Zeta potential supports

The seeding can be performed under vacuum [102] or by electrophoretic deposition in aqueous or non-aqueous medium [103]. The latter method has been applied to the rapid synthesis of A-type zeolite membranes. Two strategies can be used for an electrostatic attachment of the seeds to the support either a fine-tuned surface charge by pH control and measurement of the support zeta-potential or the adsorption of positively charged polymers [104], and immersion in a suspension whose pH is such that the seed particles are negatively... 

The deposition-reduction (DR) method is based on the weak electrostatic interactions of polymer surfaces with the oppositely charged Au(III) complex ions, leading to the reduction of Au(III) exclusively on the polymer surfaces. Appropriate anionic or cationic Au(III) precursors are chosen based on the zeta potentials of polymer supports (Figure 3.6) [43]. 

Figure 5-2 Distribution of + and - ions around the surface of an electrophoretic support. Fixed on the surface of the solid is a layer of - ions, (These may be + ions under suitable conditions.) A second layer of + ions is attracted to the surface. These two layers compose the Stern potentiai.The large, diffuse layer containing mostly + ions is the electro kinetic or zeta (Q potential. Extending farther from the surface of the solid is homogeneous solution.The Stern potential plus the zeta potential equals the electrochemical potential, or epsilon (e) potential.

The results with the thiocyanate solutions indicate a fairly high zeta potential over the whole salt concentration range, the variation being between —40 and —60 mV. This is consistent with the considerably thicker foam films formed in the presence of thiocyanate ions and supports the idea that thiocyanate ions are more strongly bound to sulfoxide groups than chloride ions. 

The faster increase of the zeta potential above pH 6.5, from —70 mV to -110 mV at pH 7.2, may be attributed to the supplementary electrical negative charges resulting from the dissociation of the hydrogen bonded silanol groups. This result was additionally supported by the determination of the dissociation constant of the Al-OH group from the acid-base titration curve. 

Zeta potential measurements show that particles coated with NOM have the greatest negative charge (results not shown). This supports the hypothesis that salts present in the NOM allow the colloids to... 

The onset pH for the formation of the Co(H20)4(OH)2 is 8.5 [34] and, consequently, is it possible that, under the present experimental conditions, significant amoimts of Co(H20)e and Co(H20)5(OH) will be present in solution during the preparation of the catalysts. Furthermore, if the carbon nanofibers were not oxidized before the catalyst preparation, very low amounts of cobalt was loaded on the carbon nanofibers support. Thus in correspondence with the zeta potential results electrostatic interaction between the negatively charged carbon nanofiber surface and the positively charged cobalt species will be needed for the preparation of the catalysts. 

EOF is also pH dependent. For example, in columns having silica support particles, ionizable silanols will cause these columns to exhibit a more pronounced dependency of EOF on pH than do other columns. The silanols begin to ionize at pH 2 and will continue to ionize progressively (based on the regiospecificity of a given silanols p Ta) until approximately pH 8-9, at which point the preponderance of silanols are fully ionized. The zeta potential will therefore increase, and it is for this reason that the electroosmotic velocity increases with increasingly alkaline solutions. 

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