Surface Structure of Nanoparticles

FIGURE 2.3 Relationships between total and surface content Cx of (a) alumina and titania, (c) silica in SA, ST and AST samples (b) relationship between ratio C /Cx and the total content of the second phases, and (d) relationship between the surface content of alumina or titania and the peak temperature of TPD-MS thermograms of desorbed water. (Adapted from J. Colloid Interface Sci., 314, Gun ko, V.M., Blitz, J.P., Gude, K. et ah. Surface structure and properties of mixed fumed oxides, 119-130, 2007a, Copyright 2007, with permission from Elsevier.) 

Nuclear Magnetic Resonance Studies of Interfacial Phenomena 

FIGURE 2.4 Optical spectra of DMAAB adsorbed onto different nanooxides (sample weight was selected to provide close surface area of all samples). (Adapted from Appl. Surf. Sci., 253, Gun ko, V.M., Nychiporuk, Yu.M., Zarko, V.l. et al., Relationships between surface compositions and properties of surfaces of mixed fumed oxides, 3215-3230, 2007d, Copyright 2007, with permission from Elsevier.) 

Contributions (%) of Different Centers with Si and Al in SA, ST, and AST Samples Determined as Relative Integral Intensity of the Bands Obtained by Deconvolution of the 2 Si CP/MAS and Al MAS NMR Spectra 

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Before the introduction of STM, high-resolution (HR-)TEM was the primary technique for determination of the surface structures of nanoparticle model catalysts (14,54,74,77,197,198,211,226-230). For technological catalysts, it is still the only method that provides a direct atomic-scale characterization of metal nanoparticles and of the oxide support (211,231-238). Although TEM is unable to detect adsorbed molecules (in contrast to the methods discussed above), it is briefly mentioned here because HR-TEM was sometimes employed to corroborate STM data characterizing model catalysts and, in particular, to demonstrate the internal... 

However, in the case of multimetallic catalysts, the problem of the stability of the surface layer is cmcial. Preferential dissolution of one metal is possible, leading to a modification of the nature and therefore the properties of the electrocatalyst. Changes in the size and crystal structure of nanoparticles are also possible, and should be checked. All these problems of ageing are crucial for applications in fuel cells. 

Hernandez J, SoUa-GuUon J, Herrero E, Aldaz A, Feliu JM. 2005. Characterization of the surface structure of gold nanoparticles and nanorods using strucmre sensitive reactions. J Phys ChemB 109 12651-12654. 

The electronic structure and hence optical properties of nanomaterials depend on the core size. For example, nanoparticles of core size >3 nm show surface plasmon resonance, which is due to the excitation of surface plasmons of nanoparticles by light. When the size of gold nanoparticles comes down to around 1 nm, which is equal to the de Broglie wavelength of the conduction electrons, the electronic bands... 

Infrared Spectroscopy. Infrared (1R) spectroscopy is also used for understanding the structure of the bimetallic nanoparticles. Carbon monoxide can be adsorbed on the surface of metals, and the 1R spectra of the adsorbed CO depend on the kind of metal. These properties are used for analyzing the surface structure of metal nanoparticles. The inverted core/shell structure, constructed by sacrificial hydrogen reduction, was probed by this technique (44). 

Chen L.X., Rajh T., Wang Z., Thumauer M.C. (1997) XAFS Studies of Surface Structures of Ti02 Nanoparticles and Photocatalytic Reduction of Metal Ions, J. Phys. Chem. B.. 101(50), 10688-10697. 

In this chapter aspects of nucleation, aggregation and growth processes that give rise to specific microstructures and forms of nanomaterials are considered. Next the way in which the surface structure of nanoparticulates may differ from the interior, and how physical structure may be modified by reduced particle size is examined. The various techniques by which nanoparticle structure, size, microstructure, shape and size distribution are determined are then considered with examples. Finally some of the outstanding problems associated with nanoparticle structure and growth are identified, emphasizing natural processes and compositions. 

Chen LX, Rajh T, Ja ger W, Nedeljkovic J, ThumauEMC (1999) X-ray absorption reveals surface structure of titanium dioxide nanoparticles. J Synch Rad 6 445-447 Cheng B, Kong J, Luo J, Dong Y (1993) Materials Science Progress 7 240-243 (in Chinese)... 

EdenM (1961) A two-dimensional growth process. 4th Berkeley Symp Math, Stat, Prob 4 223-239 Eng PJ, Trainor TP, Brown GE, Waychunas GA, Newville M, Sutton SR, Rivers ML (2000) Structure of the hydrated a-Al203 (0001) surface. Science 288 1029-1033 Frenkel AI (1999) Solving the structure of nanoparticles by multiple-scattering EXAFS analysis. J Synch Rad 6 293-295... 

A. Jurgensen, and G, A, Waychunas, Analysis and simulation of the structure of nanoparticles that undergo a surface-driven structural transformation, J. Chem. Phys., 120 11785-11795, 2004... 

We analyzed the relation between absorbance spectrum of 2D self-assembled silver nanoparticle arrays and size and concentration of the nanoparticles. The high sensitivity of these parameters can be the basis for proper characterization of close-packed metal nanoparticle structures. For express optical diagnostics we provided the simple approximation for dependence of the resonance wavelength on size and surface concentration of nanoparticles. 

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