Catalytic nanoparticles and magnetic nanocatalysts in organic reactions: A mini review

Nanocatalysts, as a part of nanotechnology, have been seen very useful for various fileds of applications capturing a large contribution of the world market. Indeed, several unsolved issues of catalysts have been reconsidered by employing the new nanocatalysts including single core metal atoms and ions with surrounding holes. Moreover, it was expected that the future of catalytic reactions, especially those organic ones, will deal with the nanocatalyst applications. To this aim, the features of catalytic nanoparticles and magnetic nanocatalysts regarding evaluation of their advantages and applications in organic reactions were investigated in this work. Developments of catalytic nanoparticles and magnetic nanocatalysts were discussed in this work regarding the novel applications of such materials at the nanoscale for approaching advantageous features. Increased availability, activity, and stability are very important for applications of the catalysts in various organic reactions. Therefore, it is a must to discuss features of such nanocatalytic systems to provide more information about their advantages and even disadvantages of their applications.

Catalysis by Metallic Nanoparticles in Solution: Thermosensitive Microgels as Nanoreactors

Metallic nanoparticles have been used as catalysts for various reactions, and the huge literature on the subject is hard to overlook. In many applications, the nanoparticles must be affixed to a colloidal carrier for easy handling during catalysis. These “passive carriers” (e.g. dendrimers) serve for a controlled synthesis of the nanoparticles and prevent coagulation during catalysis. Recently, hybrids from nanoparticles and polymers have been developed that allow us to change the catalytic activity of the nanoparticles by external triggers. In particular, single nanoparticles embedded in a thermosensitive network made from poly(N-isopropylacrylamide) (PNIPAM) have become the most-studied examples of such hybrids: immersed in cold water, the PNIPAM network is hydrophilic and fully swollen. In this state, hydrophilic substrates can diffuse easily through the network, and react at the surface of the nanoparticles. Above the volume transition located at 32°C, the network becomes hydrophobic and shrinks. Now hydrophobic substrates will preferably diffuse through the network and react with other substrates in the reaction catalyzed by the enclosed nanoparticle. Such “active carriers”, may thus be viewed as true nanoreactors that open new ways for the use of nanoparticles in catalysis. In this review, we give a survey on recent work done on these hybrids and their application in catalysis. The aim of this review is threefold: we first review hybrid systems composed of nanoparticles and thermosensitive networks and compare these “active carriers” to other colloidal and polymeric carriers (e.g. dendrimers). In a second step we discuss the model reactions used to obtain precise kinetic data on the catalytic activity of nanoparticles in various carriers and environments. These kinetic data allow us to present a fully quantitative comparison of different nanoreactors. In a final section we shall present the salient points of recent efforts in the theoretical modeling of these nanoreactors. By accounting for the presence of a free-energy landscape for the reactants’ diffusive approach towards the catalytic nanoparticle, arising from solvent-reactant and polymeric shell-reactant interactions, these models are capable of explaining the emergence of all the important features observed so far in studies of nanoreactors. The present survey also suggests that such models may be used for the design of future carrier systems adapted to a given reaction and solvent.

CO2-switchable polymer-hybrid silver nanoparticles and their gas-tunable catalytic activity

A new type CO₂-switchable AgNPs hybrids show switchable and monotonous tunable catalytic activity for the reduction of 4-nitrophenol by varying the flow rate of CO₂purged into the reaction system.

Carbon-Doped Hollow Titania with Tuneable Shell Architecture for Supercapacitors

A new trend in supercapacitor research has focussed on the construction of inexpensive electrode materials with high capacitor performances. In this study, we demonstrate the successful preparation of carbon-doped hollow titania spheres. The as-prepared titania spheres not only exhibit an advantage over existing methods because they are created in situ by directly carbonizing cationic polystyrene templates without the addition of carbon precursors, but also feature a narrow pore size distribution and a tuneable shell architecture. When the materials were applied as supercapacitor anodes, the electrochemical results reveal the superior performances of the supercapacitors over that of commercial P25. The higher performances were attributed to carbon doping. Thus, the reported C-doped hollow titania shows more potential as electrode materials for high-performance supercapacitors.

Switchable polymer reactor composed of mussel-inspired polymer that contains Au nanoparticles

A novel polymer reactor capable of adapting to switch in aqueous media was presented. Consisting of a mussel-inspired polymer and Au nanoparticles, this polymer reactor shows a promising prospect for tunable catalysis occurring in aqueous media.