Graphene oxide/hydroxyapatite composite coatings fabricated by electrophoretic nanotechnology for biological applications

Graphene oxide (GO) was firstly employed as nanoscale reinforcement fillers in hydroxyapatite (HA) coatings by a cathodic electrophoretic deposition process, and GO/HA coatings were fabricated on pure Ti substrate. The transmission electron microscopy observation and particle size analysis of the suspensions indicated that HA nanoparticles were uniformly decorated on GO sheets, forming a large GO/HA particle group. The addition of GO into HA coatings could reduce the surface cracks and increase the coating adhesion strength from 1.55 ± 0.39 MPa (pure HA) to 2.75 ± 0.38 MPa (2 wt.% GO/HA) and 3.3 ± 0.25 MPa (5 wt.% GO/HA), respectively. Potentiodynamic polarization and electrochemical impedance spectroscopy studies indicated that the GO/HA composite coatings exhibited higher corrosion resistance in comparison with pure HA coatings in simulated body fluid. In addition, superior (around 95% cell viability for 2 wt.% GO/HA) or comparable (80–90% cell viability for 5 wt.% GO/HA) in vitro biocompatibility were observed in comparison with HA coated and uncoated Ti substrate.     

Deposition and characterization of diamond-like carbon films by microwave resonator microplasma at one atmosphere

Diamond-like carbon (DLC) films have been deposited at atmospheric pressure by microwave-induced microplasma for the first time. Typical precursor gas mixtures are 250 ppm of C₂H₂ in atmospheric pressure He. Chemically resistant DLC films result if the Si (100) or glass substrate is in close contact with the microplasma, typically at a standoff distance of 0.26 mm. The films deposited under this condition have been characterized by various spectroscopic techniques. The presence of sp³ CH bonds and ‘D’ and ‘G’ bands were observed from FTIR and Raman spectroscopy, respectively. The surface morphology has been derived from SEM and AFM and shows columnar growth with column diameters of approximately 100 nm. Likely due to the low energy of ions striking the surface, the hardness and Young's modulus for the films were found to be 1.5 ± 0.3 GPa and 60 ± 15 GPa respectively with a film thickness of 2 μm. The hypothesis that a high flux of low energy ions can replace energetic ion bombardment is examined by probing the plasma. Rapid deposition rates of 4–7 μm per minute suggest that the method may be scalable to continuous coating systems.     

Separation and purification of fullerenols for improved biocompatibility

Isoelectric focusing was used to separate the different components of fullerenols based on their different electronegativities induced by the surface chemical functionalities and structures. Purified fractions of fullerenols were analyzed and characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results showed that four fractions of fullerenols could be separated by isoelectric focusing, and all fractions had a general formula of C₆₀(OH)_m(O)_n where the values of m and n might vary with their isoelectric points. Results from the capillary electrophoresis studies showed that the negative surface charge densities were different among the fractions of fullerenols, which indicated that the net surface negative charge was determined by the degree of CO functionalization. In vitro cytotoxicity assays were also performed to determine the effect of purified fullerenols on cytotoxicity and DNA stability in Raw 264.7 cells. Although the fullerenols had low cytotoxicity, the composition of fullerenols with the highest negative charge density (?1.913 ± 0.008 × 10^?4 C) and smaller size (3.92 ± 0.71 nm) was found to induce DNA damage. Therefore, crude fullerenols must be separated and purified in order to obtain fullerenols with low degree of CO functionalization and good biocompatibility.     

Synthesis,pyrolysis of a novel liquid SiBCN ceramic precursor and its application in ceramic matrix composites

SiBCN ceramic precursor, polyborosilazane, was synthesized through a novel method which used sodium borohydride as boron source. Vinyl silazane with SiCl was converted to vinyl silazane with SiH structure, followed by hydroboration reaction and subsequent high-temperature reaction to form soluble polyborosilazane liquid. The process of precursor-to-ceramic conversion was almost completed before 800 °C and the cross-linked polyborosilazane precursor exhibited higher ceramic yield 75.6% at 1200 °C. The SiBCN ceramic annealed at 1400 °C contained BN, SiN and SiC bonds with smooth and dense surface and still retained principally amorphous structure up to 1600 °C. In addition, the viscosity of the polyborosilazane was 65 mPa.s, which can efficiently prepare ceramic matrix composite by means of precursor infiltration and pyrolysis (PIP). The density of as-obtained ceramic matrix composite (CMC) was 1.82 g/cm³, and the average bending strength, bending modulus and tensile strength were 265.2 MPa, 37.5 GPa and 158.6 MPa, respectively.     

