Differences In Adsorption Properties Research Articles

Simultaneous adsorption of anionic and cationic species on UiO-66 and MIL-125 MOFs: Mechanisms & selectivity

Metal-organic frameworks (MOFs) have attractive properties, including regular pore structure, high specific surface area, tunable surface properties, and abundant active sites. Such properties have boosted their recent development in many fields, including water treatment. In this study, MOFs composed of tetravalent metals (Ti4+ and Zr4+) and dicarboxylate linker (terephthalate – BDC) were modified using surface functionalization and/or pore structure through defect engineering to enhance adsorption properties. It has been shown that the Ti-containing materials (MIL-125) show a greater affinity for cationic species, while the Zr-containing samples (UiO-66) have a higher affinity for anionic species. Surface charge and electrostatic interactions could account for such a difference in adsorption properties. Zeta potential measurements showed that MIL-125 has a more negative surface charge for both non-functionalized and amino-functionalized versions, which favors the interaction with cationic molecules. On the other hand, UiO-66 has a more positive surface, which facilitates interactions with anionic molecules. Within each MOF family, the non-functionalized structures emerged as the best-performing materials. Specifically, MIL-125(H) and UiO-66(H)_5eq, with 5eq denoting the amount of H2O added during synthesis, showed superior performance. Furthermore, by performing simultaneous adsorption experiments with anionic and cationic contaminants, it was found that the adsorption of the anionic dye acid orange 7 (AO7) onto the UiO-66 framework is primarily based on specific interactions between the sulfonic group (-SO3-) within the AO7 molecule and the inorganic core Zr6O4(OH)4 of UiO-66. The interaction between MIL-125 and the cationic dye methylene blue (MB) was found to be more delocalized, based on electrostatic and π-π interactions between the benzene domains. Finally, except for MIL-125(H), all the tested MOFs showed high stability in water and in the adsorption process. The higher stability of UiO-66 over MIL-125 materials can be attributed to steric effects and lower metal electronegativity. Compared to MIL-125(H), the higher stability of MIL-125(NH2) is probably related to the formation of intramolecular hydrogen bonds.

Understanding the adsorption and potential tear film stability properties of recombinant human lubricin and bovine submaxillary mucins in an in vitro tear film model

The wetting and adsorption properties for two glycoproteins, recombinant human lubricin and bovine submaxillary mucins (BSM) were evaluated on hydrophilic and hydrophobic glass dome surfaces in a simplified in vitro tear film model. We show that both recombinant human lubricin (rh-lubricin) and BSM solutions render surfaces hydrophilic and when the fluid films reach 500 nm or less, the fluids resist evaporation-driven breakup through a volumetric flux across the surface, which we believe is due to evaporation-driven solutocapillary flows. rh-Lubricin was able to maintain a wet film without spontaneous breakup for longer periods of time than BSM at lower concentrations, which we attribute to differences in adsorption properties, measured by QCM-D, that result from surface charge and structural differences (confirmed by zeta potential, DLS, and SAXS measurements).

Computer aided design of water-resistant adsorbent for formaldehyde abatement

Formaldehyde is a well-known indoor air pollutant that is regulated by authorities worldwide. Formaldehyde has adverse health effects in humans, especially as a sensory irritant to the eyes and to the upper air way, and more importantly, it is a known carcinogen. Adsorption by carbon adsorbents is an old, but indispensable cleaning technology for combating indoor formaldehyde. In this study, we report isotherms and 2D-density distributions by conducting comprehensive Monte Carlo simulation. The effects of the functional group and pore size were investigated. We found that formaldehyde has a different response when the number of functional group and pore size change from that of water. Therefore, by tuning pore size and functionalities it may be feasible to produce real materials that retain effective capture of formaldehyde but which avoid pore blocking by water based on the differences in adsorption properties between water and formaldehyde.

