Sorbate Structure Research Articles

Cluster adsorption of L-histidine on carbon nanotubes at different temperatures

The adsorption isotherms of L-histidine on MKN-SWCNT-S1 CNTs from aqueous solution at temperatures of 25, 35, 45, 55, 65 and 80 °C were interpreted within the framework of the single-layer cluster adsorption model. A new approach to determine the equilibrium parameters of the cluster adsorption isotherm equation and sorbate structure on CNTs, as well as a nonlinear modelling method, was applied. To confirm the cluster nature of amino acid adsorption on CNTs, the clustering criterion proposed in the previous work was applied, and the cluster structure was evaluated, which is significant for the application of CNTs in biomedicine. The found equilibrium parameters of adsorption were applied to the determination of thermodynamic characteristics of adsorption (changes in Gibbs energy, enthalpy and entropy) of L-histidine on CNTs and the character of adsorption was analysed.

Aluminosilicate Mineralogy and the Sorption of Organic Cations: Interplay between Electrostatic Barriers and Compound Structural Features.

Current predictive models of organic cation sorption assume that sorbates interact with all sites on aluminosilicate minerals in the same manner. To examine whether differences in aluminosilicate structure and the resultant changes in electrostatic potential influence the sorption of organic cations, seven smectites were chosen with different proportions of isomorphic substitutions (origin of clay charge) located in octahedral versus tetrahedral layers and with the presence or absence of aluminosilicate interlayers. Sorption coefficients for 14 benzylamine derivatives with systematic differences in compound structures were collected to understand the possible influence of aluminosilicate mineralogy. Benzylamine compounds with methyl group substitution on the charged amine or with electron-donating or -withdrawing ring substituents displayed decreases in cation exchange-normalized sorption coefficients (KCEC), by up to one order of magnitude, between hectorite (100% isomorphic substitution in the octahedral layer) and nontronite (100% isomorphic substitution in the tetrahedral layer). To understand this difference across aluminosilicates, stochastic molecular models of the various aluminosilicate minerals with interlayers were performed. These models showed that negative charge density associated with tetrahedral sites results in high positive electrostatic energy barriers within the interlayer, creating a penalty for compounds with positive charge spread over a larger compound surface area as occurs from primary to quaternary amines. Conversely, clays with charge originating from octahedral sites produce low electrostatic potential barriers within the interlayer, decreasing the penalty for quaternary amine sorption. Trends for nine cationic pharmaceutical compounds, which varied in size, group alkylation, and/or polar substituents, demonstrated similar decreases in KCEC values to aluminosilicate minerals with high electrostatic energy barriers. Overall, aluminosilicate mineralogy was found to exert a large influence (0.5-1 order of magnitude in sorption coefficients) on organic cation sorption. The application of atomistic electrostatic potential mapping of both sorbent and sorbate structures provided insights to explain trends in sorption coefficients that could not be described by the basic electrostatic potential theory or by assuming that sorbate structure moieties yielded additive sorption contributions.

Research of Surface-Active Properties of Waste of Processing of Tin Ores

The object of research is the waste of enrichment of ories of the closed mining enterprise “Solnechny GOK” of the Khabarovsk territory of the Far Eastern Federal district. The article discusses the results of research of surface-active properties of waste of enrichment of tin ories due to their impact on the environment and public health. Sodium oxalate, trilon B, methylene blue, sodium humate were used as sorbates. Methods for the determination of interaction of waste with the sorbates – thermal effect and discoloration of colored complexing agents in the presence of the waste. Titrimetric methods were used to determine the number of reaction centers of waste. For to determine the nature of the active centers of wastes was use the extinguish of the foam generated by the anionic and nonionic surfactants. The influence of molar mass and structure of sorbates on the nature of their interaction with the waste surface is shown. High molecular polydentate complexing agent form a surface film. Low molecular weight sorbates contribute to the formation of soluble complexes of heavy metals and pollution of water systems. The revealed physico-chemical properties will allow to predict the increase in the probability of groundwater contamination by low molecular weight organic complexing agents and also probability of the best fixing of soils on waste in the presence of high-molecular organic substances of soil absorption complex.

