Two series of TiO2 thin films were prepared based on soluble precursor powders: The first run originated directly from an alcohol-based coating solution whereas for the second batch the aqueous precursor powder sol had previously undergone a hydrothermal treatment. The respective microstructures were characterized by electron microscopy, the phase evolution was monitored by X-ray diffraction. Ellipsometric porosimetry (EP) was employed to reveal changes of porosity and pore size induced by thermal treatment of the films.
Soluble TiO2 precursor powders were hydrothermally treated to yield coating solutions. Films from these sols were compared with those directly obtained by dissolving the precursor powders. Results indicate that crystallization to anatase is induced under hydrothermal conditions and the resulting films mostly maintain their porosity throughout thermal treatment. In contrast to that coatings processed from as-dissolved precursor powders undergo more extensive densification
The aim of this work was an investigation of structural and electrical properties of ZnO/Zn2-xFexTiO4 (x?=?0.7, 1, 1.4) powders. The compounds obtained by sol-gel method are characterized by several techniques: X-ray diffraction (XRD), N2 adsorption–desorption isotherms, scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), electrical and dielectrical measurements. The XRD, SEM and XPS analysis confirmed the formation of ZnFeTiO4 inverse spinel structure. The electrical and dielectrical properties of ZnO/Zn2-xFexTiO4 (x?=?0.7, 1, 1.4) were measured by impedance spectroscopy, revealing a decrease in the electrical conductivity and the dielectric constant with Fe content.
Bismuth ferrite (BiFeO3) nanopowder have been successfully synthesized for the first time via a microwave-assisted sol-gel combustion method by using citric acid as fuel. The resulting nanopowder was characterized using FT-IR, TG-DTA, XRD, EDX, VSM, SEM, and UV-Vis DRS. A ferromagnetic hysteresis loop with a saturation magnetization (MS) of 0.66?emu?g?1 has been observed at room temperature in the sample. The optical properties of the nanosized BiFeO3 showed its small band gap (=2.08?eV) indicates a possibility of utilizing much visible light for photocatalysis.
Powders of Sm0.6Sr0.4CoO3-δ and La0.6Sr0.4CoO3-δ were synthesized using wet chemical technique. Structural and surface properties of synthesized materials were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), IR spectroscopy, and scanning electron microscopy (SEM). The influence of pH on the phase state, chemical composition, morphology, and fractal dimension of the synthesized powders were investigated. It was found that the change of pH has the influence on phase composition of synthesized powders. The increase of solution pH allows one to obtain homogeneous samples at lower temperatures down to 900–950?°C.
Boron Nitride (BN) particles were functionalized with vinyl-trimethoxysilane (VTMS) and incorporated into a hybrid polymer (ORMOCER®) resin. The thermal conductivity and mechanical properties of the resulting composite were compared to materials prepared using unmodified particles. Results indicate that the chemical bonding between grain surface and ORMOCER® matrix has a pronounced effect on the final performance of the respective compounds.
The surface of BN particles was functionalized prior to their incorporation into a hybrid polymer (ORMOCER®) matrix, thermal, electrical and mechanical properties of the resulting composites were characterized.
As p–n heterojunction photocatalysts usually possess dramatically improved photocatalytic activity than single photocatalysts, a novel ZnO/Cu2O heterojunction was designed by a facile self-templating method in this study. The crystal structure, chemical composition, surface morphology, and optical property of ZnO/Cu2O heterojunction were investigated to clarify the structure-property correlation. Scanning electron microscope and transmission electron microscope images proved the uniform core-shell submicrospheres of ZnO/Cu2O, in which a three-dimensional flower-like ZnO core was coated by a shell comprised of Cu2O nanoparticles. The photoresponse result showed that the band gap of the ZnO/Cu2O core-shell submicrospheres became narrow, and the absorption edge shifted from the ultraviolet region (380?nm) to the visible region (500?nm) compared with the pure ZnO microflowers. For the degradation of Rhodamine B under visible light, the photocatalytic efficiency of ZnO/Cu2O submicrospheres reached 96% within 40?min of reaction time, which was 3.8 times higher than that of pure ZnO microflowers and up to 4.5 times than that for pure Cu2O nanoparticles. The remarkable visible light-driven photocatalytic performance is mainly attributed to the extended photoresponse range and effective separation of the photo-generated electron-hole pairs in the unique heterojunction.
