Preparation and characterization of BaTiO3–natural muscovite composites

Journal of Materials Science: Materials in Electronics - Natural muscovite (nM) exhibiting magnetic vortex states are ball milled into fine powder and mixed in different relative ratios (weight %)...     

Preparation and characterization of α-Fe2O3–CeO2 composite

In our previous study we attempted to see the effect of cerium doping (Ce/Fe ratio 0.015 to 0.074) on goethite matrix and conversion of doped goethite to hematite. In the present communication, nano-structured α-Fe₂O₃–CeO₂ composite with Fe/Ce weight ratio as 1.1 has been synthesized by calcination of goethite-cerium hydroxide precursor prepared by co-precipitation method. It was observed that co-precipitation of cerium along with iron in hydroxide medium resulted in hindering the formation of crystalline order as the precursor formed showed poorly crystallized goethite and almost no crystallinity in Ce(OH)₄. Calcination of the precursor at 400 °C showed the formation of hematite together with a broad peak corresponding to cerium oxide whereas at 800 °C, two distinct phases of α-Fe₂O₃ and CeO₂ were observed. The Mössbauer spectra showed the presence of a paramagnetic component both for the precursor as well as for the sample calcined at 400 °C but on raising the calcination temperature to 800 °C, the paramagnetic component disappeared and the spectrum corresponding to pure α-Fe₂O₃ phase was observed. The microstructure of the product obtained by calcining at 800 °C showed rod like structure (30 to 50 nm width and 300 to 500 nm length) of α-Fe₂O₃ having equi-dimensional CeO₂ particles on and around the surface. Besides the rods, equi-dimensional particles and agglomerates corresponding to CeO₂ were also observed. The results show that co-precipitation followed by calcinations gives nanorods hematite with CeO₂ particles bonded to its surface.     

Synthesis and characterization of barium borosilicate glass–Al2O3 composites

Barium borosilicate glass with composition 30BaO–60B₂O₃–10SiO₂ glass was prepared by melt-quenching technique. Different weight % of crystalline Al₂O₃ was mixed with the glass powder and sintered at optimum temperature. The changes in the structure and thermal properties of the glass with alumina content were investigated by X-ray powder diffraction, FT-IR spectroscopy and differential thermal analysis. The variations in the coefficient of thermal expansion and dielectric properties with composition were also studied and correlated with the structural changes.     

AC electrical and optical characterization of epoxy–Al2O3 composites

The AC electrical and optical characterizations of epoxy–alumina (Al₂O₃) composites have been investigated. Sheets filled with alumina were prepared with different alumina concentrations (0, 2, 5, 8, 10, and 15 wt%). The AC electrical properties were measured by using impedance spectroscopy as a function of applied frequency in range from 50 kHz to 1 MHz and filler concentration. The results obtained showed that the applied frequency and filler concentration was found to influence the AC electrical conductivity and dielectric behavior of the prepared composites. The UV-optical results obtained were analyzed in terms of the absorption formula for non-crystalline materials. The absorption coefficient and the optical energy gap (E_opt) have been obtained from the direct allowed transitions in k-space at room temperature. The tail widths (ΔE) of the localized states in the band gap were evaluated using the Urbach-edges formula. It was found that both (E_opt) and (ΔE) vary with the alumina concentration dispersed in the epoxy matrix. The refractive index (n) for the composites was determined from the collected transmittance and reflectance spectra. The dispersion behavior of the refractive index is discussed in terms of the single oscillator model.     

Synthesis,characterization and photocatalytic activity of neodymium,nitrogen and neodymium–nitrogen doped TiO2

TiO₂ doped with 0.1–10% Nd³⁺ or 1.8% nitrogen or co-doped with both dopants as well as Nd₂Ti₂O₇ are synthesized by a sol–gel. The phase composition, crystal structure, morphology, optical properties and binding energies of the doped titania were investigated. The photocatalytic activity was tested for malachite green dye degradation and compared with the results obtained by dopant-free TiO₂ synthesized using the same procedure and with the commercial Degussa P25 product. The influence of the dopant type and relative content, temperature of ignition in the course of the synthesis, pH of the reaction medium and the type of the illumination light on the efficiency of the prepared catalysts were determined. A positive effect of Nd- and N-doping on the apparent degradation rate constant under UV irradiation and negative one of Nd-presence at solar illumination is found. Nd–N-codoping has a negative effect on the photocatalytic activity.     

