Magnetically Separable Nanocatalysts: Bridges between Homogeneous and Heterogeneous Catalysis

Heterogenization of heteropoly compounds: a review of their structure and synthesis

The heterogenization of different types of heteropoly compoundsviasix popular methods from those published over the past recent 15 years is reviewed.

Application of biological-based nano and nano magnetic catalysts in the preparation of arylbispyranylmethanes

Nano 2-carbamoylhydrazine-1-sulfonic acid, carbamoylsulfamic acid and their related nano magnetic core–shell catalysts as biological-based nano catalysts with a urea moiety were used in the synthesis of arylbispyranylmethanes.

Novel magnetic nanoparticles with ionic liquid tags as a reusable catalyst in the synthesis of polyhydroquinolines

{Fe₃O₄@SiO₂@(CH₂)₃Im}C(NO₂)₃ as a novel nanostructured heterogeneous reusable catalyst was used for the four component preparation of the polyhydroquinoline derivatives under mild and eco-friendly reaction conditions.

Synthesis and characterization of functionalized titania-supported Pd catalyst deriving from new orthopalladated complex of benzophenone imine: catalytic activity in the copper-free Sonogashira cross-coupling reactions at low palladium loadings

Efficient catalytic activity of TiO₂-supported Pd catalyst in the copper, amine and phosphine free Sonogashira cross-coupling reactions at low Pd-loadings.

The first report on the preparation of boehmite silica sulfuric acid and its applications in some multicomponent organic reactions

Boehmite silica sulfuric acid was prepared at room temperature using commercially available materials and applied as a nanocatalyst for the preparation of DHQs and PHQs.

CuFe2O4 magnetic nanoparticle catalyzed odorless synthesis of sulfides using phenylboronic acid and aryl halides in the presence of S8

The ligand-free synthesis of sulfides is reported in the presence of CuFe₂O₄ as a magnetically reusable nanocatalyst in PEG.

PtCo bimetallic nanoparticles with high oxidase-like catalytic activity and their applications for magnetic-enhanced colorimetric biosensing

A novel magnetic-enhanced colorimetric assay was constructed based on aptamer conjugated PtCo bimetallic nanoparticles with high oxidase-like catalytic activity, high water solubility, low cell toxicity, and superparamagnetic properties.

Proof of Concept: Magnetic Fixation of Dendron-Functionalized Iron Oxide Nanoparticles Containing Palladium Nanoparticles for Continuous-Flow Suzuki Coupling Reactions

A new concept for the magnetic immobilization of catalytically active material has been developed for continuous-flow Suzuki cross-coupling reactions. The reversible immobilization of the magnetic catalyst material inside a novel capillary microreactor has been achieved by utilizing a newly designed reactor housing with 208 small permanent magnets. As a catalyst material, magnetic Fe3O4 nanoparticles decorated with polyphenylenepyridyl dendrons and loaded with Pd nanoparticles have been employed. Both batch and continuous-flow experiments prove the activity of the catalyst and the applicability of this new microreactor concept.

Carbon for engineering of a water-oxidizing catalyst

Herein we report that the reaction of KMnO4 with cobalt nanoparticles coated with multiple graphene layers forms a promising catalyst toward water oxidation. The compound was characterized by scanning electron microscopy, energy-dispersive spectroscopy, high resolution transmission electron microscopy, X-ray diffraction, electronic spectroscopy, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy. In addition to the Mn oxide-based characteristics of the catalyst, it is a conductive, self-healing, recycling, highly dispersible, magnetically separable, environmentally friendly, and nano-sized catalyst for water oxidation. The turnover frequency for the catalyst toward water oxidation is 0.1 and 0.05 (mmol O2 per mol Mn s) in the presence of cerium(iv) ammonium nitrate and photo-produced Ru(bpy)3(3+).

Magnetic and dendritic catalysts

The recovery and reuse of catalysts is a major challenge in the development of sustainable chemical processes. Two methods at the frontier between homogeneous and heterogeneous catalysis have recently emerged for addressing this problem: loading the catalyst onto a dendrimer or onto a magnetic nanoparticle. In this Account, we describe representative examples of these two methods, primarily from our research group, and compare them. We then describe new chemistry that combines the benefits of these two methods of catalysis. Classic dendritic catalysis has involved either attaching the catalyst covalently at the branch termini or within the dendrimer core. We have used chelating pyridyltriazole ligands to insolubilize catalysts at the termini of dendrimers, providing an efficient, recyclable heterogeneous catalysts. With the addition of dendritic unimolecular micelles olefin metathesis reactions catalyzed by commercial Grubbs-type ruthenium-benzylidene complexes in water required unusually low amounts of catalyst. When such dendritic micelles include intradendritic ligands, both the micellar effect and ligand acceleration promote faster catalysis in water. With these types of catalysts, we could carry out azide alkyne cycloaddition ("click") chemistry with only ppm amounts of CuSO4·5H2O and sodium ascorbate under ambient conditions. Alternatively we can attach catalysts to the surface of superparamagnetic iron oxide nanoparticles (SPIONs), essentially magnetite (Fe3O4) or maghemite (γ-Fe2O3), offering the opportunity to recover the catalysts using magnets. Taking advantage of the merits of both of these strategies, we and others have developed a new generation of recyclable catalysts: dendritic magnetically recoverable catalysts. In particular, some of our catalysts with a γ-Fe2O3@SiO2 core and 1,2,3-triazole tethers and loaded with Pd nanoparticles generate strong positive dendritic effects with respect to ligand loading, catalyst loading, catalytic activity and recyclability. In other words, the dendritic catalysts were more efficient and more stable than their nondendritic γ-Fe2O3@SiO2 analogues. The bulk at the dendritic periphery helps to localize the metal nanoparticles at the SPION core surface, which confers these advantages. We could also use sonification as a remarkably simple and efficient method to impregnate the SPIONs with dendrimer-encapsulated PdNPs. Catalysis within the hydrophobic dendrimer pockets that include ligands leads to rapid turnover with or without a γ-Fe2O3@SiO2 core. In addition, catalytically active metal nanoparticles are more robust when they are loaded onto the surface of a γ-Fe2O3@SiO2 dendritic core. Herein, we illustrate this chemistry with examples including olefin metathesis, click chemistry, cross carbon-carbon bond forming reactions, and selective alcohol oxidation.

