Specific surface area water adsorption

In this work, the various organic wastes were carbonized with the super-heated water vapor at 623 K. The specific surface areas and adsorption characteristics of the carbonized materials have been studied. 

Minimizing Adsorbed Impurities on Colloids The purity of many coagulated colloids is improved by digestion. During this process, water is expelled from the solid to give a denser mass that has a smaller specific surface area for adsorption. 

There are complexities. The wetting of carbon blacks is very dependent on the degree of surface oxidation Healey et al. [19] found that q mm in water varied with the fraction of hydrophilic sites as determined by water adsorption isotherms. In the case of oxides such as Ti02 and Si02, can vary considerably with pretreatment and with the specific surface area [17, 20, 21]. Morimoto and co-workers report a considerable variation in q mm of ZnO with the degree of heat treatment (see Ref. 22). 

Make a numerical estimate, with an explanation of the assumptions involved, of the specific surface area that would be found by (a) a rate of dissolving study, (b) Harkins and Jura, who find that at the adsorption of water vapor is 6.5 cm STP/g (and then proceed with a heat of immersion measurement), and (c) a measurement of the permeability to liquid flow through a compacted plug of the powder. 

ACC) having very high specific surface area, adsorption capacity and mechanical strength, has gained increasing in studies of the removal of many pollutants from waste water by adsorption in recent years [5, 6-13],... 

In the absence of knowledge of the surface area of cement hydrates available for adsorption at the time of addition, it is difficult to estimate how many layers of water-reducing admixture molecules are adsorbed, but attempts have been made [40] indicating that over 100 layers may be formed with calcium lignosulfonate and salicylic acid at normal levels of addition. However, these calculations were based on specific surface areas of 0.3-1.0 m g-l, whereas other studies [27, 38, 39] have indicated... 

Adsorption Properties. Due to their large specific surface areas, carbon blacks have a remarkable adsorption capacity for water, solvents, binders, and polymers, depending on their surface chemistry. Adsorption capacity increases with a higher specific surface area and porosity. Chemical and physical adsorption not only determine wettability and dispersibility to a great extent, but are also most important factors in the use of carbon blacks as fillers in rubber as well as in their use as pigments. Carbon blacks with high specific surface areas can adsorb up to 20 wt% of water when exposed to humid air. In some cases, the adsorption of stabilizers or accelerators can pose a problem in polymer systems. 

Silica MCM-41 was synthesized hydrothermally at 373 K for 7 days by using water glass and n-hexadecyltrimethylammonium bromide in a manner similar to that reported by Beck et al. [2]. The quality of MCM-41 prepared here was examined by the measurements of XRD, specific surface area and pore size distribution (calculated from N2 adsorption isotherm), and TEM. 

Figure 3 shows the water-vapor adsorption isotherms measured on the silane-treated fibers along with those obtained on the untreated fibers. A complete discussion of the water adsorption isotherms of the untreated fibers has already been reported [8]. Here, two new features are immediately evident. First, the presence of the silane overlayer has greatly enhanced the water adsorption capacity of the fibers, and, second, the silane-treated fibers that contain 4% and 6% B,0, adsorb significantly more water than the 0% B20, fibers. It is important to note that these data have been normalized to the specific surface areas of the... 

The fact that all the fibers adsorb water in excess of the expected monolayer amounts suggests that the water adsorption is multilayer in nature, or that there is pore space which is accessible to water molecules—but not accessible to the Kr used to measure the specific surface area. The XPS analyses showed that the silane overlayers increased in thickness in the 4% and 6% B,03 fibers. But the increase in water adsorptivity with % B,03 is not in direct proportion to the increase in silane overlayer thickness it is considerably larger. This suggests that B,0, has influenced the chemical and physical structure of the adsorbed silane overlayer. It is likely that there is microporosity, free volume, and/or reactive sites within the silane overlayer, in general. 

The water adsorption capacity of the silane-treated fibers—at low pressure where only the most reactive sites are sampled—was 5-10 times the specific surface area. It is proposed that the excess water adsorption capacity of the silane-treated fibers is associated with sites within the silane overlayer. These may be hydroxyls, strained siloxanes, boroxanes, free volume, or microporosity. These sites provide a mechanism for physical and chemical adsorption, swelling, and rearrangement of the adsorbed silane in the presence of water. These observations are consistent with the idea that the adsorbed silane is a chemically... 

Solid-Phase Extractions Using XAD Resins. The Amberlite XAD series (Rohm and Haas Co., Philadelphia, PA, USA) have been most often used for isolation of marine DOM by SPE. XAD resins are nonionic macroporous copolymers that differ in pore size, surface area, and polarity. Their generally large specific surface areas and more-or-less reversible adsorption of organic solutes from aqueous solution have made them well-suited for isolation of selected fractions of DOM from natural waters. Even though XAD resins have been used far more often to... 

The effect of solvent type and aminosilane concentration has been evaluated. The third component in the reaction system is the silica substrate. The surface of the silica gel carries the active sites for adsorption. The concentration of these sites varies with varying silica type, its specific surface area and pretreatment temperature. Additionally, surface adsorbed water has a clear effect on the reaction mechanism. Isotherm data, reported in the previous paragraph, only accounted for fully hydrated or fully dehydrated silica. The effect of the available surface area and silanol number remains to be assessed. Information on these parameters allows the correlation of data from studies in which different silica types have been used. In this part the effect of these parameters in the loading step is discussed. Silica structural effects on the ultimate coating, after curing, are evaluated in the next paragraph. 

Summarizing we may state that, as adsorption isotherms revealed the formation of an equilibrium in the initial stage of the reaction, total loading data after two hours of reaction and filtration reveal that specific surface area and mean pore size are the controlling parameters in the loading step. Surface water causes hydrolysis and polymerization. On a dehydrated surface, a surface coverage irrespective of the number of hydroxyls is formed. For silica dehydroxylated at elevated temperature (1073 K) a different behaviour is observed, suggesting the participation of strained siloxanes. 

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