Preparation and characterization of Au/CeO2–Al2O3 monoliths

Porous CeO₂–Al₂O₃ monoliths with hierarchical pore structure were prepared by mixing boehmite particles with solutions containing different amounts of cerium chloride and aluminum nitrate. The monoliths were functionalized with gold nanoparticles using the incipient wetness method. The resulting materials were characterized by X-ray diffraction, nitrogen sorption, mercury porosimetry, UV–vis spectroscopy and transmission electron microscopy. The catalysts were tested in liquid phase glucose oxidation, comparing continuously stirred batch reactor and continuous-flow fix-bed reactor setups.     

Preparation and characterization of hydroxyapatite/polycaprolactone–chitosan composites

Hydroxyapatite (HA)/polycaprolactone (PCL)–chitosan (CS) composites were prepared by melt-blending. For the composites, the amount of HA was varied from 0% to 30% by weight. The morphology, structure and component of the composites were evaluated using environmental scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscope. The tensile properties were evaluated by tensile test. The bioactivity and degradation property were investigated after immersing in simulated body fluid (SBF) and physiological saline, respectively. The results show that the addition of HA to PCL–CS matrix tends to suppress the crystallization of PCL but improves the hydrophilicity. Adding HA to the composites decreases the tensile strength and elongation at break but increases the tensile modulus. After immersing in SBF for 14 days, the surface of HA/PCL–CS composites are covered by a coating of carbonated hydroxyapatite with low crystallinity, indicating the excellent bioactivity of the composites. Soaking in the physiological saline for 28 days, the molecular weight of PCL decreases while the mass loss of the composites and pH of physiological saline increase to 5.86% and 9.54, respectively, implying a good degradation property of the composites.     

Preparation and photocatalytic activity of highly ordered mesoporous TiO2–SBA-15

TiO₂–SBA-15 complex materials with highly ordered mesostructures have been prepared by a one-step hydrothermal synthesis method of titanium tetraisopropoxide (TTIP) and tetraethoxysilane (TEOS) in an acidic solution using surfactant P123 (EO₂₀PO₇₀EO₂₀) as structure-directing reagent. The prepared materials were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction patterns (SAXRD), Fourier transformed infrared spectroscopy (FT-IR) and N₂ adsorption–desorption experiments. The resulting TiO₂–SBA-15 complex materials showed highly ordered mesoporous structure with uniform pore sizes of 5.95 and 8.24 nm, high specific surface areas S_BET of 689 m² g^? 1 and 347 m² g^? 1 at different hydrothermal temperatures (100 °C and 130 °C). The photocatalytic activity of these TiO₂–SBA-15 mesoporous materials has been studied by 4-chlorophenol decomposition under UV light irradiation. The TiO₂–SBA-15 mesoporous materials prepared at the TiO₂:SiO₂ mass ratios of 25:75, 40:60 and 50:50 showed higher photocatalytic activity than that prepared at the TiO₂:SiO₂ mass ratio of 75:25.     

Synthesis and characterisation of W–Bi–S-tridoped TiO2 nanoparticles with enhanced photocatalytic activity

In the present work, W–Bi–S-tridoped TiO₂ nanoparticles were synthesised by a simple sol–gel method. The structure and morphology of as-prepared W–Bi–S-tridoped TiO₂ were characterised by using X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy and UV–Vis diffuse reflectance spectrum. It was found that the W–Bi–S-tridoped TiO₂ nanoparticles were well crystallised with a small size distribution. The absorption edge of TiO₂ was extended into visible-light region obviously after being doped with W, Bi and S. The photocatalytic degradation of methylene blue was used as a probe reaction to evaluate the efficiency of W, Bi and S doping. The W–Bi–S-tridoped TiO₂ exhibited the best photocatalytic activity, compared with TiO₂, S-TiO₂, W–S–TiO₂ and Bi–S–TiO₂. The mechanism that enhanced photocatalytic activity might be attributed to the synergistic effect of W, Bi and S.     

Synthesis, characterization and magnetic properties of polyaniline/γ-Fe2O3 composites

Conducting polyaniline/γ-Fe₂O₃ (PANI/FE) composites have been synthesized using an in situ deposition technique by placing fine-graded γ-Fe₂O₃ in a polymerization mixture of aniline. The composites are characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and infrared (IR) spectroscopy. The electrical properties such as d.c. and a.c. conductivities are studied by sandwitching the pellets of these composites between the silver electrodes. It is observed that the conductivity increases up to a composition of 20 wt.% of γ-Fe₂O₃ in polyaniline and decreases thereafter. The initial increase in conductivity is attributed to the extended chain length of polyaniline, where polarons possess sufficient energy to hop between favourable sites. Beyond 20 wt.% of γ-Fe₂O₃ in polyaniline, the blocking of charge carrier hop occurs, reducing conductivity values. The magnetic properties such as hysteresis characteristics and normalized a.c. susceptibility are also measured, which show a strong dependence on content of γ-Fe₂O₃ in polyaniline. Because of superparamagnetic behaviour of these composites, they may find extensive technological applications, especially for absorbing and shielding applications in microwave frequencies.     

