Silicates physical adsorption

Adsorption (including both physical adsorption and ion exchange) by clay minerals and silicates... 

Clay minerals are structure of aluminum- and silicate-oxides. Such structures have free bond and vacancies on selective site of the mineral structure allowing them to participate in both physical adsorption and chemical reactions modifying the available concentration of the chemicals in the environment. 

Adsorption of the colorless form onto silicic acid57 or silica gel8 immediately produces a highly colored matrix which in certain cases, depending on the structure of the pyran, can be reversibly photobleached.7 The brightly colored matrix indicates that the open partly ionic form is the more stable in the highly polar silica gel environment undoubtedly physical adsorption forces also contribute to the stability of this form. 

Chitin metal silicates coprecipitates [53] Coprecipitation of a metal silicate on chitin particles offers industrial potential for use as a single filler which has binding as well as super-disintegration properties and can be used in directly compressed tablets or in wet granulation methodologies. The coprecipitation process causes physical adsorption of the metal silicates onto chitin particles (Fig. 2.39) without any chemical interaction which has been proved by IR and XRPD analysis. 

The surface of magnesium silicate is composed of free hydroxyl groups (silanol groups) the most reactive groups on the surface. They provide the sites for the physical adsorption of organic particles and can easily... 

The effect of potassium in the form of potassium carbonate or potassium silicate on reduction of NO, on coal chars was also investigated [108-111]. The best materials were prepared by pyrolysis of coal at 1300 K with high KOH/coal ratio [108]. On these adsorbents, at temperature smaller than 473 K, physical adsorption is predominant while the true NO, reduction by char occurs at T> 473 K with formation of Nj and COj. The results indicated that a material with the high surface area should be used to promote adsorption of NO, and potassium remaining in chars catalyzes NO reduction in the presence of oxygen [109]. 

The few data that are.available have been assembled by Voronkov, Zelchan, and Lukevits (4a). In some cases it is not possible to decide whether the reported amount of silica is greater than could have been present as Si(OH)4 in solution in the body j fluids. Thus if the organism consisted of 50% water and 10% ash and the water were saturated with amorphous silica, the silica in the ash would be 0.05%. Generally, the. silica is no lower than 0.1-0.2% based on ash. Skin, feathers, intestines, etc., which. can be exposed to contact with materials from outside, are all higher in silica. For example, feathers may contain up to 77% silica in the ash, strongly suggesting the > possibility of physical adsorption of colloidal silica or silicates. Also, earlier data - may indicate a falsely high silica level because of interference by phosphorus in the. silicomolybdate test. 

A problem that has plagued GC from its beginning has been the physical adsorption of polar or polarizable analyte species, such as alcohols or aromatic hydrocarbons, on the silicate surfaces of column packings or capillary walls. Adsorption causes distorted peaks, which arc broadened and often exhibit a tail (recall Figure 26-5). Adsorption occurs with silanol groups that form on the surface of silicates by reaction with... 

V. Mittal and V. Herle, Physical adsorption of organic molecules on the surface of layered silicate clay platelets A thermogravimetric study. Journal of Colloid and Interface Science, 327 (2008), 295-301. 

Physical Properties. Physical properties of importance include particle size, density, volume fraction of intraparticle and extraparticle voids when packed into adsorbent beds, strength, attrition resistance, and dustiness. These properties can be varied intentionally to tailor adsorbents to specific apphcations (See Adsorption liquid separation Aluminum compounds, aluminum oxide (alumna) Carbon, activated carbon Ion exchange Molecular sieves and Silicon compounds, synthetic inorganic silicates). 

The crystalline mineral silicates have been well characterized and their diversity of stmcture thoroughly presented (2). The stmctures of siHcate glasses and solutions can be investigated through potentiometric and dye adsorption studies, chemical derivatization and gas chromatography, and laser Raman, infrared (ftir), and Si Fourier transform nuclear magnetic resonance ( Si ft-nmr) spectroscopy. References 3—6 contain reviews of the general chemical and physical properties of siHcate materials. 

The adsorption of various aliphatic alcohols from benzene solutions onto silicic acid surfaces has been studied.t The experimental isotherms have an appearance consistent with the Langmuir isotherm. Both the initial slopes of an n/w versus c plot and the saturation value of n/w decrease in the order methanol > ethanol > propanol > butanol. Discuss this order in terms of the molecular structure of the alcohols and the physical significence of the initial slope and the saturation intercept. Which of these two quantities would you expect to be most sensitive to the structure of the adsorbed alcohol molecules Explain. 

The adsorption of liquid ethyl alcohol on AljOj occurs by H bonding (1108), and without doubt other proton donors are similarly affected. Some part of adsorption from binary solutions (e.g. ethyl alcohol and benzene) is explained by the three-step process alcohol H bonds to the surface, chemisorbs, and then the second component (and more alcohol) physically adsorb on this layer. (See Section 11.2.1 for a discussion of the similar action of water on silicic acid.) Such hydroxyl-covered surfaces are industrially important in cracking and other catalytic processes (2172, 956), and in drying. Plank and Drake (1646) discuss the influence of H bonds in the formation of such materials. 

One of the essential features of the solid-liquid interface is that the adsorbing substance may not only be bound to the surface by relatively weak physical forces, but also may form true chemical bonding with molecules or ions located at the surface of the solid phase. This phenomenon, referred to as the chemisorption, may seem to invalidate the polarity equalization rule at the interface between a polar crystal (e.g. silicate or sulfide) and a polar medium (water) the adsorption due to chemical bond formation may occur in such a way that the hydrocarbon chains are facing the water phase (Fig. III-9, a). At sufficiently high concentrations of chemisorbing surfactant, when the entire solid surface is covered with a monolayer, the formation of a second, oppositely oriented, surfactant layer starts, i.e., regular surfactant adsorption... 

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