Nanoparticles electronic properties

Oluwafemi, O. S. and Revaprasadu, N. (2009). Study on Growth Kinetics of Hexadecylamine capped CdSe Nanoparticles using its electronic properties. Physical B Condense matter, 404,1204-1208. 

Size reduction of metal particles results in several changes of the physico-chemical properties. The primary change is observed in the electronic properties of the metal particles which can be characterized by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively) as well as Auger-electron spectroscopy (AES) measurements. Furthermore, morphology of the metal nanoparticles is highly sensitive to the environment, such as ion-metal interaction (e.g. metal-support interaction)... 

In Section 2 the general features of the electronic structure of supported metal nanoparticles are reviewed from both experimental and theoretical point of view. Section 3 gives an introduction to sample preparation. In Section 4 the size-dependent electronic properties of silver nanoparticles are presented as an illustrative example, while in Section 5 correlation is sought between the electronic structure and the catalytic properties of gold nanoparticles, with special emphasis on substrate-related issues. 

Particle size and the method of nanoparticle preparation (including the capping agent used) determine the physical and electronic properties of the quantum dots produced. This gives chemists the unique ability to change the electronic and chemical properties of a semiconductor material by simply controlling particle size and preparative conditions employed. There are various methods for the preparation of nanoparticles however, not all methods work well for the preparation of compound semiconductor nanocrystallites. 

Owing to their unique (tunable-electronic) properties, semiconductor (quantum dots) nanocrystals have generated considerable interest for optical DNA detection [12], Recent activity has demonstrated the utility of quantum dot nanoparticles for enhanced electrical DNA detection [33, 34, 50], Willner et al. reported on a photoelectrochemical transduction of DNA sensing events in connection with DNA cross-linked CdS nanoparticle arrays [50], The electrostatic binding of the Ru(NH3)63+ electron acceptor to the dsDNA... 

The inner cavity of carbon nanotubes stimulated some research on utilization of the so-called confinement effect [33]. It was observed that catalyst particles selectively deposited inside or outside of the CNT host (Fig. 15.7) in some cases provide different catalytic properties. Explanations range from an electronic origin due to the partial sp3 character of basal plane carbon atoms, which results in a higher n-electron density on the outer than on the inner CNT surface (Fig. 15.4(b)) [34], to an increased pressure of the reactants in nanosized pores [35]. Exemplarily for inside CNT deposited catalyst particles, Bao et al. observed a superior performance of Rh/Mn/Li/Fe nanoparticles in the ethanol production from syngas [36], whereas the opposite trend was found for an Ru catalyst in ammonia decomposition [37]. Considering the substantial volume shrinkage and expansion, respectively, in these two reactions, such results may indeed indicate an increased pressure as the key factor for catalytic performance. However, the activity of a Ru catalyst deposited on the outside wall of CNTs is also more active in the synthesis of ammonia, which in this case is explained by electronic properties [34]. 

These studies indicate that the charge transfer at the metal-oxide interface alters the electronic structure of the metal thin film, which in turn affects the adsorption of molecules to these surfaces. Understanding the effect that an oxide support has on molecular adsorption can give insight into how local environmental factors control the reactivity at the metal surface, presenting new avenues for tuning the properties of metal thin films and nanoparticles. Coupled with the knowledge of how particle size and shape modify the metal s electronic properties, these results can be used to predict how local structure and environment influence the reactivity at the metal surface. 

Previous studies in conventional reactor setups at Philip Morris USA have demonstrated the significant effectiveness of nanoparticle iron oxide on the oxidation of carbon monoxide when compared to the conventional, micron-sized iron oxide, " as well as its effect on the combustion and pyrolysis of biomass and biomass model compounds.These effects are derived from a higher reactivity of nanoparticles that are attributed to a higher BET surface area as well as the coordination of unsaturated sites on the surfaces. The chemical and electronic properties of nanoparticle iron oxide could also contribute to its higher reactivity. In this work, we present the possibility of using nanoparticle iron oxide as a catalyst for the decomposition of phenolic compounds. 

Supported nanoparticles (1-1.5 nm) based on Ru4Pt2 entities have been obtained by using a Ru4Pt2(CO)i8 precursor on carbon black and fullerene soot [63]. XANES analysis showed differences between the interaction of nanoparticles with both carbon black and fullerene supports. In particular, a change in the electronic properties of the nanoparticles on fullerene is proposed this change was related to a strong interaction between the nanoparticle and a surface-atom, probably via the formation of a Ru-carbide phase. 

The SMSI effect in Mn-promoted Ru/Ti02 catalysts was studied in more detail making use of the SSIMS technique, as well as with TEM, and selective chemisorption experiments. The SSIMS technique revealed the presence of TiO c forming two new surface sites, TiO -Ru and TiO-Mn. These species were found to be located at the immediate vicinity of the Ru nanoparticles. These new surface sites were considered to alter the electronic properties of the Ru metal surface and, as a consequence, the product selectivity. 

The addition of promoter elements to cobalt-based Fischer-Tropsch catalysts can affect (1) directly the formation and stability of the active cobalt phase structural promotion) by altering the cobalt-support interfacial chemistry, (2) directly affect the elementary steps involved in the turnover of the cobalt active site by altering the electronic properties of the cobalt nanoparticles electronic promotion) and (3) indirectly the behaviour of the active cobalt phase, by changing the local reaction environment of the active site as a result of chemical reactions performed by the promoter element itself synergistic promotion). 

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