Nitrophenol adsorption, surface area

The specific surface area of only the pyrocarbon (Sc) was determined by p-nitrophenol (PNP) adsorption (assuming preferable adsorption of PNP onto carbon deposits) from an aqueous solution of hydrochloric acid, studied using a Specord M-40 (Karl Zeiss, Jena) UV/vis spectrophotometer at 400 nm. This technique was described in detail elsewhere.12... 

Abstract. Several series of pyrocarbon/silica adsorbents were prepared using fumed oxides of different specific surface areas, and mesoporous silica gel Si-100, as inorganic matrices. Different synthetic and natural polymers as well as glucose were used as carbon precursors. Solutions of phosphoric acid at various concentrations were utilized to prepare functionalized hybrid carbon-silica adsorbents. Nitrogen, p-nitrophenol and Cd(II) adsorption isotherms as well as AFM, XRD and XRF methods were used to estimate the structural and adsorption characteristics of the adsorbents. 

Table 1 Proportions of total amino groups and p-CD (determined by elemental analysis), accessible amines (titration by conductimetry), specific surface areas, pore radii and adsorption capacities of lead cation and p-nitrophenol for the different samples...

The important role of electrostatic interactions is clearly seen in the study of Moreno-Castilla et al. [69] which dealt with the adsorption of substituted phenols (whose pKa ranged from 7.13 for /j-nitrophenol to 10.17 for p-cresol) on a series of well characterized activated carbons, all of which exhibited the expected decrease in uptake at high pH values. Table 27 summarizes the key results. Sample CP-10, with the highest surface area and the most developed porosity, had the highest adsorption capacity for all phenols. However, the pH at which the adsorp-... 

Giles, C.H. and Nakhwa, S.N. (1962). Adsorption XVI The measurement of specific surface areas of finely divided solids by solution adsorption. J. Appl. Chem., 12, 266-73. Lopez-Gonzalez, J., de, D., Valenzuela-Calahorro, C., et al. (1988). Adsorption of p-nitrophenol by active carbons prepared from obve wood. An. Quim., 84B, 47—51. Femandez-Cobnas, J., Denoyel, R., and Rouquerol, J. (1991). Characterization of activated charcoals by adsorption from solution. Stud. Surf. Sci. Catal., 62, 399—408. Somasundaran, P. and Fuerstenau, D.W. (1966). Mechanisms of alkyl sulfonate adsorption at the alumina-water interface. J. Phys. Chem., 70, 90-6. 

Properties BET specific surface area (fraction <2 pm, Na-form) 22.4 m7g [100], specific surface area 7.9 mVg, from p-nitrophenol adsorption from xylene [711,1147,2277,2278]. 

Sometimes mercury porosimetry and adsorption ofp-nitrophenol from an aqueous solution [245, 246] are also used to determine the surface area. The disadvantages of mercury intrusion technique will be discussed below. Regarding the method of adsorption firom solution, its drawback is associated, first of all, with the uncertainty in the determination of the cross-sectional area of the p-nitrophenol molecules, in which the benzene rings may adsorb either transversely or parallel to the surface. Also some sorbents swell in water, and this may lead to a misrepresentation of the surface area of the adsorbing resin in dry state. 

Moreno-Castilla investigated the adsorption behavior of mono-substituted phenols of different solubilities on activated carbons obtained from an original and demineralized bituminous coal. The adsorption capacity of the activated carbon was found to depend on the surface area and the porosity of the carbon, the solubility of the phenolic compound, and the hydrophobicity of the substituent. The relative affinity of the phenolic compound toward the carbon surface was related to the donor-acceptor complexes formed between the basic sites on the carbon surface and the organic ring of the phenol. The adsorption was also influenced by the pH of the solution. Marsh and Campbell observed that the adsorption of p. nitrophenol at low concentrations on polyfurfuryl alcohol and polyvinylidene chloride activated carbons was extremely sensitive to the microporous structure of these carbons and showed adsorption isotherms similar to those of nitrogen or carbon dioxide. The adsorption of p.nitrophenol was so strong at low clc values that the adsorption... 

Surface areas of hydrophilic (hydroxylated) silicas have been measured by adsorption of nitrophenol from water or benzene (79) and phenol from decane or carbon tetrachloride (80, 81). The system must be anhydrous and the solvents dried by molecular sieves. The phenol may be determined by bromine titration or interferometer. Stearic acid is adsorbed from anhydrous methanol and determined by difference by potentiometric titration with alkali. Ttie data given indicate that each stearic acid molecule covers only 20.6 A (82). 

In summary, the utility of micro-SERS spectroscopy for the evaluation of potential-dependent interfacial com-petititve and displacement reactions at chargwl surface has been demonstrated. The data obtained allow the determination of the chemical identity, structure, orientation, competitive and displacement adsorption of cationic surfactants and nitrophenol in the first adsorption layer. The examples of these measurements in the field of surfactants and organic pollutants reviewed in this article were selected to illustrate the sensitivity, molecular specificity of adsorption processes, accuracy, ease of substrate preparation, and manifold applications of Raman analysis. The spatial resolution of the laser microprobe, coupled with the 10 enhancement of the Raman cross-section, means that picogram quantities of material localized to pm-sized surfaces areas can be detected and identified by SERS vibrational spectroscopy. 

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