Silica-coated Magnetite Particles Research Articles

Application of Silica–Coated Magnetite on a Steel Plate and its Frictional and Thermal Effect

The magnetite (Fe3O4) particles that have been coated using tetraethyl orthosilicate (TEOS) as silica precursors were used as the additive in the lubricant. The effects of silica-coated magnetite additive on the thermal properties of ferro-lubricant and reducing the friction on a steel plate have been investigated. The characterizations were conducted at both conditions: with and without the addition of Fe3O4 particles. The characterization using TEM proposed that the average particle size of the silica-coated magnetite particles is 150 nm. The TGA/DSC curves of the silica-coated magnetite particles suggested a gradual weight loss obtained as the temperature increased. The endothermic peak was obtained at ~37 and 50 °C. The silica-coated magnetite particles’ additive increases both the density and viscosity of 0.84 g/cm3 and 134.29 cSt. The silica-coated magnetite particles additive in the lubricant enhances the thermal conductivity and specific heat of 0.151 W/m.K and 1600 J/kg.K. Ferro-lubricant reduces the friction coefficient up to 0.02 (static) and 0.005 (dynamic). The wear resistance of the plate could be improved as analyzed using an optical microscope. These results demonstrate a promising application of the silica-coated magnetite particles as an additive in the lubricant. Therefore improving wear resistance and cooling during the friction process.

Biomass Derivative Valorization Using Nano Core-Shell Magnetic Materials Based on Keggin-Heteropolyacids: Levulinic Acid Esterification Kinetic Study with N-Butanol

Magnetic materials based on Keggin heteropolyacids immobilized on mesoporous silica-coated magnetite particles with a core-shell structure were synthesized. The activity of the catalyst was studied in the esterification reaction of levulinic acid with n-butanol, and its kinetics was studied by the systematic variation of several reaction parameters, such as stirring speed, catalyst loading, molar ratio of reactants, and temperature. It was also seen that the reaction was free from any external mass transfer as well as intraparticle diffusion limitations and was intrinsically kinetically controlled. A second-order kinetic equation was found to be consistent with the experimental data. Also, an experimental activation energy of 17 kcal/mol was found. A solvent-free condition for this reaction has also added the green chemistry perception to the reaction. In addition, the resulting catalyst can be used repeatedly without significant decrease in activity.

The effect of polymer and gold functionalization on the magnetic properties of magnetite nanoparticles

Silica coated magnetite particles ([email protected]) functionalized with gold [email protected] + Au), or gold plus poly (vinylpyrrolidone) (PVP) (Fe3O[email protected] + Au + PVP) were synthesized. Their structural and magnetic properties were studied using a combination of experimental techniques including electron micr oscopy (EM), superconducting quantum interference device (SQUID) magnetrometry, and electron paramagnetic resonance (EPR) spectroscopy. The saturation magnetization (MS) of particles functionalized with gold and gold plus PVP were found to be 67.24 emu/g and 65.78 emu/g respectively. Both functionalized ensembles maintained a large percentage (78–80%) of their MS values compared to pristine magnetite. The coercivity (HC) for pristine magnetite was 227.25 Gauss compared to 200.00 Gauss for [email protected] + Au and 228.57 Gauss for [email protected] + Au + PVP. Furthermore, these magnetic particles, being biologically compatible and resistant to oxidation, were functionalized with an antibody designed to target A431 oral cancer cells. The result demonstrates high specificity of binding compared to non-functionalized particles, attributable to a favorable interaction between gold and the antibody making them excellent candidates for applications like bio-separation and imaging.

