Adsorbent forms cloths

On standing, gelatinous aluminium hydroxide, which may initially have even more water occluded than indicated above, is converted into a form insoluble in both acids and alkalis, which is probably a hydrated form of the oxide AI2O3. Both forms, however, have strong adsorptive power and will adsorb dyes, a property long used by the textile trade to dye rayon. The cloth is first impregnated with an aluminium salt (for example sulphate or acetate) when addition of a little alkali, such as sodium carbonate, causes aluminium hydroxide to deposit in the pores of the material. The presence of this aluminium hydroxide in the cloth helps the dye to bite by ad sorbing it—hence the name mordant (Latin mordere = to bite) dye process. 

Activated charcoal was originally regarded as a relatively inexpensive adsorbent with an assortment of pores of ill-defined size and shape. However, in recent years considerable progress has been made in the development of tailor-made porous carbons such as molecular sieves, activated carbon fibres and carbon composites (Marsh et al., 1997). Superactive carbons are now made on a commercial scale with BET areas of around 3000 m2g-1. Activated carbons can be manufactured as fine particles or granules or in the form of a cloth, felt or consolidated membrane. The properties of some of these special types of activated carbon are discussed in Chapter 12. 

It was once taken for granted that adsorbents were required in the form of fine powders, porous granules or extrudates. However, other physical forms such as porous fibres are now available for special applications such as membranes for gas separation or water treatment Carbon cloth provides an interesting example of a highly active form of fibrous carbon. 

Because of a sorption mechanism of metal ions onto activated carbon that involves surface complexation, the DLM model was successfully applied to describe adsorption of metal ions onto this adsorbent. For example, the adsorption of Cd and Zn " " onto activated carbon in the form of powder or granules was modeled [19]. The modeling of the adsorption of Cu " ", Ni +, and Pb " " onto activated carbon cloths allowed complexation constants to be calculated ... 

The primary application of silica gel is as a drying agent. Packets of silica gel are found in many consumer products, such as electronic equipment, hardware tools, clothing, CD and DVD discs, and foodstuffs. Because of its ability to adsorb moisture from the surrounding air, silica gel prevents rust and other forms of oxidation. Silica gel also has similar applications in industry. For example, it is used to dry compressed air, air conditioning systems, and natural gas. The compound is also used to bleach petroleum oils and as an anti-caking agent for cosmetics and pharmaceuticals. 

Adjective Dyes, Mordants.—The dyes classed as adjective are those which do not form stable combinations with fibers and, as a consequence, when they are used, the material to be dyed must be treated first with some substance with which the dye combines. Such substances are called mordants. The combination between the dye and the mordant may be physical or chemical. Finely divided substances, such as silica, sulphur, and calcium phosphate, adsorb dyes readily, and serve as useful mordants in certain cases. Albumen is used in calico-printing, as it unites with substantive dyes directly. When cotton cloth which has been printed with a mixture of the dye and albumen is steamed, the protein is coagulated and the color becomes fixed. 

Many dyes, such as aluminon, cannot be used directly to dye cotton cloth because the dyes are not held firmly by the fibers and are removed by washing. When aluminum hydroxide is precipitated on cotton, it is strongly adsorbed. If aluminon is then applied, a colored lake is formed with the aluminum hydroxide on the fiber, and this color is fast. The aluminum hydroxide is called a mordant. 

Activated carbon material is a versatile material, from granular to fibre form, with desirable properties such as large surface area, adsorptivity, high thermal conductivity, fire resistance, robustness and wide availability. Both activated carbon granules and activated carbon fibres are employed in permeable protective clothing to absorb/adsorb chemicals. ... 

Moisture on the cloth is necessary to achieve oxidation. Between 5.5 to 11% w/w moisture is needed for nitrogen tetroxide to adsorb on cellulose. With low moisture content, only nitration takes place w hile y dth high moisture content nitric acid is formed, but nitration predominates. The log of the amount of adsorbed nitrogen tetroxide is proportional to the reciprocal of the temperature (Yasnitskii et ai, 1972) and the oxidation of cellulose is proportional to the amount of previously adsorbed nitrogen tetroxide (Yasnitskii et ai, 1971). 

The Function of Detergency. The cleaning action of detergents is based on their ability to emulsify or disperse different types of soil and hold it in suspension in water. The workhorse involved in this job is the surfactant, a compound used in all soaps and determents. This abUity comes from the surfactant s molecular structiu"e and surface activity. When a soap or determent product is added to water that contains insoluble materials like dirt, oil, or grease, surfactant molecules adsorb onto the substrate (clothes) and form clusters called micelles, which surround the immiscible droplets. The micelle itself is water soluble and allows the trapped oil droplets to be dispersed throughout the water and rinsed away. While this is a simplified explanation, detergency is a complex set of interrelated functions that rehes on the diverse properties of surfactants, their interactions in solution, and their unique ability to disrupt the surface tension of water. 

Industrial carbon adsorbents are complex products difficult to classify on the basis of their behaviour, surface characteristics, properties or utility. However, they are usually categorised according to their particle shapes and size into powdered, granulated, spherical, pelletised or fibrous (in the form of felt or cloth) activated carbons. These categories can be further sub-divided according to their various properties, e.g. porous structural or surface chemical structural characteristics. 

ACEs in the form of felt or cloth have come under the spotlight in recent years as an adsorbent for purifying water. The first studies on this new material were carried out mainly in the gaseous phase and showed it to be very effective in removing contaminants from air. Its high specific surface area and microporosity endow ACF with good adsorptive properties both in the gaseous and the liquid phase. 

---