Halogen plasma erosion resistance of rare earth oxide films deposited on plasma sprayed alumina coating by aerosol deposition

Dense yttria, erbia and dysprosia films with thicknesses of 44.8 ± 1.7, 51.6 ± 0.9 and 36.8 ± 3.1 μm, respectively, were deposited on plasma sprayed alumina coating by aerosol deposition (AD). The rare earth oxide films remarkably enhanced the erosion resistance of the plasma sprayed alumina coating upon exposure to the halogen gas plasma. The enhanced plasma erosion resistances were related to their low surface porosity as well as the low vapor pressures of the rare earth fluorides and chlorides compared with those of corresponding aluminum halogenides. Electrical breakdown voltages of the samples with yttria, erbia and dysprosia films on the plasma sprayed alumina coating were 5.5, 6.2 and 5.3 kV, respectively, at room temperature and 4.0, 4.2 and 3.9 kV, respectively, at 573 K. The breakdown voltages at RT and 573 K were more than double that of the plasma sprayed alumina coating without the AD films.     

Carbon fibers from dry-spinning of acetylated softwood kraft lignin

An acetylated softwood kraft lignin was dry-spun into precursor fibers and successfully processed into carbon fibers with a tensile strength exceeding most values reported in prior studies on lignin-based carbon fibers. Limited acetylation of lignin hydroxyl groups enabled dry-spinning of the precursor using acetone (solvent) followed by thermo-oxidative stabilization. Resulting carbon fibers (∼7 μm diameter) displayed a tensile modulus, strength, and strain-to-failure values of 52 ± 2 GPa, 1.04 ± 0.10 GPa, and 2.0 ± 0.2%, respectively. Because of solvent diffusion during dry-spinning, fibers displayed a crenulated surface that can provide a larger specific interfacial area for enhanced fiber/matrix bonding in composite applications.     

Photocatalytic hydrogen production by Au–MxOy (MAg,Cu, Ni) catalysts supported on TiO2

Au–M_xO_y (MAg, Cu, Ni) nanoparticles supported on TiO₂–P25 were prepared by the deposition–precipitation method and were evaluated for the photocatalytic water splitting reaction for hydrogen production, using a mixture of water–methanol (1:1). The combinations of Au–Cu₂O/TiO₂ and Au–NiO/TiO₂ effectively increased the hydrogen production (2064 and 1636 μmol·h^− 1·g^− 1) obtained by Au/TiO₂ (1204 μmol·h^− 1·g^− 1). The higher photoactivities achieved by Au–Cu₂O and Au–NiO nanoparticles deposited on TiO₂ were attributed to an enhancement of the electron charge transfer from TiO₂ to the Au–M_xO_y systems and the effect of surface plasmon resonance of gold nanoparticles.     

Mechanical properties of Hi-Nicalon fiber-reinforced celsian composites after high-temperature exposures in air

