A generalized scale of free energy of excess adsorption of solute and absolute composition of the interfacial phase

Moles of a surfactant (gamma2(1)) absorbed per unit area of the solid-liquid interface estimated analytically from the difference of the solute molality in the bulk phase before and after adsorption have been quantitatively related to the absolute compositions deltan1 and deltan2 of the solvent and solute forming the inhomogeneous surface phase in contact with the bulk phase of homogeneous composition. By use of isopiestic experiments, negative values of gamma2(1) for the adsorption of inorganic salts onto a solid-liquid interface have been calculated in the same manner. From the linear plot of gamma2(1) versus the ratio of the bulk mole fractions of the solute and solvent, values of deltan1 and deltan2 have been evaluated under a limited range of concentrations. For the adsorption of the surfactant and the inorganic salt respectively onto the fluid interface, gamma2(1) values have been evaluated from the surface tension concentration data using the Gibbs adsorption equation. Gamma2(1) based on the arbitrary placement of the Gibbs dividing plane near the fluid interface is quantitatively related to the composition of the inhomogeneous surface phase. Also, the Gibbs equation for multicomponent solutions has been appropriately expressed in terms of a suitably derived coefficient m. Integrating the Gibbs adsorption equation for a multicomponent system, the standard free energy change, deltaG degrees, per unit of surface area as a result of the maximum adsorption gamma2(m) of the surfactant at fluid interfaces due to the change of the activity alpha2 of the surfactant in the bulk from zero to unity have been calculated. A similar procedure has been followed for the calculation of deltaG degrees for the surfactant adsorption at solid-liquid interfaces using thermodynamically derived equations. deltaG degrees values for surfactant adsorption for all such systems are found to be negative. General expressions of deltaG degrees for negative adsorption of the salt on fluid and solid-liquid interfaces respectively have also been derived on thermodynamic grounds. deltaG degrees for all such systems are positive due to the excess spontaneous hydration of the interfacial phase in the presence of inorganic salt. Negative and positive values of deltaG degree for excess surfactant and salt adsorption respectively have been discussed in light of a generalized scale of free energy of adsorption.     

Sulfate adsorption and surface precipitation on a volcanic ash soil (allophanic andisol)

Sulfate strongly adsorbs on metal oxides and soils with variable charges. However, its surface precipitation has not been clearly evaluated and its adsorption mechanism has been in dispute. In the present study, an allophanic andisol, a typical volcanic ash soil having both negative and positive variable charges, was used to identify the adsorption mechanism of sulfate. Sulfate adsorption isotherms were obtained by a batch method at pH values of 4, 5, 6, and 7 in a wide range of concentrations in an Na-H-SO(4)-OH system. Theoretical isotherms were applied to the measured values for the evaluation. The surface precipitation was detected by the measured adsorption isotherms, and the BET isotherm confirmed the presence of multilayer adsorption. Stronger and weaker adsorption sites were suggested by using the Langmuir isotherm for the monolayer adsorption. The adsorption energies obtained from the Langmuir equation and recent spectroscopic analysis suggested that the stronger adsorption corresponded to an inner-sphere surface complex and that the weaker adsorption corresponded to outer-sphere surface complexation. The BET and Langmuir equations showed three types of adsorption mechanisms for the sulfate adsorption on the soil.     

Adsorption of benzoic acid onto high specific area activated carbon cloth

The adsorption of benzoic acid from aqueous solution onto high area carbon cloth at different pH values has been studied. Over a period of 125 min the adsorption process was found to follow a first-order kinetics and the rate constants were determined for the adsorption of benzoic acid at pH 2.0, 3.7, 5.3, 9.1, and 11.0. The extents of adsorption and the percentage coverage of carbon cloth surfaces were calculated at 125 min of adsorption. Adsorption isotherms at pH values of 2.0, 3.7, and 11.0 were derived at 25 degrees C. Isotherm data were treated according to Langmuir and Freundlich equations and the parameters of these equations were evaluated by regression analysis. The fit of experimental isotherm data to both equations was good. It was found that both the adsorption rate and the extent of adsorption at 125 min were the highest at pH 3.7 and decreased at higher or lower pH values. The types of interactions governing in the adsorption processes are discussed considering the surface charge and the dissociation of benzoic acid at different pH values.     

