Diverse hard template synthetic methodologies are being employed for the synthesis of mesostructured metal oxide and carbon nanomaterials, with the application of mesoporous silica as the hard template. We describe the main differences and advantages/disadvantages between the soft and hard templated synthetic routes, provide an overview of the synthesis and characteristics of different templating mesoporous silica nanomaterials and discuss on practical aspects of the hard template synthetic methodology for obtaining various metal-oxide and carbon-based mesostructured nanomaterials. Also, we cover various recent applications of thus constructed mesostructured metal oxide and carbon nanomaterials, such as sensing, energy storage, fuel cells, and catalysis, which demonstrate the highly promising character of the hard template methodology for the synthesis of a new generation of nanomaterials with broad application potential.
In this work single phase hexagonal YMnO 3 powders were prepared starting from Y(CH 3 COO) 3 Á xH 2 O, Mn(CH 3 COO) 2 Á 4H 2 O, KMnO 4 and KOH using methods of conventional (280 1C for 6 h) or microwave assisted hydrothermal synthesis (200 1C for 2 h) followed by calcination at 1200 1C for 2 h. According to FESEM analysis the calcined powders consisted of submicronic YMnO 3 particles, which were uniform in shape and size. Ceramic samples were obtained by sintering the as-synthesized powders at 1400 1C for 2 h. XRD analysis confirmed the presence of the single phase hexagonal YMnO 3 . SEM analysis showed a dense and homogeneous microstructure with typical inter-and intra-grain cracks. Magnetic measurements indicated ferrimagnetic properties that were explained by non-stoichiometry of the obtained compound and an excess of manganese that was confirmed by ICP analysis.
In this study, the possibility to stabilize O2-ion conductors in Bi2O3-V2O5
system was investigated. Six pseudo-binary Bi2O3-V2O5 mixtures [3.50 <
x(V2O5) < 8.50 mol%] were thermally treated at 1000?C for 1 h. The samples
were characterized by XRD, HRTEM/SAED, DTA and EIS techniques. The
high-temperature reaction between ? Bi2O3 and V2O5 resulted in formation of
microcrystalline single-phase specimens containing the phase based on
?-Bi2O3 if V2O5 content was ? 4.63 mol%. The obtained phases exhibited main
diffraction peaks corresponding to the simple cubic ?-Bi2O3 (space group
Fm-3m) but Rietveld refinement showed a threefold repeat on a simple cubic
sublattice indicating that the true unit cell is 3?3?3 supercell. Within
proposed supercell, the octahedrally coordinated V5+ ions fully occupy 4a
Wyckoff position and partially occupy 32f. The Bi3+ ions are placed at the
rest of 32f and at 24e and 48h with full occupation. In total, 22 % of
anionic sites are vacant. The ionic conductivity of phase with the lowest
dopant content, i.e. Bi 103V5O167, amounts 0.283 S cm-1 at 800?C with the
activation energy of 0.64(5) eV, which is comparable to the undoped ?-Bi2O3
known as the fastest ion conductor.
Developing highly efficient semiconductor metal oxide (SMOX) sensors capable of accurate and fast responses to environmental humidity is still a challenging task. In addition to a not so pronounced sensitivity to relative humidity change, most of the SMOXs cannot meet the criteria of real-time humidity sensing due to their long response/recovery time. The way to tackle this problem is to control adsorption/desorption processes, i.e., water-vapor molecular dynamics, over the sensor’s active layer through the powder and pore morphology design. With this in mind, a KIT-5-mediated synthesis was used to achieve mesoporous tin (IV) oxide replica (SnO2-R) with controlled pore size and ordering through template inversion and compared with a sol-gel synthesized powder (SnO2-SG). Unlike SnO2-SG, SnO2-R possessed a high specific surface area and quite an open pore structure, similar to the KIT-5, as observed by TEM, BET and SWAXS analyses. According to TEM, SnO2-R consisted of fine-grained globular particles and some percent of exaggerated, grown twinned crystals. The distinctive morphology of the SnO2-R-based sensor, with its specific pore structure and an increased number of oxygen-related defects associated with the powder preparation process and detected at the sensor surface by XPS analysis, contributed to excellent humidity sensing performances at room temperature, comprised of a low hysteresis error (3.7%), sensitivity of 406.8 kΩ/RH% and swift response/recovery speed (4 s/6 s).
Yttrium manganite (YMnO 3) is widely investigated multiferroic material with potential use in many technological applications. In this paper, we report on the preparation and characterization of multiferroic hexagonal YMnO3 ceramics obtained by chemical synthesis route. Precursor powders were prepared by the polymerizable complex method from citrate precursors. After calcination at 900°C the powders contained mixture of Y-Mn-O phases which were further sintered at different temperatures. XRD analysis revealed that sintering at 1400°C resulted in the formation of pure hexagonal YMnO 3. Density of the obtained ceramics was 96 %TD. The ceramic samples proved to have multiferroic properties-they are antiferromagnetic below 42 K with linear dependence of magnetization as a function of applied magnetic field. The ferroelectric measurements performed at room temperature showed remanent polarization of 0.21 µC/cm 2 and the coercive field of 6.0 kV/cm for the YMnO 3 sample sintered at 1400°C. The magnetization curves measured at 2 and 5 K for the powder samples calcined at 900°C and ceramic samples sintered at 1300°C exhibited a hysteresis loop due to a small concentration of Mn 3 O 4 in the samples.
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