Determining major factors controlling phosphorus removal by promising adsorbents used for lake restoration: A linear mixed model approach

Phosphorus (P) removal from lake/drainage waters by novel adsorbents may be affected by competitive substances naturally present in the aqueous media. Up to date, the effect of interfering substances has been studied basically on simple matrices (single-factor effects) or by applying basic statistical approaches when using natural lake water. In this study, we determined major factors controlling P removal efficiency in 20 aquatic ecosystems in the southeast Spain by using linear mixed models (LMMs). Two non-magnetic -CFH-12® and Phoslock®- and two magnetic materials -hydrous lanthanum oxide loaded silica-coated magnetite (Fe-Si-La) and commercial zero-valent iron particles (FeHQ)- were tested to remove P at two adsorbent dosages. Results showed that the type of adsorbent, the adsorbent dosage and color of water (indicative of humic substances) are major factors controlling P removal efficiency. Differences in physico-chemical properties (i.e. surface charge or specific surface), composition and structure explain differences in maximum P adsorption capacity and performance of the adsorbents when competitive ions are present. The highest P removal efficiency, independently on whether the adsorbent dosage was low or high, were 85–100% for Phoslock and CFH-12®, 70–100% for Fe-Si-La and 0–15% for FeHQ. The low dosage of FeHQ, compared to previous studies, explained its low P removal efficiency. Although non-magnetic materials were the most efficient, magnetic adsorbents (especially Fe-Si-La) could be proposed for P removal as they can be recovered along with P and be reused, potentially making them more profitable in a long-term period.

Phagocytic cell responses to silica-coated dithiocarbamate-functionalized iron oxide nanoparticles and mercury co-exposures in Anguilla anguilla L.

Immune system responses in fish are considered as suitable and sensitive biomarkers for monitoring aquatic pollution. However, a clear knowledge gap persists in the literture on the immunotoxic potential of engineered nanoparticles toward aquatic organisms such as fish. Employing major enzymatic- (glutathione reductase, GR; glutathione peroxidase, GPX; glutathione sulfo-transferase, GST; catalase, CAT) and thiol- (non-protein thiols, NP-SH; total glutathione, TGSH)-based defense biomarkers, this study assessed the response of phagocytes isolated from peritoneum (P-phagocytes), gill (G-phagocytes), head kidney (HK-phagocytes), and spleen (S-phagocytes) of European eel (Anguilla anguilla L.) to silica-coated magnetite particles (Fe3O4@SiO2/SiDTC, hereafter called IONP; size range: 82 ± 21 to 100 ± 30nm; 2.5mgL(-1)) alone and IONP and mercury (Hg; 50μgL(-1)) concomitant exposures. Responses of previous biomarkers were studied in P-phagocytes, G-phagocytes, HK-phagocytes, and S-phagocytes collected during 0, 2, 4, 8, 16, 24, 48, and 72h of exposures. Contingent to hour of exposure to IONP, Hg, and IONP + Hg GST, GPX, CAT, NP-SH, and TGSH exhibited their differential responses in all the phagocytic cells considered. In particular, under IONP exposure, the potential occurrence of the GSH-independent antioxidant defense was indicated by the observed herein inhibition in the enzymatic- and thiol-based defense in A. anguilla phagocytes. In contrast, the response of P-, G-, HK-, and S-phagocytes to the increasing Hg exposure period reflected an increased detoxification activity. Notably, the occurrence of an antagonism between IONP and Hg was depicted during late hours (72h) under IONP + Hg concomitant exposure, where elevations in the defense biomarkers were depicted. Overall, the P-, G-, HK-, and S-phagocytic cells exhibited a differential induction in the studied enzymes and thiols to counteract impacts of IONP, Hg, and IONP + Hg concomitant exposures. Future studies on the fish immunotoxicity responses to IONP exposure in multi-pollution conditions can be benefited with the major outcomes of the present study.