Preparation and characterization of the microstructure,dielectric and magnetoelectric properties of multiferroic Sr3CuNb2O9–CoFe2O4 ceramics

Different research methods were used to study the microstructural and magnetoelectric properties of multiferroic Sr₃CuNb₂O₉–CoFe₂O₄ (SCNO–CFO). X-ray verification provides fundamental information about the local symmetry of the two-phase SCNO–CFO ceramic. P4mm unit cell with minimal tetragonality and a cubic Fd-3m structure have been found for SCNO and CFO, respectively. Some additional traces of cupric oxide were also detected. SEM observations confirmed that the microstructure is built of various crystallites forming a two-component electroceramics and CuO-rich grain boundary segregation. Impedance spectroscopy studies reveal the thermally activated dielectric relaxations. The temperature-dependent behavior of the diffuse dielectric anomalies was successfully described by the modified Debye equation. Finally, magnetoelectric measurements clearly confirm intrinsic coupling between the piezoelectric and magnetic phases of SCNO–CFO.     

Synthesis,characterization and photocatalytic behavior of TiO2–SiO2 mesoporous composites in hydrogen generation from water splitting

TiO₂–SiO₂ mesoporous composite photocatalysts with different proportions (in wt%) of TiO₂ and SiO₂ (TiO₂–SiO₂ = 20:80, 40:60, 60:40, 80:20 and 100:0) were prepared by loading TiO₂ on as-synthesized Si–MCM-41 using sol–gel method. The physicochemical properties of composites were investigated by powder X-ray diffraction, N₂ adsorption–desorption measurements, transmission electron microscopy and UV–Vis diffuse reflectance spectroscopy. It is revealed that the titanium species are dispersed as TiO₂ having interaction with the surface of the support. Even at high TiO₂ loading, the mesostructural feature of MCM-41 was found to be intact without pore blockages. The change in morphology of TiO₂ particle was observed with increase in TiO₂ loading which may be due to different environment for the growth of TiO₂. The photocatalytic evaluation of composites was carried out in production of hydrogen by water splitting. Among the prepared samples, mesoporous composite containing 60 % TiO₂ (MTi60) has shown the best results (0.08805 mmol of H₂/h/g of TiO₂) compared to other composite photocatalysts. The catalytic performance of this sample was further enhanced (~8 times) after loading 1 % Pt in water splitting (0.70161 mmol of H₂/h/g of TiO₂). 1 % Pt loaded on pure TiO₂ (MTi100) showed hydrogen evolution of the magnitude 0.26 mmol of H₂/h/g of TiO₂. TiO₂–SiO₂ mesoporous composite photocatalyst showed much higher activity (~1.9 times) than amorphous silica-embedded titania catalyst having same composition.     

Processing,microstructure and properties of ultrasonically processed in situ MgO–Al2O3–MgAl2O4 dispersed magnesium alloy composites

AZ91 alloy matrix composites are synthesized by in situ reactive formation of hard MgO and Al₂O₃ particles from the addition of magnesium nitrate to the molten alloy. The evolved oxygen from decomposition of magnesium nitrate reacts with molten magnesium to form magnesium oxide and with aluminium to form aluminium oxide. Additionally, these newly formed oxides react with each other to form MgAl₂O₄ spinel. Application of ultrasonic vibrations to the melt increased the uniformity of particle distribution, avoided agglomeration, and decreased porosity in the castings. Ultrasound induced physical phenomena such as cavitation and melt streaming promoted the in situ chemical reactions. Well dispersed, reactively formed hard oxides increased the hardness, ultimate strength, and strain-hardening exponent of the composites. Presence of well-dispersed hard oxide particles and stronger interface resulting from cavitation-enhanced wetting of reactively formed particles in the AZ91 alloy matrix improved the sliding wear resistance of the composites.     

