Molecular nanoparticles

R. Signorell, M. K. Kunzmann, and M. A. Suhm, FTIR investigation of non volatile molecular nanoparticles. Chem. Phys. Lett. 329, 52 60 (2000). 

Third, the notion (and reality) of such structural infractions as twins and coherent intergrowths - as is seen by Yacaman et al. in a 923-atom nanoalloy of AuPd [35] - is meaningless in our molecular bimetallic nanoparticles. In the nanoaUoys of Yacaman et al. [35, 42] and others [43], one may discern directly, by aberration-corrected electronic microscopy, thin bands of hexagonal close-packed and face-centered cubic packed sheets. In a typical molecular nanoparticle of the kind that we have studied (also by aberration-corrected electron microscopy [39]), it is directly established (in line with theoretical predictions [44]) that a single bimetallic cluster of RUj Pt does indeed possess molecular character. Furthermore, when six or more such clusters coalesce into larger entities containing ca 200 atoms they adopt the regular crystalline, and faceted state of a bulk metal. 

An example is provided by mixed matrix membranes (MMM). Basically they are constituted of inorganic molecular nanoparticles (such as zeolites, carbon molecular sieves, etc.) imbedded in polymers. MMMs open up new perspectives in gas separation. A main application for sustainable development is the purification of... 

Fig. 13.11 Hyperbranched polyglycidol as a molecular nanoparticle, with its core/shell topology.

The recent progress in polymer synthesis and nanotechnology is stimulating the development of adhesives with improved performance. A few percent of nanometer-scale additives can be added to formulations in order to achieve significant changes in property profiles. Molecular nanoparticles and nanometer-scale, highly branched polymers can be dispersed in order to facilitate energy dissipation at the crack tip by means of multiple plastic deformation. The self assembly of nanoparticles forms skeleton-like superstructures which account for... 

This method can be used to make large templates and supra-molecular nanoparticles for multi-functional CND fabrication. 

FIGURE 9.48 Self-assembly of M]2L24 molecular nanoparticles 60 with 24 MMA units. 

Current synthesis techniques provide an unprecedented level of control over nanoparticle shape and composition, resulting in an almost limitless catalog of nanoparticles with varying geometry and interactions.Examples of different shapes include spheres, rods, cubes and other polyhedra, plates, ° and multipods, along with molecular nanoparticles such as carbon fullerenes, porphyrin squares, polyhedral oligomeric silsesquioxane (POSS)... 

This novel reaction paves the way towards the synthesis of polyfunctionalized borane clusters (closomers) bearing large organic groups attached to the B12 core. With diameters greater than 1 nm, these novel compounds can be considered true molecular nanoparticles. We discuss them in detail later on in this chapter. Further information on the preparation and reactivity of borane compounds can be found in the more specialized chemistry literature [6]. 

Polyhedral heterocarborane clusters are promising materials for nanotechnology. This is evident from the interesting applications discussed in this chapter, which include molecular nanoparticles, nanomedicines, and molecular-scale machines and devices. The use of carboranes as building blocks in the computational design of nanostructured materials remains open to novel discoveries that will be possible only by pursuing further research in this fascinating area of molecular chemistry. 

Clusters are intennediates bridging the properties of the atoms and the bulk. They can be viewed as novel molecules, but different from ordinary molecules, in that they can have various compositions and multiple shapes. Bare clusters are usually quite reactive and unstable against aggregation and have to be studied in vacuum or inert matrices. Interest in clusters comes from a wide range of fields. Clusters are used as models to investigate surface and bulk properties [2]. Since most catalysts are dispersed metal particles [3], isolated clusters provide ideal systems to understand catalytic mechanisms. The versatility of their shapes and compositions make clusters novel molecular systems to extend our concept of chemical bonding, stmcture and dynamics. Stable clusters or passivated clusters can be used as building blocks for new materials or new electronic devices [4] and this aspect has now led to a whole new direction of research into nanoparticles and quantum dots (see chapter C2.17). As the size of electronic devices approaches ever smaller dimensions [5], the new chemical and physical properties of clusters will be relevant to the future of the electronics industry. 

Possible applications of MIP membranes are in the field of sensor systems and separation technology. With respect to MIP membrane-based sensors, selective ligand binding to the membrane or selective permeation through the membrane can be used for the generation of a specific signal. Practical chiral separation by MIP membranes still faces reproducibility problems in the preparation methods, as well as mass transfer limitations inside the membrane. To overcome mass transfer limitations, MIP nanoparticles embedded in liquid membranes could be an alternative approach to develop chiral membrane separation by molecular imprinting [44]. 

In the transmission electron microscopy (TEM) images, the starch nanoplatelets (SNPs) are believed to aggregate as a result of hydrogen bond interactions due to the surface hydroxyl groups [13] (Fig. lA). Blocking these interactions by relatively large molecular weight molecules obviously improves the individualization of the nanoparticles. The acetylated starch and cellulose nanoparticles (SAcNPs and CelAcNPs) appeared more individualized and monodispersed than their unmodified counterparts with a size of about 50 nm (Fig. IB C). 

Due to particles extrusion, crystal lattice deformation expands to the adjacent area, though the deformation strength reduces gradually (Figs. 10(a)-10(other hand, after impacting, the particle may retain to plow the surface for a short distance to exhaust the kinetic energy of the particle. As a result, parts of the free atoms break apart from the substrate and pile up as atom clusters before the particle. The observation is consistent with results of molecular dynamics simulation of the nanometric cutting of silicon [15] and collision of the nanoparticle with the solid surface [16]. 

This reduction can also be carried out with molecular hydrogen and as such is probably not of any commercial interest. However, it is suited for the study of the catalytic properties of the ultrafine powders and serves as a characterization and optimization technique for the titanium nitride nanoparticles in this study. 

Recent advances of the Seeman group led to the construction of a nanomechanical device from DNA [89]. In this molecular apparatus, the ion-dependent transition of B-DNA into the Z-conformation is used to alter the distance between two DNA DX domains attached to the switchable double helix. Atomic displacements of about 2-6 nm were attained. Ionic switching of nanoparticles by means of DNA supercoiling has also been reported [53]. Additional advances regarding the use of DNA is nanomechanical devices have been reported by Fritz et al., who showed that an array of cantilevers can be used to... 

The sacrificial core approach entails depositing a coating on the surface of particles by either the controlled surface precipitation of inorganic molecular precursors from solution or by direct surface reactions [2,3,5,6,8,9,33-35,38], followed by removal of the core by thermal or chemical means. Using this approach, micron-size hollow capsules of yttrium compounds [2], silica spheres [38], and monodisperse hollow silica nanoparticles [3,35] have been generated. 

The application of ly transition metal carbides as effective substitutes for the more expensive noble metals in a variety of reactions has hem demonstrated in several studies [ 1 -2]. Conventional pr aration route via high temperature (>1200K) oxide carburization using methane is, however, poorly understood. This study deals with the synthesis of supported tungsten carbide nanoparticles via the relatively low-tempoatine propane carburization of the precursor metal sulphide, hi order to optimize the carbide catalyst propertira at the molecular level, we have undertaken a detailed examination of hotii solid-state carburization conditions and gas phase kinetics so as to understand the connectivity between plmse kinetic parametera and catalytically-important intrinsic attributes of the nanoparticle catalyst system. 

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