Magnetic Organosilica Research Articles

Amine-containing yolk-shell structured magnetic organosilica nanocomposite as a highly efficient catalyst for the Knoevenagel reaction.

The yolk-shell structured silica nanocomposites have been considered by many researchers due to their specific physical and chemical properties. These materials have been widely used in adsorption and catalysis processes. Especially, the void space of yolk-shell nanostructures can provide a unique environment for storage, compartmentation, and confinement in host-guest interactions. In this paper, for the first time, the preparation, characterization, and catalytic application of a novel amine-containing magnetic methylene-based periodic mesoporous organosilica with yolk-shell structure (YS-MPMO/pr-NH2) are developed. The magnetic periodic mesoporous organosilica nanocomposite was synthesized through surfactant-directed co-condensation of bis(triethoxysilyl)methane (BTEM) and tetraethoxysilane around Fe3O4 nanoparticles. After Soxhlet extraction, the surface of YS-MPMO nanocomposite was modified with 3-aminopropyl trimethoxysilane to deliver YS-MPMO-pr-NH2 nanocatalyst. This catalyst was characterized by using EDX, FT-IR, VSM, TGA, XRD, nitrogen-sorption, and SEM analyses. The catalytic activity of YS-MPMO/pr-NH2 was studied in the Knoevenagel reaction giving the corresponding products in a high yield and selectivity. The YS-MPMO/pr-NH2 nanocatalyst was recovered and reused at least four times without a significant decrease in efficiency and activity. A leaching test was performed to study the nature of the catalyst during reaction conditions Also, the catalytic performance of our designed nanocomposite was compared with some of the previous catalysts used in the Knoevenagel reaction.

An ion imprinted magnetic organosilica nanocomposite for the selective determination of traces of Cd(II) in a minicolumn flow-through preconcentration system coupled with graphite furnace atomic absorption spectroscopy.

In this paper we present the determination of ultratraces of cadmium ions in water by means of a minicolumn (MC) flow-through preconcentration system coupled with graphite furnace atomic absorption spectrometry. The core of the system is a lab-made ion imprinted magnetic organosilica nanocomposite which is employed as filler of the MC for the selective retention of the analyte. In this case superparamagnetic magnetite nanoparticles were coated with an amine-functionalized shell and ion imprinted with Cd(II) by a simple sol-gel co-condensation method. The setup was completed with the inclusion of a magnet fixed around the packed MC. This assembly - which is studied with an MII material for the first time here - allowed a homogeneous distribution of the solid on the walls of the MC, leaving a hole in the center and enabling the absence of material bleeding or obstructions to the free movement of fluids. Ion imprinted (MII) and non-imprinted (MNI) materials were studied for comparison purposes. Both were characterized and compared by DRX, FTIR, and SEM and their magnetic behavior by magnetization curves. Batch experiments showed an equilibration time of less than 10 minutes and a maximum adsorption pH of around 7 for both solids. The maximum capacity for MII was greater than that of MNI (200 mg g-1 and 30 mg g-1 respectively) and thus, the former was chosen for analytical purposes. Under MC dynamic conditions, sample and elution flow rates, volumes of the sample and eluant, and type and concentration of the most suitable eluant have been thoroughly investigated and optimized. Under the optimal experimental conditions, the MII filler showed a preconcentration factor of 200, a limit of detection of 0.64 ng L-1, a linear range of 2.5-100 ng L-1, RSD% of 1.9 (n = 6; 10 ng L-1) and a lifetime of more than 800 cycles of concentration-elution with no loss of sensitivity or need for refilling. The effect of potentially interfering ions on the percent recovery of cadmium was also studied. The proposed method was successfully applied to the determination of traces of Cd(II) in osmosis and tap water with recoveries of 98.0-101.3%. A comparison with similar methods is also provided.

Ionic liquid functionalized magnetic organosilica nanocomposite: A powerful and efficient support for manganese catalyst

A novel Mn-containing ionic liquid and ethyl based magnetic organosilica with core-shell structure (Fe3O4@OS/IL-Mn) is prepared, characterized and applied as powerful and recoverable nanocatalyst. The Fe3O4@OS/IL-Mn was prepared via simultaneous coating of tetramethoxysilane (TMOS) and 1,2-bis(triethoxysilyl)ethane (BTEE) over magnetite nanoparticles (MNPs) followed by treatment with ionic liquid and manganese acetate. This catalyst was characterized using scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), energy dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction (PXRD), vibrating sample magnetometer (VSM) and FT-IR spectroscopy. The Fe3O4@OS/IL-Mn was used as an efficient catalyst for the one-pot preparation of biologically useful 2H-indazolo-[2,1-b]-phthalazin-trions under green conditions. The recoverability, reusability and durability of the designed catalyst have also been studied under applied conditions.

Magnetic organic-silica hybrid supported Pt nanoparticles for carbon sequestration reaction

We revealed a new protocol to support Pt nanoparticles on magnetic ionic liquid functionalized organosilica nanoparticle matrix. The proposed catalyst system was synthesized by sol–gel condensation method, where two silica precursors [tetraethyl orthosilicate (TEOS) and bis-silylated ionic liquid monomer] were used to carry hydrophobic magnetic nanoparticles. The Pt metal was supported on the skeleton of magnetic organosilica hybrid nanoparticles by adsorbing platinum salt (Na2PtCl4) (replaced by ion exchange method). Furthermore, sodium borohydride was used to reduce platinum salt to Pt NPs. The synthesized catalytic system was used for CO2 hydrogenation reaction under high-pressure reaction condition. An external magnetic field was used to informally recover the catalyst and further recycled for three runs (without ionic liquid medium). Task-specific ionic liquids were also manipulated as a reaction medium not only to capture the CO2 gas but also to improve the reaction in a more precise manner. Desired results were attained while using 1,3-di (N, N-dimethylaminoethyl)-2-methylimidazolium nonafluorobutanesulfonate ([DAMI][CF3CF2CF2CF2SO3]) task-specific ionic liquid and we isolated the formic acid in good TON/TOF value. We easily reused the catalytic system up to 8 runs without decreasing the performance and stability of the catalytic system.