Lithium disilicate (Li2Si2O5) glass-ceramics were fabricated through two sol–gel methods: the nitrate route and the alkoxide route. Thermal analysis revealed different crystallization processing of two gel-derived powders. Li2Si2O5 powders were obtained after heat treatment at 800?°C. These powders were pressed and pressureless sintered under 900–1030?°C. Microstructure of sintered samples revealed the grain size and morphology of Li2Si2O5 ceramics. Although grain size in both samples increased with increasing sintering temperature, samples from the alkoxide route derived powders had more uniform grain size and pore distribution. In addition, open porosity decreased in both samples with increasing sintering temperature. Unlike familiar nucleation that resulted in grain growth mechanism, the Li2Si2O5 particles developed into irregular large size grains at first, and then grew into rod-shaped grains.
Mg–Ti substituted strontium hexa-ferrites nanopowders (SrFe12?x(MgTi)x/2O19, x?=?0–3) were prepared by the sol–gel method. The morphology, structure and composition of the nanostructures were examined by field emission scanning electron microscopy (FESEM) and X-ray diffraction. The effect of Mg–Ti doping on the magnetic properties of the powders was investigated by vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) at ambient temperature. Experimental results showed that the materials exhibit hexagonal structures with tunable magnetic properties. The saturation magnetization and the coercive field (Hc) decreased through the Mg and Ti substitution. FMR proved that by incorporation of Mg and Ti in strontium ferrite lattice, crystalline anisotropy, and microwave absorption can be tuned. SrFe12?x(MgTi)x/2O19 ferrites are good candidate for applications at X-band microwave frequencies. A low field absorption signal was observed with the same phase as the FMR absorption in all doped ferrites.
Phase pure, mesoporous, and crystalline V2O5 is synthesized by acid hydrolysis technique and subsequently heat treatment is carried out at 450, 500, 550, and 600?°C in air. The as-synthesized and heat-treated powders are thoroughly studied by X-ray diffraction, electron microscopy, dynamic light scattering, and spectroscopic techniques. A unique morphological tuning of V2O5 powders from as small as ~80?nm tiny nanorod to as large as a ~2.5?μm hexagonal grain as microstructural unit blocks is observed. A qualitative mechanism is suggested for particle growth. Further, the powders are pelletized and subsequently sintered in air at the same temperatures of 450, 500, 550, and 600?°C at which the powders were heat treated. Finally, nanomechanical properties of bulk pelletized V2O5 such as nanohardness and Young’s modulus are also evaluated by nanoindentation technique at nine different loads e.g., 10, 30, 50, 70, 100, 300, 500, 700, and 1000?mN.
MgF2 coating solutions were solvothermally treated at 160?°C for different time periods, this procedure induced crystallization and particle growth. Antireflection coatings prepared on glass from these solutions were compared to films derived from untreated precursor material. Ellipsometric porosimetry (EP) was employed to characterize structural features of coatings on glass as function of annealing temperature. Based on precursor solutions that had undergone solvothermal treatment antireflective coatings with a peak transparency exceeding 99% were prepared on PMMA substrates.
Solvothermal treatment of MgF2 precursor solutions results in crystallization of particles that can directly be applied to PMMA substrates for λ/4 antireflective films.