Synthesis,characterization, photocatalytic evaluation,and toxicity studies of TiO2–Fe3+ nanocatalyst

Based on our previous work on the green preparation of Ag–TiO₂ photocatalyst with bactericidal activity under visible light, we extended our studies to the synthesis of TiO₂–Fe³⁺ materials with enhanced photocatalytic activity for the degradation of recalcitrant organic pollutants in water. TiO₂–Fe³⁺ nanopowders were synthesized using a robust, environmentally friendly procedure. Established amounts of Fe(NO₃)₃·9H₂O and titanium tetraisopropoxide (TTIP) were mixed using glacial acetic acid as solvent. Hydrolysis of TTIP–Fe³⁺ was accomplished using a 30 % (W/V) Arabic gum aqueous solution. TiO₂–Fe³⁺ nanopowders were obtained by thermal treatment at 400 °C. In order to elucidate the structure of these photocatalysts, microscopic and spectroscopic characterization techniques were applied. The high resolution transmission electron microscopy (HRTEM) analysis indicated the presence of uniformly distributed particles with average particle size of about 9 nm. According to the HRTEM lattice fringes, ring pattern, and selected area electron diffraction pattern, the crystalline part of the samples consists of anatase (PDF 01-086-1157 with the lattice constant of 3.7852, 9.5139 Å and 90°) as dominant phase. X-ray photoelectron spectroscopy (XPS) was applied to determine the oxidation state of iron. The XPS provides evidence for Fe³⁺ surface species in the TiO₂–Fe³⁺ composite. Complete degradation of aqueous solutions (20 ppm) of methylene blue and/or methyl orange was accomplished after 4 h of treatment using 150 mg of TiO₂–Fe³⁺/150 mL of dye solution. The in vitro toxicity of the materials was tested. The materials showed no toxicity against human red blood cells.     

Synthesis,characterization and in vitro bioactivity of sol-gel-derived SiO2–CaO–P2O5–MgO bioglass

In this study, the synthesis of SiO₂–CaO–P₂O₅–MgO bioactive glass was performed by the sol-gel method. Sol-gel-derived bioglass material was produced both in powder and in discs form by uniaxial pressing, followed by sintering at 700 °C. The obtained material was evaluated by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), thermal gravimetric analysis (TGA) and differential scanning caloremetry (DSC) analyses. The biocompatibility evaluation of the formed glass was assessed through in vitro cell culture [alkaline phosphatase (AP) activity of osteoblasts] experiments and immersion studies in simulated body fluid (SBF) for different time intervals while monitoring the pH changes and the concentration of calcium, phosphorus and magnesium in the SBF medium. The SEM, XRD and FTIR studies were conducted before and after soaking of the material in SBF. At first, an amorphous calcium phosphate was formed; after 7 days this surface consisted of deposited crystalline apatite. The present investigation also revealed that the sol-gel derived quaternary bioglass system has the ability to support the growth of human fetal osteoblastic cells (hFOB 1.19). Finally, this material proved to be non-toxic and compatible for the proposed work in segmental defects in the goat model in vivo.     

Preparation and characterization of hybrid antimicrobial materials based on Zn–Lu composites

The development of advanced functional materials, capable of providing effective antimicrobial activity, has a big demand from the contemporary society. Advanced functional antimicrobial amorphous silica composites (ASC) are prepared by using sol–gel process and modified by Zn ions and rare-earth element Lu. The preparation conditions are optimized by single-factor analysis, and as-prepared functional hybrids are characterized by scanning electron microscopy (SEM), X-ray diffraction analysis, X-ray photoelectron spectroscopy (XPS), atomic adsorption spectrometry and inductively coupled plasma analyses. The presence of homogeneously mixed Zn and Lu, in the form of ZnO and Lu₂O₃, and dense micropores is confirmed by SEM and XPS. The amorphous structure and large surface area are beneficial for better antimicrobial performance. The as-prepared Zn–Lu ASC exhibited excellent antimicrobial properties against Escherichia coli and Staphylococcus aureus. We demonstrate that the addition of rare-earth element, Lu, has rendered synergistic effect on antimicrobial properties by increasing the release of Zn ions and generating excess reactive oxygen species. The present study provides a mechanistic insight and novel approach to fabricate functional antimicrobial materials for a wide range of applications.     

Synthesis,structural, thermal and optical properties of TeO2–Bi2O3–GeO2–Li2O glasses

In this study, synthesis and characterization of novel quaternary tellurite glass system TeO₂–Bi₂O₃–GeO₂–Li₂O is presented. The compositions include TeO₂ and GeO₂ as glass formers while different proportion of Bi₂O₃ and Li₂O act as network modifiers. Differential thermal analysis, X-ray diffraction, scanning electron microscopy energy dispersive X-ray spectroscopy, laser ablation inductively coupled plasma mass spectrometry, UV–Vis and Raman spectroscopy are applied to study the structural, thermal and optical properties of the studied glasses. Obtained glasses possess a relatively low glass transition temperature (around 300 °C) if compared to other tellurite glasses, show good thermal transparency in the visible and near infra-red (from 2.4 to 0.4 μm) and can double the frequency of laser light from its original wavelength of 1064 nm to its second-harmonic at 532 nm (i.e. second harmonic generation).