Palladium containing periodic mesoporous organosilica with imidazolium framework (Pd@PMO-IL): an efficient and recyclable catalyst for the aerobic oxidation of alcohols

Pd-Coordinated Salinidol-Modified Mixed MOF: An Excellent Active Center for Efficient Nitroarenes Reduction and Selective Oxidation of Alcohols

Selective oxidation of active and inactive alcohol substrates and reduction of nitroarenes is a highly versatile conversion that remains a challenge in controlling functionality and adjustments in metal-organic frameworks (MOFs). On the other hand, it offers an attractive opportunity to expand their applications in designing the next generation of catalysts with improved performance. Herein, a novel mixed MOF consisting of supported 2-hydroxybenzamide (mixed MOF-salinidol) has been fabricated by post-synthetic modifications of mixed MOF. Subsequently, the prepared nanocomposites were modified to impart catalytic sites using palladium chloride ions mixed with MOF-salinidol/Pd (II). After successfully designing and structurally characterizing nanocomposites, we evaluated their activity in oxidizing primary and secondary alcohols using aerobic conditions with molecular oxygen and an air atmosphere. In addition, the stability of (mixed MOF-salinidol/Pd (II)) catalysts under catalytic conditions was also demonstrated by comparing the Fourier-transform infrared spectrum, scanning electron microscopy image, and ICP-OES method before and after catalysis. Based on the results, the active surface area of the synthesized nanocatalyst is large, which highlights its unique synergistic effect between post-synthetic modified MOF and Pd, and furthermore, the availability of catalytic sites from Pd, as demonstrated by outstanding catalytic activity.

Magnetic ethylene-based periodic mesoporous organosilica supported palladium: An efficient and recoverable nanocatalyst for Suzuki reaction

In the present study, a novel magnetic ethylene-based periodic mesoporous organosilica supported Pd-Schiff base complex (Fe₃O₄@PMO/SB-Pd) was prepared, characterized and applied as a recoverable nanocatalyst for green synthesis of Suzuki products. Chemical composition, magnetic and thermal behavior, morphology and particle size of Fe₃O₄@PMO/SB-Pd were investigated by using FT-IR, TGA, EDX, VSM, PXRD, TEM and Scanning electron microscopy (SEM) analyses. The Fe₃O₄@PMO/SB-Pd nanocomposite was applied as an efficient nanocatalyst in the Suzuki reaction under ultrasonic conditions giving corresponding products in high yield. Some advantages of this study are simple purification of products, the use of water solvent, easy catalyst separation, short reaction time and high catalyst efficiency and recoverability.

Supported copper on a diamide-diacid-bridged PMO: an efficient hybrid catalyst for the cascade oxidation of benzyl alcohols/Knoevenagel condensation

In this study, a novel periodic mesoporous organosilica (PMO) containing diamide-diacid bridges was conveniently prepared using ethylenediaminetetraacetic dianhydride to support Cu(ii) species and affording supramolecular Cu@EDTAD-PMO nanoparticles efficiently. Fourier transform infrared (FT-IR) and energy dispersive X-ray (EDX) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller (BET) analysis, and high-resolution transmission electron microscopy (HRTEM) results confirmed the successful synthesis of Cu@EDTAD-PMO. The stabilized Cu(ii) nanoparticles inside the mesochannels of the new PMO provided appropriate sites for selective oxidation of different benzyl alcohol derivatives to their corresponding benzaldehydes and subsequent Knoevenagel condensation with malononitrile. Therefore, Cu@EDTAD-PMO can be considered as a multifunctional heterogeneous catalyst, which is prepared easily through a green procedure and demonstrates appropriate stability with almost no leaching of the Cu(ii) nanoparticles into the reaction medium, and easy recovery through simple filtration. The recycled Cu@EDTAD-PMO was reused up to five times without significant loss of its catalytic activity. The stability, recoverability, and reusability of the designed heterogeneous catalyst were also studied under various reaction conditions.

