MAO-preparation of nanocrystalline hydroxyapatite-titania composite films: Formation stages and effect of the growth time

The HAp-TiO₂ nanostructured layers with a porous morphology were fabricated through micro arc oxidation technique for different times, i.e. 3, 6, and 10 min. Compositional studies, performed by XRD and XPS techniques, showed that the layers consisted of hydroxyapatite, anatase, calcium titanate, and α-TCP phases. Based on the XRD results, it was observed that the hydroxyapatite relative content reached its maximum value at intermediate times. As an important achievement, it was figured out that the HAp phase gradually grows on a titania inner layer which forms within preliminary stages of the MAO treatment. Considering the XRD patterns, the hydroxyapatite crystalline size was determined as ∼48 nm which is favorable for bio-applications. Based on the SEM and AFM observations, the layers exhibited a porous morphology with a rough surface where the pores size increased with time. The highest porosity and roughness was achieved at intermediate times. The layers fabricated for intermediate growth times exhibited the most appropriate physical and chemical properties for bio-applications.     

Photoinduced charge property of nanosized perovskite-type LaFeO3 and its relationships with photocatalytic activity under visible irradiation

In this paper, ABO₃-type perovskite LaFeO₃ nanosized photocatalysts were synthesized by a sol-gel method, using citric acid (HOOCCH₂C(OH)(COOH)CH₂COOH) as complexing reagent and La(NO₃)₃·6H₂O and Fe (NO₃)₃·9H₂O as raw materials. The as-prepared samples also were characterized by several testing techniques, such as thermogravimetry-differential thermal analysis (TG-DTA), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET), infrared spectrum (IR), ultraviolet-visible diffuse reflection spectrum (UV-vis DRS), photoluminescence spectrum (PL), surface photovoltage spectroscopy (SPS) and electrical field induced surface photovoltage spectroscopy (EFISPS). The sample activity of different LaFeO₃ nanoparticles for degrading Rhodamine B solution under visible irradiation (λ > 400 nm) was evaluated. The effects of thermal treatment temperature on photoinduced charge property and photocatalytic activity were mainly investigated, together with their relationships. The results show that the LaFeO₃ sample calcined at 500 °C exhibits higher activity, and the activity decreases with increasing calcination temperature, which is in good agreement with the characterization results. The weaker is the PL and SPS signal, the higher is the photocatalytic activity. Moreover, the activity of all as-prepared LaFeO₃ samples is higher than that of international P-25 TiO₂ under visible irradiation.     

Preparation and characterization of Ni-Cu-P/CNTs quaternary electroless composite coating

Ni-Cu-P/carbon nanotubes (CNTs) quaternary composite coatings were successfully obtained on low carbon steel matrix by electroless plating. The effects of CNTs concentration in the bath on the microstructure of the composite coatings, CNTs content in the composite coatings and the hardness of composite coatings before and after heat treatment at 400 °C have been studied. In addition, the corrosion resistance of Ni-Cu-P/CNTs composite coatings was evaluated by anodic polarization curves in 3.5 wt.% NaCl solution at room temperature. It was noted that the CNTs concentration remarkably influenced the surface morphology of the coatings. With increasing CNTs concentration, both the CNTs content in the composite coatings and the hardness of composite coatings increased at first and then decreased. And the composite coatings after heat treatment provided higher hardness than the as-deposited coatings. The corrosion resistance of Ni-Cu-P/CNTs composite coatings is excellent compared with that of Ni-Cu-P coatings.     

Self-assembly of diverse alumina architectures and their morphology-dependent wettability

This work reports the fabrication of diverse nanostructured alumina films under high-field anodization in oxalic-acid electrolytes. Different surface morphologies of these alumina films can be obtained by adjusting reaction parameters, which was ascribed to the anisotropic chemical etching induced by the reaction heat and the concentration gradient of the oxalic-acid solution along the nanopore channels during the high-field anodization process. These alumina surfaces without coating low energy materials show remarkable morphology-dependent wettability. Specially, the alumina surface consisting of porous underlayer and nanowire pyramids with no chemical modification reveals excellent super water-repellent behavior for the first time. This study could provide a new approach for designing functional surfaces with tunable wettability.     

Preparation of superhydrophobic boehmite and anatase nanocomposite coating films

Developing a surface with water-repelling and self-cleaning ability has attracted much interest in nano-technology. We prepared superhydrophobic films in this study using a mixture of small anatase particles and large boehmite particles. Additionally, a N₂ automated adsorption apparatus, atomic force microscopy and contact angle meter were employed to examine the effects of the added boehmite and anatase to the boehmite ratio on the roughness, micropore ratio and contact angle of the hydrophobic films.As boehmite addition increased from 0 to 8 wt.%, the average roughness increased up to 30 nm, which resulted in the water contact angles increasing from 105° to 155°. The hardness of the films increased from 6B to 2H. The addition of a proper amount of small anatase particles into the large boehmite particles could lead to increasing the micropore ratio in the films, which would enhance the contact angle.     

