystal and grain size and, furthermore, loss of porosity and the decrease in surface area, affecting the photocatalytic activity (98%, 95%, 74%, and 50% degradation, respectively). All the ceramic samples follow a pseudo-first-order reaction.
RESUMO
To date, the formation mechanisms of TiO2, as well as its heterostructures, have not been clarified. Moreover, detailed research on the transition from a tetragonal anatase phase to the monoclinic phase of the TiO2(B) phase and their interface structure has been quite limited until now. In the present study, we report on the sonochemical synthesis of TiO2-anatase with a crystallite size of 5.2 ± 1.5 nm under different NaOH concentrations via the hydrothermal method. The use of alkaline solution and the effect of the temperature and reaction time on the formation and structural properties of TiO2-anatase nanopowders were studied. The effects of NaOH concentration on the formation and transformation of titanate structures are subject to thermal effects that stem from the redistribution of energy in the system. These mechanisms could be attributed to three phenomena: (1) the self-assembly of nanofibers and nanosheets, (2) the Ostwald ripening process, and (3) the self-development of hollow TiO2 mesostructures.
RESUMO
A Metal-Organic Framework (MOF), iron-benzenetricarboxylate (Fe(BTC)), has been studied for the adsorptive removal of azo-dye Orange II from aqueous solutions, where the effect of various parameters was tested and isotherm and kinetic models were suggested. The adsorption capacities of Fe(BTC) were much higher than those of an activated carbon. The experimental data can be best described by the Langmuir isotherm model (R² > 0.997) and revealed the ability of Fe(BTC) to adsorb 435 mg of Orange II per gram of adsorbent at the optimal conditions. The kinetics of Orange II adsorption followed a pseudo-second-order kinetic model, indicating the coexistence of physisorption and chemisorption, with intra-particle diffusion being the rate controlling step. The thermodynamic study revealed that the adsorption of Orange II was feasible, spontaneous and exothermic process (-25.53 kJ·mol-1). The high recovery of the dye showed that Fe(BTC) can be employed as an effective and reusable adsorbent for the removal of Orange II from aqueous solutions and showed the economic interest of this adsorbent material for environmental purposes.