Encapsulated Silica Particles Research Articles

Superhydrophilic and underwater superoleophobic ceramic membranes grafted by layered polydopamine and polydopamine encapsulated silica particles for efficient separation of oil-in-water emulsions

Owing to frequent oil spills and the increasing discharge of oily wastewater, oil pollution has threatened the sustainability of the ecosystem. Ceramic membranes (CM) have been employed for oily wastewater treatment because of their mechanical and chemical stability, but a suitable separating layer is required to treat surfactant-stabilized oil-in-water emulsions effectively. Herein, a separating layer was rationally designed on the CM surface by combining cross-linked layered polydopamine (CL-LPDA) and polydopamine-encapsulated silica particles (SiO2@PDA) with appropriate permeation flux and antifouling characteristics. The resulting CL-LPDA-SiO2@PDA-CM demonstrated superhydrophilicity with a water contact angle of 0° and underwater superoleophobicity with an underwater oil contact angle of 157°, making it an ideal membrane for separating oil-in-water emulsions. The designed membrane could treat a surfactant-stabilized oil-in-water emulsion with a maximum separation efficiency of 97 % and a permeation flux of 109.76 L m−2h−1. The CL-LPDA-SiO2@PDA-CM has also shown significant resistance to fouling under 20 cycles of observation, and the flux recovery ratio (FRR) was higher than 90 %, indicating that pore-clogging could be effectively prevented in the separating layer.

High expression and biosilica encapsulation of alkaline-active carbonic anhydrase for CO2 sequestration system development

Carbonic anhydrase (CA) is a biocatalyst for CO2 sequestration because of its distinctive ability to accelerate CO2 hydration. High production and efficient immobilization of alkaline-active CAs are required, because one potential application of CA is its use in the alkaline solvent-based CO2 absorption/desorption process. Here, we designed and applied an α-type CA from Hahella chejuensis (HCA), which was reported as highly active in alkaline conditions, but was mostly expressed as insoluble forms. We found that the signal peptide-removed form of HCA [HCA(SP-)] was successfully expressed in the soluble form [∼70mg of purified HCA(SP-) per L of culture]. HCA(SP-) also displayed high pH stability in alkaline conditions, with maximal activity at pH 10; at this pH, ∼90% activity was maintained for 2h. Then, we prepared HCA(SP-)-encapsulated silica particles [HCA(SP-)@silica] via a spermine-mediated bio-inspired silicification method. HCA(SP-)@silica exhibited high-loading and highly stable CA activity. In addition, HCA(SP-)@silica retained more than 90% of the CA activity even after 10 cycles of use in mild conditions, and ∼80% in pH 10 conditions. These results will be useful for the development of practical CO2 sequestration processes employing CA.

Nano-Fe3O4 -encapsulated silica particles bearing sulfonic acid groups as a magnetically separable catalyst for the green and efficient synthesis of 14-aryl-14H-dibenzo[a,i]xanthene-8,13-dione derivatives

In this research, an efficient and environmentally friendly ("green") method for one-pot synthesis of xanthene derivatives was developed in the presence of Fe3O4@SiO2–SO3H nanoparticles. The functionalization of silica-coated Fe3O4 magnetite nanoparticles (Fe3O4@SiO2) using chlorosulfonic acid was afforded by nano-Fe3O4 encapsulated-silica particles bearing sulfonic acid (Fe3O4@SiO2–SO3H) that could be applied as a reusable and efficient heterogeneous nanocatalyst. The multicomponent reactions of 2-hydroxy-1,4-naphthoquinone, β-naphthol and aldehydes were carried out under reflux conditions to obtain some 14-aryl-14H-dibenzo[a,i]xanthene-8,13-dione derivatives. Being a simple procedure with environmental benignness, excellent yields, short reaction times, simple purification and facile catalyst separation are the advantages of this protocol. Fe3O4@SiO2–SO3H was readily recovered using an external magnet and could be reused several times without significant loss of reactivity. The catalyst was fully characterized by vibrating sample magnetometry (VSM), Fourier transform-infrared (FT-IR) spectrometry, scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, energy dispersive X-ray spectroscopy (EDAX) and transmission electron microscopy (TEM).