Hybrid catalyst containing nano-sized LaMnO3 and carbon black for high yield and selective ketonization of n-butanol

An attempt has been made to synthesize a two-component hybrid material for highly selective catalytic ketonization of n-butanol. The perovskite-type oxide nano-crystallites were synthesized in the presence of carbon black particles by thermal transformation of equimolar mixture of lanthanum and manganese hydroxides into the perovskite-type oxide. The two-component material was tested as a catalyst for unconventional conversion of n-butanol to heptanone-4. The catalyst exhibited very high selectivity and yield towards the products, despite low content of LaMnO₃ in the two-component material (less than 10% by weight). The low oxide content led to the reduction of the cost of catalyst fabrication and is compensated by its high dispersion (grains ca. 20-30 nm in diameter) providing high conversion and yield comparable to pure-oxide catalysts. Catalyst fabrication is simple and environment friendly since it does not require organic solvents and excess amount of heavy metals (La and Mn).     

Sonochemical synthesis of (3-aminopropyl)triethoxysilane-modified monodispersed silica nanoparticles for protein immobilization

3-Aminopropyltriethoxysilane modified monodispersed silica nanoparticles were synthesized by a rapid sonochemical co-condensation synthesis procedure. The chemical nature of surface organic modifier on the obtained modified silica nanoparticle was characterized by ¹³C and ²⁹Si MAS Nuclear Magnetic Resonance (NMR) spectroscopies, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA)- differential scanning calorimetry (DSC). Due to the strengthened positive surface charge of the silica nanoparticles by the modification with aminopropyl groups, the capability for bovine serum albumin (BSA) adsorption was significantly increased as compared with bare silica nanoparticles. 80 mg/g BSA was adsorbed on modified silica nanoparticles, whereas only 20 mg/g BSA could be loaded on pure silica nanoparticles. The enhanced positive surface charge repelled proteins with net positive charge and the modified silica nanoparticles exhibited negligible adsorption of lysozyme, thus a selective adsorption of proteins could be achieved.     

One-step synthesis of hydrophobic mesoporous silica ellipsoidal particles with a bimodal mesopore system

Highly CH₃-functionalized mesoporous silica ellipsoidal particles with bimodal mesopore structure were prepared via a one-step route using polymethylhydrosiloxane (PMHS) and tetraethoxysilane (TEOS) with triblock copolymer P123 as template under acidic conditions. N₂ adsorption–desorption, XRD, HRTEM, SEM and ²⁹Si MAS NMR were used to characterize the obtained material. The introduction of PMHS into the synthetic system led to the formation of a bimodal mesopore system consisting of framework mesopores of ∼7.2 nm and textural mesopores of ∼29.4 nm. The two scale pores were directly observed in HRTEM images and indirectly proved by the two-step increase in N₂ adsorption–desorption isotherm. Also, PMHS played an important role in morphology controlling and organic functionalization, ensuring monodisperse ellipsoidal particle morphology and high CH₃ functionalization degree of the mesoporous silica product. Subjected to removing highly diluted nonylphenol from aqueous solution, the hydrophobic bimodal mesoporous silica ellipsoidal particles showed high adsorption performance.     

Enhanced thermal transfer and bending strength of SiC/Al composite with controlled interfacial reaction

The interface and its effect on the thermal conductivity and bending strength of SiC/Al composite were investigated. The results indicated that the compact interfacial layer could be obtained when holding the SiC particles for 4 h at 1200 °C. The decrease of the holding time reduced the thickness of the interfacial layer, yet harmful for the thermal transfer of the interface due to the formation of pores and Al₄C₃. The prolongation of the holding time introduced SiO₂ layer owning the very low instinct thermal conductivity, resulting in the increase of interfacial thermal resistance. However, the addition of SiO₂ layer seems less harmful for the interfacial thermal transfer with respect to the thin SiO₂ layer. The critical thickness of SiO₂ layer is confirmed to be 210 nm. Very similar to the variation of thermal conductivity, the bending strength follows a first increase until reaches a maximum value 435 MPa and then trends to decrease. The composite after T6 treatment exhibits a better bending strength compares to T2 treated composite.     