The surface-active properties of waste processing of tin ore raw materials

The article presents the results of a study of the surface-active properties of tin ore wastes due to their impact on the environment and public health. The object of the study is the ore dressing waste from the closed mining enterprise “Solnechny GOK” of the Khabarovsk region of the Far Eastern Federal District. Sodium oxalate, Trilon B, methylene blue, sodium humate were used as sorbates. Methods of establishing the fact of interaction of waste with sorbates focused on the discoloration of colored complexing agents in the presence of waste. The use of titrimetric methods allowed us to establish the number of reaction centers of waste. To determine the nature of the active centers of the waste, foam quenching formed by anionic and non-ionic surfactants was applied. The effect of the molar mass and the structure of sorbates on the nature of their interaction with the surface of the waste is shown. Low molecular weight sorbates promote the formation of soluble complexes of heavy metal compounds and contamination of groundwater. High molecular polydentate complexing agents form surface films. The revealed physicochemical properties will make it possible to predict an increase in the probability of contamination of groundwater with low molecular weight organic complexing agents, as well as the probability of a better fixation of soil on waste in the presence of high molecular weight organic substances of the soil absorption complex.

Cooperative model of the histidine and alanine adsorption on single-walled carbon nanotubes

The isotherm of histidine adsorption from an aqueous solution by carbon nanotubes MKN-SWCNT-S1 is constructed. The isotherm has the shape of a sigmoid. The alanine adsorption isotherm by these carbon nanotubes was constructed in previous work and has the shape of two-plateau isotherm. The model is considered describing the adsorption of molecules from the solution with the formation of clusters of i molecules (i = 1,2, … n) on the sorbent surface for which analytical expressions of the isotherm are obtained. This model makes it possible to clarify the sorbate structure on the sorbent surface using the experimental isotherm of adsorption.It is shown that the obtained experimental isotherm of histidine adsorption reflects the cooperative amino acid sorption, consisting in the formation on the sorbent's surface the monomers and clusters of 4 and 8 layers of histidine zwitterion ions. Experimental isotherm of alanine adsorption reflects the cooperative amino acid sorption, consisting in the formation of monomers and seven-dimensional clusters on the sorbent surface. The experimental adsorption isotherms and the proposed model were used to determine the monolayer capacities of the CNT to the investigated amino acids and to estimate specific surface area of nanotubes.

Компьютерное моделирование межчастичных взаимодействий в фазе анионообменника при необменной сорбции аминокислот

Исследованы межчастичные взаимодействия в фазе анионообменника АВ-17в Сl-форме при необменном поглощении биполярных ионов глицина, фенилаланина и триптофана. Квантово-химическое моделирование образующихся структур проводили с помощью программы Gaussian 03 методом гибридного функционала плотности B3LYP в базисе 6-31G++(d,p). Показано, что усложнение строения радикала аминокислоты приводит к уменьшению выигрыша энергии сорбции

Sorption of organic cations onto silica surfaces over a wide concentration range of competing electrolytes

The fundamental understanding of organic cation-solid phase interactions is essential for improved predictions of the transport and ultimate environmental fates of widely used substances (e.g., pharmaceutical compounds) in the aquatic environment. We report sorption experiments of two cationic model compounds using two silica gels and a natural aquifer sediment. The sorbents were extensively characterized and the results of surface titrations under various background electrolyte concentrations were discussed. The salt dependency of sorption was systematically studied in batch experiments over a wide concentration range (five orders of magnitude) of inorganic ions in order to examine the influence of increasing competition on the sorption of organic cations. The organic cation uptake followed the Freundlich isotherm model and the sorption capacity decreases with an increase in the electrolyte concentration due to the underlying cation exchange processes. However, the sorption recovers considerably at high ionic strength (I>1M). To our knowledge, this effect has not been observed before and appears to be independent from the sorbent characteristics and sorbate structure. Furthermore, the recovery of sorption was attributed to specific, non-ionic interactions and a connection between the sorption coefficient and activity coefficient of the medium is presumed. Eventually, the reasons for the differing sorption affinities of both sorbates are discussed.