Recent advanced development of metal-loaded mesoporous organosilicas as catalytic nanoreactors

Ordered periodic mesoporous organosilicas have been widely applied in adsorption/separation/sensor technologies and the fields of biomedicine/biotechnology as well as catalysis. Crucially, surface modification with functional groups and metal complexes or nanoparticle loading has ensured high efficacy and efficiency. This review will highlight the current state of design and catalytic application of transition metal-loaded mesoporous organosilica nanoreactors. It will outline prominent synthesis approaches for the grafting of metal complexes, metal salt adsorption and in situ preparation of metal nanoparticles, and summarize the catalytic performance of the resulting mesoporous organosilica hybrid materials. Finally, the potential prospects and challenges of metal-loaded mesoporous organosilica nanoreactors are addressed.

Synergistic catalysis within core-shell Fe3O4@SiO2 functionalized with triethylene glycol (TEG)-imidazolium ionic liquid and tetramethylpiperidine N-oxyl (TEMPO) boosting selective aerobic oxidation of alcohols

HYPOTHESIS

It is expected that incorporation of 2, 2, 6, 6-tetra-methyl piperidine-N-oxyl radical (TEMPO) and an imidazolium bromide bearing hydrophilic triethylene glycol (TEG) groups on Fe₃O₄@SiO₂ core-shell may not only result in a novel highly water-dispersible/magnetically separable multi-functional catalyst system for metal-free aerobic oxidation of alcohols, which operates through a synergistic relay pathway, but it could potentially provide a strong platform for simultaneous separation and recycling of all components.

EXPERIMENTS

The catalyst was prepared by anchoring TEMPO moieties onto a magnetic core-shell Fe₃O₄@SiO₂ functionalized with an ionic liquid bearing TEG groups. The materials was characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption isotherms, thermal gravimetric analysis, and elemental analysis. The performance of the catalyst was evaluated and quantitatively measured in the aerobic oxidation of alcohols in water.

FINDINGS

The catalyst exhibited excellent and stable colloidal dispersion in water and high performance in the aerobic oxidation of various types of alcohols under metal- and halogen-free reaction conditions. As hypothesized, strong synergistic effect between functionalized components was seen in the described reaction. The catalyst displayed excellent dual-adjustable-selectivity in the oxidation of primary alcohols to either the corresponding aldehydes or carboxylic acids by tuning the reaction solvent and/or reaction time and excellent recycling behavior through a "double-separation-strategy".

Imidazolium-based mesoporous organosilicas with bridging organic groups for microextraction by packed sorbent of phenoxy acid herbicides, polycyclic aromatic hydrocarbons and chlorophenols

The authors describe the preparation of two kinds of periodic mesoporous organosilicas (PMOs). The first kind is monofunctional and has a bridged alkyl imidazolium framework (PMO-IL). The other is a two-dimensional (2D) hexagonal bifunctional periodic mesoporous organosilica (BFPMO) with bridged IL-phenyl or -ethyl units. The CPMOs were utilized as highly sensitive and stable sorbents for microextraction by packed sorbent. The materials were characterized by SEM, TEM, FT-IR, and N₂ adsorption-desorption analysis. The adsorption capacities of the sorbents were investigated by using phenoxy acid herbicides as model analytes. The effects of bifunctionality and type of additional surface groups (phenyl or ethyl) on the efficiency of the extraction is emphasized. Three kinds of environmental contaminants, viz. phenoxy acid herbicides (CPAs), polycyclic aromatic hydrocarbons and chlorophenols were then studied with respect to their extraction by the sorbents. The interactions between the CPAs and the sorbents were evaluated by pH-changing processes to explore the interactions that play a major role. The selectivity of the sorbents was investigated by extraction of other types of analytes of with various polarity and charge. The BFPMOs display the typical good chemical stability of silica materials. The extraction properties are much better compared to commercial silicas. This is assumed to be due to the highly ordered mesoporous structures and the different types of probable interactions with analytes. The performance of the method was evaluated by extraction of CPAs as model analytes from aqueous samples, and quantification by GC with FID detection. Under optimized conditions, low limits of detection (0.1-0.5 μg.L^-1) and a wide linearity (0.5-200 μg.L^-1) were obtained. The method was applied to the trace analysis of CPAs in farm waters and rice samples. Graphical abstract Monofunctional periodic mesoporous organosilica with bridged alkyl imidazolium frameworks and bi-functional periodic mesoporous organosilica containing bridged ionic liquids and phenyl or -ethyl, have been successfully synthesized and utilized in microextractions by packed sorbent sorbents.

