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,characterization and photocatalytic activity of Bi2O3–MgO composites

A series of Bi₂O₃–MgO composites were synthesized by solvent-thermal method. It was found that the Bi₂O₃–MgO composites perform much better than TiO₂ (P25), Bi₂O₃ and MgO in the photocatalytic degradation of rhodamine B (RhB) in the presence of HCl and under irradiation of visible light (λ > 400 nm). The effects of Bi/Mg molar ratio, crystallization temperature of Bi₂O₃–MgO and reaction conditions on photocatalytic activity were studied. The best performance was observed over the composite with Bi:Mg molar ratio equal to 2:1 that had been subject to crystallization at 120 °C for 20 h. In addition, the photocatalytic efficiency of the composite can be significantly enhanced by the presence of hydrochloric acid. The prepared samples were characterized by XRD and UV–vis DRS techniques. The relationships between the structure and photocatalytic performance of the as-prepared Bi₂O₃–MgO samples were also investigated.     

Structural and electrical properties of La-modified BiFeO3–BaTiO3 composites

In the present investigation, La-modified solid solutions of BiFeO₃ (BFO) and BaTiO₃ (BT) in different molar ratios [i.e., (Bi_0.5?x La _x Ba_0.5)(Fe_0.5Ti_0.5)O₃, with x = 0.0, 0.05, 0.10 and 0.15)] have been synthesized using a solid-state reaction route. Structural and electrical properties of single phase (with minor secondary phase) of BFO–BT system have been studied in details to understand their ferroelectric and other properties. Preliminary X-ray diffraction analysis confirms the formation of a new system, which is different from that of its parent compounds. Substitution of a small amount BaTiO₃ into BiFeO₃ enhances dielectric and ferroelectric responses and reduces electrical leakage or tangent loss. The ac conductivity obeys Jonscher’s universal power law. The electrical behavior of the samples was investigated by impedance spectroscopy in a wide temperature range (25–525 °C) at different frequency (1 kHz–1 MHz). The impedance spectroscopy of the materials also confirms the origin of the relaxation mechanism in the system.     

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.     

Preparation and characterization of self-assembled percolative BaTiO3–CoFe2O4 nanocomposites via magnetron co-sputtering

BaTiO₃–CoFe₂O₄ composite films were prepared on (100) SrTiO₃ substrates by using a radio-frequency magnetron co-sputtering method at 750 °C. These films contained highly (001)-oriented crystalline phases of perovskite BaTiO₃ and spinel CoFe₂O₄, which can form a self-assembled nanostructure with BaTiO₃ well-dispersed into CoFe₂O₄ under optimized sputtering conditions. A prominent dielectric percolation behavior was observed in the self-assembled nanocomposite. Compared with pure BaTiO₃ films sputtered under similar conditions, the nanocomposite film showed higher dielectric constants and lower dielectric losses together with a dramatically suppressed frequency dispersion. This dielectric percolation phenomenon can be explained by the ‘micro-capacitor’ model, which was supported by measurement results of the electric polarization and leakage current.     

Synthesis and characterization of chitosan–carbon nanotube composites

Acid functionalized single walled carbon nanotubes were covalently grafted to chitosan by first reacting the oxidized carbon nanotubes with thionyl chloride to form acyl-chlorinated carbon nanotubes which are subsequently dispersed in chitosan and covalently grated to form composite material, CNT–chitosan, 1, which was washed several times to remove un-reacted materials. This composite has been characterized by FTIR, 13C NMR, TGA, SEM and TEM and has been shown to exhibit enhanced thermal stability. The reaction of 1, with poly lactic acid has also been accomplished to yield CNTchitosan–g-poly(LA), 2 and fully characterized by the above techniques. Results showed covalent attachment of chitosan and chitosan–poly lactic acid to the carbon nanotubes.     

Preparation and characterization of fenofibrate-loaded PLA–PEG microspheres

A series of biodegradable block copolymer of poly(lactide)(PLA)/poly(ethylene glycol) (PEG) were prepared by Ring-Opening polymerization of D, L-lactide, using stannous octoate as a catalyst. By nanoprecipitation method, the PLA-PEG can be made into microspheres containing fenofibrate, which is a kind of important cholesterol-lowering drugs. The purpose of this study is to investigate the effect of the copolymer composition on the size, the entrapment and the release behavior of the fenofibrate loaded microspheres. The microspheres can be achieved with small size below 100 nm, better encapsulation efficiencies of more than 55.3% and slower release rates. The release of fenofibrate from microsphere would reach the balance first, when the microsphere prepared by high proportion of hydrophilic PEG block. And the release property of fenofibrate/PLA-PEG microsphere was better than Lipanthyl (a commercial capsule of fenofibrate). It was observed that the composition of PLA-PEG copolymer played a major role in encapsulation efficiency of microspheres and release rates.     

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.     

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.     

Preparation and characterization of the carbon–Microsilica composite sorbent

In this paper, Microsilica, one kind of industry solid waste, was utilized firstly to prepare carbon–Microsilica composite sorbent with core–shell structures from a partial carbonization, mixture, and sulfonation process. The prepared composite sorbent was characterized with XPS, FT-IR, SEM, XRD and gas sorption experiments. The characterization results indicated BET surface area (S_BET) and total pore volume (V_total) of the prepared composite sorbent enhance 255% and 136% than Microsilica, respectively, and an abundant of oxygen functional groups, such as carboxyl and sulfonic groups, were introduced into the surface of the prepared composite sorbent. The adsorption capacity of the prepared composite sorbent for methylene blue (MB) and Cr(VI) also was investigated and compared with Microsilica and activated carbon, the results shown that the adsorption capacity of the prepared composite sorbent for methylene blue and Cr(VI) enhance 406.6% and 657.5% than Microsilica, and reach about 70.0% and 72.3% of activated carbon adsorption capacity, respectively. This paper proposed a new approach of comprehensive utilization of Microsilica with a uncomplicated process, and the prepared carbon–Microsilica composite sorbent with excellent adsorbent performance could be used as a potential substitute of activated carbon for heavy metal ion or organic dye adsorption in waste water.     