The differential Gibbs free energy of sorption of an ionizable organic compound: eliminating the contribution of solute–bulk solvent interactions

Sorption of ionizable organic compounds (IOCs) from solutions is of great significance in multiple processes but its understanding is complicated by IOC speciation. Experimental separation of contributions of differently ionized species to the overall IOC sorption is not always feasible, due to the possibility of sorbent changes/decomposition upon varying pH. Even when such a separation is successful, accounting of ionized solute–bulk solvent interactions is not obvious. Therefore, actual interactions in a sorbed phase are “masked” by solute–bulk solvent interactions, thus complicating relating IOC sorption interactions to a compound structure. A new thermodynamic concept is proposed which reformulates the differential Gibbs free energy of IOC sorption in such a way that the initial thermodynamic state of the sorption process is the solution reference state associated with a non-ionized form of IOC. Hence, IOC ion–bulk solvent interactions are excluded from consideration. These redefined differential Gibbs free energies of sorption do not require separating the whole IOC sorption into the contributions of different species; however, if such a separation is possible, it converts the overall sorption process into the two quantified steps: (1) neutral IOC sorption and (2) turning on the sorbed IOC ion–sorbent interactions. The suggested definition of the sorption process makes also possible the further elimination (or minimizing) of IOC–bulk solvent interactions, by converting the molecular IOC solution reference state to another molecular reference state in an inert medium (i.e., the gas phase or inert solvents). Finally, the differential Gibbs free energies of sorption “cleaned” of IOC–bulk solvent interactions can be examined in terms of organic sorbate structure effects, with the focus on the interactions in a sorbed state. The concept is illustrated by the experimental data on soil sorption of IOCs from aqueous solutions.

Equilibrium parameters of a liquid—vapor system and thermodynamic characteristics of adsorption of cyclic and cage hydrocarbons in squalane

The thermodynamic characteristics of adsorption of adamantane molecules and its alkyl derivatives, as well as some mono- and bicyclic hydrocarbons C10H n , were studied by equilibrium gas liquid chromatography on a column packed with the stationary liquid phase squalane under the conditions of infinitely low concentrations of the sorbate in the gas phase. The influence of specific features of the molecular structure of sorbates on the regularities of their retention on the column with squalane was shown. For the first time we obtained the limiting activity coefficients and excess thermodynamic functions of mixing, which made it possible to study in detail the thermodynamics of dissolution of cage molecules in the nonpolar liquid bulk. The changes in the molar isobaric heat capacity of sorbates during adsorption were determined by the chromatographic method. For reference compounds, these values agree well with the results of direct calorimetric measurements of the change in the molar standard isobaric heat capacity during vaporization.

Regularities in adsorption of anthocyans by natural clays

Regularities of adsorption by clay of some commercial sorts of anthocyans extracted from plant materials are investigated. The interrelation between sorption ability and structure of sorbates is revealed. Introduction of organic solvent is shown providing a possibility of targeted changing sorption properties of system and sorption purification of anthocyans.

Effects of Native Organic Material and Water on Sorption Properties of Reference Diesel Soot

Soot has been considered as a potentially important sorbent for organic contaminants in soils, sediments, and aerosols. This paper demonstrates that native (authigenic) extractable organic material (EOM) and surface-covering water on soot may have a substantial influence on sorption properties of the soot. Sorption isotherms were determined for apolar and weakly polar sorbates (n-octane, cyclooctane, n-propylbenzene, naphthalene) from an aqueous solution to a standard reference material of diesel soot (SRM 2975) in the original state and after extraction with methanol. For all sorbates tested, removal of EOM from soot by methanol caused the sorption isotherms to be more nonlinear (decrease of Freundlich exponents by 0.19-0.25) compared to the untreated soot. The changes in the isotherms depend on both sorbate structure and sorbate concentration and can be accounted for by two opposing roles that EOM could have on the sorption properties of soot (i) enhancing the overall sorption by absorbing the sorbate into the EOM phase, and (ii) attenuating the sorbate adsorption to the soot carbon surface through sorption competition or site blockage. The n-alkane-to-cycloalkane sorption coefficient ratios (Kn/Kc) indicated that the removal of EOM altered the sorption mode for alkanes from absorption to adsorption. A comparison of the sorption isotherms measured in aqueous suspensions with the soot-air sorption coefficients reported for SRM 2975 in the literature showed that sorption to "soot in water" is significantly weaker than sorption to "soot in air", indicating that complete surface coverage with water suppresses the sorption by soot.

Recent developments in the molecular modeling of diffusion in nanoporous materials

Molecular modeling has become a useful and widely used tool to predict diffusion coefficients of molecules adsorbed in the pores of zeolites and other nanoporous materials. These simulations also provide detailed, molecular-level information about sorbate structure, dynamics, and diffusion mechanisms. We review recent advances in this field, including prediction of various transport coefficients (Fickian, Onsager, Maxwell–Stefan) for single-component and multicomponent systems from equilibrium and non-equilibrium molecular dynamics (MD) simulations, elucidation of anomalous diffusion effects induced by the confining pore structure, and prediction of slow diffusion processes beyond the reach of MD simulations.