BN/SiC-coated Hi-Nicalon fiber-reinforced celsian matrix composites (CMCs) were annealed for 100 h in air at various temperatures to 1200 °C, followed by flexural strength measurements at room temperature. Values of yield stress and strain, ultimate strength, and composite modulus remain almost unchanged for samples annealed up to 1100 °C. A thin porous layer formed on the surface of the 1100 °C annealed sample and its density decreased from 3.09 to 2.90 g/cm³. The specimen annealed at 1200 °C gained 0.43% weight, was severely deformed, and was covered with a porous layer of thick shiny glaze which could be easily peeled off. Some gas bubbles were also present on the surface. This surface layer consisted of elongated crystals of monoclinic celsian and some amorphous phase(s). The fibers in this surface ply of the CMC had broken into small pieces. The fiber–matrix interface strength was characterized through fiber push-in technique. Values of debond stress, σ_d, and frictional sliding stress, τ_f, for the as-fabricated CMC were 0.31 ± 0.14 GPa and 10.4 ± 3.1 MPa, respectively. These values compared with 0.53 ± 0.47 GPa and 8.33 ± 1.72 MPa for the fibers in the interior of the 1200 °C annealed sample, indicating hardly any change in fiber–matrix interface strength. The effects of thermal aging on microstructure were investigated using scanning electron microscopy. Only the surface ply of the 1200 °C annealed specimens had degraded from oxidation whereas the bulk interior part of the CMC was unaffected. A mechanism is proposed explaining the various steps involved during the degradation of the CMC on annealing in air at 1200 °C.     

Carbon nanotube growth at 420 °C using nickel/carbon composite thin films as catalyst supports

Nickel/carbon composite (Ni/C) thin films were used as catalyst supports for the growth of vertically aligned multiwalled carbon nanotubes (MWCNTs) at temperature as low as 420 °C. Nickel nanoparticles embedded within the carbon matrix of Ni/C films have served as catalysts for the synthesis of nanotubes by PECVD using acetylene/ammonia plasma. Two different nickel contents (40 at.% and 60 at.%) in the films were used. Analysis indicated a diffusion of nickel atoms in the form of nanoparticles to the film surface upon annealing. This diffusion depends on both annealing temperature and nickel concentration in the films and affects the MWCNT growth at low temperature. The MWCNT synthesis was tested at growth temperature ranging between 335 and 520 °C. The growth of MWCNTs at 420 °C was only achieved by using Ni/C films with a high nickel content (60 at.%). These MWCNTs did not present considerable loss in their growth rate and structural quality compared to MWCNTs grown on classical substrates (Ni catalysts deposited on TiN), at higher temperature (520–600 °C). The results suggest that carbon saturation at the surface and subsurface of nickel catalysts of the Ni/C films is responsible for the improvement of MWCNT growth at low temperature.     

Three small-scale laboratory steeping and wet-milling procedures for isolation of starch from sorghum grains cultivated in Sahara of Algeria

Starch was isolated from white and red sorghum. The values of thousand kernel weight, test weight, starch and protein contents were respectively 33.05 ± 0.5 (g), 692.85 ± 0.65 (g/l), 65.05 ± 0.19% and 12.27 ± 0.18% for the white sorghum grains and 27.70 ± 0.13 (g), 736.55 ± 0.25 (g/l), 66.37 ± 0.31% and 12.59 ± 0.03% for the red sorghum grains.Three small-scale laboratory steeping procedures were used: steeping in NaOH solution, in SO₂ solution and in SO₂ solution containing lactic acid. The effect of the concentration of steeping solutions and time of steeping on starch isolate and yield were studied. The starch recovery, starch purity, moisture, amylose, protein content and particle size distribution ranged from 64.8% to 80.4%, 92.61 ± 0.54% to 99.29 ± 0.55%, 11.84% to 14.43%, 27.71 ± 0.41% to 29.88 ± 0.56%, 0.31 ± 0.01% to 0.78 ± 0.01% and 4.0 μm to 36 μm, respectively.The high grain quality traits and isolated starch properties indicated that Algerian sorghum cultivars can have many applications in nutrition and food technology.     

HF etching effect on sandblasted soda-lime glass properties

Our objective in this work is to study the HF etching chemical treatment effect on the mechanical and optical properties of soda-lime glass eroded with 200 g fixed sand mass. We followed the evolution of these properties in relation to the chemical attack duration.The results show a clear improvement of the measured properties. The strength of the eroded samples is 44.23 ± 0.91 MPa. It increases up to 57.73 ± 1.76 MPa after 15 min of treatment and reaches 181.43 ± 23.69 MPa after 1 h. This last value is much higher than the as received glass strength (117.5 ± 10.48 MPa). The optical transmission of the eroded samples is about 18.5%. During the first 2 min of the chemical treatment, an important drop of the optical transmission (12%) was observed. However, improvement of the transmission was achieved for longer chemical treatment durations. After 8 h of treatment, the optical transmission increases up to 57%. Microscopic observations show that the HF attack causes the opening and the blunting of the surface cracks. In general, the surface state is improved during the chemical treatment.     