Since the late 1960s, ceric hydrogen phosphates have attracted the attention of scientists due to remarkable ion exchange, sorption, proton-conduction and catalytic properties. In this work, through the application of various solvents, we, for the first time, have obtained monolithic aerogels based on ceric hydrogen phosphates with high porosity (~99%) and extremely low density (~10?μg/cm3). The composition and structure of aerogels were thoroughly studied with XRD, TEM, SEM, XPS, low temperature nitrogen adsorption methods, TGA/DSC, Fourier-transform infrared spectroscopy (FTIR) and small-angle neutron scattering (SANS). The aerogels were found to belong to the fibrous macroporous aerogels family.
The mesoporous silica samples with different concentrations of phosphonic acid groups on the surface were obtained by direct template synthesis. The block-copolymer Pluronic P123 was used as a template, and sodium meta-silicate with diethylphosphatoethyltriethoxysilane as precursors. According to the SAXS diffractograms, mesoporous silica samples have a p6mm hexagonal symmetry. In addition, we used sol–gel method to synthesize xerogel with the same groups for comparison. All samples possess high values of specific surface area 615–730?m2/g and sorption pore volume. FTIR and potentiometric titration methods were used to investigate the surface layer of these samples. Sorption properties of the samples with phosphonic acid groups were studied in respect to a row of metal cations, among which we focused on lead(II), cadmium(II), and dysprosium(III) cations.
The behaviour of alginate gel film in response to the tensile load is analysed in this paper. The bubbles of 0.5?mm diameter were embedded in the film by the fluidic method prior to gelation, thus providing uniform voidage over the entire film. Further, the intrinsic porosity of the gel matrix around the voids was varied by removing water through either evaporation under vacuum, or employing lyophilisation. The Poisson’s ratio and the modulus of elasticity were estimated from direct measurements. The viscoelasticity of the gel matrix was characterized from stress-relaxation measurement. The transient response to tensile loading and the evolution of stress contours were studied through numerical simulation in ANSYS. The ultimate strength was studied for the gel films with embedded voids of different sizes. The numerical simulations were validated by experimental measurements.
Degradation of three different endocrine disruptors (EDs) was thoroughly studied on prepared durable thin layers of titanium dioxide with an anatase crystalline structure. Specially constructed laboratory reactors bringing information on all individual processes (photolysis, photocatalysis, sorption) involved in decomposition of the studied EDs (17α-ethynylestradiol, bisphenol A and 4-nonylphenol) were applied. It was found that photolytic removal of EDs is the fastest degradation process; nevertheless, this method may be less effective regarding all indicators including toxicity. It was verified that individual degradation processes (photolysis and photocatalysis) showed a significantly different influence on toxicity of resulting solutions. During the photolytic process, EDs degradation caused increasing toxicity contrary to the photocatalytic process. Obtained results were corroborated by a mathematical model, which showed that a limitation step for photocatalysis is a sorption and for photolysis a toxicity of resulting products.
Systematic studies of silica gels with covalently immobilized thiosemicarbazide and formazan groups under the conditions of competitive sorption from multicomponent systems were conducted. A methodological approach to determine the selectivity of the modified sorption material with regard to Cu(II), Ni(II), Co(II), Cd(II), and Zn(II) was proposed. Solid-phase extraction in equilibrium conditions of Cu(II), Zn(II), Co(II), Cd(II), and Ni(II) on a silica gel with covalently immobilized thiosemicarbazide and formazan groups in the conditions of competitive sorption was studied. The possibility to use the pseudo-second-order kinetic equation for assessment of mutual influence at competitive sorption has been shown. We found that sorption from multicomponent solutions proceeds as a non-additive process under the conditions of an excess of functional groups.
In this work, sol–gel-based non-stick ceramic coating formulations were prepared and coated onto aluminum panels in order to investigate their surface properties. The effect of the addition of optimal amount of fluorine-containing silane compound (FAS) on the surface and adhesion properties were also investigated. The morphology, structure, and elemental chemical composition of the coatings were characterized by scanning electron microscopy, atomic force microscopy (AFM), energy dispersion spectrum (SEM/EDAX), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), respectively. Moreover, several properties of the coatings such as cross-cut adhesion, hardness, gloss, and contact angle (CA) were determined. When fluorine was introduced, the pencil hardness was increased to 6H. Fluorinated non-stick ceramic coatings were found to have good adhesion on the aluminum substrates.
