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PubMed2005

Adsorption of poly(acrylic acid) onto the surface of titanium dioxide and the colloidal stability of aqueous suspension.

The adsorption of poly(acrylic acid) (PAA) in aqueous suspension onto the surface of TiO(2) nanoparticles was investigated. FTIR spectroscopic data provided evidence in support of hydrogen bonding and chemical interaction in the case of the PAA-TiO(2) system. Adsorption isotherms demonstrated that part of the PAA initially added to the suspension was adsorbed onto the TiO(2) surface, after which there was a gradual attainment of an adsorption plateau. The adsorption density of PAA was found to increase with an increase of PAA molecular weight, while it decreased with an increase of pH. The thickness of the PAA adsorption layer was calculated based on measurements of suspension viscosities in the absence and presence of PAA. It was shown that the thickness of the adsorption layer increased with the increase of pH, PAA molecular weight, and its concentration. The surface charge density, the diffuse charge density, and the zeta potential of TiO(2) varied distinctly after PAA adsorption. The shift of pH(iep) toward a lower pH value was observed in the presence of PAA. PAA was found to stabilize the suspension of TiO(2) nanoparticles through electrosteric repulsion. The influence of factors such as PAA molecular weight and its concentration on the colloidal stability of the aqueous suspension was also investigated.

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PubMed2005

Two-dimensional gas and vacancy solution approaches in the thermodynamic description of adsorption equilibrium.

We present two approaches to description of the adsorption equilibrium in adsorbate-adsorbent systems, the treatment where the adsorbate is considered as a two-dimensional gas, and the treatment where the adsorbate and adsorbent form a solution where the adsorbate is the solute and vacancies play the role of the solvent. In the first case the application of different equations describing the state of a two-dimensional gas leads to some fundamental adsorption isotherm equations, for example, Henry, Volmer, Hill-deBoer, Fowler-Guggenheim, and Langmuir. In contrast, the application of different equations (existing in the theory of solutions) describing the activity of the solvent (e.g., the Wilson model or the model of Flory and Huggins) leads to some new adsorption equations and the assumption of the ideality of the solvent leads to the Langmuir adsorption isotherm. We present some new adsorption equations basing on the second method described above and on the Redlich-Kister and Wohl expansions. Assuming that the activity coefficients are given by the one-constant Margules equation, the two-constant Margules equation, the van Laar equation, the Wilson equation, and, finally, the Flory-Huggins equation, we derive the respective adsorption isotherm formulas. We also present the assumptions leading to the best-known adsorption equations derived applying the first method. The equation developed by Cochran et al. is also corrected, taking into account the fundamental assumptions of the Flory-Huggins theory.

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PubMed2005

Studies on the adsorption of Brij-35 and CTAB at the coal-water interface.

The adsorption behavior of polyoxyethylene (23) lauryl ether (Brij-35) and cetyl trimethyl ammonium bromide (CTAB) on coal sample has been studied. The adsorption process is found to be sensitive to pH, temperature, electrolyte concentration, and the amount of surface active agent. An attempt has been made to explain the adsorption behavior of the surfactants using the Langmuir equation. The extent of adsorption of Brij-35 on coal is found to be the highest at pH 2, which decreases with increase in pH and remains constant in the neutral and alkaline pH regions. But, the adsorption of CTAB exhibits the opposite behavior of that of Brij-35. Adsorption of any of the surfactant at the coal/water interface sharply decreases the apparent viscosity of 55 wt% coal-water slurry (CWS) at a shear rate of 100 s(-1). Electrostatic adsorption of the surfactants on the coal surface decreases the surface charge and renders the coal surface hydrophobic which is manifested in the form of high apparent viscosity of the coal-water slurry under the test conditions.

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PubMed2005

Role of copper chloride on the surface of activated carbon in adsorption of methyl mercaptan.