Enzymatic Synthesis of Glycerol Carbonate Using a Lipase Immobilized on Magnetic Organosilica Nanoflowers as a Catalyst.

For synthesizing glycerol carbonate (GC) by a reaction between glycerol (GL) and dimethyl carbonate (DMC), a lipase immobilized on magnetic organosilica nanoflowers was prepared and utilized as a biocatalyst. Candida antarctica lipase B (CALB) was chosen as a model enzyme for preparing an immobilized biocatalyst (CALB@nanoflowers). The obtained CALB@nanoflowers was characterized using scanning electron microscopy, transmission electron microscopy, and confocal laser scanning microscopy. Effects of GL/DMC molar ratio, biocatalyst amount, temperature, surfactant and molecular sieve addition, and reaction time on the conversion of GL and the selectivity of CALB@nanoflowers were investigated. The optimal catalytic performance (yield of GC: 88.66% and conversion of GL: 94.24%) was achieved under the condition of 1:20 molar ratio of GL to DMC with 0.2 g of molecular sieves added at 50 °C for 24 h. After recycling seven times, the CALB@nanoflowers maintained over 79% of its initial activity and the yield of GC was 70.31%.

Highly Efficient Aqueous Synthesis of Propargylamines through C–H Activation Catalyzed by Magnetic Organosilica‐Supported Gold Nanoparticles as an Artificial Metalloenzyme

Highly efficient magnetic organosilica‐supported gold nanoparticles were developed as an artificial metalloenzyme for the synthesis of propargylamines through C–H activation in water under an ambient atmosphere. Herein, we present a very simple and efficient method for the deposition of Au nanoparticles on porous magnetic organosilica (Fe3O4@SiO2‐Cl) through the thermal reduction of an organometallic AuIII complex. As a nucleophile, a AuIII polypyridyl coordination complex could react with alkyl halides from the Fe3O4@SiO2‐Cl to form a quaternary ammonium salt as an ionic liquid; subsequently, the ligand was oxidized and the Au nanoparticles were embedded into the porous organosilica shell. The synergic effect of the gold nanoparticles as catalytically active sites, pyridinium chloride as a phase‐transfer agent, and the magnetite nanoparticle core, which could function as a protein mimic, endow the material with high efficiency, stability, recoverability, reusability, and good turnover frequency, all of which are necessary characteristic for an artificial enzyme. A reliable catalytic procedure for the synthesis of propargylamines was identified.

Propylamine-containing magnetic ethyl-based organosilica with a core–shell structure: an efficient and highly stable nanocatalyst

A novel propylamine-containing magnetic organosilica is prepared and characterized, and its catalytic performance is investigated in the Knoevenagel reaction.

Monodisperse core-shell magnetic organosilica nanoflowers with radial wrinkle for lipase immobilization

The monodisperse core-shell magnetic organosilica nanoflowers were successfully synthesized by a method based on the bicontinuous microemulsion phase of the Winsor III system. The obtained nanoflowers with magnetic core and flower-like organosilica shell possess radial-wrinkle, tunable perpendicular channels, and high magnetization (62emu/g). The nanoflowers were employed as support for Candida antarctica lipase B (CALB) covalent immobilization. The maximum amount of CALB immobilized on the nanoflowers was 93mg/gsupport, while the specific hydrolytic activity was 22,700U/gsupport. Meanwhile, the CALB@nanoflowers showed better pH stability than free CALB and CALB@MMPS, which can remain 65% of initial activity after incubated in cyclohexane at 60°C for 96h, and remain 90% of initial activity after stored in room temperature for 42days. In addition, the CALB@nanoflowers could catalyze the synthesis of alkyl levulinates through the esterification of levulinic acid alcohols with different chain length (n-butyl alcohol, n-caprylic alcohol, n-lauryl alcohol) in a solvent-free system effectively. After recycling 10 times, the CALB@nanoflowers retained more than 85% of its initial activity in catalyzing the synthesis of butyl-levulinates and more than 96% of the initial activity in catalyzing the synthesis of long chain alkyl levulinates, which was much higher than commercial N435. With these desired characteristics, the design of hydrophobic nanoflowers with tunable wrinkle channels for lipases immobilization opens up a new way to improve the catalytic activity and stability of the lipases, and may have potential applications in various lipase-based industrial processes.

Palladium Nanoparticles Supported on Magnetic Organic-Silica Hybrid Nanoparticles

A method for supporting palladium nanoparticles on magnetically separable organosilica nanoparticles functionalized with ionic liquid groups is described. The system was prepared by sol–gel condensation of two silica precursors: tetraethyl orthosilicate (TEOS) and bis-silylated ionic liquid monomer, on hydrophobic magnetic nanoparticles modified with oleate groups. The support of palladium nanoparticles on the magnetic organo-silica hybrid nanoparticles was achieved by adsorbing palladium salts (Na2PdCl4) on their surface via ion exchange with the ionic liquid groups, followed by reduction with sodium borohydride. The resulted system was applied in three different catalytic transformations: carbonylation of iodoarenes and Heck and Suzuki coupling reactions. The catalyst demonstrated high catalytic activity and was easily separated from the reaction mixture by applying an external magnetic field. The catalyst was recycled over five times without showing a significant loss in its activity.