Adsorption of Some Surfactants onto Polyvinyl Alcohol as Hydrophobic Polymer Surface

The adsorption of different types of nonionic and anionic surfactants from aqueous solutions onto polyvinyl alcohol has been studied at different temperatures using surface tension measurements. The nonionic surfactants show Langmuirian L-shape isotherms whereas the adsorption isotherms of the anionic surfactants exhibit segmoidal shape. The experimental adsorption isotherms could be fitted to the Langmuir equation and the values of Γ_max and A_min have been calculated. The effect of temperature on the adsorption process as well as on both efficiency and effectiveness of adsorption has been studied.     

Thermodynamic analysis of the temperature dependence of OH adsorption on Pt(111) and Pt(100) electrodes in acidic media in the absence of specific anion adsorption

The effect of temperature on the voltammetric OH adsorption on Pt(111) and Pt(100) electrodes in perchloric acid media has been studied. From a thermodynamic analysis based on a generalized adsorption isotherm, DeltaG degrees , DeltaH degrees , and DeltaS degrees values for the adsorption of OH have been determined. On Pt(111), the adsorption enthalpy ranges between -265 and -235 kJ mol(-1), becoming less exothermic as the OH coverage increases. These values are in reasonable agreement with experimental data and calculated values for the same reaction in gas phase. The adsorption entropy for OH adsorption on Pt(111) ranges from -200 J mol(-1) K(-1) (low coverage) to -110 J mol(-1) K(-1) (high coverage). On the other hand, the enthalpy and entropy of hydroxyl adsorption on Pt(100) are less sensitive to coverage variations, with values ca. DeltaH degrees = -280 kJ mol(-1) and DeltaS degrees = -180 J mol(-1) K(-1). The different dependence of DeltaS degrees with coverage on both electrode surfaces stresses the important effect of the substrate symmetry on the mobility of adsorbed OH species within the water network directly attached to the metal surface.     

Adsorption of designed pyrimidine derivative ligands on an activated carbon for the removal of Cu(II) ions from aqueous solution

The adsorption of five Nalpha-substituted amino acids with a 5-nitroso-6-oxo pyrimidine as substituent on a commercial activated carbon (AC) has been studied in aqueous solution at several pH values. The adsorption processes of these organic compounds have been analyzed on the basis of the electrolytic behavior of the adsorbates. In all cases, the adsorption process is highly irreversible due to strong pi-pi interactions between the arene centers of the AC and the pyrimidine residue of the adsorbates. This interaction is consistent with XPS data and HOMO-LUMO theoretical calculations. The adsorption of these organic compounds provides a new route for the functionalization of the AC surface with carboxyl groups. In addition, the adsorption capacity of the AC/organic compound systems for Cu(II) ions in aqueous solution has been studied at different pH values. These systems show an increase of the adsorption capacity for Cu(II) compared to the AC, which is related to the AC functionalization with carboxyl groups due to the adsorbed organic compounds.     

Time-resolved determination of surface diffusion coefficients for physically adsorbed or chemisorbed species on heterogeneous surfaces,by inverse gas chromatography

A new simple method is developed for measuring surface diffusion coefficients Ds of gases adsorbed on heterogeneous surfaces, using the reversed-flow version of inverse gas chromatography. The Ds values are found in a time-resolved way, together with the corresponding adsorption energy values, the local adsorbed concentrations, and the local adsorption isotherm values. A relative dynamic adsorption rate constant, an adsorption/desorption rate constant, and a surface reaction rate constant are also found in the same experiment, together with the total diffusion coefficient of the gas in the solid bed. The method has been applied for carbon monoxide, oxygen gas, and carbon dioxide as adsorbates on 75% Pt+25% Rh catalyst supported on SiO2, at 593.8 K.     

A radiochemical study on the thermodynamics of cesium adsorption on potassium copper nickel hexacyanoferrate(II) from aqueous solutions

This paper reports a radiochemical study on the themodynamics of cesium adsorption on potassium copper nickel hexacyanoferrate(II) (KCNF) using¹³⁴Cs radionuclide as a radiotracer. The values of themodynamic parameters like H ^o , S ^o and G ^o have been calculated using the temperature dependence of cesium adsorption on KCNF. These values indicate the endothermic nature of the adsorption process. Freundlich and Langmuir izotems have shown their applicability for the adsorption of cesium on KCNF at different temperatures and their corresponding constants have been calculated and interpreted. The Dubinin-Radushkevich (D-R) equation has also been applied to the adsorption data and the values of mean free energies of the adsorption process at different temperatures have been evaluated. These values indicate that the adsorption of cesium on KCNF is expected to follow an ion exchange process.     

