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.

Highly Active Ruthenium Catalyst Supported on Magnetically Separable Mesoporous Organosilica Nanoparticles

A facile and direct method for synthesizing magnetic periodic mesoporous organosilica nanoparticles from pure organosilane precursors is described. Magnetic ethylene- and phenylene-bridged periodic mesoporous organosilica nanoparticles (PMO NPs) were prepared by nanoemulsification techniques. For fabricating magnetic ethylene- or phenylene-bridged PMO NPs, hydrophobic magnetic nanoparticles in an oil-in-water (o/w) emulsion were prepared, followed by a sol–gel condensation of the incorporated bridged organosilane precursor (1,2 bis(triethoxysilyl)ethane or 1,4 bis(triethoxysilyl)benzene), respectively. The resulting materials were characterized using high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction (XRD), solid-state NMR analysis, and nitrogen sorption analysis (N2-BET). The magnetic ethylene-bridged PMO NPs were successfully loaded using a ruthenium oxide catalyst by means of sonication and evaporation under mild conditions. The obtained catalytic system, termed Ru@M-Ethylene-PMO NPS, was applied in a reduction reaction of aromatic compounds. It exhibited very high catalytic behavior with easy separation from the reaction medium by applying an external magnetic field.

Nonsacrificial Self-Template Synthesis of Colloidal Magnetic Yolk-Shell Mesoporous Organosilicas for Efficient Oil/Water Interface Catalysis

Using interfacial reaction systems for biphasic catalytic reactions is attracting more and more attention due to their simple reaction process and low environmental pollution. Yolk-shell structured materials have broad applications in biomedicine, catalysis, and environmental remediation owing to their open channels and large space for guest molecules. Conventional methods to obtain yolk-shell mesoporous materials rely on costly and complex hard-template strategies. In this study, a mild and convenient nonsacrificial self-template strategy is developed to construct yolk-shell magnetic periodic mesoporous organosilica (YS-mPMO) particles by using the unique swelling-deswelling property of low-crosslinking density resorcinol formaldehyde (RF). The obtained YS-mPMO microspheres possess an amphiphilic outer shell, high surface area (393 m² g^-1 ), uniform mesopores (2.58 nm), a tunable middle hollow space (50-156 nm), and high superparamagnetism (34.4-37.1 emu g^-1 ). By tuning the synthesis conditions, heterojunction structured yolk-shell Fe₃ O₄ @RF@void@PMO particles with different morphologies can be produced. Owing to the amphipathy of PMO framworks, the YS-mPMO particles show great emulsion stabilization ability and recyclability under a magnetic field. YS-mPMO microspheres with immobilized Au nanoparticles (≈3 nm) act as both solid emulsifier for dispersing styrene (St) in water and interface catalysts for selective conversion of St into styrene oxide with a high selectivity of 86%, and yields of over 97%.

A bis-benzimidazole PMO ratiometric fluorescence sensor exhibiting AIEE and ESIPT for sensitive detection of Cu2+

A novel bis-benzimidazole organic siloxane precursor (BBM-Si) was prepared, and was combined with tetraethylorthosilicate (TEOS) as a mixed Si source. Then, bridged periodic mesoporous organosilica (BBM-PMO) spherical nanoparticles were synthesized by co-condensation using cetyltrimethylammonium bromide (CTAB) as structure directing agent. The optical properties showed that BBM qualifies as an “aggregation induced emission enhanced” (AIEE) molecule, exhibiting characteristics of excited-state intramolecular proton transfer (ESIPT), such as a large Stokes shift and dual fluorescence emission. For the BBM-PMO materials, the silica skeleton provides a rigid environment that limits molecular rotation, resulting in improved fluorescence emission. In particular, the BBM-PMOs exhibited dual emission of the enol and keto forms, achieving a ratiometric response to Cu²⁺ with high sensitivity and selectivity in a broad pH range. Additionally, the limit of detection was as low as 7.15 × 10⁻⁹ M in aqueous solution. The X-ray absorption near-edge spectroscopy (XANES) showed the coordination structure through the interaction between copper ions and N atoms of benzimidazole in the BBM-PMO coordinated to Cu²⁺. These results demonstrate that BBM-PMO hybrid materials have potential applications in the fields of bio-imaging and environmental monitoring.

A novel bis-benzimidazole organic siloxane precursor (BBM-Si) was prepared, and was combined with tetraethylorthosilicate (TEOS) as a mixed Si source.

Hybrid mesoporous organosilicas with molecularly imprinted cavities: towards extended exposure of active amino groups in the framework wall

Towards extended exposure of active sites in the framework of ordered mesoporous materials via molecularly imprinted cavities.

Synthesis of core-shell structured FAU/SBA-15 composite molecular sieves and their performance in catalytic cracking of polystyrene

Composite molecular sieves, FAU/SBA-15, having core-shell structure were synthesized. The synthesized composite sieves were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), pyrolysis fourier transform infrared (Py-FTIR) spectroscopy, temperature programmed desorption spectra (NH₃-TPD), UV Raman spectroscopy, nuclear magnetic resonance (NMR) and other techniques. XRD, SEM, TEM, N₂ adsorption-desorption, mass spectrometry, NMR and EDS results showed that the composite molecular sieve contained two pore channels. Py-FTIR results showed that the addition of HY molecular sieves improved the acidity of the composite zeolite. The crystallization mechanism during the growth of FAU/SBA-15 shell was deduced from the influence of crystallization time on the synthesis of FAU/SBA-15 core-shell structured composite molecular sieve. HY dissociated partially in H₂SO₄ solution, and consisted of secondary structural units. This framework structure was more stable than its presence in the isolated form on the same ring or in the absence of Al. Thus it played a guiding role and connected with SBA-15 closely through the Si-O bond. This resulted in the gradual covering of the exterior surface of FAU phase by SBA-15 molecular sieves. The presence of SBA-15 restricted the formation of the other high mass components and increased the selectivity towards ethylbenzene.

Small size mesoporous organosilica nanorods with different aspect ratios: Synthesis and cellular uptake

In the work, small size thioether-bridged mesoporous organosilica nanorod (MONRs) are successfully synthesized using cetyltrimethylammonium bromide (CTAB) as structure-directing agent and bis[3-(triethoxysilyl)propyl]tetrasulfide (TETS) and tetraethoxysilane (TEOS) as co-precursors. The MONRs have tunable aspect ratios of 2, 3, and 4 (denoted as MONRs-2, MONRs-3, and MONRs-4), small and controllable lengths (75-310nm), high surface area (570-870cm²g^-1), uniform mesopores (2.4-2.6nm), large pore volume (0.34cm³g^-1), and excellent biocompatibility. The uptake of the MONRs by multidrug resistant human breast cancer MDR-MCF-7 cells is related to their aspect ratios. The MONRs-3 shows a faster and higher cellular internalization compared to the MONRs-4 and MONRs-2, respectively. Thanks to the high cellular uptake, doxorubicin (DOX) loaded MONRs-3 show obviously improved chemotherapeutic effect on MDR-MCF-7 cancer cells. It is expected that the MONRs provide a useful platform for drug delivery and therapeutics.