Graphon, adsorption

Fig. XI-10. Isotherm of composition change or surface excess isotherm for the adsorption of (1) benzene and (2) n-heptane on Graphon. (From Ref. 141.)...

Fig. XVn-21. (a) Differential heat of adsorption of N2 on Graphon, except for Oand , which were determined calorimetrically. (From Ref. 89.) (b) Differential heat of adsorption of N2 on carbon black (Spheron 6) at 78.5 K (From Ref. 124).

Fig. XVII-23. (a) Entropy enthalpy, and free energy of adsorption relative to the liquid state of N2 on Graphon at 78.3 K (From Ref. 89.) b) Differential entropies of adsorption of n-hexane on (1) 1700°C heat-treated Spheron 6, (2) 2800°C heat-treated, (3) 3000°C heat-treated, and (4) Sterling MT-1, 3100°C heat-treated. (From Ref 18.)...

When plotted according to the linear form of the BET equation, data for the adsorption of N2 on Graphon at 77 K give an intercept of 0.004 and a slope of 1.7 (both in cubic centimeters STP per gram). Calculate E assuming a molecular area of 16 for N2. Calculate also the heat of adsorption for the first layer (the heat of condensation of N2 is 1.3 kcal/mol). Would your answer for Vm be much different if the intercept were taken to be zero (and the slope the same) Comment briefly on the practical significance of your conclusion. 

Fig. 2.25 The differential heat of adsorption of argon on carbon blacks at 78 K, before and after graphitizalion.. Spheron O, Graphon. , and El denote molar heat of sublimation and of evaporation respectively.

Fig. 5.12 (a) Water adsorption isotherms at 20°C on Graphon activated to 24-9 % burn-off, where its active surface was covered to varying extents by oxygen complex. (b) The results of (a) plotted as amount adsorbed per of active surface area (left-hand scale) and also as number of molecules of water per atom of chemisorbed oxygen (right-hand scale). (After Walker.)... 

Fig. 4.2 Equilibrium adsorption of sodium n-dodecyl sulfate on carbon black, Ti02, and Graphon at room temperature [41].

Fig. 6 Adsorption of alkyl ether sulfates on graphon (plateau values) at 25°C (product purity 98-99.5%)...

A second widely used class of adsorbates is that of dyes. Methods using these are appealing because of the ease with which analysis may be made colorimetrically. The adsorption generally follows the Langmuir equation. Graham found an apparent molecular area of 19.7 A2 for methane blue on Graphon or larger than the actual... 

Figure Ic differs markedly from those obtained for the immersion of polar solids in water initially the heat values are small but increase with increasing amounts of preadsorbed water. Thus far, only one such curve has been reported in the literature for the system Graphon-water 90). Graphon is a graphitized carbon black which has an essentially homogeneous, homopolar surface 21). Nevertheless, a small fraction of heterogeneous sites is responsible for the limited adsorption of water on the surface of this solid. Similar curves can be expected for other hydrophobic solids.

The very low water adsorption by Graphon precludes reliable calculations of thermodynamic quantities from isotherms at two temperatures. By combining one adsorption isotherm with measurements of the heats of immersion, however, it is possible to calculate both the isosteric heat and entropy change on adsorption with Equations (9) and (10). If the surface is assumed to be unperturbed by the adsorption, the absolute entropy of the water in the adsorbed state can be calculated. The isosteric heat values are much less than the heat of liquefaction with a minimum of 6 kcal./mole near the B.E.T. the entropy values are much greater than for liquid water. The formation of a two-dimensional gaseous film could account for the high entropy and low heat values, but the total evidence 22) indicates that water molecules adsorb on isolated sites (1 in 1,500), so that patch-wise adsorption takes place. 

Adsorption and Wetting Phenomena Associated with Graphon in Aqueous Surfactant Solutions... 

This paper describes a study of the dispersibility of Graphon (graphitized Spheron 6) in aqueous solutions of sodium dodecyl sulfate (SDS) an dodecyl trimethylammonium bromide (DTAB), and its relation to the adsorption behavior of the surfactants at the solid/liquid interface, with a view to determine the controlling process in the dispersibility of these systems. 

Figure 1. Adsorption of SDS on Graphon at 25° from aqueous solution after end-over-end action O and after ultrasonic irradiation X, and from solutions in 0.1M sodium chloride % (end-over-end)...

Pierce and Smith (56) have observed a Type III isotherm for water vapor on a highly graphitized carbon black (graphon, 80 square meters per gram) at 28.9° C. They suggest that water vapor adsorption occurs only on the most active sites and that the entire surface is probably never covered. 

The adsorption isotherms for carbon black and graphitised carbon black (graphon) are completely different. For graphitised carbon black a step-like adsorption isotherm is... 

Pace EL, Siebert AR (1959) Heat of adsorption of parahydrogen and orthodeuterium on graphon. J. Phys. Chem. 63 1398-1400... 

Graphon black, kindly furnished by the Cabot Corporation, was the adsorbent and its physical properties are listed in Table I. The term Graphon refers to Spheron 6 which had been heated to 2,700°-3,200°C. This graphitized nonporous carbon black is a unique form of carbon with uniform surface and high surface area. The Graphon samples were dried for 12 hrs. at 140°C. and stored in vacuo before use in the adsorption experiments. 

Table II. Effect of Solvent on the Adsorption of Polystyrene-14C on Graphon at 25.0°C.

---