PeerJ Materials Science:Ceramicshttps://peerj.com/articles/index.atom?journal=matsci&subject=12310Ceramics articles published in PeerJ Materials ScienceSynthesis of nano-TiO2 assisted by glycols and submitted to hydrothermal or conventional heat treatment with promising photocatalytic activityhttps://peerj.com/articles/matsci-132021-03-242021-03-24Lidiaine Maria SantosAntonio Eduardo da Hora Machado
TiO2 nanoparticles were successfully synthesized by the sol-gel method employing different glycols (ethylene glycol, diethylene glycol or polyethylene glycol 300), which were heat-treated in conventional oven or by hydrothermal via, obtaining photocatalysts with particle sizes and distinct crystalline structures. HRTEM analyses showed that the oxides submitted to hydrothermal treatment featured spherical morphology, being formed by partially aggregated particles with sizes varying between 2 and 5 nm. X-ray diffractograms and Raman spectroscopy confirm that anatase was predominant in all synthesized compounds, with presence of brookite phase for samples that received hydrothermal treatment or were synthesized in the presence of polyethylene glycol with heat treatment in conventional oven. The amount of brookite as well as the cell volume, deformation, network parameters and crystallinity were estimated by Rietveld refinement. The surface area and porosity of the materials were higher when the synthesis involved the use of hydrothermal treatment. These oxides are mesoporous with porosity between 14 and 31%. The oxide synthesized in the presence of ethylene glycol with hydrothermal thermal treatment (TiO2G1HT) exhibited the highest photocatalytic activity in terms of mineralization of azo-dye Ponceau 4R (C.I. 16255), under UV-Vis irradiation. This higher photocatalytic activity can be attributed to the formation of binary oxides composed by anatase and brookite and by its optimized morphological and electronic properties.
TiO2 nanoparticles were successfully synthesized by the sol-gel method employing different glycols (ethylene glycol, diethylene glycol or polyethylene glycol 300), which were heat-treated in conventional oven or by hydrothermal via, obtaining photocatalysts with particle sizes and distinct crystalline structures. HRTEM analyses showed that the oxides submitted to hydrothermal treatment featured spherical morphology, being formed by partially aggregated particles with sizes varying between 2 and 5 nm. X-ray diffractograms and Raman spectroscopy confirm that anatase was predominant in all synthesized compounds, with presence of brookite phase for samples that received hydrothermal treatment or were synthesized in the presence of polyethylene glycol with heat treatment in conventional oven. The amount of brookite as well as the cell volume, deformation, network parameters and crystallinity were estimated by Rietveld refinement. The surface area and porosity of the materials were higher when the synthesis involved the use of hydrothermal treatment. These oxides are mesoporous with porosity between 14 and 31%. The oxide synthesized in the presence of ethylene glycol with hydrothermal thermal treatment (TiO2G1HT) exhibited the highest photocatalytic activity in terms of mineralization of azo-dye Ponceau 4R (C.I. 16255), under UV-Vis irradiation. This higher photocatalytic activity can be attributed to the formation of binary oxides composed by anatase and brookite and by its optimized morphological and electronic properties.Preparation, thermal stability and electrical transport properties of vaesite, NiS2https://peerj.com/articles/matsci-22019-11-152019-11-15Helena M. FerreiraElsa B. LopesJosé F. MaltaLuís M. FerreiraMaria H. CasimiroLuís SantosManuel F.C. PereiraAntonio Pereira Gonçalves
Vaesite, a nickel chalcogenide with NiS2 formula, has been synthetized and studied by theoretical and experimental methods. NiS2 was prepared by solid-state reaction under vacuum and densified by hot-pressing, at different consolidation conditions. Dense single-phase pellets (relative densities >94%) were obtained, without significant lattice distortions for different hot-pressing conditions. The thermal stability of NiS2 was studied by thermogravimetric analysis. Both as-synthetized and hot-pressed NiS2 have a single phase nature, although some hot-pressed samples had traces of the sulfur deficient phase, Ni1-xS (<1%vol), due to the strong desulfurization at T > 340 °C. The electronic band structure and density of states were calculated by Density Functional Theory (DFT), indicating a metallic behavior. However, the electronic transport measurements showed p-type semiconductivity for bulk NiS2, verifying its characteristic behavior has a Mott insulator. The consolidation conditions strongly influence the electronic properties, with the best room-temperature Seebeck coefficient, electrical resistivity and power factor being 182 µVK−1, 2,257 µΩ m and 14.1 µWK−2 m−1, respectively, pointing this compound as a good starting point for a new family of thermoelectric materials.
Vaesite, a nickel chalcogenide with NiS2 formula, has been synthetized and studied by theoretical and experimental methods. NiS2 was prepared by solid-state reaction under vacuum and densified by hot-pressing, at different consolidation conditions. Dense single-phase pellets (relative densities >94%) were obtained, without significant lattice distortions for different hot-pressing conditions. The thermal stability of NiS2 was studied by thermogravimetric analysis. Both as-synthetized and hot-pressed NiS2 have a single phase nature, although some hot-pressed samples had traces of the sulfur deficient phase, Ni1-xS (<1%vol), due to the strong desulfurization at T > 340 °C. The electronic band structure and density of states were calculated by Density Functional Theory (DFT), indicating a metallic behavior. However, the electronic transport measurements showed p-type semiconductivity for bulk NiS2, verifying its characteristic behavior has a Mott insulator. The consolidation conditions strongly influence the electronic properties, with the best room-temperature Seebeck coefficient, electrical resistivity and power factor being 182 µVK−1, 2,257 µΩ m and 14.1 µWK−2 m−1, respectively, pointing this compound as a good starting point for a new family of thermoelectric materials.