Oxide-silica Nanocomposites Research Articles

Graphene oxide–silica nanocomposites reinforced mortars: Mechanical properties, permeability and microstructure

The purpose of this work is to study the effect of graphene oxide-silica nanocomposites on the mechanical properties, transport properties and microstructure of mortar, to reveal the working mechanism of GO-nanoSiO2 to improve the properties of mortar, so as to fully understand the mechanical and physical behavior of GO-nanoSiO2 reinforced mortar. The macroscopic test results showed that adding 0.05 wt% GO could improve the compressive strength, fracture toughness and chloride penetration resistance of mortar most effectively. The compressive strength, initial fracture toughness and unstable fracture toughness increased by 15.1%, 92.2%, and 64.7%, and the non-steady state chloride migration coefficients decreased by 49.6%. The microstructure of mortar was studied by MIP, SEM and multifractal analysis. The results showed that the addition of GO-nanoSiO2 reduces the total porosity and optimizes the pore structure of mortar, resulting in the reduction of large pores, the improvement of the homogeneity of pore distribution, and the formation of pores with poor pore connectivity, which is conducive to improving the impermeability of mortar. In the interface transition zone between aggregate and matrix, the addition of GO-nanoSiO2 decreases the porosity and Ca(OH)2 enrichment. The decrease of ITZ porosity and the presence of GO-nanoSiO2 nanosheets in ITZ can inhibit the crack propagation, thus contributing to the improvement of macroscopic fracture properties of mortar.

Effect of UV Irradiation on the Structural Variation of Metal Oxide-Silica Nanocomposites for Enhanced Removal of Erythromycin at Neutral pH

In this study, the effect of UV treatment on the physicochemical properties and structural variation of metal oxide-silica nanocomposites (Mn2O3-Fe2O3@SiO2) has been investigated. Based on the results, UV irradiation significantly affects the nanocomposite structure, where SiO2 network reconfiguration, change in surface OH group density, and surface area were observed. Erythromycin (ERY) has been chosen as a module pollutant to compare the performance of the pristine and UV-treated nanocomposites. The pristine nanocomposite had a high adsorption efficiency (99.47%) and photocatalytic activity (99.57%) at neutral pH for ERY in the first cycle, and this efficiency decreased significantly for the multiple cycles. However, different results have been observed for the UV-treated nanocomposite, where it retained its performance for ten consecutive cycles. This enhanced performance is attributed to the structural modifications after UV exposure, where increased surface area, pore volume, and OH group density resulted in an increased number of the possible mechanisms responsible for the adsorption/oxidation of ERY. Moreover, oxidation of adsorbed molecules by UV light after each cycle can also be another reason for enhanced removal. For the first time, the fate of ERY is studied using regenerated nanocomposites after the last cycle. LC/MS/MS results showed that ERY degraded in 20 min, and the produced reaction by-products were adsorbed by nanocomposites. This study could be a foundation research for the practical approaches for the regeneration of nanomaterials and the successful removal of organic pollutants from aquatic environments.

Experimental study on fracture mechanics of cementitious materials reinforced by graphene oxide–silica nanocomposites

This study aims to improve the fracture properties of cementitious materials by adding graphene oxide (GO) and graphene oxide–silica nanocomposites (GO-nanoSiO2). The pristine GO was coated with nano-silica to form GO-nanoSiO2 composites. Based on the three-point bending test, the fracture toughness and fracture energy of cementitious materials were calculated to provide comprehensive fracture mechanics characterization. The fracture surface morphology and the crack development in mortar were detected by ultra-depth microscopy and scanning electron microscopy. The results demonstrate that the addition of GO-nanoSiO2 is more beneficial to improve the fracture properties of cementitious materials than pristine GO and the amount of nano-silica grafted on GO surface affects its enhancement effect. The initial fracture toughness, unstable fracture toughness and fracture energy of mortar reinforced by GO-nanoSiO2 (0.05 wt% GO and the mass ratio of nano-SiO2/GO is 2.8) are increased by 92.2%, 64.7% and 77.5%, respectively. GO-nanoSiO2 improves the roughness of mortar fracture surface, changes the propagation mode of cracks, and makes the crack propagate along a more tortuous path which contributes to energy dissipation.