Plasma treated activated carbon impregnated with silver nanoparticles for improved antibacterial effect in water disinfection

A strategy to selectively attach more Ag nanoparticles on the external surface of activated carbon (AC) is being proposed and used as an antibacterial medium for water disinfection. Ag nanoparticles were first synthesized under UV irradiation by reducing silver nitrate with sodium citrate; the latter serving the dual purpose of both a reducing and a capping agent. Transmission electron micrographs show that Ag particles have a mean diameter of 28 nm with a standard deviation of 5 nm. The AC was treated by an oxygen plasma to increase the number of polar functional groups on the surface. This carbon-surface modification treatment increased the number of Ag nanoparticles on the external surface of AC, compared to that inside pores. Fourier transform infra-red and X-ray photoelectron spectroscopy results show that the oxygen plasma treatment leads to an increase in oxygen-containing-functional groups, such as C–O and CO, from 21.9% to 30.8%. Microbiological investigations by plate assay and shake flask tests confirmed the antibacterial nature of the AC–Ag hybrid, showing an order of magnitude increase in death rate constant from 3.72 to 41.88 h⁻¹ on plasma treatment (rate constant means rate of loss of viable cell).     

Catalytic conversion of olefins on supported cubic platinum nanoparticles: Selectivity of (1 0 0) versus (1 1 1) surfaces

The surface chemistry and catalytic conversion of cis- and trans-2-butenes on platinum (1 0 0) facets were characterized via surface-science and catalytic experiments. Temperature-programed desorption studies on Pt(1 0 0) single crystals pointed to the higher hydrogenation probability of the trans isomer at the expense of a lower extent of CC double-bond isomerization. To test these trends under catalytic conditions, shape selective catalysts were prepared by dispersing cubic platinum colloidal nanoparticles (which expose only (1 0 0) facets) onto a high-surface-area silica xerogel support. Infrared absorption spectroscopy and transmission electron microscopy were used to determine the conditions needed to remove the organic surfactants without loosing the original narrow size distribution and cubic shape of the original metal nanoparticles. Catalytic kinetic measurements with these materials corroborated the surface-science predictions, and pointed to a switch in isomerization selectivity from preferential cis-to-trans conversion with Pt(1 0 0) surfaces to the reverse trans-to-cis reaction with Pt(1 1 1) facets.     

Pi-pi interaction and hydrogen bonding in crystal structure of vanadium(V) complex containing mono hydrazone ligand: Synthesis and protein binding studies

Dioxidovanadium(V) complex containing hydrazone ligand has been synthesized in good yield, the complexes was characterized by elemental analysis, IR, UV–Visible and ¹H NMR spectroscopy. The structure of the complex has been established by Single Crystal X-ray diffraction technique. Complex crystallized with monoclinic P21/n space group with cell parameters a/Å = 11.9791(7), b/Å = 19.7898(10), c/Å = 16.4661(9), α/° = 90, β/° = 106.059(6), and γ/° = 90, respectively. The ligand bonded to metal ion in tridentate fashion through ONO donor atoms forming a distorted square pyramidal geometry around vanadium and sodium ion with their geometrical index τ = 0.33 and τ = 0.12. The binding interaction of the synthesized complex with protein (BSA) was also studied and KBSA was found to be 2.712 × 10⁷ M^− 1.     