Preparation of carbon nanotube-neodymium oxide composite and research on its catalytic performance

Carbon Nanotube-Neodymium Oxide (CNT-Nd₂O₃) composite was prepared by using acid treated carbon nanotubes (CNTs) and neodymium nitrate in the presence of sodium dodecyl sulfate and ammonia liquid. Techniques of transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and differential thermal analysis (DTA) are used to characterize the morphology, structure, composition and catalytic property of the CNT-Nd₂O₃ composite. The experimental results show that the Nd₂O₃ nanoparticles, which have an average diameter of about 30-40 nm, are loaded on the surface of carbon nanotube. Compared with pure Nd₂O₃ nanorods, the CNT-Nd₂O₃ composite can catalyze the thermal decomposition of ammonium perchlorate more effectively. The sampling methods of the experimental samples made a difference on the catalytic experiment results, and the best catalytic result was obtained when de-ionized water served as the solvent of ammonium perchlorate.     

Preparation and electrochemical properties of multiwalled carbon nanotubes-nickel oxide porous composite for supercapacitors

Porous nickel oxide/multiwalled carbon nanotubes (NiO/MWNTs) composite material was synthesized using sodium dodecyl phenyl sulfate as a soft template and urea as hydrolysis-controlling agent. Scanning electron microscopy (SEM) results show that the as-prepared nickel oxide nanoflakes aggregate to form a submicron ball shape with a porous structure, and the MWNTs with entangled and cross-linked morphology are well dispersed in the porous nickel oxide. The composite shows an excellent cycle performance at a high current of 2 A g⁻¹ and keeps a capacitance retention of about 89% over 200 charge/discharge cycles. A specific capacitance approximate to 206 F g⁻¹ has been achieved with NiO/MWNTs (10 wt.%) in 2 M KOH electrolyte. The electrical conductivity and the active sites for redox reaction of nickel oxide are significantly improved due to the connection of nickel nanoflakes by the long entangled MWNTs.     

Preparation of gold-silica heterogeneous nanocomposite particles by alcohol-reduction method

Au-silica heterogeneous nanocomposite particles were prepared by novel preparation strategy involving alcohol-reduction method using 3-aminopropyltrimethoxysilane (APTMS) as a binder between silica surface and Au nanoparticles, and using PVP as a stabilizer for Au nanoparticles. The evolution of morphology of composite particles was investigated with increasing reaction time at different Au precursor concentrations of 100 ppm and 250 ppm using UV-vis spectrophotometer and TEM. It is shown that the size of immobilized Au particles on silica surface can be controlled with the variation of reaction rate via adjusting Au precursor concentration and reaction time, but the high concentration of Au precursor hinders the immobilization of well-defined Au nanoparticles due to the slow reduction rate of Au precursor. On the basis of experimental results, the role of APTMS and PVP on the formation of composite particles and the effect of Au precursor concentration on the morphological evolution of composite particles are briefly discussed.     

Effects of porous carbon additives and induced fluorine on low dielectric constant polyimide synthesized with an e-beam

We report the synthesis of a polyimide matrix with a low dielectric constant for application as an intercalation material between metal interconnections in electronic devices. Porous activated carbon was embedded in the polyimide to reduce the dielectric constant, and a thin film of the complex was obtained using the spin-coating and e-beam irradiation methods. The surface of the thin film was modified with fluorine functional groups to impart water resistance and reduce the dielectric constant further. The water resistance was significantly improved by the modification with hydrophobic fluorine groups. The dielectric constant was effectively decreased by porous activated carbon. The fluorine modification also resulted in a low dielectric constant on the polyimide surface by reducing the polar surface free energy. The dielectric constant of polyimide film decreased from 2.98 to 1.9 by effects of porous activated carbon additive and fluorine surface modification.     

Fabrication of nanocomposite particles with superparamagnetic and luminescent functionalities

A new kind of superparamagnetic luminescent nanocomposite particles has been synthesized using a modified Stöber method combined with an electrostatic assembly process. Fe₃O₄ superparamagnetic nanoparticles were coated with uniform silica shell, and then 3-aminopropyltrimethoxysilane was used to terminate the silica surface with amino groups. Finally, negatively charged CdSe quantum dots (QDs) were assembled onto the surface of the amino-terminated SiO₂/Fe₃O₄ nanoparticles through electrostatic interactions. X-ray diffraction (XRD), transmission electron microscopy (TEM), microelectrophoresis, UV-vis absorption and emission spectroscopy and magnetometry were applied to characterize the nanocomposite particles. Dense CdSe QDs were immobilized on the silica surface. The thickness of silica shell was about 35 nm and the particle size of the final products was about 100 nm. The particles exhibited favorable superparamagnetic and photoluminescent properties.     

