The relation between adsorption isotherm shapes and the mechanism of some vapour phase and solution adsorption processes

The aim of this work was to determine the mechanisms involved in several adsorption systems from a consideration of the isotherms obtained. The problem of atmospheric pollution is first considered Sulphur dioxide and smoke (which can, be considered as being similar to a low temperature industrial carbon black) are two, of the most common pollutants occurring in city atmospheres. They are shown to act together in producing pollution problem the carbon acting as a carrier for adsorbed sulphur dioxide. In winter smoke adsorbs more sulphur dioxide than in summer due to the lower average temperature. Adsorption of the sulphur dioxide on the carbon accentuates the corrosion of metals and building stones containing calcium carbonate probably after catalytic oxidation of the sulphur dioxide to sulphuric acid. The corrosion of iron can be considered an electrolytic action, the metal acting as the anode, the sulphuric acid as the electrolyte and the carbon as carrier, bridge and cathode. Stones containing calcium or magnesium carbonate are attacked by sulphuric acid. When calcium and magnesium carbonates are converted to their respective sulphates the volume Increases are 1.7 and 4 times, causing exfoliation of the stone. Plants are affected physically by the blockage of their stomata by cartoon or chemically by destruction of their essential nutrients in the soil toy sulphuric acid. Section II deals with adsorption of solutes from solution. In Part I the adsorption of a range of basic dyes on alkaline alumina powder is considered. By comparing the surface area of the powder with the amount of dyes adsorbed, the latter are seen to be adsorbed as cationic micelles with the exception of Rhodamine B and 6GB, which, because of their molecular geometry favour adsorption as monomeric ions with a vertical edge on orientation. This is confirmed by the shape of the isotherm: "L" and types for micellar adsorption and "S" type for end-on orientation. Dyes adsorbed as micelles by ion-exchange can be desorbed completely with water or a similarly charged solute, whereas potential hydrogen bonding dyes such as Rhodamine 6GB are only partially removed by rinsing. All the basic dyes which are apparently adsorbed as large cationic micelles exhibit an anomalous (endothermic) adsorption attributable to the breakdown of micelles in solution to reform into larger micelles at the surface, probably with a different structure. An energy diagram is given to explain endothermic adsorption. Safranine T appears to favour edge-on orientation to give a monolayer at high temperature, and the disaggregation of this dye with increased temperature is studied spectroscopically. The relationship between the ratio of the . two (x, y hand) peaks and the logarithin of the temperature is linear. The plot of log, coverage factor (apparent surface area for each dye / "true" surface area) against the log, cationic weight of the dyes is linear and the line obtained is coincident with similar lines for the same dyes on graphite and formalin fixed yeast cells. Other adsorption systems: examined include phenol on chitin and also on varieties of rubber, p-nitrophenol on silica, and a mordant dye on alumina; the results are discussed in the light of the general principles of solution adsorption