Magnetically Separable Nanocatalysts: Bridges between Homogeneous and Heterogeneous Catalysis

Sonochemical synthesis of versatile hydrophilic magnetite nanoparticles

Hydrophilic magnetite nanoparticles in the size range 30-10nm are easily and rapidly prepared under ultrasonic irradiation of Fe(OH)(2) in di- and tri-ethylene glycol/water solution with volume ratio varying between 7:3 and 3:7. Structural (XRD) and morphological (SEM) characterization reveal good crystalline and homogeneous particles whereas, when solvothermally prepared, the particles are inhomogeneous and aggregated. The sonochemically prepared particles are versatile, i.e. well suited to covalently bind molecules because of the free glycol hydroxylic groups on their surface or exchange the diethylene or triethylene glycol ligand. They can be easily transferred in hydrophobic solvents too. Room-temperature magnetic hysteresis properties measured by means of Vibrating Sample Magnetometer (VSM) display a nearly superparamagnetic character. The sonochemical preparation is easily scalable to meet industrial demand.

One-pot, three-component synthesis of a library of spirooxindole-pyrimidines catalyzed by magnetic nanoparticle supported dodecyl benzenesulfonic acid in aqueous media

Dodecyl benzenesulfonic acid functionalized silica-coated magnetic nanoparticles (γ-Fe2O3@SiO2-DDBSA) were readily prepared and identified as an efficient catalyst for the synthesis of a library of spirooxindole-pyrimidine derivatives by three-component condensation reaction of barbituric acids, isatins and cyclohexane-1,3-diones. The aqueous reaction medium, easy recovery of the catalyst using an external magnet, and high yields make the protocol sustainable and economic.

Recent progress on metal core@semiconductor shell nanocomposites as a promising type of photocatalyst

The creation of core-shell nanocomposites (CSNs) has attracted considerable attention and developed into an increasingly important research area at the frontier of advanced materials chemistry. CSNs, which are nanoscaled assemblies with a chemical composition that is different on the surface compared to the core region, have found versatile applications in many fields, such as electrooptics, quantum dots, microscopy labels, drug delivery, chemical sensors, nanoreactors and catalysis. This review is primarily focused on the applications of metal core@semiconductor shell nanocomposites in heterogeneous photocatalysis, including photocatalytic nonselective processes for environmental remediation, selective organic transformations to fine chemicals and water splitting to clean hydrogen energy. It is hoped that this minireview can inspire multidisciplinary research interest in the precisely morphology-controlled synthesis of a variety of metal core@semiconductor shell nanoassemblies and their wide applications in the realm of heterogeneous photocatalysis.

Reversible clustering of magnetic nanobiocatalysts for high-performance biocatalysis and easy catalyst recycling

Reversible clusters of nanobiocatalysts are developed via non-covalent interaction among enzyme-bound iron oxide magnetic nanoparticles. Dissociation of the clusters by shaking during biotransformation enables high catalytic performance, and re-clustering by stopping shaking after reaction allows for easy magnetic separation. The novel concept is demonstrated with alcohol dehydrogenase RDR for the enantioselective reduction of 7-methoxy-2-tetralone.

Graphite-coated magnetic nanoparticle microarray for few-cells enrichment and detection

Graphite-coated, highly magnetic FeCo core-shell nanoparticles were synthesized by a chemical vapor deposition method and solubilized in aqueous solution through a unique polymer mixture modification, which significantly improved the biocompatibility and stability of the magnetic nanoparticles (MNPs). Such functionalized MNPs were proven to be very stable in different conditions which would be significant for biological applications. Cell staining, manipulation, enrichment, and detection were developed with these MNPs. Under external magnetic manipulation, the MNP-stained cells exhibited directed motions. Moreover, MNPs were printed on substrates to modulate the magnetic field distribution on the surface. Capture and detection of sparse populations of cancer cells spiked into whole blood has been explored in a microarray fashion. Cancer cells from hundreds down to only two were able to be simply and efficiently detected from 1 mL of whole blood on the MNP microarray chips. Interestingly, the cells captured through the MNP microarray still showed viability and adhered to the MNP spots after incubation, which could be utilized for cancer cell detection, localized growth, and proliferation.

Application of metal-based reagents and catalysts in microstructured flow devices

Over the years, organic synthesis has witnessed several improvements through the development of new chemical transformations or more efficient reagents for known processes. Likewise, technological advances, aiming at speeding up reactions and facilitating their work-up, have established themselves in academic as well as in industrial laboratories. In this Minireview, we highlight very recent developments in flow chemistry, focusing on organometallic reagents and catalysts. First, we describe reactions with homogeneous catalysts immobilized on different support materials using the concept of packed bed reactors. In the last chapter, we will discuss applications that utilize organometallic reagents.

Magnetic nano-Fe3O4-supported 1-benzyl-1,4-dihydronicotinamide (BNAH): synthesis and application in the catalytic reduction of α,β-epoxy ketones

A novel magnetically recoverable organic hydride compound was successfully constructed by using silica-coated magnetic nanoparticles as a support. An as-prepared magnetic organic hydride compound, BNAH (1-benzyl-1,4-dihydronicotinamide), showed efficient activity in the catalytic reduction of α,β-epoxy ketones. After reaction, the magnetic nanoparticle-supported BNAH can be separated by simple magnetic separation which made the separation of the product easier.

Nanocatalysis and prospects of green chemistry

Designing and developing ideal catalyst paves the way to green chemistry. The fields of catalysis and nanoscience have been inextricably linked to each other for a long time. Thanks to the recent advances in characterization techniques, the old technology has been revisited with a new scope. The last decade has witnessed a flood of research activity in the field of nanocatalysis, with most of the studies focusing on the effect of size on catalytic properties. This led to the development of much greener catalysts with higher activity, selectivity and greater ease of separation from the reaction medium. This Minireview describes the emerging trends in the field of nanocatalysis with implications towards green chemistry and sustainability.

Superparamagnetic plasmonic nanohybrids: shape-controlled synthesis, TEM-induced structure evolution, and efficient sunlight-driven inactivation of bacteria

Magnetic materials and noble metal-based multifunctional hybrids have attracted much attention recently due to their unique properties and potential applications in a variety of fields. However, substantial challenges remain to directly obtain water-soluble hybrids with well-defined structures and to directly combine magnetic nanoparticles with nonspherical noble metals. We describe here for the first time a simple solvothermal method to synthesize a series of novel water-soluble nanohybrids composed of shape-tuned Ag cores and a Fe(3)O(4) shell. We found that small Fe(3)O(4) grains can be well-distributed directly on the surface on the Ag seeds. Such hybrids have both plasmonic and significant superparamagnetic properties, enabling magnetic separation. The plasmon resonance frequency of Ag nanostructures can be fine-tuned through the interactions between the two components. In addition, the decorated Fe(3)O(4) nanoparticles stabilized the Ag nanostructures when exposed to air and natural light for a long time. Furthermore, an interesting structural transformation is observed in the one-dimensional Ag-Fe(3)O(4) nanowires under high-energy electron beam. The Ag core can diffuse through the porous iron oxide shell, break away, and result in the formation of Ag nanocluster-decorated iron oxide tubes. Finally, the hybrids acted as a chemical template for the synthesis of Fe(3)O(4)/Au-AgCl double-layer nanotubes that display obvious near-infrared absorption. Importantly, the double-layer nanotubes exhibited enhanced photocatalytic inactivation of bacteria at very low concentrations under natural sunlight.