P-Nitrophenol adsorption

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]. 

Fig. 7a, b. Kinetics of poly(p-nitrophenyl acrylate) chemical adsorption on aminopropyl-Aerosil at 25 °C in dimethylsulphoxide. Filled circles ester group content (pmol/g support), empty c/rc/ei p-nitrophenol release (pmol/g support), a — l%solution b — 5% solution [55]... 

Diffusion-type models have been used for the adsorption of lead, copper, p-nitrophenol, phenol, p-bromophenol, p-toluene sulfonate and dodecyl benzene sulfonate on activated carbon (Hashimoto etal., 1977 Xiu and Li, 2000 Chen and Wang, 2004 Crittenden and Weber, 1978), and ion exchange of ammonia, lead, and other heavy metals on clinoptilolite (Inglezakis and Grigoropoulou, 2003 Cincotti et al, 2001 Semmens et al, 1978 Cooney et al, 1999). 

Adsorption of p-Nitrophenol from Dilute Aqueous Solution 138... 

A similar relationship may be found in the adsorption of other atoms or molecules. Many organic substances with peripheric dipoles when adsorbed on salt layers or on the surfaces of metallic oxides show absorption spectra which are shifted appreciably to the red side of the spectrum. Thus p-nitrophenol, having a maximum of light absorption at 316 m. when adsorbed on CaF2, has its absorption spectrum shifted to the red side and is yellow instead of colorless (175), its absorption maximum being at 365 m i. (176). Adsorbed on BaF2 it shows an absorption maxi-... 

The forces responsible for a second or third layer to be adsorbed cannot be very strong. We may, therefore, not expect multimolecular adsorption to occur at moderately low relative pressures on flat and homogeneous surfaces. By means of absorption spectra a bimolecular adsorption of p-nitrophenol could be established on CaF2 or BaF2 layers (250). The absorption spectrum of the first layer was quite different from that of p-nitrophenol itself, the absorption spectrum of the second layer being practically the same as that of pure p-nitrophenol. The first layer is apparently sufficiently polarized by the salt surface, to enable a second layer to adsorb the second layer, however, cannot accumulate a third layer. It may not be entirely excluded, however, that there is no more place in the capillary space between the salt layers to accommodate a third layer of p-nitrophenol. 

Since the chloroanilines are sufficiently retained (k >5) in a 10 % v/v methanol water eluent, and the Ibuprofen enantiomers are sufficiently retained in a 30 % v/v acetonitrile buffer eluent, these solvents were selected as carrier solvents for the displacement chromatographic separations. Also, these solvents were used to determine the adsorption isotherms of p-nitrophenol and 4-t-butylcyclohexanol on beta-cyclodextrin silica. The isotherms were determined from frontal chromatographic measurements as described in (56). The isotherms are shown in Figs. 7 and 8. Since both isotherms are downwardly convex, p-nitrophenol and 4-t-butylcyclohexanol might prove useful displacers for our test solutes, provided that they are more strongly adsorbed that the solutes. 

Many trial-and-error experiments can be avoided during the development of a displacement chromatographic separation, when the isotherm of at least the most strongly adsorbed sample component is known. Therefore, as the next step, the adsorption isotherms of the most retained iscmers of chloroaniline and Ibuprofen, the examples discussed above, were determined as shown in Figs. 8 and 9. It can be seen by cxnparing the isotherms of the solute and prospective displacer pairs that indeed p-nitrophenol can be used as a displacer for the separation of the chloroaniline iscmers. The situation is more complicated with Ibuprofen and 4-t-butylcyclchexanol because their isotherms cross each other at 1.5 irM. This indicates that successful separations can be expected only below this concentration level. Other examples of crossing isotherms were also reported (69). 

Adsorption isotherms of p-nitrophenol and the most retained isomers of chloroanilines. Conditions 15 cm x 4.6 mm ID column packed with beta-cyclodextrin-silica solvent 10 % v/v methanol water temperature 30 C. 

