Peptization is the process responsible for the formation of stable dispersion of colloidal particles in water. This is particularly important in colloid chemistry or for precipitation reactions in an aqueous solution. When colloidal particles bear a same sign electric charge, they mutually repel each others and cannot aggregate together. Freshly precipitated aluminium or iron hydroxide is extremely difficult to filter because the very fine colloidal particles directly pass through a paper filter. To facilitate the filtration, the colloidal suspension must be first flocculated by adding a concentrated solution of salt to the system. Multivalent cations are more efficient flocculants than monovalent cations: AlCl3 > CaCl2 > NaCl. The electrical charges present at the surface of the particles are so "neutralised" and disappear. More correctly speaking, the
Peptization is also used in nanoparticle synthesis to make a large grouping of particles split into many primary particles. This is done by changing the surface properties, applying a charge, or by adding a surfactant.
In the synthesis of titania (titanium dioxide) nanoparticles, peptization involves adsorption of negative tetramethylammonium hydroxide (TEAH) molecules on the titania surface. This causes the surface to become negatively charged. Electrostatic repulsion of the primary particles in the agglomerated titania breaks up the agglomerate into primary particles.[1]
Antonym
Flocculation is the process inverse of peptization.
See also
References
- ^ Y. Li, T. J. White; Lim, S. H. (2004). "Low-temperature synthesis and microstructural control of titania nano-particles". Journal of Solid State Chemistry 177: 1372–1381. doi:.
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