Water, acid adsorption

Li, W.K., Gong, X.Q., Lu, G., and Selloni, A. (2008) Different reactivities of Ti02 polymorphs comparative DFT calculations of water and formic acid adsorption at anatase and brookite Ti02 surfaces. Journal of Physical Chemistry C, 112 (17), 6594-6596. 

Avena, M. J. and Koopal, L. K. (1999). Kinetics of humic acid adsorption at solid-water interfaces, Environ. Sci. Technol., 33, 2739-2744. 

Analytical methods for detecting phenol in environmental samples are summarized in Table 6-2. The accuracy and sensitivity of phenol determination in environmental samples depends on sample preconcentration and pretreatment and the analytical method employed. The recovery of phenol from air and water by the various preconcentration methods is usually low for samples containing low levels of phenol. The two preconcentration methods commonly used for phenols in water are adsorption on XAD resin and adsorption on carbon. Both can give low recoveries, as shown by Van Rossum and Webb (1978). Solvent extraction at acidic pH with subsequent solvent concentration also gives unsatisfactory recovery for phenol. Even during carefully controlled conditions, phenol losses of up to 60% may occur during solvent evaporation (Handson and Hanrahan 1983). The in situ acetylation with subsequent solvent extraction as developed by Sithole et al. (1986) is probably one of the most promising methods. 

The situation is quite different in the case of an acetic acid-water system. The energy of acetic acid adsorption on platinum is low and therefore the voltammetric curves taken in the absence and in the presence of acetic acid in the supporting electrolyte are nearly the same. However, radiometric data show that C-labeled acetic acid is adsorbed on the electrode surface. Most likely the acetic acid molecules are adsorbed on the top of the water molecules populating the electrode surface. Simultaneously recorded voltammetric and counting rate data are shown in Fig. 8. 

The surface chemistry of coesite and stishovite was studied by Stiiber (296). The packing density of hydroxyl groups was estimated from the water vapor adsorption. More adsorption sites per unit surface area were found with silica of higher density. Stishovite is especially interesting since it is not attacked by hydrofluoric acid. Coesite is dissolved slowly. The resistance of stishovite is ascribed to the fact that silicon already has a coordination number of six. Dissolution of silica to HaSiFg by hydrogen fluoride is a nucleophilic attack. It is not possible when the coordination sphere of silicon is filled completely. In contrast, stishovite dissolves with an appreciable rate in water buffered to pH 8.2. The surface chemistry of. stishovite should be similar to that of its analog, rutile. 

Porras-Rodriguez, M. Talens-Alesson, F.I. Removal of 2,4-dichlorophenoxyacetic acid from water from adsorptive micellar flocculation. Environ. Sci. Technol. 1999, 33, 3206. 

B° (chlorofoi m 1 which was submitted to partial hydrolysis performed by one of the three following methods ( i) action of 1 3 acetic acid — water at room temperature (ii) addition of 1-5 mg of p-toluenesulfonlc acid to a stirred solution of in a 19 1 chloroform water (iii) adsorption of a solution of 4 (in a mixture of chloroform and water) onto a small column of silica gel for a few hours, followed by classical elution. In each experiment, a mixture of acetates S and 6 (ratio 65 35) was obtained quantitatiuely. These deriuatiues having respectively OH-4 or OH-6 free were separated in high yield. 

Isolation of Organic Acids from Large Volumes of Water by Adsorption on Macroporous Resins... 

We have studied the effect of chemical modification on adsorption properties of natural clinoptilolite (18). Studies of water vapor adsorption show a decrease in adsorption for Dzegvi clinoptilolite, decationized and dealuminized on the water bath, with increased acid concentration, compared with the adsorption of the natural clinoptilolite. The main contribution to adsorption is from primary porosity. 

Bluensomycin was obtained from cultures of Streptomyces verticillus, or the same substance produced by any other means. For example antibiotic was prepared by growing of Streptomyces bluensis NRRL 2876 biological way and isolation from cultural solution by adsorption with a cation-exchange resin or a capillary adsorption method by elution with water-acid solution at pH from 1 to 6 or acidic water solution of acetone. 