Sorption behavior of nonylphenol in terrestrial soils.

Nonylphenol (NP) as an intermediate from anaerobic degradation of widely used nonionic surfactants occurs widespread in the environment. Partition behavior of this toxic and endocrine-disrupting chemical between soil and water was not examined until yet. The objective of this investigation was to quantify sorption and desorption behavior of 4-nonyl[14C]phenol in a set of 51 soils using the batch equilibrium approach. Kinetic studies indicated apparent equilibrium within 20 h. Sorption was influenced by sorbate structure as could be shown with branched 4-nonyl[14C]phenol and the linear 4-n-NP, respectively. Linear 4-n-NP behaves differently from the branched isomers of 4-NP. Sorption of 4-nonyl[14C]phenol tested with five different initial concentrations resulted in linearly fitted isotherms that provided calculation of sorption partition coefficients (KP). Desorption partition coefficients (KP-des) revealed hysteresis independent of soil properties but decreasing with decreasing initial NP concentrations. KP values were correlated with organic carbon content of the soils yielding a log KOC of 3.97.

Binding of Polychlorinated Biphenyls to Aquatic Humic Substances: The Role of Substrate and Sorbate Properties on Partitioning

Two ortho- (2,2{prime},5 and 2,2{prime}5,6{prime}) and a non-ortho- (3,3{prime},4,4{prime}) substituted polychlorinated biphenyl (PCB) congeners were used to study the effects of sorbate structure in binding processes to two lacustrine fulvic acids. Binding constants were determined by solubility enhancement of the solutes by the fulvic acids. The binding of the ortho-trichlorobiphenyl was significantly less than the non-ortho-substituted tetrachlorobiphenyl to both fulvic acids. Surprisingly, the measured ortho-trichlorobiphenyl binding constant to both fulvic acids was approximately the same as the ortho-substituted tetrachlorobiphenyl. The effect of the chlorines in the ortho position inhibits free rotation around the 1,1{prime} carbon bond, thereby making the molecule less able to interact effectively with the fulvic acid substrate relative to its non-ortho-substituted congeners. Finally, binding of all three PCBs to the Great Dismal Swamp fulvic acid was significantly higher than for the Pony Lake sample. This observation is attributable to the former substrate`s higher degree of aromaticity and polarizability, which can potentially interact more favorably with the PCBs through an increase in van der Waals type interactions.

Zeolite acidity ranking by the framework–sorbate interaction energy simulation

A new simulation protocol, based on molecular mechanics with systematic sampling, was developed to calculate efficiently the adsorption structure of sorbates on zeolite without long-time simulations. Using this technique in combination with the force field parameters appropriately chosen, the interaction energies between zeolite framework and sorbates were calculated. They could reproduce the tendency of the experimental heat of adsorption of ammonia, pyridine, 2-methylpyridine, and isopropylamine on mordenite, ZSM-5, and Y. The higher heat of adsorption could be explained from the favorable framework–sorbate interaction, the importance of which should be recognized. The simulation procedure established here allows the selection of the best types of zeolite from a large number of candidates for its simplicity by ranking them according to their acidity or activity, and would assist catalyst development in industry by providing a research guideline.

Organic Cosolvent Effects on Sorption Kinetics of Hydrophobic Organic Chemicals by Organoclays

Data obtained from batch kinetics sorption experiments for naphthalene and diuron using two organoclays [trimethylphenylammonium (TMPA)-clay and benzyldimethyltetradecylammonium (BDTDA)-clay] in aqueous and methanol−water systems were analyzed with a first-order one-site mass transfer model (OSMTM) to obtain kinetic parameters. The mass transfer coefficient (e) exponentially decreased as the sorption coefficient (Kp) increased, and a log-linear increase in e was observed with an increase in the volume fraction of cosolvent (f c) in the system. Regression equations relating e to f c, measured in mixed solvents, could be extrapolated to f c = 0 to obtain the coefficients in aqueous systems. The organic cosolvent effects on the sorption kinetics behavior of naphthalene and diuron depended on the sorbate structure, the cosolvent fraction, and the arrange ment of the exchanged quaternary alkylammonium ions in montmorillonite-clay interlayers.