The role of operational parameters on the uptake of mercury by dithiocarbamate functionalized particles

Abstract Sorbents based on silica and silica coated magnetite particles have been functionalized with dithiocarbamate groups, aiming at the uptake of mercury. The uptake capacity of the synthesized materials were evaluated systematically for variable operational parameters including degree of functionalization, sorption time, sorbent dose, and initial Hg(II) concentration. Removal efficiencies of 99.6–99.9% were achieved in 8–24 h, regardless the sorbent dose, type of substrate and degree of functionalization. All sorbents were able to decrease an initial Hg(II) concentration of 50 μg/L to values circa 100 times lower than the guideline value for drinking water quality (1 μg/L), with the additional advantage of magnetic separation by application of an external magnetic field, in the case of the silica coated magnetite. The high capacity of these materials for Hg(II) uptake from water is attributed to their functionalization due to the strong complexation of the mercury ions and dithiocarbamate groups. The modelling of the kinetic and the equilibrium results was well described by common kinetic and equilibrium equations.

Synthesis and characterization of magnetically separable Ag/AgCl–magnetic activated carbon composites for visible light induced photocatalytic detoxification and disinfection

A magnetic adsorptive photocatalyst composite Ag/AgCl–magnetic activated carbon (A-MAC) was proposed and investigated. Magnetic activated carbon was prepared by impregnation of AC with silica-coated magnetite particles synthesized via chemical co-precipitation and a modified Stöber process, and was then used to synthesize Ag/AgCl–MAC composites by a facile deposition-precipitation-photoreduction method. The prepared composites were characterized by X-ray diffraction, transmission and scanning electron microscopies, respectively, X-ray photoelectron spectroscopy, N2 sorption, and ultraviolet-visible light diffuse reflectance spectroscopy. The magnetic properties of the composites were studied by superconducting quantum interference device magnetometry, and they were found to exhibit quasi-superparamagnetic behaviour. The visible light induced photoactivities of the samples were studied for the degradation of model organic pollutants, methyl orange and phenol, and cyclic degradation experiments were performed by recovering the composite by magnetic separation between runs. The prepared composites were also found to possess good activity for photocatalytic disinfection, inducing a 3-log reduction in Escherichia coli K-12 in 40min under irradiation. The incorporation of silica-coated magnetite into AC was thought to influence morphology in the final photocatalyst-adsorbent composites, and the role of silica in preventing iron oxide dissolution in the photoreactive system was investigated and discussed.

Brain glutathione redox system significance for the control of silica-coated magnetite nanoparticles with or without mercury co-exposures mediated oxidative stress in European eel (Anguilla anguilla L.)

This in vitro study investigates the impact of silica-coated magnetite particles (Fe3O4@SiO2/SiDTC, hereafter called IONP; 2.5mgL(-1)) and its interference with co-exposure to persistent contaminant (mercury, Hg; 50μgL(-1)) during 0, 2, 4, 8, 16, 24, 48, and 72h on European eel (Anguilla anguilla) brain and evaluates the significance of the glutathione (GSH) redox system in this context. The extent of damage (membrane lipid peroxidation, measured as thiobarbituric acid reactive substances, TBARS; protein oxidation, measured as reactive carbonyls, RCs) decreased with increasing period of exposure to IONP or IONP + Hg which was accompanied with differential responses of glutathione redox system major components (glutathione reductase, GR; glutathione peroxidase, GPX; total GSH, TGSH). The occurrence of antagonism between IONP and Hg impacts was evident at late hour (72h), where significantly decreased TBARS and RC levels and GR and glutathione sulfo-transferase (GST) activity imply the positive effect of IONP + Hg concomitant exposure against Hg-accrued negative impacts [vs. early (2h) hour of exposure]. A period of exposure-dependent IONP alone and IONP + Hg joint exposure-accrued impact was perceptible. Additionally, increased susceptibility of the GSH redox system to increased period of exposure to Hg was depicted, where insufficiency of elevated GR for the maintenance of TGSH required for membrane lipid and cellular protein protection was displayed. Overall, a fine-tuning among brain glutathione redox system components was revealed controlling IONP + Hg interactive impacts successfully.