Preparation and characterisation of lanthanum doped BaTiO3 nanosize polycrystals by sol–gel processing

Abstract

Sol–gel processing has been refined to prepare lanthanum doped barium titanate nanosize polycrystal powders, La_xBa_1-xTiO₃ (x=0.05, 0.15, 0.20, 0.25), in the presence of Ba(OAc)₂, La(OAc)₃, and Ti(OⁿBu)₄ as starting materials with 0.7 mol L^-1 total concentration of precursor. The sol was obtained by cosolubilised hydrolysis of starting materials using HOAc as medium and catalysis with pH～3.8. The wet gel was acquired by concentrating and aging at room temperature. The wet gel to dry gel conversion was carried out at 50°C for ～24 h. First the dry gel was characterised by differential thermal analysis–thermal gravimetry (DTA–TG) and then it was calcined at various temperatures (600, 700, 800, 900°C) to prepare the nanocrystals. The final synthesised polycrystals were characterised by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, and scanning electron microscopy.     

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO₂ (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO₂ = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO₂ = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO₂ = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.     

Preparation and luminescent properties of Eu-doped BaTiO3 thin films by sol–gel process

Eu-doped BaTiO₃ thin films with a pseudo-cubic perovskite structure were successfully fabricated on magnesia substrates at low temperature by using a high-concentration sol–gel process, in which the newly developed gel-aging process on substrate was employed. Film microstructure, crystallinity, sintering properties and photoluminescence (PL) were investigated. The xerogel thin films exhibited strong PL associated with Eu³⁺ ions under ultraviolet excitation at room temperature; the PL was visible to naked eyes. The intensity maximum of PL was reached with doping concentration of about 8 mol%. Sintering above 600 °C caused reduction of europium, resulting in a rapid quenching of Eu³⁺ emission and enhancement of Eu²⁺ emission.     

Synthesis and microstructural characterization of Al–Ni3Al composites fabricated by press-sintering and shock-compaction

Aluminum matrix composites reinforced with nanocrystalline Ni3Al intermetallic particles, were synthesized using powder metallurgy techniques. Nanocrystalline Ni3Al was obtained by mechanical alloying of Ni75–Al25 stoichiometric mixture from elemental powders after 900 ks of milling with a 5 nm grain size average. Mixture powders of aluminum with 0.007, 0.02 and 0.04 volume fractions of Ni3Al intermetallic particles were compacted using two different compaction methods, the cold isostatic press and sintered at 873 K and the shock-compaction technique. Microstructure of shock-compacted composites showed fine particles of a few microns and also coarse particles less than 100 μm homogeneously distributed on the matrix, also the presence of micro-cracks and low porosity. However the nanoscale features of intermetallic was retained. On the other hand, the press and sintered composites showed good densification. The densities of the composites were about 90% and 94% of the theoretical density for the shock-compacted and press-sintered process, respectively. Finally, the results of hardness measurements showed that the nanocrystalline Ni3Al reinforcement improves the hardness of Al matrix for all conditions. The highest hardness was obtained for the Al–4 vol.%Ni3Al shock-compacted composite.     

Microstructural characterization of electroconductive Si3N4–TiN composites

Electroconductive Si₃N₄–TiN composites from Si and TiN powders have been fabricated by in situ reaction-bonding and post-sintering under N₂ atomosphere. The values of fracture strength and electrical resistivity in the Si₃N₄–50 wt.% TiN composite were 531 MPa and 2.5×10⁻² Ω cm, respectively. The dispersion of TiN particles inhibited the abnormal growth of rod-like Si₃N₄ grains with large size in diameter. An amorphous phase observed in most grain boundaries and triple points is attributed to liquid phase sintering. Many dislocations formed by the difference of thermal expansion coefficients were observed in Si₃N₄ and TiN grains.     

Microwave assisted hydrothermal synthesis and characterization of ZnO–TNT composites

TiO₂ nanotubes with different contents of ZnO (3–40 wt.% ZnO) have been successfully synthesized by microwave assisted hydrothermal process by using commercial TiO₂-P25 as a precursor. The phase and crystallinity of the obtained ZnO–TNT were analyzed by X-ray Diffraction (XRD). The surface area of the ZnO–TNT was determined by BET method. The effect of the different contents of ZnO on morphology of TiO₂ nanotubes was investigated by SEM and TEM. Optical properties and band gap energy of ZnO–TNT were calculated by using UV–vis DRS spectroscopy and modified Kubelka–Munk equation. Photocatalytic performance of ZnO–TNT was investigated by degradation of rhodamine B (RhB) dye under UV and visible light irradiation. Increasing ZnO content in TNT gradually decreased the diameter and length of nanotubes. Furthermore, addition of 40 wt.% ZnO into the TNT exceeded the saturation limit of ion exchangeability of Zn²⁺ and Na⁺ ions and aggregation of finely dispersed ZnO particles on the surface of TNT were observed. The ZnO–TNT has shown relatively larger band gap energies than that of TiO₂-P25. However, ZnO–TNT has shown considerable increase in photo-activity for degradation of RhB dye in visible light as compared to UV light irradiation.     

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.