In this paper, adsorption characteristics of methyl mercaptan on virgin activated carbon and copper chloride impregnated activated carbons were studied by using a dynamic adsorption method in a fixed bed. The activated carbons were characterized by nitrogen adsorption, XRD, TGA and solubility tests. The impregnation of copper chloride on the activated carbon significantly enhanced the adsorption capacity of methyl mercaptan, despite a notable decrease in microporosity. It is likely that copper chloride may act as adsorption site for methyl mercaptan. Copper chloride on the activated carbon in a range of 3-20 wt% Cu content was present mostly in the amorphous form of CuCl(2), according to the results of the solubility, XRD and TGA tests. Starting at 10 wt% in Cu loading, the adsorption capacity for methyl mercaptan decreases gradually. It is likely that a decrease in the degree of copper chloride dispersion and an accessibility of small pores may lead to the decrease in the adsorption capacity of the activated carbon for methyl mercaptan.

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PubMed2005

Adsorption and desorption of copper and zinc in the surface layer of acid soils.

The environmental and health effects of the contamination of soils by heavy metals depend on the ability of the soils to immobilize these contaminants. In this work, the adsorption and desorption of Cu and Zn in the surface layers of 27 acid soils were studied. Adsorption of Cu(II) from 157-3148 mumol L(-1) solutions was much greater than adsorption of Zn(II) from solutions at the same concentration. For both Cu and Zn, the adsorption data were fitted better by the Freundlich equation than by the Langmuir equation. Multiple regression analyses suggest that Cu and Zn adsorption depends to a significant extent on pH and CEC: for both metals these variables accounted for more than 80% of the variance in the Freundlich pre-exponential parameter K(F), and pH also accounted for 57% of the variance in 1/n for Zn and, together with carbon content, for 41% of the variance in 1/n for Cu. The percentage of adsorbed metal susceptible to desorption into 0.01 M NaNO3 was greater for Zn than for Cu, but in both cases depended significantly on pH, decreasing as pH increased. In turn, both pH(H2O) and pH(KCl) are significantly correlated with cation exchange capacity. Desorption of metal adsorbed from solutions at relatively low concentration (787 mumol L(-1)) exhibited power-law dependence on Kd, the quotient expressing distribution between soil and soil solution in the corresponding adsorption experiment, decreasing as increasing Kd reflected increasing affinity of the soil for the metal. The absence of a similarly clear relationship when metal had been adsorbed from solutions at relatively high concentration (2361 mumol L(-1)) is attributed to the scant between-soil variability of Kd at these higher concentrations. In general, adsorption was greater and subsequent desorption less in cultivated soils than in woodland soils.

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PubMed2005

Zinc stable isotope fractionation during its adsorption on oxides and hydroxides.

Adsorption of Zn on goethite, hematite, birnessite, pyrolusite, corundum, and gibbsite was studied using a batch adsorption technique as a function of pH, zinc concentration in solution, and time of exposure. Adsorption from 0.01 M NaNO3 solutions undersaturated with respect to zinc (hydr)oxide at 3 MeOZn+ complexes, where Me=Fe, Mn, and Al, was used to describe the dependence of adsorption equilibria on aqueous solution composition in a wide range of pH and Zn concentration. The logarithms of surface stability constant for Zn interaction with metal oxy(hydr)oxides (>MeOH0+Zn2+-->MeOZn+) vary from -2.5 to 0.5. They are higher for oxy(hydr)oxides than for anhydrous oxides. Stable isotopes of zinc in several filtrates were measured using an ICP-MS Neptune multicollector which made it possible, for the first time, to assess the degree of isotopic fractionation between 66Zn and 64Zn during zinc adsorption on mineral surfaces. The isotopic offset between aqueous solution and mineral surfaces (Delta(66/64)Zn(soln/solid)=delta((66/64)Zn)(solution)-delta((66/64)Zn)(surface)) was found to be weakly dependent on percentage of adsorbed metal and equals 0.20+/-0.03, 0.17+/-0.06, -0.10+/-0.03, -0.10+/-0.09, and -0.13+/-0.12 per thousand for goethite, birnessite, pyrolusite, corundum, and Al(OH)3. For hematite, Delta(66/64)Zn varies from -0.61+/-0.10 per thousand at pH 5.5 to -0.02+/-0.09 per thousand at 5.8 MeOZn(H2O)(n) complexes (available literature data on X-ray absorption spectroscopy). Apparently, the fine structure of surface complexes and the position and bond strength for second neighbors of zinc are likely to control its isotopic fractionation during adsorption on mineral surfaces. Our results strongly suggest that inorganic processes controlling zinc isotope adsorption on soil and sediment minerals should be of second-order importance compared to biological factors.