A new method for determination of heavy metal adsorption parameters in compacted clay by batch tests

Evaluation of adsorption properties of pollutants on artificial or natural clay strata is normally considered in investigations of soil and groundwater pollution. Batch adsorption tests can be used to obtain the adsorption parameters of clay particles; however, the results from these tests are usually very different from the adsorption of actual clay strata. If the adsorption parameters obtained by batch tests are used to directly evaluate the properties of adsorption of pollutants onto compacted clay, the predicted groundwater and soil pollution will be unsafe. Although the column diffusion tests are closer to the actual situation, they may require much more time, and diffusion and adsorption occur simultaneously in tests, making it difficult to accurately determine the adsorption parameters. To solve this problem, batch adsorption and column diffusion tests were conducted using three kinds of clay materials to investigate the mechanism of the differences in adsorption properties of heavy metal on clay particles and in compacted clay. The amount of adsorption per unit particle surface area of clay particles was found to be equal to that per unit pore surface area of compacted clay. A new simplified method was proposed to determine the adsorption parameters in compacted clay. It is easy to use and provide a reference for prediction and evaluation of soil and groundwater pollution.

Difference in adsorption properties of Fe(III), Mo(VI) oxides and Fe(III) molybdate as a cause of high selectivity of methanol oxidation on iron molybdate catalyst

Difference in adsorption properties of Fe(III), Mo(VI) oxides and Fe(III) molybdate as a cause of high selectivity of methanol oxidation on iron molybdate catalyst

A contrastive study of adsorption behaviors on polyurethane fiber with diester/diurethane tethered and non-tethered azo disperse dyes

To look for a way to improve the fastness properties of disperse dyes on PU fibers, six diurethane/diester tethered azo disperse dyes were prepared and applied to the dyeing of polyurethane fibers. Their detailed adsorption behaviors including the dyeing rate, build-up properties, surface-adsorbed state of dyes and colorimetric properties were investigated as well as compared with those of non-tethered azo dyes. The results showed that there were great differences in adsorption properties between the two types of dyes. The excellent build-up performance of the non-tethered dyes was caused by the crystal growth on the surface of polyurethane fibers, and the serious aggregation of dyes on the surface of fibers would alter the color shade, decrease the chroma and produce poor colorfastness properties. When the tethered dyes were applied to polyurethane fibers, owing to their larger molecular sizes, a higher temperature (120 °C) was needed to finish the dyeing process within a conventional time of 30–40 min, and the crystal growth on the surface of polyurethane fibers was obviously restricted, so that the color of dyed PU fibers became bright and the colorfastness was notably improved. With additional dye concentration, a medium color depth was obtained. It was further demonstrated that the tethering modification of azo disperse dyes to enhance the colorfastness on polyurethane fibers was feasible.

Stratification of Granular Activated Carbon Filters for Advanced Wastewater Treatment

Advanced wastewater treatment with granular activated carbon (GAC) is a promising option to reduce emissions of organic micropollutants (OMP) into the aquatic environment. Frequent back-washes of the GAC filters are required due to high particle concentration in the treated wastewater but lead to stratification. Differences in adsorption capacities of individual strata are not known. The present study aimed at investigating physical and chemical differences at different filter depths of a stratified GAC filter. Two different commercial products were stratified during repeated filter bed expansions and sectioned into vertical fractions. Bulk densities, grain size distributions and ash contents of the individual fractions differed significantly. Adsorption tests with pulverized GAC from different levels showed great vertical differences in adsorption properties. OMP removals determined in the upper part of a GAC filter therefore cannot be extrapolated downwards. Both physical and chemical vertical heterogeneities with regard to adsorption capacities and residence times at different filter depths should be considered in the filter design, in the monitoring of a GAC filter, and in the interpretation of the GAC filter performance. Good correlations between abatements of UV light absorption and OMP removals were found for the virgin GAC throughout the non-uniform filter.

Rate of bubble coalescence following dynamic approach: collectivity-induced specificity of ionic effect.

A simple, quantitative model is suggested to explain the specificity of ions with respect to inhibition of bubble coalescence following a dynamic approach. For the first time, the mode of thinning of the film in between the bubbles, as determined by the density of the bubble dispersion, is recognized as a determining factor. The specificity of the ionic effect is explained by a major difference in adsorption properties of ions, which is enhanced by the film thinning. This leads to charge separation that forms an electrical double layer at each interface of the thin, liquid film, and consequently to electrostatic repulsion. This effect is described by a simple theoretical model that consists of two fundamental equations: mass conservation of each ion in the film, and the Gibbs adsorption equation. In addition, we explain the rapid coalescence of bubbles in purified water under dynamic conditions, which is in contrast with the very slow coalescence under quasi-static conditions.

