Carbon zeta potential

Zeta-Potentials of Carbon Black Dispersions in Hydrocarbons with OLOA-1200 Dispersant (14-16)... 

Initial studies were made with the Rank Bros, electrophoresis unit, using the dilute supernatant suspension over a dispersion of 3.33g of carbon black per liter of dodecane equilibrated for 24 hours with the added 0L0A-1200. The electrophoretic mobility (u) of 1-3 pm clumps of particles was observed at a field of 100 volts per centimeter. The zeta-potentials ( ) were calculated... 

Figure 9. Zeta-potential of carbon black dispersed in dodecane with OLOA-1200 dispersant (23°C.). Sampled from dispersions of 3.33 g of carbon black per liter of dodecane. Reproduced with permission from Ref. (14). Copyright 1983, Elsevier Science Publishers.

Figure 10. Distribution of zeta-potentials of carbon black in kerosene with 0.1% OLOA-1200. Average zeta-potential was -HOmV.

Figure 11. Potential energy diagram for two spherical carbon black particles of radius 0.2 ym with Debye lengths and zeta potentials determined for 0.2% and 0.8% solutions of OLOA-1200 in odorless kerosene.

It can also be seen from Fig. 5.33 that with the increase of (1-carbonic sodium-2-acetaic sodium) propanic sodium dithio carbonic sodium (TX4), the negative zeta potential of marmatite, pyrrhotite and arsenopyrite increase. The negative zeta potential reach the maximum and remained stable at the concentration of TX2 60 mg/L. The zeta potential in the presence of TX2 increases in the order of arsenopyrite > pyrrhotite > marmatite, which is corresponding to the adsorption order of TX2 on the three minerals. Figure 3.33 also suggests that the adsorption of anionic depressant TX2 on negatively charged marmatite, arsenopyrite and pyrrhotite may be due to the chemical interaction. 

Figure 7 Zeta potential of calcium carbonate as a function of Na polyacrylate dose...

P 67] Simulations were made following experiments made previously [156], Therein 0.11 mM Rhodamine B solutions in 20 mM carbonate buffer were mixed with the same carbonate buffer. For the buffer solution, the physical properties of water were approximated. For Rhodamine B, a diffusion coefficient of 2.8 10-6 cm2 s-1 was taken. Electroosmotic flow was applied for liquid transport. For all of the walls in the domain the electroosmotic (EO) mobility was set to 3.4 10-4 cm2 V-1 s 1, which corresponds to a zeta potential (Q of-44.1 mV. The electric field in the outlet channel was 1160 V cm-1. The Reynolds number was 0.22. The electric field strength was set low in order to decrease diffusive (pre-)mixing prior to the groove structure. 

A persistent question regarding carbon capacitance is related to the relative contributions of Faradaic ( pseudocapacitance ) and non-Faradaic (i.e., double-layer) processes [85,87,95,187], A practical issue that may help resolve the uncertainties regarding DL- and pseudo-capacitance is the relationship between the PZC (or the point of zero potential) [150] and the point of zero charge (or isoelectric point) of carbons [4], The former corresponds to the electrode potential at which the surface charge density is zero. The latter is the pH value for which the zeta potential (or electrophoretic mobility) and the net surface charge is zero. At a more fundamental level (see Figure 5.6), the discussion here focuses on the coupling of an externally imposed double layer (an electrically polarized interface) and a double layer formed spontaneously by preferential adsorp-tion/desorption of ions (an electrically relaxed interface). This issue has been discussed extensively (and authoritatively ) by Lyklema and coworkers [188-191] for amphifunctionally electrified... 

The influence of ions on electrokinetic effects can be readily explained with the aid of Stern s concept of the double layer. Substances like silicon carbide, cellulose, sulfur and carbon, which do not ionize, are negatively charged in contact with water and the addition of small amounts of uni-univalent electrolytes tends to increase this charge. It is probable that in these cases the negative zeta-potential is due in the first place to the firm attachment to the surface of hydroxyl ions from the water and possibly also of anions from the electrolyte. An equivalent number of positive ions, some closely held in the fixed part of the double layer and the remainder in the diffuse portion, will be left in the solution. The potential gradient between the solid surface and the bulk of the liquid, which is pure water or a dilute solution, is shown diagrammatically in Pig. 128,1. If the electrolyte concentration is increased, there will be... 

In the context of a study of foam flotation of powdered activated carbon (PAC), Zouboulis et al. [143] noted large and different pH effects when an anionic surfactant was used instead of a cationic one. For the cationic surfactant, best recovery (at low surfactant concentration) was achieved at the highest pH, in agreement with electrostatic arguments (see Section IV.B.l) for the anionic surfactant, an intermediate pH was the best. The authors also measured the zeta potential of the carbon in the presence and absence of the surfactants and concluded that the specific chemical nature and the dissociation of each surfactant. 

In the virtually ignored study by Dai (with three nonself citations in five years) [521], the paper by Graham [451] is not cited either, but the key issue is both identified and clarified. Based on the results summarized in Fig. 21, the author concluded that electrostatic interaction between cationic dyes and the surface of activated carbon has a great effect on adsorption capacity. Below the isoelectric point of the activated carbon (when the positive zeta potential was above 60 mV), the capacity is significantly reduced due to electrostatic repulsion between cationic dyes and the carbon surface. In a follow-up study, while still failing to acknowledge earlier important contributions to the resolution of the key issues, Dai [522] reinforced and confirmed the electrostatic attraction vs. repulsion arguments. The author used anionic dyes (phenol red, carmine, and titan yellow) and... 

The study of Lafrance and Mazet [549] not only provided further confirmation of the beneficial effect of cations (Na ) but also clarified its mechanism by analyzing the effect of sodium salt concentration on the zeta potential of a commercial powdered activated carbon (see Section I V.B. 1). The reported uptakes of a commercial. sodium humate remained <100 mg/g (at 10 mg/L). In the study of Annesini et al. [556], even at humic acid concentrations of 20 mg/L the uptake did not exceed 10 mg/g. These uptakes should be contrasted with those reported recently by Newcombe and Drikas [566] and illustrated in Fig. 23 at low pH, when electrostatic repulsive forces (see Section IV.B. 1) are eliminated, the uptake at comparable concentrations can be as high as 200-300 mg/g. 

Murata and Matsuda [629] compared the electrophoretically determined zeta potentials and pH values of a series of carbon blacks (see Fig. 24) and correlated them with the concentration of acidic surface functional groups. Similarly, Tobias... 

FIG. 24 Relationship between the surface chemistry and the electrochemistry of commercial and chemically pretreated carbon blacks (a) correlation between the concentration of acidic functional groups (determined by titrations) and zeta potential (determined by electrophoresis) (b) conelation between zeta potential and the slurry pH. (Adapted from Ref. 629.)... 

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