Fabrication and catalytic properties of ordered cyclopalladated diimine monolayer : investigation on catalytic mechanism

"Channel-like" self-assembled monolayers having aliphatic and aromatic diimines (denoted as Si@1DIS, Si@2DIS and Si@3DIS) immobilized on substrates and their palladacycle monolayers (Si@1DIS-Pd, Si@2DIS-Pd and Si@3DIS-Pd) were prepared and characterized. Their catalytic performances were investigated using the Suzuki coupling reaction as a model. Si@3DIS-Pd showed the highest catalytic activity in water without ligands, and better recyclability than that of Si@2DIS-Pd and Si@1DIS-Pd. The reason was the carbon in the aliphatic diimine of Si@2DIS-Pd and Si@1DIS-Pd was easily hydrolyzed because of the active hydrogen of α-C, resulting in poor recyclability. Control of the amount of catalyst could be achieved by modulating the diameter of the channel-like structure, which also affected the catalytic activity. The catalytic process and mechanism were investigated systematically and proposed based on the experimental results obtained by the water contact angle, ultraviolet spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry and atomic force spectroscopy. Changes in the morphology of monolayer surfaces during the catalytic process with or without stirring presented a clear process from order to disorder, and indicated that the reaction was a heterogeneous catalytic process occurring on the surface of the catalyst monolayer.

Nickel containing ionic liquid based ordered nanoporous organosilica: a powerful and recoverable catalyst for synthesis of polyhydroquinolines

The synthesis, characterization and catalytic application of a novel nickel containing ionic liquid based ordered mesoporous organosilica are demonstrated.

An Fe3O4@P4VP@FeCl3 core–shell heterogeneous catalyst for aerobic oxidation of alcohols and benzylic oxidation reaction

A novel Fe₃O₄@P4VP@FeCl₃ core–shell catalyst has been developed through coordination interaction between P4VP and FeCl₃, which was utilized in selective oxidation of alcohols using molecular oxygen as the oxidant.

Amine-functionalized ionic liquid-based mesoporous organosilica as a highly efficient nanocatalyst for the Knoevenagel condensation

A novel aminopropyl-containing ionic liquid-based mesoporous organosilica was prepared and characterized and its catalytic performance was studied in the Knoevenagel condensation.

Synergistic catalysis within TEMPO-functionalized periodic mesoporous organosilica with bridge imidazolium groups in the aerobic oxidation of alcohols

Anchoring TEMPO within the nanospaces of a PMO with bridged imidazolium groups led to an powerful bifunctional catalyst (TEMPO@PMO-IL-Br), which showed enhanced activity in the metal-free aerobic oxidation of alcohols.

Rice husk derived nanosilica supported Cu(ii) complex: an efficient heterogeneous catalyst for oxidation of alcohols using TBHP

We have developed a heterogenized catalyst of Cu(ii) complex immobilized onto nanosilica obtained from rice husk (RH), through Schiff-base condensation between 3-aminopropyltriethoxysilane (APTES) functionalized nanosilica and acetamide.

A novel iron(iii)-based heterogeneous catalyst for aqueous oxidation of alcohols using molecular oxygen

The first example of an iron(iii)-based heterogeneous catalyst for alcohol oxidation reactions in water employing molecular oxygen has been reported. Interestingly, the immobilized catalyst shows superior activity over its homogeneous counterpart.

Periodic mesoporous organosilica with ionic-liquid framework supported manganese: an efficient and recyclable nanocatalyst for the unsymmetric Hantzsch reaction

We have described the catalytic application of a manganese containing ionic liquid-based ordered mesoporous organosilica in the synthesis of polyhydroquinolines.

Recent advances in hybrid periodic mesostructured organosilica materials: opportunities from fundamental to biomedical applications

Periodic mesoporous organosilica nanostructures functionalized with various active functional groups: from design to biomedical applications.