SnCl4-functionalized nano-Fe3O4encapsulated-silica particles as a novel heterogeneous solid acid for the synthesis of 1,4-dihydropyridine derivatives

A simple and general synthetic method for the synthesis of 1,4-dihydropyridines under ultrasonic irradiation was developed using Fe3O4@SiO2–SnCl4as an efficient catalyst.

Nano-Fe3O4 encapsulated-silica particles bearing sulfonic acid groups as an efficient, eco-friendly and magnetically recoverable catalyst for synthesis of various xanthene derivatives under solvent-free conditions

This report describes an efficient method for the synthesis of 1,8-dioxo-octahydroxanthene, 14H-dibenzo[a,j]xanthene, 12-aryl-tetrahydrobenzo[a]xanthenes-11-one and 13-aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraone derivatives in the presence of a catalytic amount of nano-iron oxide encapsulated silica particles bearing sulfonic acid groups. Results present an efficient, environmentally friendly and magnetically recoverable catalyst under solvent-free conditions at 110–130°C.

Preparation of Hemicyanine Dye Encapsulated Silica Particles and their Application in Cotton Fabrics

Trans-4- [p- (N, N-Die (2-hydroxyethyl)) styry-N-ethyl pyridinium bromide (DHEASPBr-C2), a hemicyanine fluorescent dye, was encapsulated into silica nanoparticles by co-hydrolysis and co-condensation of organosilanes in the presence of the dye. The dye containing silica nanoparticles were applied onto cotton fabrics. Scanning electron microscopy (SEM), UVvis spectra, single-photon emission fluorescence spectra and reflectance spectra of the samples were characterized. The SEM results showed that the particle size (ranging from 100-200 nm) and dye encapsulating (1.5-8.1 mg dye per g silica matrix) could be adjusted by the concentration of fluorescent dye and organosilanes. The reflectance of the treated cotton fabrics showed that there were obvious adsorption spectra in 410 - 540 nm and emission spectra in 560 - 700 nm.

PMMA Encapsulated Silica Particles by Dispersion Polymerization in Supercritical Carbon Dioxide

AbstractPMMA encapsulated silica particles were synthesized by the dispersion polymerization of MMA in supercritical carbon dioxide (scCO2). Nanosized silica particles pretreated with 3‐(trimethoxysilyl) propyl methacrylate (γ‐MPS) were used as seeds in the polymerization. Polymeric stabilizer, poly(dimethylsiloxane)‐b‐poly (methacrylic acid) (PDMS‐b‐PMA) copolymer provided sufficient stabilization to the silica/PMMA composite latexes in scCO2 to produce spherical particles. SEM and TEM analysis revealed that the composite particles have core‐shell type morphology.

Filler–filler interactions and viscoelastic behavior of polymer nanocomposites

This work presents the main results obtained within a project on mechanical properties of polymer based nanocomposites. The specific point was how to analyze and model the filler–filler interactions in the description of the viscoelastic behavior of these materials. This paper aims at presenting the general strategy used by the different partners to address this question, together with original experimental results and micro-mechanical modeling. Different nanocomposite materials were fabricated using the latex route, leading to random dispersions of rigid submicronic particles (PS = polystyrene, silica) in a flexible polybutylacrylate matrix at various volume fractions. In addition, encapsulated silica particles in a styrene–acrylate copolymer were produced, leading, after film formation, to a limited number of contacts between silica fillers. The processing route of these encapsulated particles was optimized and the resulting morphology was analyzed by TEM experiments. In the case of random mixtures, a strong effect of reinforcement appears in the rubbery field of the soft phase when the filler content is above a critical fraction (percolation threshold). The reinforcement in the rubbery plateau can be still exacerbated in the case of the PS particles if the material undergoes a heat treatment above the main relaxation of the PS phase. These experimental results illustrate the difference between geometrical percolation (when particles are just in contact) and mechanical percolation (with strong interactions between the fillers). The comparison of the results for PS and silica fillers shows once more that the strength of the interactions plays an important role. To account for the whole set of experimental data, two ways of modeling were explored: (i) homogenization methods based on generalized self-consistent schemes and (ii) a discrete model of spheres assembly which explicitly describes the ability of the contacts to transmit efforts.