Structure of Dipole Chains in an MFI Type Molecular Sieve

Several experimental methods demonstrate that adsorbed p-nitroaniline (pNA) forms a highly ordered guest structure in the pores of the MFI type molecular sieve Sb-Silicalite-1. The pNA molecules were located in the intersections of the two interconnected pore systems using single-crystal X-ray structure analysis. The molecular axes of the pNA molecules were found to deviate uniformly by 11° from the direction of the straight channels. The symmetry of the loaded molecular sieve crystals is altered by the pNA adsorption which is connected with the loss of inversion symmetry characterizing the unloaded crystals. The molecular orientation of the occluded pNA was confirmed by polarized Raman spectroscopy. Additionally, the Raman spectra inedicate the absence of intermolecular hydrogen bonding. Optical SHG (second harmonic generation) studies confirm the loss of inversion symmetry which is caused by the formation of oriented dipole chains with a preferred direction over macroscopic regions in the crystal. This sorbate structure is explained by a special uptake mechanism of the pNA molecules entering the molecular sieve pores. The pNA dipole chains in the MFI type framework match the lattice; they are weakly interconnecting and they are collectively aligned into the same direction.

Quantitative structure‐activity relationships for evaluating the influence of sorbate structure on sorption of organic compounds by soil

AbstractThe purpose of this work was to investigate the effect of sorbate structure, by using the quantitative structure‐activity relationship (QSAR) approach, on sorption of organic compounds by two soils with different amounts of organic matter. Miscible displacement experiments were performed with several organic contaminants representing six classes of nonpolar, nonionizable organic chemicals, including chlorinated aliphatics, chlorobenzenes, polycyclic aromatic hydrocarbons (PAHs), n‐alkylbenzenes, methylated benzenes, and polychlorinated biphenyls (PCBs). The breakthrough curves were analyzed by using a bicontinuum model wherein sorption is assumed to be instantaneous for a fraction of the sorbent and rate limited for the remainder. The QSAR approach was used to investigate the dependency of both equilibrium and nonequilibrium sorption coefficients on topological descriptors representing structural properties of the solutes. For both equilibrium and nonequilibrium parameters, the first‐order valence molecular connectivity (1Xv) was found to be the best topological descriptor. Most of the rate‐limited sorption behavior could be explained by accounting for the size and structure of the solute molecule, as indicated by the good correlation between the rate coefficient and 1Xv. This supports the contention that rate‐limited sorption in these systems is controlled by a physical diffusion mechanism, consistent with the polymer diffusion model. Based on this model, the calculated diffusion‐length ratios for the Borden and Mt. Lemmon soils, which have a large difference in organic‐matter contents, compare favorably to the values determined from the measured rate data.

Influence of sorbate structure on nonequilibrium sorption of organic compounds

The authors investigate the relationship between sorbate structure and nonequilibrium sorption. The rate-limited sorption of compounds representing eight classes of organic chemicals, including chlorinated benzenes, unsubstituted and alkyl-substituted aromatics, chlorinated ethenes and ethanes, chlorinated phenols, nitrogen heterocycles, s-triazines, substituted amides, and substituted ureas, was examined by use of a single sorbent (sandy aquifer material) and the miscible displacement technique. The breakthrough curves were analyzed by using a bicontinuum model wherein sorption is assumed instantaneous for a fraction of the sorbent and rate limited for the remainder. Sorbate structure was shown to exert minimal impact on the nature of rate-limited sorption for nonionic, low-polarity compounds comprising relatively simple structures and for ionogenic compounds in neutral form. In contrast, sorbate structure appeared to have a significant impact for compounds comprising more complex structures (i.e., pesticides). First-order reverse rate constants determined for the pesticides were at least 1 order of magnitude smaller than those of the non-pesticides. This difference was attributed to differences in degree of constraint on diffusion within the polymeric structure of organic matter.

Weak base polystyrene anion exchangers II Relation between their structure and structure of sorbates

AbstractThe influence of the structure of styrene‐divinylbenzene copolymers, which make up the matrix of weak base anion exchangers with mono‐ and diethanolamine functional groups on their sorption properties in relation to acid dyes with increasing molecule size has been investigated. It has been found that the copolymer gel heterogeneity induced by the presence of an inert diluent has a marked effect on the degree of sorption and its course. The acid dyes with a higher sulfonic group content were found to be sorbed mainly by the formation of aggregates in the ion exchanger, and the homogeneity of their structure facilitates the process.