Comparison of adsorption isotherms of single-ringed compounds between carbon nanomaterials and porous carbonaceous materials over six-order-of-magnitude concentration range

Understanding the mechanisms controlling the differences in adsorption properties between carbon nanomaterials (CNMs) and porous carbonaceous materials—particularly, the structure–activity correlations—is critical for exploring CNMs as special adsorbents for environmental applications. In this study, batch adsorption isotherms of 4-chloronitrobenzene (planar, aromatic) to three CNMs (single-walled carbon nanotubes/SWNT, multi-walled carbon nanotubes/MWNT, and graphene) and three porous carbonaceous materials (two activated carbons/ACs, and a template-synthesized mesoporous carbon/CMK-3) were compared with those of trans-1,2-dichlorocyclohexane (nonplanar, aliphatic) to the respective adsorbents. The isotherms covered a concentration range of over six orders of magnitude. After being normalized by the adsorbent total surface area, adsorption of 4-chloronitrobenzene to CNMs was stronger than to ACs and CMK-3, likely due to strong π–π stacking between 4-chloronitrobenzene and the well-crystallized and open accessed graphitic surfaces of CNMs. In contrast, the surface area-normalized adsorption of trans-1,2-dichlorocyclohexane was stronger to ACs and CMK-3 than to CNMs, which can be attributed to the stronger micropore-filling effect with porous carbonaceous materials. The proposed adsorption mechanisms were verified by examining the adsorption properties of 1,2-dichlorobenzene and 1,4-dichlorobenzene to SWNT and one of the ACs, as well as modeling the adsorption data with Polanyi theory-based Dubinin–Ashtakhov model.

First-principle study of atomic oxygen and nitrogen adsorption on (1 1 1) β-cristobalite as a model of thermal protection coverage

Atomic oxygen and nitrogen adsorption on the Si site of the (111) face of ideal β-cristobalite is studied within the cluster model using the density functional approach. The M06 and B3LYP functionals are found to be the most appropriate for studying atomic adsorption on silica. The calculations show significant difference in adsorption properties with respect to previously studied (100) β-cristobalite face, but do not reveal remarkable effect of the surface relaxation.

Quantifying Differences in the Impact of Variable Chemistry on Equilibrium Uranium(VI) Adsorption Properties of Aquifer Sediments

Uranium adsorption–desorption on sediment samples collected from the Hanford 300-Area, Richland, WA varied extensively over a range of field-relevant chemical conditions, complicating assessment of possible differences in equilibrium adsorption properties. Adsorption equilibrium was achieved in 500–1000 h although dissolved uranium concentrations increased over thousands of hours owing to changes in aqueous chemical composition driven by sediment-water reactions. A nonelectrostatic surface complexation reaction, >SOH + UO22+ + 2CO32- = >SOUO2(CO3HCO3)2–, provided the best fit to experimental data for each sediment sample resulting in a range of conditional equilibrium constants (logKc) from 21.49 to 21.76. Potential differences in uranium adsorption properties could be assessed in plots based on the generalized mass-action expressions yielding linear trends displaced vertically by differences in logKc values. Using this approach, logKc values for seven sediment samples were not significantly different. However, a significant difference in adsorption properties between one sediment sample and the fines (<0.063 mm) of another could be demonstrated despite the fines requiring a different reaction stoichiometry. Estimates of logKc uncertainty were improved by capturing all data points within experimental errors. The mass-action expression plots demonstrate that applying models outside the range of conditions used in model calibration greatly increases potential errors.