The adsorption of quaternary ammonium salts at a mercury solution interface: Part II. Non-symmetrical quaternary ammonium salts

The adsorption of triethyl alkyl (and allyl) ammonium bromides on a mercury electrode has been investigated. The isotherms and values of the free energy of adsorption yield information on the mode of adsorption of the cations. The formation of partial bimolecular films on the surface of mercury by the cations studied has been described and a simple explanation put forward concerning the mechanism of destruction of these films.     

Rediscovering the problem of interpretation of chromatographically determined enthalpy and entropy of adsorption of different adsorbates on carbon materials. Critical appraisal of literature data

Adsorbate-adsorbent and adsorbate-adsorbate interactions having decisive influence on the distribution of adsorbate between gas-solid phases in inverse gas chromatography (IGC) have been thermodynamically explained. Specific retention volumes, second adsorption virial coefficients and Kováts retention indices, likewise their dependencies on column temperature, T, number of carbon atoms, n(C) (or methylene groups CH(2)) and mutual ones have been briefly presented. The results of the molar differential enthalpy and entropy of adsorption obtained for different carbon materials employing inverse gas chromatography have been collected and interpreted. An attempt has been made to elucidate abnormal behaviour of the specific and net retention volumes, the second adsorption virial coefficients and the Kováts retention indices, e.g., the magnitudes on which the values of the afore-mentioned thermodynamic values have been determined and compared. The detailed analysis of the errors associated with the experimental parameters necessary for calculating retention volumes, second adsorption virial coefficients and Kováts retention indices has been presented.     

Rapid and efficient removal of Hg(II) from aqueous solution by potassium hexa-titanate: A radiotracer study

The adsorption of mercury(II) on potassium titanate has been studied in chloride media at different pH values, adsorbate concentrations and temperatures. Effect of different ligands and acid concentrations on the uptake was also investigated. Desoprtion studies were also done to check the reversibility of the process. Interestingly a more or less constant and high value of adsorption has been found at different temperatures, pH values and concentrations and a decrease in the uptake with an increase in the bulk acid concentration was observed.     

Adsorption of dioctyldimethylammonium chloride at water/hexane interface

The adsorption behavior of dioctyldimethylammonium chloride at water/ hexane interface has been studied by measuring the interfacial tension as a function of temperature and pressure at various bulk concentrations. By applying the thermodynamics of adsorption at interfaces to the experimental results, the thermodynamic quantity changes associated with adsorption and the interfacial density of dioctyldimethylammonium chloride have been evaluated.The interfacial tension vs temperature and concentration curves have shown the breaks and it has been concluded that the first order phase transition takes place between a gaseous and an expanded state. The entropy and volume changes associated with adsorption have shown the remarkable dependence on temperature and pressure and have been found to decrease with increasing the molality. Also the energy change associated with adsorption has been evaluated and it has been concluded that the adsorption of dioctyldimethylammonium chloride at water/hexane interface is enhanced by negative values of the partial molar energy change. Further, all the thermodynamic quantities have been characterized by the discontinuous change attributable to the phase transition.     

Surface analysis of pyrite applying ESCA

Summary X-ray photoelectron spectroscopy (ESCA) has been applied to investigate the adsorption of xanthate on pyrite immersed in potassium ethyl xanthate solution at different pH values. The xanthate adsorption complex on the pyrite surface was confirmed as the precursor of dixanthogen.     

Adsorption of Promethazine hydrochloride with KSF Montmorillonite

Adsorption of Promethazine hydrochloride (PHCl) onto KSF Montmorillonite from aqueous solution has been investigated. Experiments were conducted at various pH values, ionic backgrounds and solution temperatures. The pseudo-second-order equation successfully predicted the adsorption among the tried kinetics models (pseudo-first-order, pseudo-second-order and intraparticle diffusion). Langmuir, Freundlich and DR adsorption models were used to describe equilibrium isotherms and the isotherm constants were obtained. The increase in solution temperature caused a decrease in the adsorption capacity values found from Freundlich and DR isotherm. The adsorption type can be explained by combined ion exchange and physisorption. Thermodynamic parameters of adsorption of Promethazine hydrochloride (PHCl) onto KSF were also evaluated. The surface morphologies of KSF and PHCl loaded KSF were examined using a scanning electron microscope (SEM). FTIR measurements of samples were also conducted.     

