Influence of Sintering Strategy on the Characteristics of Sol-Gel Ba1-xCexTi1-x/4O3 Ceramics

Single-phase Ce³⁺-doped BaTiO₃ powders described by the nominal formula Ba_1−xCe_xTi_1−x/4O₃ with x = 0.005 and 0.05 were synthesized by the acetate variant of the sol-gel method. The structural parameters, particle size, and morphology are strongly dependent on the Ce³⁺ content. From these powders, dense ceramics were prepared by conventional sintering at 1300 °C for 2 h, as well as by spark plasma sintering at 1050 °C for 2 min. For the conventionally sintered ceramics, the XRD data and the dielectric and hysteresis measurements reveal that at room temperature, the specimen with low cerium content (x = 0.005) was in the ferroelectric state, while the samples with significantly higher Ce³⁺ concentration (x = 0.05) were found to be in the proximity of the ferroelectric–paraelectric phase transition. The sample with low solute content after spark plasma sintering exhibited insulating behavior, with significantly higher values of relative permittivity and dielectric losses over the entire investigated temperature range relative to the conventionally sintered sample of similar composition. The spark-plasma-sintered Ce-BaTiO₃ specimen with high solute content (x = 0.05) showed a fine-grained microstructure and an almost temperature-independent colossal dielectric constant which originated from very high interfacial polarization.

Synthesis of a well-dispersed CaFe2O4/g-C3N4/CNT composite towards the degradation of toxic water pollutants under visible light

Herein, we fabricated a ternary photocatalyst composed of CaFe₂O₄, multiwalled carbon nanotubes (CNTs) and graphitic carbon nitride (g-C₃N₄) via a simple hydrothermal route. CaFe₂O₄ acted as a photosensitizer medium and the CNT acted as a co-catalyst, which remarkably enhanced the photocatalytic performances of g-C₃N₄ towards the degradation of hexavalent chromium (Cr(vi)) and the antibiotic tetracycline (TC) under visible light irradiation. To investigate the morphological and topological features of the photocatalyst, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) analyses were performed. The surface properties and oxidation state of the CaFe₂O₄/g-C₃N₄/CNT composite were determined by X-ray photoelectron spectroscopy (XPS). The recombination rate of the charge carriers and the band gap values of the as-synthesized catalysts were analyzed by photoluminescence spectroscopy (PL) and diffused reflectance spectroscopy (UV/Vis DRS) studies, respectively. Besides the degradation reactions, the high hydrogen production rate of 1050 μmol h⁻¹ under visible light using the CaFe₂O₄/g-C₃N₄/CNT composite loaded with 5 wt% CNT was observed. The superior photocatalytic performances of the CaFe₂O₄/g-C₃N₄/CNT composite can be ascribed to the effective heterojunction formed between g-C₃N₄ and the CaFe₂O₄ matrix, in which the CNT act as a conducting bridge in the system, promoting the production of photoinduced charge carriers in the semiconductor system. Finally, the plausible photocatalytic mechanism towards the degradation of pollutants and hydrogen production was discussed carefully.

Herein, we fabricated a ternary photocatalyst composed of CaFe₂O₄, multiwalled carbon nanotubes (CNTs) and graphitic carbon nitride (g-C₃N₄) via a simple hydrothermal route.