Recent Progress on Transition Metal Catalyst Separation and Recycling in ATRP

Atom transfer radical polymerization (ATRP) is a versatile and robust tool to synthesize a wide spectrum of monomers with various designable structures. However, it usually needs large amounts of transition metal as the catalyst to mediate the equilibrium between the dormant and propagating species. Unfortunately, the catalyst residue may contaminate or color the resultant polymers, which limits its application, especially in biomedical and electronic materials. How to efficiently and economically remove or reduce the catalyst residue from its products is a challenging and encouraging task. Herein, recent advances in catalyst separation and recycling are highlighted with a focus on (1) highly active ppm level transition metal or metal free catalyzed ATRP; (2) post-purification method; (3) various soluble, insoluble, immobilized/soluble, and reversible supported catalyst systems; and (4) liquid-liquid biphasic catalyzed systems, especially thermo-regulated catalysis systems.

Nanocrystal TiO₂ Engulfed SiO₂-Barium Hexaferrite for Enhanced Electrons Mobility and Solar Harvesting Potential

Barium hexaferrite embedded-silica-titania photocatalyst (TiO2-SiO2-BaFe12O19) was synthesized through sol-gel, liquid catalytic phase transformation and solid reaction routes. The magnetic photocatalyst was aimed to harvest the photoenergy from the sunlight, minimize the electron-holes recombination rate, improve the long lifetime charge-carriers transfer to maximize the photocatalytic activity and enhances the separation and reusability of it. The as-synthesized photocatalyst was characterized and the photocatalytic activity was evaluated for the reduction of 2, 4-dichlorophenol (2, 4-DCP) under direct sunlight. The presence of SiO2 interlayer in TiO2-SiO2-BaFe12O19 prevents the phase transformation of magnetic core. TiO2-SiO2-BaFe12O19 benefits the magnetic separation with appreciable magnitude of coercivity (5035.6 Oe) and saturation magnetization (18.8256E-3 emu/g), respectively. The ferrite ions from the magnetic core which dispersed into TiO2 matrix exhibited an evident shift of the absorption in the visible region. This was again confirmed with the reduced band gap energy of 1.90 eV. Furthermore, TiO2-SiO2-BaFe12O19 destructed 100% of 2, 4-DCP compound within 150 min under very bright sunlight with an average irradiance of 820.8 W/m2 (results not shown). The embedding of BaFe12O19 with a SiO2 layer onto TiO2 nanocrystals contributed for an excellent solar-light utilization and ease magnetic separation of the nanosized photocatalyst.

Air- and water-resistant noble metal coated ferromagnetic cobalt nanorods

Cobalt nanorods possess ideal magnetic properties for applications requiring magnetically hard nanoparticles. However, their exploitation is undermined by their sensitivity toward oxygen and water, which deteriorates their magnetic properties. The development of a continuous metal shell inert to oxidation could render them stable, opening perspectives not only for already identified applications but also for uses in which contact with air and/or aqueous media is inevitable. However, the direct growth of a conformal noble metal shell on magnetic metals is a challenge. Here, we show that prior treatment of Co nanorods with a tin coordination compound is the crucial step that enables the subsequent growth of a continuous noble metal shell on their surface, rendering them air- and water-resistant, while conserving the monocrystallity, metallicity and the magnetic properties of the Co core. Thus, the as-synthesized core-shell ferromagnetic nanorods combine high magnetization and strong uniaxial magnetic anisotropy, even after exposure to air and water, and hold promise for successful implementation in in vitro biodiagnostics requiring probes of high magnetization and anisotropic shape.

C-H arylation of triphenylene, naphthalene and related arenes using Pd/C

A highly selective arylation of a number of polyaromatic hydrocarbons (PAHs) with aryliodonium salts and Pd/C as the only reagent is reported. The first C-H functionalization of triphenylene is explored, and proceeds at the most sterically hindered position. This non-chelate assisted C-H functionalization extends the reactivity profile of Pd/C and provides controlled access to π-extended PAHs, an important aspect of work towards the preparation of nanographenes. Mechanistic studies suggest in situ formation of catalytically active insoluble nanoparticles, and that the reaction likely proceeds via a Pd(0)/Pd(ii) type reaction manifold.