Hydroxyapatite composites with multiwalled carbon nanotubes

The structure of composites based on hydroxyapatite filled with multiwalled carbon nanotubes was investigated using differential scanning calorimetry analysis and X-ray diffraction spectroscopy. Hydroxyapatite was prepared by the wet synthesis in the presence of pristine and oxidised carbon nanotubes. An influence of nature of functional groups of the nanotubes boundary layer on a crystallinity of the inorganic part was evaluated using differential scanning calorimetry analysis and X-ray diffraction spectroscopy. Morphology of composites obtained was studied by nitrogen adsorption/desorption technique and scanning electron microscopy. The hydroxyapatite/nanotubes interface was characterised using electrochemical methods. The parameters of the electrical double layer: A density of surface charge versus pH, zeta potential versus pH were described. The study has shown that the synthesis of hydroxyapatite/nanotube composites by formation of inorganic part in the presence of carbon filler significantly affect the microstructure, phase composition, crystallinity, hydroxyl content, chemical composition of the mineral part, as well as thermal properties and electrokinetic properties of composite

Luminescent Sol-Gel Glasses from Silicate–Citrate–(Thio)Ureate Precursors

Recent advancements in synthesis and analysis of the composites based on silica and carbon quantum dots have revealed great potential of such systems in bioimaging, sensor, as well as solid-state lighting applications. Most of the synthetic methods for obtaining such materials are still relatively complex and costly. The aim of this work was to study the luminescent properties of silica-based composites prepared by the simple sol-gel method using low-cost silicate–citrate–(thio)ureate precursors. The glassy composites were prepared by acid hydrolysis of ethyl silicate (40%) in aqueous solution of citric acid ureates or thioureates with the citric acid-to-(thio)urea molar ratio of 1:1, 1:1.5 or 1:3. The results of spectrofluorimetric analysis have shown that heat-treated at 270 °C such silica gels upon UV excitation (with an optimum at λexc = 360 nm) emit light in a visible spectrum (400–600 nm). Upon this, photoluminescence efficiency of ureate-derived glasses (quantum yield 70.53% for 1:1.5 sample) appeared to be much higher than that for thioureate-derived glasses (quantum yield 11.25% for 1:3 sample) suggesting that the preparation conditions to obtain the glasses with optimal photoluminescence characteristics are quite different in case of urea and thiourea. Thus, citrate–ureate-derived silica glasses already demonstrate very good potential to be efficient materials for different fluorescence-related applications

A New Route for Preparation of Hydrophobic Silica Nanoparticles Using a Mixture of Poly(dimethylsiloxane) and Diethyl Carbonate

Organosilicon layers chemically anchored on silica surfaces show high carbon content, good thermal and chemical stability and find numerous applications as fillers in polymer systems, thickeners in dispersing media, and as the stationary phases and carriers in chromatography. Methyl-terminated poly(dimethylsiloxanes) (PDMSs) are typically considered to be inert and not suitable for surface modification because of the absence of readily hydrolyzable groups. Therefore, in this paper, we report a new approach for surface modification of silica (SiO2) nanoparticles with poly(dimethylsiloxanes) with different lengths of polymer chains (PDMS-20, PDMS-50, PDMS-100) in the presence of diethyl carbonate (DEC) as initiator of siloxane bond splitting. Infrared spectroscopy (IR), elemental analysis (CHN), transmission electron microscopy (TEM), atomic force microscopy (AFM), rotational viscosity and contact angle of wetting were employed for the characterization of the raw fumed silica and modified silica nanoparticles. Elemental analysis data revealed that the carbon content in the grafted layer is higher than 8 wt % for all modified silicas, but it decreases significantly after sample treatment in polar media for silicas which were modified using neat PDMS. The IR spectroscopy data indicated full involvement of free silanol groups in the chemisorption process at a relatively low temperature (220 °C) for all resulting samples. The contact angle studies confirmed hydrophobic surface properties of the obtained materials. The rheology results illustrated that fumed silica modified with mixtures of PDMS-x/DEC exhibited thixotropic behavior in industrial oil (I-40A), and exhibited a fully reversible nanostructure and shorter structure recovery time than nanosilicas modified with neat PDMS. The obtained results from AFM and TEM analysis revealed that the modification of fumed silica with mixtures of PDMS-20/DEC allows obtaining narrow particle size distribution with uniform dispersity and an average particle size of 15–17 nm. The fumed silica nanoparticles chemically modified with mixtures of PDMS-x/DEC have potential applications such as nanofillers of various polymeric systems, thickeners in dispersing media, and additives in coatings

Effect of Carbon Nanotubes Surface Modification on Structure of Forcibly Ordered Films of Filled Polystyrene

The effect of surface modification of multi-walled carbon nanotubes (MWCNTs) with different modifiers on the filler dispersibility in polystyrene and the influence of the external magnetostatic field on the structure of obtained composites have been studied. The surface modification of as-synthesised and oxidized carbon nanotubes was performed by treatment with hydrochloric acid or ammonia hydroxide solutions. The composite films were casted on glass plates with or without the influence of magnetostatic field at the desired directions of the magnetic lines. A combination of MWCNTs surface treatment and directed influence of the magnetostatic field was shown to be an effective route to change the structure of composites