Synthesis and characterization of magnetic iron oxide – silica nanocomposites used for adsorptive recovery of palladium (II)

ABSTRACT Magnetic iron oxide-silica shell nanocomposites (IONP@SiO2) have been prepared in a two-step procedure. IONPs were obtained by coprecipitation of iron salts, and coated by silica in sol-gel method under sonication. Two IONP/silica ratios and two drying methods, heating in oven and supercritical CO2 drying, were used. The samples were analyzed using X-ray diffraction (XRD), infrared spectroscopy, magnetic measurements, small-angle neutron scattering (SANS), nitrogen sorption, and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray analysis (EDX). The iron oxide silica nanocomposites obtained via supercritical drying exhibited higher values of the specific surface area and of saturation magnetization compared to the samples synthesized with the same iron oxide content but obtained after drying at 60 °C. Pd(II) adsorption experiments were performed on the materials prepared by supercritical drying. The maximum adsorption capacity 6.5 mg/g showed that the materials can be used as good and cheap adsorbent for palladium ions from aquatic environment.

Effects of catalysts on structural and adsorptive properties of iron oxide-silica nanocomposites

Iron oxide-silica nanocomposites were prepared by sol-gel method using ammonia (NH3), acetic acid (CH3COOH) and hydrochloric acid (HCl) catalysts to generate different pH values for the reaction conditions. As starting precursors, for the silica, respectively, for the iron oxide, tetraethylorthosilicate (TEOS) and iron-III-acetylacetonate were used. The physico-chemical characterization of the materials revealed that the sample obtained with HCl catalyst displays the largest surface area (300 m2/g), the most compact network structure, highest surface roughness, biggest crystallite size (14 nm), magnetization (7 emu/g) and superparamagnetic behavior. These materials were tested for adsorption of Cr6+ and Zn2+ from aqueous solution. Sample M-HCl presented the highest surface area and was further used for adsorption of metal ions. Kinetic, thermodynamic and equilibrium adsorption measurements studies were made for Cr6+ and Zn2+. To establish the material behavior from a thermodynamic point of view, temperature and contact time of adsorption process, activation energy, free energy, of standard enthalpy and entropy were calculated. The kinetic behavior was modelled by pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models and the adsorption characteristics were determined by modelling the experimental data with Langmuir, Freundlich and Sips isotherms.

Enhanced catalyst dispersion and structural control of Co3O4-silica nanocomposites by rapid thermal processing

We synthesized cobalt tetroxide (Co3O4) silica nanocomposites based on the conventional tetraethyl orthosilicate (TEOS) monomer and ethoxy polysiloxane (ES40) oligomer by sol-gel chemistry coupled with rapid thermal process (RTP). The physicochemical properties and structural formation of cobalt oxide silica nanocomposites were comprehensive characterized. By using ES40, well-controlled, homogeneous nanoparticle dispersion and size of Co3O4 with 5 nm within the silica matrix were achieved leading to fractal-like morphology. The concentration of the Co3O4 nanocatalyst was also significantly enhanced by more than 50 folds. Fenton-like HCO3−/H2O2 catalytic system using acid orange 7 and nanocomposites was examined for organic degradation. 98% AO7 and naphthalene intermediates degradation efficiency was achieved after 20 min with ES40-derived catalyst, which was three to ten folds faster than that of the TEOS-derived catalyst and the commercial Co3O4 catalyst. The combined use of ES40 sol-gel and RTP enabled a simple way to nanomaterial preparation and lowers overall processing time.

Synthesis of nano-scale zero-valent iron-reduced graphene oxide-silica nano-composites for the efficient removal of arsenic from aqueous solutions.

Design and synthesis of arsenic adsorbents with high performance and excellent stability has been still a significant challenge. In this study, we anchored nano-zero-valent iron (NZVI) on the surface of graphene-silica composites (GS) with high specific surface area, forming the NZVI/GS nano-composite. The prepared nano-materials were used to remove As(III) and As(V) through adsorption from aqueous solutions. The results indicated that NZVI particles were dispersed well on the surface of GS, and the NZVI/GS showed great potential to remove As(III) and As(V). Adsorption performance of NZVI/GS for As(III) and As(V) highly depended on the pH of solutions. The experimental data fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm model. The calculated maximum adsorption capacities of NZVI/GS for As(III) and As(V) were up to 45.57 mg/g and 45.12 mg/g at 298 K, respectively, and the adsorption equilibrium could be reached within 60 min. The residual concentrations of As(III) and As(V) after treatment with 0.4 g/L NZVI/GS can meet with the drinking water standard of WHO when the initial concentrations were below 4 mg/L and 3 mg/L, respectively. Moreover, the as-prepared NZVI/GS had excellent anti-interference ability during the process of As removal in the presence of foreign ions. During the As removal process, As(III) was oxidized to As(V), which could be removed through adsorption by electrostatic attraction and complexation. These results indicated that the as-synthesized NZVI/GS composite is a promising adsorbent for the removal of arsenic from aqueous solutions.