Magnesium hydroxide and magnesium oxide nanostructures have been prepared by microwave/hydrothermal technique using magnesium metal in hydrogen peroxide (H2O2). The applied power of the microwave was 700?W for 10?min at 145?°C. The method produced Mg(OH)2 powder as a base material for MgO by calcinations at 550?°C for 2?h. X-ray diffraction data confirms the microwave production of Mg(OH)2 and (MgO) through the agreement with the standard JCDPS cards. Scanning electron microscopy shows nanoplates morphology for Mg(OH)2 and large-scale nanoplates with a hexagonal shape for MgO. The fundamental direct optical band gap of Mg(OH)2 equals 5.8?eV while for MgO equals 5.2?eV from the analysis of diffused reflectance data. MgO has higher dielectric constant than Mg(OH)2 at the higher frequencies. AC electrical conductivity increases with increasing the applied frequency for both materials. The microwave-hydrothermal technique shows a promising method for production of magnesium compounds from magnesium metal which can be used in different aspects such as catalysis, wastewater treatment, pharmaceutical and coated materials.
Nuclear magnetic resonance (NMR) spectroscopy offers an element-selective, inherently quantitative and experimentally very flexible approach for the structural elucidation of non-crystalline materials. The present review introduces the basic concepts of this technique, highlighting the use of advanced NMR methodology for characterizing short- and intermediate range order in bioactive glass systems. The current state of the literature in this field is summarized in a comprehensive manner. NMR can give clear-cut and quantitative answers about the extent of network polymerization, the spatial distribution of the network former and network modifier species, and the structural roles of Group III elements introduced into these networks. These results facilitate our understanding of the influence of bioglass compositions upon the dissolution kinetics and bioactivities of these glasses. A particular mission of this review is to highlight the utility of non-routine, more advanced experimentation, in the hope of their increased usage and circulation in future applications.
The main six nuclear isotopes used in obtaining high-resolution magic-angle spinning NMR spectra for the structural characterization of bioactive glasses
It is well known that the first step of the sol-gel method consists in obtaining of amorphous or incipient crystallized materials that could be kept in the same state or could be transformed into vitreous or crystallized materials by adequate thermal treatments. In the present study, examples regarding the relevance of the thermal analysis methods for the characterization of the sol–gel-derived oxide systems, inorganic–organic hybrids, and composite nanomaterials are discussed. For the oxide systems, case studies regarding undoped and doped monocomponent oxides and polycomponent systems are discussed. In the case of inorganic–organic hybrids, the correlation between the type of precursors and the thermal behavior is presented. For the composite nanomaterials, examples for thermal behavior of two types of nanocomposites, namely both compositionally and structurally different, as well as inorganic–organic hybrid sol-gel nanocomposites are shown. In all studied cases, the thermal analysis methods allow obtaining important information not only on thermal behavior but also on the chemical composition of the as-prepared gels and powders. Different structural investigations methods (XRD, FTIR, and Raman) sustain the results obtained by thermal investigations.
ZrC–ZrO2 composite ceramic microspheres were prepared by internal gelation combined with carbothermic reduction using fructose as a chelating agent and carbon source. Fructose in the precursor solution formed complex with zirconium ions, which was conducive to the refining of the microstructure of the sintered composite. ZrC–ZrO2 composite with ZrC content as high as 60?wt% could be prepared.
In this paper, fructose was used as a chelating agent and an organic carbon source to prepare ZrCO microspheres by internal gelation and carbothermic reduction. The fructose in the precursor solution could form complex with zirconium ions, which was conducive to the refining of the microstructure of the sintered composite. ZrC–ZrO2 composite with crystal size of ZrO2 and ZrC in nanometer range and ZrC content as high as 60?wt% could be successfully prepared.