Effects of chemical functional groups on the polymer adsorption behavior onto titania pigment particles

The effects of functional groups on polymer adsorption onto titania pigment particles have been investigated as a function of pH and ionic strength using polyacrylic acid and modified polyacrylamides. The polyacrylamides include the homopolymer, an anionic copolymer with hydroxyl and carboxylate group substitution, and a nonionic copolymer with hydroxyl group substitution. Adsorption isotherms and infrared spectroscopy were used to examine the polymer-pigment interactions. The adsorption of the polyacrylic acid and anionic polyacrylamide on titania pigment is greatest when electrostatic repulsion is absent or reduced. At low pH values, below the pigment isoelectric point (IEP), or at high ionic strength, the adsorption density of the anionic polymers on titania pigment is high, while at higher pH values above the pigment IEP, the adsorption density decreases. But the adsorption of nonionic polymers on titania pigment is not influenced by either ionic strength or pH. Acrylamide groups were found to hydrogen bond with the titania pigment surface, independent of pH. With the inclusion of hydroxyl functional groups into the polyacrylamide chain, the polymer adsorption density increased without increased adsorption affinity. Carboxylate functional groups in the anionic polymers strongly interact with the pigment surface, producing the highest adsorption density at low pH values. All polymers exhibit Langmuir adsorption behavior with hydrogen bonding found as the dominant mechanism of adsorption in addition to electrostatic interaction occurring for the anionic polymers.     

碳纳米管对苯胺的吸附行为

碳纳米管有较大的比表面,有利于用作吸附剂。当前研究主要集中在对气体,尤其是对H2气的吸附。近年来,也有人将碳纳米管应用于环境保护领域,Long等使用碳纳米管除去二恶英,Li等用碳纳米管吸附溶液中的Cd^2 都取得了满意的效果。苯胺类化合物是国家严格控制的一类污染物,使用碳纳米管对苯胺的吸附研究尚未见报道。     

113mIn radioisotope generator system

Tin-indium generator systems were made with commercial hydrated zirconium oxide, silica gel and hydrated zirconium oxide prepared by the AMPHLETT method. The adsorption capacity of tin has been determined by both spectrophotometric analysis and gammaspectrometry. Zirconium break-through has been determined and compared with the literature values. The dependence of the adsorption capacity on the particle size has been investigated. The effect of autoclaving on the generator systems has been examined.     

Bioinert surface to protein adsorption with higher generation of dendrimer SAMs

Interactions between proteins and biomaterial surfaces correlate with many important phenomena in biological systems. Such interactions have been used to develop various artificial biomaterials and applications, in which regulation of non-specific protein adsorption has been achieved with bioinert properties. In this research, we investigated the protein adsorption behavior of polymer brushes of dendrimer self-assembled monolayers (SAMs) with other generations. The surface adsorption properties of proteins with different pI values were examined on gold substrates modified with poly(amidoamine) dendrimer SAMs. The amount of fibrinogen adsorption was greater than that of lysozyme, potentially because of the surface electric charge. However, as the generations increased, protein adsorption decreased regardless of the surface charge, suggesting that protein adsorption was also affected by density of terminal group.     

An experimental study of gas adsorption on fractal surfaces

The validity of the fractal versions of the FHH and BET theories for describing the adsorption of butane and nitrogen on a variety of partially dehydroxylated silica surfaces has been tested. The fractal dimensions obtained from adsorption data have been compared with those obtained completely independently using SAXS. It was found that the fractal dimensions obtained from butane adsorption isotherms, using both the fractal FHH and fractal BET theories, agreed well with the corresponding values obtained from SAXS over overlapping length scales. However, in general, a systematic deviation between the fractal dimension obtained from nitrogen adsorption and that obtained from SAXS was observed. The fractal dimensions obtained from nitrogen adsorption were consistently larger than those obtained from SAXS, which is the opposite of what has often been found in the literature. It has been suggested that the differences in the suitability of the adsorption theories tested to describe butane and nitrogen adsorption is due to the significant difference between the interaction strengths of these two different molecules with silica surfaces. A modified theory that can account for the discrepancy between the fractal dimensions obtained from nitrogen adsorption and SAXS has been proposed. The implications of the new theory for the accuracy of nitrogen adsorption BET surface areas for silicas are discussed.     

On the adsorption of cadmium(II) ions on a HMDE from KF + thiourea aqueous solutions: A chronocoulometric study

The adsorption of cadmium(II) ions from thiourea aqueous solutions has been studied by double potential step chronocoulometry (DPSSC). The adsorption is strong on mercury electrodes and it has been studied as a function of thiourea concentration, cadmium(II) concentration and potential. A discrepancy between the double-layer charge values from either blank solutions or solutions containing reactant obtained by this technique has been found.