Efficiency issues in Ce doped YAG nanocrystals

Nanoparticles of Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺, 1%) were synthesized via the glycothermal method. The particle sizes were estimated by transmission electron microscopy, X-ray diffraction, surface area determination and by dynamic light scattering. We found primary particles of 10–14 nm in diameter, which form agglomerates of approximately 100 nm. For the 4f → 5d transition of Ce³⁺ an internal quantum efficacy of up to 46% was measured. The particles consist of 6–10% of 1,4-butanediol attached on the surface, as determined by carbon content measurements in combination with IR and absorption spectroscopy. In particular, limiting drawbacks due to inevitable surface coatings for glycothermal syntheses and nanoscale associated scattering are elucidated.     

Influence of multi-walled carbon nanotubes on electrochemical performance of transparent graphene electrodes

In this work, carbon-carbon nanocomposites as transparent electrodes were prepared by a chemical reduction of graphite oxide (GO) and multi-walled carbon nanotubes (MWNTs). The electric, optical, and electrochemical properties of graphene-MWNT nanocomposites (G-MCs) were investigated as a function of the MWNT content. It was found that chemically bonded G-MCs were successfully formed with a reduction of the functional groups of the GO and acid-treated MWNTs, resulting in the conjugation of 1D MWNTs onto a 2D graphene surface. The electrical conductivity of the graphene was significantly enhanced by introducing the MWNTs. In addition, the G-MCs showed improved current density and high efficiency compared with graphene alone. This indicated that the improved electrochemical performance of the G-MCs can be attributed to the increase in the activity and electrical conductivity enhanced by π-π interaction between graphene and MWNTs.     

Improvement of SiCf/SiC density by slurry infiltration and tape stacking

SiC fiber-reinforced SiC–matrix ceramic composites (SiC_f/SiC) were fabricated by vacuum infiltration of a SiC slurry into Tyranno™-SA grade-3 fabrics coated with a 200 nm-thick pyrolytic carbon (PyC) layer followed by hot pressing using a transient eutectic-phase. The density of the composite was improved using a special infiltration apparatus with a pressure gradient and alternating tape insertion between fabrics. Their overall properties were compared with those of monolithic SiC and composite containing chopped fibers. Although the density of the composites decreased with increasing fiber fraction, SiC_f/SiC containing 50 vol.% fibers had a density of 3.13 g/cm³, which is the highest reported thus far. The composites containing continuous fibers had a maximum flexural strength of 607 MPa and a step increase in the stress–displacement behavior during the three-point bending test due to fiber reinforcement, which was not observed in the monolith.     

Microwave hydrothermal synthesis of nanoporous cobalt oxides and their gas sensing properties

In this paper, the precursors were synthesized by microwave hydrothermal method using Co(NO₃)₂·6H₂O as raw material, CO(NH₂)₂ and KOH as precipitants, respectively. The precursors and calcined products were characterized by XRD, FESEM, and BET-BJH. The results show that both constituent and synthetic condition can determine the products morphology. When using KOH as precipitant, hollow Co₃O₄ nanorings were obtained whose precursor was synthesized at 140 °C for 3 h and calcined at 500 °C in air for 2 h. While using CO(NH)₂, Co₃O₄ like-nanochains were obtained whose precursor was synthesized at 110 °C for 1 h and calcined at 420 °C in air for 2 h, and Co₃O₄ nanosheets were obtained while their precursor was synthesized at 140 °C for 3 h and calcined at 500 °C in air for 2 h. The sensitivity test of Co₃O₄ to alcohol reveals that the hollow Co₃O₄ nanorings show the best sensitivity, porous Co₃O₄ like-nanochains are superior to that of the porous nanosheets.     

Fabrication of a nitrided coating on a novel Ni-Cr nanocomposite with increased surface hardness

A novel type of Ni-Cr nanocomposite that had a nanocrystalline Ni matrix dispersing Cr nanoparticles was developed by electrodeposition. During plasma nitriding at 560 °C for 10 h, the nanocomposite formed a surface hard coating in which the Cr nanoparticles were internally converted into CrN. The coating decreased in thickness but increased in hardness with the increase in the Cr content from 10.8 to 30 (by wt.%). Moreover, the Cr content increase caused a shift of the hardest area of the nitrided coating from the innermost to the topmost surface, as a result of the change in the nitridation mechanism of the composite from the internal to external.     

Synthesis and characterization of SnO-carbon nanotube composite as anode material for lithium-ion batteries

SnO-carbon nanotube composite was synthesized by a sol-gel method. The electrochemical behavior of the composite using an anode active material in lithium-ion batteries was investigated. It was found that the composite showed enhanced anode performance compared with the unsupported SnO or carbon nanotube (CNT). The capacity fade of the composite electrode was reduced over unsupported SnO or CNT. We attribute the results to the conductivity and ductility of the CNT matrix, and the high dispersion of SnO.