Waterborne polyurethane/graphene oxide-silica nanocomposites with improved mechanical and thermal properties for leather coatings using screen printing

Waterborne polyurethane (WPU) has been broadly used as adhesive and coating materials in many applications. In this work, the graphene oxide-silica (GOSI) nanocomposites, used as nanofillers in the WPU matrix, were produced by functionalizing graphene oxide with epoxy groups and nanosilica with amine groups using silane terminated coupling agents. The nanocomposite surface structures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The polymer nanocomposite films show the excellent improvement in the mechanical and thermal properties. In the fractured surface study of the composite films by SEM, it was observed that the agglomeration of GO appears while the GOSI is uniformly distributed in the WPU matrix. Furthermore, the WPU/GOSI have regained the maximum tensile strength properties after two weeks of hydrolysis. The GOSI nanocomposites have enhanced interfacial crosslinking with the WPU matrix which is the prime reason for such development in the mechanical properties. The screen printing method was illustrated to cast the thin and transparent layer WPU nanocomposites on the leather surfaces. The WPU/GOSI coatings exhibit outstanding tear resistance, surface adhesiveness, and abrasion resistance properties. This approach of using GOSI composites as nanofiller in the polymer matrix may pave a novel path for surface coating strategies.

Photoinduced formation of reactive oxygen species and electrons from metal oxide–silica nanocomposite: An EPR spin-trapping study

Metal oxide nanocomposites with photocatalytic activity have the potential for many applications in environmental remediation and biomedicine. In this study, we investigated the formation and stabilization of electrons/holes from three metal oxide–silica nanocomposites (CuO–SiO2, Fe2O3–SiO2 and ZnO–SiO2) under irradiation by electron paramagnetic resonance (EPR) technology. The characteristic EPR signals with g=2.00070–2.00105, ΔHp-p=2.17–2.37G were determined, which corresponded to lattice-trapped electrons. Moreover, the generation of active species from CuO–SiO2, Fe2O3–SiO2 and ZnO–SiO2 in aqueous solution under irradiation was also systematically studied. The results showed that all the three nanocomposites could generate hydroxyl radical, singlet oxygen and electron. CuO–SiO2 was more effective than Fe2O3–SiO2 and ZnO–SiO2 in producing hydroxyl radical and electrons, while ZnO–SiO2 was the most efficient in generating singlet oxygen. In addition, CuO–SiO2 exhibited most obviously photocatalytic activity toward degradation of bisphenol A, followed by Fe2O3–SiO2 and ZnO–SiO2. These findings will provide vital insights into photocatalytic mechanisms and potentially photoinduced toxicity of metal oxide–silica nanocomposites.

Iron oxide-silica nanocomposites yielded by chemical route and sol–gel method

Magnetic nanoparticles yielded by chemical route were surface modified with stabilizing agents being further coated by sol–gel method with silica shell to be used for various applications. Iron oxide magnetic cores were dispersed in water by single citrate layer and, respectively, by double oleate hydrophilic coating. Sol–gel reaction with tetraethylorthosilicate provided further coating with silica that confers increased reactivity for ligand coupling. Microstructural and magnetic properties were investigated by standard methods evidencing nanometric size, good crystallinity, and superparamagnetic behavior. Comparative analysis evidenced similar crystallite size for both citrate- and oleate-coated magnetic nanoparticles, while granularity was changed after silica adding. Saturation magnetization diminished less for oleate-stabilized nanoparticles than for citrate-stabilized ones after silica coating and moderate thermal treatment. Such prepared magnetic nanocomposites could have possible utilization as magnetic vectors for targeted biomolecules.

Synthesis based on the wet impregnation method and characterization of iron and iron oxide-silica nanocomposites

The present work describes an easy procedure for the preparation of iron-silica and iron oxide-silica composites using the wet impregnation method and subsequent heat treatment in different atmospheres. In this way, a specific composite can be produced with a high content of iron or an iron oxide phase (about 24 wt.%) uniformly dispersed in the silica matrix. No pre-treatment before calcinations was necessary to obtain the magnetic phases. Material characterization is also reported.