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PubMed2005

Kinetics and equilibrium adsorption of Cu(II), Cd(II), and Ni(II) ions by chitosan functionalized with 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol.

Chitosan biopolymer chemically modified with the complexation agent 2[-bis-(pyridylmethyl)aminomethyl]-4-methyl-6-formylphenol (BPMAMF) was employed to study the kinetics and the equilibrium adsorption of Cu(II), Cd(II), and Ni(II) metal ions as functions of the pH solution. The maximum adsorption of Cu(II) was found at pH 6.0, while the Cd(II) and Ni(II) maximum adsorption occurred in acidic media, at pH 2.0 and 3.0, respectively. The kinetics was evaluated utilizing the pseudo-first-order and pseudo-second-order equation models and the equilibrium data were analyzed by Langmuir and Freundlich isotherms models. The adsorption kinetics follows the mechanism of the pseudo-second-order equation for all studied systems and this mechanism suggests that the adsorption rate of metal ions by CHS-BPMAMF depends on the number of ions on the adsorbent surface, as well as on their number at equilibrium. The best interpretation for the equilibrium data was given by the Langmuir isotherm and the maximum adsorption capacities were 109 mg g-1 for Cu(II), 38.5 mg g-1 for Cd(II), and 9.6 mg g-1 for Ni(II). The obtained results show that chitosan modified with BPMAMF ligand presented higher adsorption capacity for Cu(II) in all studied pH ranges.

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PubMed2005

An in situ ATR-FTIR study of polyacrylamide adsorption at the talc surface.

The adsorption of a low molecular weight unmodified polyacrylamide (Polymer-N) and a hydroxyl-substituted polyacrylamide (Polymer-H) onto talc was studied using in situ particle film ATR-FTIR spectroscopy in the multiple internal reflection mode. Spectra of the adsorbed polymer were collected as a function of increasing concentration and as a function of time. Measurement of the peak intensities of the adsorbed polymer allowed adsorption isotherms and adsorption kinetics to be determined for both polymers. Langmuir adsorption isotherm analysis of in situ data yielded Gibbs free energies of adsorption (deltaG0(ads)) for Polymer-N and Polymer-H of -44.5 and -45.7 kJ/mol, respectively, which correlate well with similar values determined from ex situ adsorption isotherms. Kinetic analysis indicated that the adsorption of both polymers was a pseudo-first-order process. The apparent rate constants for Polymer-N and Polymer-H were 0.10 and 0.15 min(-1), respectively. Absence of spectral shifts in the spectra of adsorbed polymer is indicative of a hydrophobic interaction between the polyacrylamides and the talc surface.

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PubMed2005

Temperature effect on the zeta potential and fluoride adsorption at the alpha-Al2O3/aqueous solution interface.

The effect of temperature and pH on the zeta potential of alpha-Al2O3 and adsorption of fluoride ions at the alpha-Al2O3/aqueous solution interface has been investigated through electrophoretic mobility measurements and adsorption studies, to delineate mechanisms involved in the removal of fluoride ions from water using alumina as adsorbent. When the temperature increases from 10 to 40 degrees C, the pH of the point of zero charge (pH(pzc)) shifts to smaller values, indicating proton desorption from the alumina surface. The pH(pzc) increases linearly with 1/T, which allowed estimation of the standard enthalpy change for the surface-deprotonation process. Fluoride ion adsorption follows a Langmuir-type adsorption isotherm and is affected by the electric charge at the alpha-Al2O3/aqueous solution interface and the surface density of hydroxyl groups. Such adsorption occurs through an exchange between fluoride ions and surface-hydroxyl groups and it depends on temperature, pH, and initial fluoride ion concentration. At 25 and 40 degrees C, maximum fluoride adsorption density takes place between pH 5 and 6. Increasing the temperature from 25 to 40 degrees C lowers the adsorption density of fluoride.