Infrared, Raman and Magnetic Resonance Spectroscopic Study of SiO2:C Nanopowders

Abstract Optical and magnetic properties of SiO2:C nanopowders obtained by chemical and thermal modification of fumed silica were studied by Fourier transform infrared spectroscopy, Raman, continuous wave (CW) electron paramagnetic resonance (EPR), echo-detected EPR and pulsed electron nuclear double resonance (ENDOR) spectroscopy. Two overlapping signals of Lorentzian lineshape were detected in CW EPR spectra of the initial SiO2:C. The EPR signal at g = 2.0055(3) is due to the silicon dangling bonds, which vanishes after thermal annealing, and the second EPR signal at g = 2.0033(3) was attributed to the carbon-related defect (CRD). The annealing of the SiO2:C samples gives rise to the increase of the CRD spin density and shift to the higher g-values due to the appearance of the oxygen in the vicinity of the CRD. Based on the temperature-dependent behavior of the CRD EPR signal intensity, linewidth and resonance field position we have attributed it to the spin system with non-localized electrons hopping between neighboring carbon dangling bonds, which undergo a strong exchange interaction with a localized spin system of carbon nanodots. The observed motional narrowing of the CRD EPR signal in the temperature interval from 4 to 20 K indicates that electrons are mobile at 4 K which can be explained by a quantum character of the conductivity in the vicinity of the carbon layer. The electrons trapped in quantum wells move from one carbon nanodot to another by hopping process through the energy barrier. The fact that echo-detected EPR signal at g = 2.0035(3) was observed in SiO2:C sample annealed at T ann ≥ 700 °C serves as evidence that non-localized electrons coexist with localized electrons that have the superhyperfine interaction with surrounding 13C and 29Si nuclei located at the SiO2:C interface. The presence of the superhyperfine interaction of CRD with 1H nuclei indicates the existence of hydrogenated regions in SiO2:C sample

Cleavage of Organosiloxanes with Dimethyl Carbonate: A Mild Approach To Graft-to-Surface Modification

In this work, we explore the depolymerization of poly­(dimethylsiloxane) (PDMS-100) and poly­(methylphenylsiloxane) (PMPS) using dimethyl carbonate (DMC) and develop a surface functionalization method by utilizing the DMC-imparted active methoxy end groups of the partially depolymerized polysiloxanes. The efficiency of dimethyl carbonate as a reagent for organosiloxane cleavage was confirmed by means of ¹H NMR spectroscopy, size-exclusion chromatography, and viscosity measurements. The reaction of fumed silica with organosiloxanes (PMPS, PDMS-50) in the presence of DMC was investigated using the ζ-potential, ²⁹Si and ¹³C solid-state NMR spectroscopy, IR spectroscopy, CHN analysis, contact angle goniometry, thermogravimetric analysis, scanning and transmission electron microscopy (TEM), and rheology. It was found that the interaction of PMPS/DMC with an SiO₂ surface produced hydrophobic and thermally stable moieties (up to 550 °C) with a densely packed (average 2.2 groups/nm²) alkylsiloxane network for SiO₂/PMPS + DMC in comparison with SiO₂/PMPS (average 1.4 groups/nm²). Surface functionalization was successfully attained at a relatively moderate temperature of 200 °C. Scanning electron microscopy data show that the average size of aggregates of PMPS/DMC-modified silica nanoparticles is smaller than that of the initial silica and silica modified with neat PMPS. TEM images reveal uniform distribution of the PMPS/DMC mixture across the SiO₂ surface. Rheology studies show thixotropic behavior in industrial oil (I-40A), a fully reversible nanostructure and shorter structure recovery time for fumed silica modified in the presence of DMC

Effect of Hydration Procedure of Fumed Silica Precursor on the Formation of Luminescent Carbon Centers in SiO2:C Nanocomposites

The effect of hydration procedure of fumed silica precursor on photoluminescent properties of carbonized silica (SiO2:C) nanocomposite after chemo/thermal treatments is studied. Main structural effect is the formation of chemical bonding of phenyl groups to silica surface via multiple CSiO bonding bridges. Synthesized samples demonstrate very broad photoluminescence (PL) bands in near ultraviolet and visible ranges with maximum intensity dependent on temperature of thermal annealing. Two main trends in luminescence properties are: 1) hydration-induced blue shift of PL in comparison with PL of unhydrated series; 2) red shift of PL bands with increasing synthesis temperature regardless hydration procedure. Temperature dependent evolution of light emission bands is discussed in terms of surface carbon nanoclusters formation and aggregation processes. It is assumed that blue shift of PL bands in the hydrated series is associated with the decreased surface mobility of carbon atoms and clusters as a result of increased chemical bonding with silica surface that slows down carbon thermally stimulated clusterization/aggregation processes