Sol–gel synthesis and characterization of iron oxide–silica nanocomposites

AbstractThe films of iron oxide–silica nanocomposites have been prepared using the sol–gel process and spin‐coating technique. The film morphology was dependent on precursors, additives, ageing duration and the molar ratios between iron (Fe) and silicon (Si) of the coating solution. Hematite was derived from iron oxide sol while those obtained from silica and iron oxide–silica sols were relatively amorphous, indicating that crystallization and particle growth of hematite were inhibited by the silica network. Hydroxypropylcellulose (HPC) was found to reduce cracks successfully. It increased the film porosity and did not interrupt the crystallization of the host. The film containing a Fe:Si:HPC ratio of 50:50:0.005 showed the smoothest surface. Copyright © 2004 John Wiley & Sons, Ltd.

Magnetic properties of γ-Fe2O3–SiO2 aerogel and xerogel nanocomposite materials

The properties of aerogel and xerogel iron oxide–silica nanocomposites prepared by the sol–gel method were investigated by thermal analysis, X-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy and susceptibility measurements. Pure maghemite nanoparticles were obtained starting from both xerogel and aerogel samples, with particles of average size around 5 nm which tend to aggregate into the silica matrix. The role of magnetic interparticle interactions, which have a strong influence on the magnetic properties, is discussed.

Preparation of Aerogel and Xerogel Nanocomposite Materials

ABSTRACTSol-gel method was used to prepare nickel oxide-silica and iron oxide-silica nanocomposites materials in form of aerogels and xerogels. The samples were characterized by thermal analysis, X-ray diffraction, N2 physisorption and transmission electron microscopy techniques. The variation of the supercritical solvent extraction conditions gives rise to differences in the morphological characteristics of the aerogels. These differences influence the size of the nickel oxide nanoparticles in nickel containing aerogels. On the other hand they do not affect the structure and size of the iron oxide nanoparticles in iron containing aerogels. The differences between the xerogel and aerogel nanocomposites are discussed.

Characterization of iron oxide-silica nanocomposites in flames: Part II. Comparison of discrete-sectional model predictions to experimental data

A discrete-sectional model accounting for particle formation by chemical reaction and growth by coagulation and condensation is developed to predict the evolution of the nanocomposite aerosol size distribution in a multicomponent iron-silicon system in a flame. Particle formation by nucleation of the vapor is represented by an Arrhenius-type rate expression, with the rate constant being obtained from experiments and simulation results reported in the literature. Precursor vapor concentrations and the second aerosol volume moment predictions are compared to laser-induced fluorescence (LIF) and light scattering intensity measurements from experiments described in Part I20 of the paper. The results elucidate the important formation and growth mechanisms of nanocomposite ferric oxide-silica particles in flame reactors. The role of operating parameters such as precursor characteristics and temperature profiles on the final product characteristics is established.

In situ characterization of vapor phase growth of iron oxide-silica nanocomposites: Part I. 2-D planar laser-induced fluorescence and Mie imaging

Planar laser-based imaging measurements of fluorescence and particle scattering have been obtained during flame synthesis of iron-oxide/silica superparamagnetic nanocomposites. The theory and application of laser-induced fluorescence, the spectroscopy of FeO(g), and the experimental approach for measurement of gas phase precursors to particle formation are discussed. The results show that the vapor phase FeO concentration rapidly rises at the primary reaction front of the flame and is very sensitive to the amount of precursor added, suggesting nucleation-controlled particle growth. The FeO vapor concentration in the main nucleation zone was found to be insensitive to the amount of silicon precursor injected, indicating that nucleation occurred independently for the iron and silicon components. Light scattering measurements indicate that nanocomposite particles sinter faster than single component silica, in agreement with TEM measurements.

Magnetic iron oxide–silica nanocomposites. Synthesis and characterization

Composite materials containing nanoparticles of maghaemite (γ-Fe2O3) dispersed in a silica matrix have been made by polymerizing a silica precursor (triethoxysilane or silicic acid) inside an aqueous sol of maghaemite particles. After gelation, the examination of xerogels by electron microscopy does not reveal noticeable aggregation of particles. The structure and composition of the silica matrices were deduced from 29Si MAS NMR spectroscopy. Thermal analysis, FTIR and NIR spectroscopic studies showed that the particles and silanol groups of the matrix remain solvated in the composite materials. No Si–O–Fe bonds are formed in the xerogels and the dispersion of particles in the matrix seems to result from the mutual solvation of particle surfaces and remaining silanol groups, as indicated by strongly associated hydrogen-bonded water molecules.