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PubMed2006

Adsorptive removal of tannin from aqueous solutions by cationic surfactant-modified bentonite clay.

The removal of tannin from aqueous media by cationic surfactant-modified bentonite clay was studied in a batch system. The surfactant used was hexadecyltrimethylammonium chloride. Adsorbent characterizations were investigated using X-ray diffraction, infrared spectroscopy, surface area analysis, and potentiometric titration. The effects of pH, contact time, initial solute concentration, adsorbent dose, ionic strength, and temperature on the adsorption of tannin onto modified clay were investigated. The adsorbent exhibited higher tannin removal efficiency (>99.0%) from an initial concentration of 10.0 micromol/L at pH 3.0. Adsorption capacity decreased from 90.1 to 51.8% with an increase in temperature from 10 to 40 degrees C at an initial concentration of 25.0 micromol/L. The adsorption process was found to follow pseudo-first-order kinetics. Film diffusion was found to be the rate-limiting step. Tannin adsorption was found to decrease with increase in ionic strength. The tannin equilibrium adsorption data were fitted to Langmuir and Freundlich isotherm models, the former being found to provide the best fit of the experimental data. The maximum monolayer adsorption capacity for tannin was 69.80 micromol/g at 30 degrees C. Comparison of adsorption capacity of the modified clay with reported adsorbents in the literature was also presented. Adsorbed tannin on modified clay can be recovered by treatment with 0.1 M NaOH solution. Regeneration experiments were tried for four cycles and results indicate a capacity loss of <10.0%. From the results it can be concluded that the surfactant-modified clay could be a good adsorbent for treating tannin-contaminated waters.

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PubMed2006

Adsorption of atrazine on soils: model study.

The adsorption of the widely used herbicide atrazine onto three model inorganic soil components (silica gel, gamma-alumina, and calcite (CaCO(3)) was investigated in a series of batch experiments in which the aqueous phase equilibrated with the solid, under different solution conditions. Atrazine did not show discernible adsorption on gamma-alumina (theta=25 degrees C, 3.8<pH<12.1) or calcite (theta=25 degrees C, 7.7<pH<11.7). Significant and completely reversible adsorption from solutions was found for silica gel suspensions. The adsorption isotherms obtained for atrazine uptake on silica gel particles were best fitted with the Freundlich model. An increase of the ionic strength of the electrolytic solution induced an increase of the surface concentration of atrazine on silica gel, indicating significant electrostatic interactions between atrazine and silica gel particles, possibly through interaction with the surface silanol groups of the solid substrate. Increase of the pH value of the electrolyte solution from 6 to 9 considerably decreased the amount of atrazine adsorbed on the silica gel substrate. Decrease of the solution pH from 6 to 3 had only a slight effect on the surface concentration of the adsorbed atrazine. The adsorption of atrazine on silica gel increased when the temperature was decreased from 40 to 25 degrees C, an indication that the adsorption is exothermic. The calculated enthalpy of adsorption ( approximately 10 kJ/mol) indicates that the uptake at the solid-liquid equilibrium pH (6.1) was largely due to physisorption.

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PubMed2006

Simultaneous adsorption at the liquid/solid and liquid/gas interfaces.

