In Situ Precipitation of Metal Precursors

The deposition of the active phase on a support depends on the surface charges of the support and of precursor in suspension. The surfaces of the particles in a polar medium develop loadings caused by ionization process in which functional groups are present in the material or even ionized by the ion adsorption. This affects the distribution of the charge near ions, increasing the concentration of counter ions near the surface. Thus, an electrical potential is generated, which decreases exponentially away from the surface, as expressed by Eq. (13.1). The adsorbed ions cause decreasing electric potential, as illustrated in Fig. 13.5a  

The adsorption of charged ions oti the surface leads to the formation of the so-called electrical double layer, which can be divided into two regions, the Stem layer and the diffusion layer as shown in Fig. 13.5a. The Stem layer indicates ions strongly adsorbed at the surface, while the diffusion layer is a region in which the distribution of the ions is determined by the balance between the electrostatic forces and thermal motion. 

This phenomenon is known as electrophoresis. The particles and ions strongly adsorbed (Stem layer) move as a unit, and the electric potential at the border of the unit where the sliding takes place between the phases is known as the zeta potential (Setz 2009). The zeta potential is influenced by the pH of the system since the H+ and OH ions affect the surface charge of the particle and thus the zeta potential 

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In situ precipitation of metal precursors Synthesis in confined spaces—microemulsion Sonochemical synthesis Deposition-precipitation Sol-gel method Thermal decomposition... 

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