Titania, zeta potential

There are about 4-5 surface hydroxy groups per square nanometer on anatase and these are of two different types. One type is basic in nature and can be exchanged by F". This type of site is responsible for the adsorption of acidic species onto the surface and initiates the adsorption of base sensitive compounds such as Mo02(acac)2. The second type of surface hydroxide is acidic. It interacts strongly with base and initiates the adsorption of acid sensitive compounds such as Fe(acac)3.2 This amphoteric nature of titania is illustrated by the zeta potential versus pH curve shown in Fig. 9.9. Cationic catalyst precursers are adsorbed at pH values greater than 7-8 and anionic species from solutions having a pH less than about 5. 

Oguchi, T., Tamatani, M., and Koishi, M., Contact electrification and zeta potential in titania pigments, Nippon Kagaku Kaishi, 6, 902, 1984. 

Spanos, N. and Koutsoukos, P.C., Calculation of zeta potential from electrokinetic measurements on titania plugs, J. Colloid Interf. Sci., 214, 85, 1999. 

Seshadri, K.S. et al.. Estimation and comparison of pore charge on titania and zirconia membranes prepared by sol-gel route using zeta potential measurement, J. Sol-Gel Sci. Technol., 28, 327, 2003. 

Kosmulski, M., Zeta potential of submicron titania particles in mixed solvents, in Fine Particle Sciences and Technology, Pelizzetti, E., ed., Kluwer, Dordrecht, 1996, p. 185. 

B. van Lent, B. Klinksiek, Korrelation physikalischer mit anwendungstechnischen GroBen bei Dispersionen. Chem. Ing. Tech. 69(6), 793-798 (1997). doi 10.1002/cite.330690605 P. Wilhelm, D. Stephan, On-line tracking of the coating of nanoscaled silica with titania nanoparticles via zeta-potential measurements. J. Colloid Interface Sci. 293(1), 88-92 (2006). doi 10.1016/j.jcis.2005.06.047... 

The results fix>m anidysis of the zeta potential curves tor the pure materials and the composites are presented in Fig. 3. From tins curve it was obvious that in the composites tire amoimt of titania at the surface was well below the bulk composition. Since the composite... 

Determination of the Point of Zero Zeta Potential of Titania... 

Figure 4.11 Specific electric conductivity (top) and zeta potential versus concentration of NaAOTin hexadecane ) [464] and cyclohexane (O) [467]. Zeta potentials were measured on titania [467] and surface potentials on spherical poly(methyl methacrylate) (PMMA) particles [464].

Although it is not completely clear how surfaces are charged in nonpolar media, two processes seem to dominate [470] surfactant adsorption and proton exchange. If surfactant is present in the solution, it will strongly influence the surface charge of particles due to adsorption to the surface [469]. The effect of surfactant is often not simple. Very different dependencies of the zeta potential on the concentration have been observed [471]. Two examples are plotted in Figure 4.11 (bottom). One shows the zeta potential of titania particles in cyclohexane and the other the surface potential of PMMA particles in hexadecane, both at different concentrations of NaAOT. 

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