Physical adsorption from binary or higher-order liquid mixtures on solids is often accompanied by adsorption phenomena at the liquid/gas interface. As long as the adsorption effects are comparable, both interfaces have to be included in the respective thermodynamic equations. A purely phenomenological thermodynamic description in terms of excess quantities is given of the simultaneous adsorption from multicomponent liquid mixtures at the liquid/solid and liquid/gas interfaces. In order to illustrate the thermodynamic procedure, the individual and simultaneous adsorption excess isotherms of three binary liquid mixtures at the liquid/Teflon and liquid/vapor interfaces are calculated from experimental surface-tension and contact-angle data taken from the literature. Special attention is focused on the estimation of error in calculated adsorption isotherms. A line of approach is given to find the confidence limits of adsorption isotherms that cover the entire mole fraction scale. The isotherms as well as their confidence limits are presented and discussed.

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PubMed2006

Adsorption of poly(ethylene oxide) at the air/water interface: a dynamic and static surface tension study.

The adsorption of polyethylene oxide (PEO) homologues in a wide range of molecular weight (from M(PEO)=200 to 10(6)) at the air/aqueous solution interface was investigated by dynamic and static surface tension measurements. An approximate estimate for the lower limit of PEO concentration was given at which reliable equilibrium surface tension can be determined from static surface tension measurements. It was shown that the observed jump in the earlier published sigma-lg(c(PEO)) curves is attributable to the nonequilibrium surface tension values at low PEO concentrations. The adsorption behavior of short chain PEO molecules (M(PEO)1000) is similar to that of the ordinary surfactants. The estimated standard free energy of PEO adsorption, DeltaG(0), increases linearly with the PEO molecular weight until M(PEO)=1000. In this molecular weight range, DeltaG(0) was found to be approximately the fifth of the hydrophobic driving force related to the adsorption of a surfactant with the same number of methylene groups. In the case of the longer chain PEOs the driving force of adsorption is so high that the adsorption isotherm is near saturation in the experimentally available polymer concentration range. Above a critical molecular weight the PEO adsorption reveals universal features, e.g., the surface tension and the surface density of segments do not depend on the polymer molecular weight.

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PubMed2003

Adsorption of crude oil on anhydrous and hydrophobized vermiculite.

This publication reports the adsorption of crude oil on vermiculite samples, expanded and hydrophobized with carnauba (Copernícia Cerífera) wax. The adsorption studies were performed by using columns filled with the vermiculite matrices and by dispersion of the vermiculite samples in an oil-water (50 ppm of oil) emulsion. The hydrate vermiculite exhibits a very low adsorption capacity against crude oil. On the other hand, anhydrous (expanded) and hydrophobized matrices show a high adsorption capacity. The 10% hydrophobized matrix show a 50% increased adsorption capacity, in comparison with the expanded one. For adsorption performed in the water-oil emulsion, saturation of the solid hydrophobized matrix is achieved after 60 min. The hydrophobized samples exhibit adsorption factors in the 0.7-1.0 range.

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PubMed2003

Physicochemical characterization and adsorption behavior of calcined Zn/Al hydrotalcite-like compound (HTlc) towards removal of fluoride from aqueous solution.

A Zn/Al hydrotalcite-like compound (HTlc) was prepared by co-precipitation (at constant pH) method and was characterized by XRD, TG/DTA, FTIR, and BET surface area. The ability of Zn/Al oxide to remove F- from aqueous solution was investigated. All the adsorption experiments were carried out as a function of time, pH, concentration of adsorbate, adsorbent dose, temperature etc. It was found that the maximum adsorption takes place within 4 h at pH 6.0. The percentage of adsorption increases with increase in the adsorbent dose, but decreases with increase in the adsorbate concentration. From the temperature variation it was found that the percentage of adsorption decreases with increase in temperature, which shows that the adsorption process is exothermic in nature. The adsorption data fitted well into the linearly transformed Langmuir equation. Sulfate and phosphate were found to have profound effects on fluoride removal. Thermodynamic parameters such as DeltaG0, DeltaH0, and DeltaS0 were calculated. The negative value of DeltaH0 indicates that the adsorption process is exothermic. The apparent equilibrium constants (Ka) are also calculated and found to decrease with increase in temperature. With 0.01 M NaOH the adsorbed F- could be completely desorbed from Zn/Al oxide in 6 h.