Fast Solvating Gas Chromatography of Environmentally Important Compounds Using Polymer-Encapsulated Silica Particles

Rapid separations of selected environmentally important polar compounds using polymer-encapsulated silica stationary phases and a carbon dioxide mobile phase under solvating gas chromatography (SGC) conditions are reported. Ten underivatized short chain aldehydes and ten nitrogen-containing herbicides were separated within 1 min and 5 min, respectively, using a 30 cm×250 μm i. d. column packed with diol-bonded, polyethylenimine (PEI)-coated, and hexamethyldisilazane (HMDS)-end-capped silica particles (5 μm, 120 Å). Seven organophosphorus pesticides were resolved in less than 5 min using a 30 cm×250 μm i. d. column packed with polymethylhydrosiloxane-deactivated and SE-54 encapsulated silica particles. Separation numbers per unit time increased with pressure and temperature ramps. Both rapid pressure and temperature programming can be used to increase the speed of SGC. The effects of pressure and temperature on apparent retention factors of solutes with various polarities were investigated using diol-PEI-HMDS silica particles in SGC.

Fast Solvating Gas Chromatography of Environmentally Important Compounds Using Polymer-Encapsulated Silica Particles

Rapid separations of selected environmentally important polar compounds using polymer-encapsulated silica stationary phases and a carbon dioxide mobile phase under solvating gas chromatography (SGC) conditions are reported. Ten underivatized short chain aldehydes and ten nitrogen-containing herbicides were separated within 1 min and 5 min, respectively, using a 30 cm×250 μm i. d. column packed with diol-bonded, polyethylenimine (PEI)-coated, and hexamethyldisilazane (HMDS)-end-capped silica particles (5 μm, 120 Å). Seven organophosphorus pesticides were resolved in less than 5 min using a 30 cm×250 μm i. d. column packed with polymethylhydrosiloxane-deactivated and SE-54 encapsulated silica particles. Separation numbers per unit time increased with pressure and temperature ramps. Both rapid pressure and temperature programming can be used to increase the speed of SGC. The effects of pressure and temperature on apparent retention factors of solutes with various polarities were investigated using diol-PEI-HMDS silica particles in SGC.

Solvating gas chromatography using ammonia as mobile phase

In this study, the use of ammonia as the mobile phase in packed capillary column solvating gas chromatography (SGC) was investigated. Fused-silica capillary columns (0.9 m×250 μm I.D.) packed with 15 μm octadecyl bonded and polydimethylsiloxane encapsulated silica particles (300 Å) were evaluated under SGC conditions. Flame ionization detection was used for detection. Anilines, aliphatic (primary, secondary, and tertiary) amines, and aliphatic diamines were separated under SGC conditions. Although ammonia was converted from a liquid to a gas along the column, no significant loss in column efficiency was observed.

Separation of polar compounds by solvating gas chromatography with carbon dioxide mobile phase

In this study, the separation of polar compounds in solvating gas chromatography (SGC) was investigated. Capillary columns (250 μm i.d.) packed with deactivated siliceous particles, including SE-54 encapsulated silica particles, diol-bonded silica particles, and polyethylenimine (PEI) coated particles, and nonsiliceous particles of styrene-divinylbenzene were used. Plar compounds that were used as test solutes included ketones, aldehydes esters, nitro-containing compounds, alcohols, phenols, fatty acids, and amines. It was found that capillary columns packed with SE-54 encapsulated particles were suitable for the separation of medium polar compounds, columns packed with diol bonded silica particles could be used for separation of strongly polar compounds such as fatty acids, and columns packed with PEI coated silica particles were suitable for the separation of basic compounds such as alkylamines under SGC conditions. Columns containing the polymeric particles could be used for the separation of medium polar compounds and weak bases, however, low column efficiency was observed. SGC was found to provide better separation of polar compounds than high pressure gas chromatography (HPGC). A sample of a peppermint oil was separated within 8 min under SGC conditions.