Magnetisch abtrennbare Nanokatalysatoren: Brücken zwischen homogener und heterogener Katalyse

Synthesis of small-sized, porous, and low-toxic magnetite nanoparticles by thin POSS silica coating

In this communication, we report the synthesis of small-sized (<10 nm), water-soluble, magnetic nanoparticles (MNPs) coated with polyhedral oligomeric silsesquioxanes (POSS), which contain either polyethylene glycol (PEG) or octa(tetramethylammonium) (OctaTMA) as functional groups. The POSS-coated MNPs exhibit superparamagnetic behavior with saturation magnetic moments (51-53 emu g(-1)) comparable to silica-coated MNPs. They also provide good colloidal stability at different pH and salt concentrations, and low cytotoxicity to MCF-7 human breast epithelial cells. The relaxivity data and magnetic resonance (MR) phantom images demonstrate the potential application of these MNPs in bioimaging.

Highly efficient degradation of organic dyes by palladium nanoparticles decorated on 2D magnetic reduced graphene oxide nanosheets

We report a novel and effective strategy to synthesize Pd/Fe₃O₄-PEI-RGO nanohybrids for highly efficient degradation of organic dyes.

Recycling nanoparticle catalysts without separation based on a pickering emulsion/organic biphasic system

A conceptually novel methodology is explored for in situ recycling of nanoparticle catalysts based on transforming a conventional organic/aqueous biphasic system into a Pickering emulsion/organic biphasic system (PEOBS). The suggested PEOBS exists as two phases, with the nanoparticle catalyst "anchored" in the Pickering emulsion phase, but is "continuous" between the organic phase and the continuous phase of the Pickering emulsion. Aqueous hydrogenations are used to evaluate the reaction performances of PEOBS, and the underlying principles of PEOBS are preliminarily elaborated. The unique properties of PEOBS lead to many intriguing findings, which are unlikely to be achieved in the reported biphasic systems. PEOBS exhibits more than a fourfold enhancement in catalysis efficiency in comparison with a conventional biphasic system. Impressively, PEOBS enables the organic product to be facilely isolated through simple decantation and the nanoparticle catalyst can be recycled in situ without the need for "separation". Its recycling effectiveness is justified by ten reaction cycles without significant catalyst loss. The simple protocol, in conjunction with the stability to simultaneously achieve high catalysis efficiency and excellent catalyst recyclability, makes PEOBS a promising methodology to develop more sustainable nanocatalysis.

Pickering-emulsion inversion strategy for separating and recycling nanoparticle catalysts

With the recent advances in nanoscience and nanotechnology, more and more nanoparticle catalysts featuring high accessibility of active sites and high surface area have been explored for their use in various chemical transformations, and their rise in popularity among the catalysis community has been unprecedented. The industrial applications of these newly discovered catalysts, however, are hampered because the existing methods for separation and recycling, such as filtration and centrifugation, are generally unsuccessful. These limitations have prompted development of new methods that facilitate separation and recycling of nanoparticle catalysts, so as to meet the burgeoning demands of green and sustainable chemistry. Recently, we have found that Pickering-emulsion inversion is an appealing strategy with which to realize in situ separation and recycling of nanoparticle catalysts and thereby to establish sustainable catalytic processes. We feel that at such an early stage, this strategy, as an alternative to conventional methods, is conceptually new for readers but that it has potential to become a popular method for green catalysis. This Concept article aims to provide a timely link between previous efforts and both current and future research on nanoparticle catalysts, and is expected to facilitate further investigation into this strategy.

Pd/C as a catalyst for completely regioselective C-H functionalization of thiophenes under mild conditions

The completely C3-selective arylation of thiophenes and benzo[b]thiophenes was achieved by using Pd/C as a heterogeneous catalyst without ligands or additives under mild reaction conditions. The practicability of this transformation is demonstrated by notable functional group tolerance and the insensitivity of the reaction to H2 O and air. This method is also applicable to nitrogen- and oxygen-containing heterocycles, yielding the corresponding C2-arylated products. Three-phase tests along with Hg-poisoning and hot-filtration tests suggest that the catalytically active species is heterogeneous in nature.

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.