Onset coarsening-coalescence kinetics of γ-type related Al2O3 nanoparticles: Implications to their assembly in a laser ablation process

An onset coarsening-coalescence event based on the incubation time of cylindrical mesopore formation and a significant decrease of specific surface area by 50% and 70% relative to the dry pressed samples was determined by N₂ adsorption–desorption hysteresis isotherm for two Al₂O₃ powders having 50 and 10 nm in diameter respectively on an average and with γ-type related structures, i.e. γ- and its distortion derivatives δ- and/or θ-types with {1 0 0}/{1 1 1} facets and twinning according to transmission electron microscopy. In the temperature range of 1100–1400 °C, both powders underwent onset coarsening-coalescence before reconstructive transformation to form the stable α-type. The apparent activation energy for such a rapid coarsening-coalescence event was estimated as 241 ± 18 and 119 ± 19 kJ/mol, for 50 and 10 nm-sized particles, respectively indicating easier surface diffusion and particle movement for the latter. The size dependence of surface relaxation and onset coarsening-coalescence of the γ-type related Al₂O₃ nanoparticles agrees with their recrystallization–repacking upon electron irradiation and accounts for their assembly into nano chain aggregates or a close packed manner under the radiant heating effect in a dynamic laser ablation process.     

Graphene-based RuO2 nanohybrid as a highly efficient catalyst for triiodide reduction in dye-sensitized solar cells

This study is the first to report the synthesis of graphene-based RuO₂ nanohybrid materials and their application as a counter electrode (CE) in dye-sensitized solar cells (DSCs). Ru nanoparticles (RuNPs) with an average size of 9 nm were uniformly immobilized on the surface of reduced graphene oxide (RGO) with the simultaneous co-reduction of Ru precursor ions and graphene oxide (GO) to Ru atoms and RGO, respectively, through dry plasma reduction (DPR) under atmospheric pressure and at near room temperature without using any toxic chemicals. Since RuNPs are more susceptible to oxidation, Ru atoms located on the surface of RuNPs are further oxidized to RuO₂ in atmosphere. The resulting RuO₂-RGO nanohybrid with a very small amount of Ru exhibits low charge transfer resistance, low diffusion impedance and good long-term stability. The application of RuO₂-RGO nanohybrid as an alternative CE for DSCs leads to high energy conversion efficiency of 8.32 ± 0.15%, which is comparable to the value of 8.16 ± 0.13% of DSCs based on a Pt-NP CE prepared by DPR. This study also discusses the influence of hydrogen species existing in either precursor ions or graphenes on the formation of uniform and well-dispersed NPs on the substrates.     

Supercritical carbon dioxide immobilization of glucose oxidase on polyurethane/polypyrrole composite

Glucose oxidase (GOX) was immobilized on polyurethane/polypyrrole (PU/PPY) composite foam via supercritical fluid immobilization (SFI) towards the preparation of biosensors. Buffer solution was used as the immobilization medium along with scCO₂. To provide insight into the relation between the scCO₂ and the GOX-buffer solution, the GOX-buffer solutions were subjected to scCO₂ and the protein amounts of the GOX-buffer solutions before and after scCO₂ exposure were determined at 80, 100 and 150 bar and 30, 40 and 50 °C for an exposure time of 24 h. The protein amount in GOX-buffer solution decreased in all cases after exposure to scCO₂. The lowest and highest loss in GOX amounts observed were 2.9 and 36.4 μg at 80 bar, 30 °C and 100 bar, 50 °C, respectively. The effects of immobilization pressure (80, 100 and 150 bar), temperature (30, 40 and 50 °C) and time (4, 24 and 72 h) on the activities of the GOX-immobilized PU/PPY composites were investigated. At 30 °C immobilization temperature, the activity values of the GOX-immobilized PU/PPY composites were slightly increased as the pressure was increased from 80 to 100 bar. Further increase in immobilization pressure from 100 to 150 bar at 30 °C caused a decrease in the activity values. At 40 °C immobilization temperature, increasing the immobilization pressure from 80 to 100 bar did not provide an increase in activity values, but further increase to 150 bar caused a decrease in the activity values. At 100 bar immobilization pressure, decrease in temperature enhanced the activity values of the samples. When immobilization was performed via SFI, the activity values were doubled compared to the immobilization at atmospheric conditions. Among all the immobilization pressures and temperatures investigated, both the highest activity (U/cm²) and the highest specific activity (U/mg) were obtained for the samples processed at 100 bar, 30 °C.