Hedges, J.I., and Hare, PE. (1987) Amino acid adsorption by clay minerals in distilled water. Geochim. Cosmochim. Acta 51, 255-259. 

IV sites. A protonated pyridine has never been observed, and the Lewis acid sites on titanium oxides cannot be converted into Br0nsted sites by water vapor adsorption (217). Although Jones and Hockey (216) suggest that the chemistry of surface hydroxyl on rutile corresponds more closely to that of the OH" ion rather than that of the hydroxyl group, no surface reactions similar to that observed with alumina [Eq. (14)] have since been reported. 

Results of Calculations (CTP, CNDO/BW) of the Energetic Characteristics for Different Forms of Water Molecule Adsorption on Acid-Base Sites of H Forms of Zeolites as a Function of the Strength of the Acid site"... 

The presence of surface OH groups or H2 O molecules can play a primary role in adsorption. For example, a microcalorimetric study of the adsorption of stearic acid, from heptane solution, on ferric oxide (Husbands et al., 1971) revealed that preadsorbed water enhanced adsorption of stearic acid. When adsorption takes place from a dry organic liquid, residual surface water may act as special agent. This was shown for the adsorption of a silane coupling agent (y-amino-propyl-triethoxysilane) on silica covered with water molecules for 6 < 1 (Trens and Denoyel, 1996). By the simultaneous determination of adsorption isotherms and the enthalpies of displacement (of heptane by various silanes) it was demonstrated that the amine function was able to displace some of the surface water and make it available for the hydrolysis of the silane into trisilanol, whereas the residual water was able to promote the formation of siloxane bonds between the trisilanol molecules and the surface. 

Bentonite rocks have many uses in the chemical and oil industries and also in agriculture and environmental protection. The usefulness of bentonite for each of these applications is based on its interfacial properties. These properties are determined by geological origin, chemical and mineral composition (especially montmorillonite content), and particle size distribution, and they include the specific surface area (internal and external), cation-exchange capacity (CEC), acid-base properties of the edge sites, viscosity, swelling, water permeability, adsorption of different substances, and migration rate of soluble substances in bentonite clay. 

Hedges, J. I., and P. E. Hare. 1987. "Amino acid adsorption by clay minerals in distilled water." Geochimica Cosmochimica Acta 51 255-259. 

Properties Platelet-type crystalline structure. High porosity, high void volume to surface area ratio, low density, large range of particle size. Insoluble in water and organic solvents soluble in hot concentrated sulfuric acid. Water vapor adsorption capacity of expanded vermiculite less than 1%, liquid adsorption dependent on conditions and particle size, ranges 200-500%. Noncombustible. 

Leenheer and Huffman (1976) have developed a fractionation procedure for aquatic organic solutes called dissolved organic carbon (DOC) fractionation. The procedure for the analytical DOC fractionation is shown in Figure 3. Hydrophobic solutes are first removed from water by adsorption on Am-berlite XAD-8 resin, hydrophilic bases in the effluent are removed by cation-exchange resins, and hydrophilic acids in the effluent are removed by anion-exchange resins. Aquatic humic substances occur primarily in the... 

An extensive list of TVj for quartz, silica gel, rutile, anatase, Sn02, CeOa, a and X AI2O3, boehmite, hematite, amorphous Fe(OH)3, o-FeOOH, MgO and ZnO determined by means of isotope exchange, IR spectroscopy, adsorption-desorption of water, acid-base titration (in this case the number of acidic and basic sites can substantially differ) and chemical reactions of surface OH groups with different species after removal of physisorbed water has been collected by James and Parks [9]. 

Some mention should be made of a pseudo-activated carbon prepared by treating wood, peat, molasses, and similar materials with concentrated sulfuric or phosphoric acid, and heating to 120° to 300° C.69,70 The pseudo-carbon residue, after being washed with water, has adsorptive and ionic-exchange properties. These pseudocarbons should be used in their original wet state because drying causes a loss of adsorptive power. 

---