Core–shell magnetite-silica dithiocarbamate-derivatised particles achieve the Water Framework Directive quality criteria for mercury in surface waters

The sorption capacity of nanoporous titanosilicate Engelhard titanosilicate number 4 (ETS-4) and silica-coated magnetite particles derivatised with dithiocarbamate groups towards Hg(II) was evaluated and compared in spiked ultra-pure and spiked surface-river water, for different batch factors. In the former, and using a batch factor of 100m(3)/kg and an initial Hg(II) concentrations matching the maximum allowed concentration in an effluent discharge, both materials achieve Hg(II) uptake efficiencies in excess of 99% and a residual metal concentration lower than the guideline value for drinking water quality. For the surface-river water and the same initial concentration, the Hg(II) uptake efficiency of magnetite particles is outstanding, achieving the quality criteria established by the Water Framework Directive (concerning Hg concentration in surface waters) using a batch factor of 50m(3)/kg, while the efficiency of ETS-4 is significantly inferior. The dissimilar sorbents' Hg(II) removal efficiency is attributed to different uptake mechanisms. This study also highlights the importance of assessing the effective capacity of the sorbents under realistic conditions in order to achieve trustable results.

Magnetorheological fluid based on submicrometric silica-coated magnetite particles under an oscillatory magnetic field

An experimental study conducted on the rheological properties of a magnetorheological fluid based on submicrometric silica-coated magnetite particles dispersed in silicone oil is presented. We investigated the rheological behaviour when the system is simultaneously exposed to a static field and a sinusoidal field used as a perturbation. The results show that the perturbation modifies the rheological behaviour of the system and can be used to control its physical properties; however, the changes that are induced are smaller than expected from previous results for the aggregation of particles under magnetic perturbations. We discussed this difference in terms of the ratio between the magnetic energy and the thermal energy. We observed that a threshold magnetic field exists; below it, the yield stress is practically zero, whereas above it, the yield stress grows quickly. We discuss this result in terms of a model based on chain length distribution.

Comparison of different strategies for the assembly of gold colloids onto Fe3O4@SiO2 nanocomposite particles

Three strategies were employed for the assembly of gold nanoparticles on silica-coated magnetite particles (SCMPs). In strategy I, citrate-coated gold nanoparticles were attached on the surface of amine-SCMPs. In strategy II, amine-SCMPs were coated with carboxylated gold nanoparticles via amide bond formation. In strategy III, the thiol-SCMPs surface was coated with gold nanoparticles. Among the above examined strategies, coating amine-SCMPs with gold nanoparticles via strategy I resulted in a better coverage and stronger intensity of absorption bands. Furthermore, results obtained through strategy I showed that decreasing the pH of the solution from 7 to 3 leads to a further red-shift of the plasmon absorption peak for the prepared particles. Moreover, the effect of amine-SCMPs’ zeta potential on the coverage with citrate-coated gold nanoparticles was studied. The results revealed that increasing the EDS concentration from 25 to 90mM results in a higher coverage of gold nanoparticles on the SCMPs surface.

Sonochemical coating of magnetite nanoparticles with silica

Magnetite nanoparticles were coated with silica through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under ultrasonic irradiation. The ultrasonic irradiation was used to prevent the agglomeration of the magnetite particles and accelerate the hydrolysis and condensation of TEOS. TEM, DLS, XRF, VSM, TG and sedimentation test were used to characterize the silica-coated magnetite particles. The dispersibility of silica-coated magnetite particles in aqueous solution was improved significantly and the agglomerate particle size was decreased to 110 nm. It was found that the agglomerate particle size of silica-coated magnetite particles was mainly decided by the coating temperature and the pH value in the silica-coating process. The weight ratio of silica in silica-coated magnetite particles was mainly decided by the pH value in the silica-coating process. The dispersibility of silica-coated magnetite particles was mainly decided by the agglomerate particle size of the suspension. The oxidation of magnetite particles in air was limited through the coated silica. The magnetism of silica-coated magnetite particles decreased slightly after silica-coating.

