Isoelectric point Langmuir

Leyva et al. (2001) studied Sb(III) adsorption to hydroxyapatite. They conducted adsorption isotherms in closed vessels at Sb concentrations of 0.05-50 mg/L, constant I (0.01 m), constant solid phase concentrations of 10g/dm3 at pH values between 5 and 8. The hydroxyapatite was characterized by X-ray diffraction (XRD), SF.M-F.DS, X-ray photoelectron spectroscopy (XPS), and infrared (IR) spectroscopy. Langmuir adsorptions models revealed Fmax of 6.7 x 10 xmol/m2 and Xads = 1.5 x 103dm3/mol. As Sb adsorption occurred, the isoelectric point (pHicp) of the hydroxyapatite changed from 4.0 to 12.0. The decline in the pHjep during sorption as well as the absence of... 

The ZPC of a solid is the pH of an aqueous solution in contact with the solid when the solid has a net surface charge of zero. The ZPC depends on the composition of the solid and the concentration and chemistry of the electrolytes in the aqueous solution. In situations where surface charges are only controlled by the adsorption of OH- or H+, the ZPC is the isoelectric point (Faure, 1998), 218-219 (Langmuir, 1997), 350 (Drever, 1997), 93. Unfortunately, isoelectric points and ZPCs are not consistently defined or utilized in the literature. That is, some authors refer to the isoelectric point of particular solid sample when they are actually referring to its ZPC as the term is defined in this chapter. 

FIGURE 5.8 Theoretical analysis of an amphifunctionally electrified interface (a) effect of pH and externally applied potential on the interfacial double-layer potential and (b) potential necessary to apply across the interface to reach the isoelectric point as a function of pH. Electrolyte concentration, 0.01 M protolytic site density, 3 x 1018/m2 point of zero charge, pHPZC = 4.5 inner-layer capacitance, 0.05 F/m2 outer-layer capacitance, 0.30 F/m2. (Adapted from Duval, J., et al., Langmuir, 17, 7573, 2001.)... 

A Ithough the adsorption of polymers onto solid surfaces has been thor-oughly studied (I), relatively few studies can be found in the literature on the adsorption of proteins onto polymer surfaces. In 1905, Landsteiner and Uhliz (2) discussed the interaction of serum proteins with synthetic surfaces. Blitz and Steiner (3) showed that albumin adsorption onto solid surfaces increased with increasing albumin concentration and that adsorption was nearly irreversible. Hitchcock reported (4) that adsorption of egg albumin onto collodion membranes followed a Langmuir isotherm with maximum adsorption occurring near the isoelectric point. Later, Kemp and Rideal (5) reported that protein adsorption onto solids conforms with Langmuir adsorption. 

Determined by titration (the authors refer to it as the isoelectric point). Maximum surface coverage obtained from the Langmuir isotherm. Source Ref 206. 

Bullard, J.W. and Cima, M.J., Orientation dependence of the isoelectric point of TiOj (rutile) surfaces, Langmuir, 22, 10264, 2006. 

Kosmulski, M., Confirmation of the differentiating effect of small cations in the shift of the isoelectric point of oxides at high ionic strengths, Langmuir, 18, 785, 2002. 

Chau, L.K. and Porter, M.D., Surface isoelectric point of evaporated silver films Determination by contact angle titration, J. Colloid Interf. Sci., 145, 283, 1991. Burgisser. C.S. et al., Chromatographic charge density determination of materials with low surface area, Langmuir, 10, 855, 1994. 

Rezwan, K., Meier, L.P, and Gauckler, L.J., A prediction method for the isoelectric point of binary protein mixtures of bovine serum albumin and lysozyme adsorbed on colloidal titania and alumina particles, Langmuir, 21, 3493, 2005. 

Assemi, S. et ah. Isoelectric point of fluorite by direct force measurements using atomic force microscopic, Langmuir, 22, 1403, 2006. 

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