Abstract. A variety of pyrocarbon/silica gel adsorbents were prepared using commercial mesoporous silica gels Si-40, Si-60, and Si-100 as matrices modified by carbon deposits from pyrolysis of several organic precursors. The second type of hybrid carbon-mineral adsorbents was synthesized using spent natural palygorskite utilized in paraffin purification. The adsorbents were then heated, hydrothermally treated, or modified by additional deposition of carbon. Changes in the structural and adsorption characteristics of hybrid adsorbents before and after treatments were analyzed by microscopy, p-nitrophenol and nitrogen adsorption isotherms, and TG, TEM, XRD, and XRF methods. 

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. 

Figure 3. p-Nitrophenol (PNP) adsorption isotherms (A) and distribution junctions of changes in the Gibbs free energy on the PNP adsorption (B) on carbosils prepared from glucose and Si-100.6... 

Indicators, if their ionizable groups are present almost exclusively at the surface, and if the colour and optical density of both forms are unaffected by this adsorption, may be used for determining the pH at the surface. Using the triethanolamine salt of cetane sulphonic acid, the pu at the surface of the micelles was found colorimetrically by diphenylazo-o-nitrophenol. p-nitrophenol was employed to find the pu in the solution curiously it was more difficult to find a suitable indicator for the bulk than for the surface pH, since almost all indicators are more or less adsorbed at the surface of these paraffin chain salts. Preliminary experi-... 

For example, adsorptives as diverse as iodine (Puri and Bansal, 1965 Kipling, 1965 Molina-Sabio et al., 1985 Femandez-Colinas et al., 1989), p-nitrophenol (Giles and Nakhwa, 1962 Lopez-Gonzalez et al., (1988), salicylic acid (Femandez-Colinas et al., 199 la,b) and various surfactants (Somasundaran and Fuerstenau, 1966) have been used for that purpose in dilute aqueous solution. Organic molecules in hydrocarbon solutions have included lauric acid (de Boer et al., 1962). 

A preparation in two steps has been chosen hrst a new hybrid silica precursor P-CDAPS, containing P-CD groups and amine functions, has been prepared and characterized. Then, this precursor has been co-condensed with tetraethyl orthosilicate (TEOS) via a sol-gel process involving the use of surfactant. We chose the anionic surfactant sodium dodecylsulfate (SDS). The chemical and structural characterization combined with adsorption tests of p-nitrophenol and lead nitrate led to the evaluation of the accessibility and the effectiveness of the binding functions in these hybrid materials. 

Adsorption capacities were studied -by Atomic Emission Spectroscopy (Vista-Pro ICP-OES from VARIAN) for lead analysis and -by UV Spectrometry (Nicolet Evolution 300 from ThermoElectron Corporation) for p-nitrophenol determination. 

Results of adsorption capacities tests are gathered in Table 1. Samples prepared in the presence of SDS present good efficiency towards Pb cations and p-nitrophenol. By comparing two samples with equivalent numbers of accessible amines (e.g TbS 1 and Tb3), we can see that these samples adsorb the same quantities of Pb cations. 

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...

On the other hand, the adsorption of p-nitrophenol is better for samples prepared in the presence of SDS. Indeed, for the same quantity of pCD, TbS2 is more efficient for p-NP adsorption than Tb2. 

A number of molecules have become favourites for study at liquid interfaces and there have been a number of investigations of the adsorption behaviour of p-nitrophenol... 

Lynam, M. M. Kilduff, J. E. Weber, W. J. Adsorption of p-Nitrophenol from Dilute Aqueous Solution An Experiment in Physical Chemistry with an Environmental Approach, J. Chem. Educ. 1995, 72, 80-84. 

Haderlein, S.B., Schwarzenbach, R.P. (1993) Adsorption of substituted nitrobenzenes and nitrophenols to mineral surfaces. Environ. Sci. Technol. 27, 316-326. 

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