Synthesis and characterization of monodisperse ultra-thin silica-coated magneticnanoparticles

A systematic study of the formation of silica-coated magnetite particles via a modified reversemicroemulsion approach was investigated by using transmission electron microscopy (TEM),x-ray diffraction (XRD) and a superconducting quantum interference device (SQUID). Theresults show that the surfactant Igepal CO-520 played an important role in the reactionsystem, and the thickness of the silica shell could be controlled by the concentration of thereaction agents. The developed ultra-thin silica-coated magnetic particles with a∼2 nm thin silica shell have a high saturated magnetization around15 emu g−1.

Engineering and characterization of mesoporous silica-coated magnetic particles for mercury removal from industrial effluents

Mesoporous silica coatings were synthesized on dense liquid silica-coated magnetite particles using cetyl-trimethyl-ammonium chloride (CTAC) as molecular templates, followed by sol–gel process. A specific surface area of the synthesized particles as high as 150 m 2/g was obtained. After functionalization with mercapto-propyl-trimethoxy-silane (MPTS) through silanation reaction, the particles exhibited high affinity of mercury in aqueous solutions. Atomic force microscopy (AFM), zeta potential measurement, thermal gravimetric analysis (TGA), analytical transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS) were used to characterize the synthesis processes, surface functionalization, and mercury adsorption on the synthesized magnetite particles. The loading capacity of the particles for mercury was determined to be as high as 14 mg/g at pH 2. A unique feature of strong magnetism of the synthesized nanocomposite particles makes the subsequent separation of the magnetic sorbents from complex multiphase suspensions convenient and effective.

Investigation of formation of silica-coated magnetite nanoparticles via sol–gel approach

A systematic investigation of the formation of silica-coated magnetite particles via sol–gel approach was conducted using transmission electron microscope (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results show that reaction parameters including the type of alcohol, the volume ratio of alcohol to water, the amount of catalyst and the amount of precursor play important roles on the formation of silica-coated magnetite particles, and the obtained silica-coated magnetite nanoparticles possess superparamagnetic property.

Synthesis and Characterization of Polypyrrole– Magnetite–Silica Particles

The synthesis of colloidal polypyrrole–magnetite-silica nanocomposites is described. First, silica-coated magnetite particles were prepared by the aqueous deposition of silica onto ultrafine (5–20 nm) magnetite particles via controlled hydrolysis of sodium silicate. Then pyrrole was chemically polymerized using (NH4)2S2O8, H2O2/Fe3+/HCl, or FeCl3oxidants in the presence of these silica-coated magnetite particles to yield colloidal dispersions of polypyrrole–magnetite–silica particles. The magnetite contents of these materials were as high as 17.5% by mass. Vibrating sample magnetometry measurements confirmed that these nanocomposites were superparamagnetic, with bulk saturation magnetization values of up to 10.9 emu g−1. Disc centrifuge photosedimentometry was used to assess particle size and degree of dispersion, yielding weight-average particle diameters in the range 100–520 nm. Electron microscopy studies indicated a rather ill-defined particle morphology but provided some evidence for the magnetite component within the nanocomposites. Stable colloidal dispersions were obtained using the H2O2/Fe3+/HCl and (NH4)2S2O8, oxidants, whereas FeCl3-based syntheses yielded only flocculated particles or macroscopic precipitates under similar conditions. Solid-state electrical conductivities of nanocomposites synthesized using (NH4)2S2O8, H2O2/Fe3+/HCl, and FeCl3were about 10−3, 10−2, and 10−1S cm−1, respectively.

Synthesis of poly(pyrrole)–silica–magnetite nanocomposite particles

Pyrrole is polymerised in the presence of ultrafine silica-coated magnetite particles; the resulting colloidal poly(pyrrole)–silica–magnetite nanocomposites have a conducting polymer content of 75 mass% and exhibit superparamagnetism.