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PubMed2003

Influence of heat treatment of rayon-based activated carbon fibers on the adsorption of formaldehyde.

The influence of heat treatment of rayon-based activated carbon fibers on the adsorption behavior of formaldehyde was studied. Heat treatment in an inert atmosphere of nitrogen for rayon-based activated carbon fibers (ACFs) resulted in a significant increase in the adsorption capacities and prolongation of breakthrough time on removing of formaldehyde. The effect of different heat-treatment conditions on the adsorption characteristics was investigated. The porous structure parameters of the samples under study were investigated using nitrogen adsorption at the low temperature 77.4 K. The pore size distributions of the samples under study were calculated by density functional theory. With the aid of these analyses, the relationship between structure and adsorption properties of rayon-based ACFs for removing formaldehyde was revealed. Improvement of their performance in terms of adsorption selectivity and adsorption rate for formaldehyde were achieved by heat post-treatment in an inert atmosphere of nitrogen.

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PubMed2003

Adsorption isotherms of homologous alkyldimethylbenzylammonium bromides on sodium montmorillonite.

The adsorption of homologous alkyldimethylbenzylammonium bromides, [C(6)H(5)CH(2)N(CH(3))(2)R]Br, on sodium montmorillonite from aqueous NaCl solutions at room temperature has been studied. R stands for the methyl-, butyl-, hexyl-, octyl-, decyl-, and dodecyl-group, and the corresponding ammonium cations will be denoted as C1+, C4+, C6+, C8+, C10+, and C12+, respectively. C1+, the reference cation, attains the plateau region of adsorption at a level close to the cation exchange capacity (CEC) of the clay. The chain-length dependence on adsorptivity of the homologous cations exhibits an unexpected peculiarity. In the case of short-chain homologues of C1+ their adsorption onto sodium montmorillonite decreases in the order C1+>C4+>C6+. This behavior is due, presumably, to the growing steric hindrances at the surface of clay, which occur because of the limited area available for the bulky organic cations at the exchange sites. These limitations appear to be out-balanced in the case of higher homologues for which the increasingly growing hydrophobic effects lead to the expected sequence of adsorptivity of the cations, i.e., C1+<C8+<C10+<C12+. The extent of adsorption of the long-chain homologous cations at the plateau region exceeds the CEC value and indicates the commencement of formation of a bilayer or admicelle. As expected, the adsorption data for the short-chain homologues fit fairly well to the Langmuir isotherm, whereas the data for the C10+ and C12+ cations show an increasing departure from linearity of the corresponding plots. Results of X-ray analysis of organo-clays fully loaded with C1+, C4+, and C12+ cations suggest that in the case of short-chain homologues, the ammonium cations lay flatly and interact relatively strongly with the montmorillonite packet surface, whereas the long-chain homologue forms an interdigitated system of coiled hydrocarbon chains.

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PubMed2003

Adsorption of arsenate from water using neutralized red mud.

The potential for using seawater-neutralized red mud (Bauxsol), a waste from aluminum manufacturing, as an adsorbent for removing As(V) (arsenate) from water is studied. Herein, adsorption characteristics are investigated and it is shown that adsorption follows the Langmuir model, with the adsorption constants indicating the feasibility of the process. Furthermore, the adsorption is found to increase with decreasing pH (i.e., ligand-like adsorption), higher adsorbent dosages, and lower initial arsenate concentrations. The effects of ions are also tested and it is shown that the adsorption of arsenate decreases in the presence of HCO3-, while Cl- has little effect, and Ca2+ increases the adsorption. Water quality assessment after treatment with Bauxsol indicates that none of the trace elements tested are released from the adsorbent. A TCLP leaching test also reveals that the used adsorbent is not toxic. It is foreseen that Bauxsol may be developed into an efficient low-cost adsorbent for (pre-) treating arsenate contaminated waters.

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