Epoxidation of alkenes and their derivatives over Ti-YNU-1

The catalytic properties of Ti-YNU-1 for the epoxidation of various alkenes and their derivatives have been investigated in detail, and further were made a comparison with those of Ti-Beta. The much higher efficiency of Ti-YNU-1 than Ti-Beta was observed in catalyzing the epoxidation of alkenes and their electron-rich analogues. Although it was less active in the epoxidation of α,β-unsaturated ketones, it showed much higher stability. In contrast, Ti leaching from the framework sites occurred to Ti-Beta, and the leaching degree increased with the carbon number of ketones. It was also shown that the catalytic conditions, including the Ti content in samples, H 2O 2/substrate ratio, reaction temperature and time, acid washing and catalyst amount, significantly influenced the activity, selectivity and H 2O 2 efficiency. Co-oxidation of different alkenes led to the activity and epoxide selectivity being different from those obtained in the oxidation of single olefin as a result of the differences in adsorption properties of substrates over various titanosilicates, which affected the diffusion of substrate molecules and accounted for the unique shape-selectivity of Ti-YNU-1.

N-Paraffins adsorption with 5A zeolites: The effect of binder on adsorption equilibria

The effect of binder on adsorption equilibria of n-paraffins on 5A zeolite was investigated. Some differences in adsorption properties were found between binderless 5A zeolite and 5A zeolite with binder. Compared with binderless zeolite, 5A zeolite with binder showed lower adsorption capacities, larger coalescing factors of characteristic curves, and lower heats of adsorption for n-paraffins. The adsorption amounts comparison and scanning electron microscopes (SEM) analysis indicated that the influence of binder on adsorption capacities of n-paraffins on 5A zeolite adsorbent could be ascribed to the dilution and blocking effects which were brought to zeolite crystals by binder. The binder may change the polar interactions between adsorbates and adsorbent therefore affects the characteristic curves. A decrease in heats of adsorption is mainly due to the adsorption of some adsorbate molecules on the surface of the binder.

Probing the basicity of regular and defect sites of alkaline earth metal oxide surfaces by BF3 adsorption: a theoretical analysis.

The basicity of regular and low-coordinate (LC) sites (steps, edges and corners) at the surface of alkaline earths with NaCl structure (MgO, CaO, SrO, and BaO) has been investigated by using BF3 as a probe molecule. B-O and B-F distances; O-B-F bond angles; B-F asymmetric stretching frequencies; O, B and F 1s core-level binding energies; and the interaction energy of adsorbed BF3 were determined by means of DFT calculations on cluster models. These adsorption properties were compared with those of complexes of BF3 with molecules with various basicities (water, ammonia, phosphine, etc.). We show that many properties of adsorbed BF3, and in particular the experimentally accessible shifts in vibrational frequency, in B and F 1s core levels, and in BF3 desorption temperature, exhibit a linear correlation with the surface basicity as measured by the vertical ionization potential of the oxide anions. On the other hand, shifts of the O 1s core level binding energy do not provide a simple way to detect surface basicity. On a given oxide surface, the differing basicities of various sites result in measurable differences in adsorption properties. This suggests the potential use of BF3 as a probe molecule for titrating LC sites on the surface of ionic oxides.

Effects of aluminum content on the separation properties of MFI membranes

MFI membranes with almost identical film thickness and defect distribution but different Si/Al ratio were evaluated by separation of butane and hexane isomers. Film thickness was evaluated by SEM and defect distribution by porosimetry. When the temperature was varied, the membranes showed similar separation trends for butanes, but clear differences were observed for hexane separation. The hexane separation factor varied with temperature for the silicalite-1 membrane but was constant for the ZSM-5 membrane. It is believed that this difference may be a result of differences in adsorption properties.

Correlation between structure characteristics and adsorption properties of regenerated cellulose fibers

We correlate fine structure with the adsorption behavior of new (lyocell) and conventional (viscose, modal) regenerated cellulose fibers. We have studied the molecular structure, the fine structure and, most important of all, the amorphous regions and voids in the system. Differences in adsorption properties of all three-fiber types were determined by using several methods for quantification of water, dye and iodine adsorption. The structural analysis shows that higher molecular weight, a higher degree of crystallinity and a higher molecular orientation are found in lyocell fibers [1]. Our results obtained by several independent methods demonstrate clearly that the adsorption properties of cellulose fibers depend, with the exception of the portion and orientation of amorphous regions, predominantly on the void system (diameter, volume and inner surface of voids) [2].

Adsorption of Benzoic Compounds onto Stainless Steel Particles

Equilibrium experiment was conducted to investigate the factors determining the adsorption of benzoic acid (BA) and its derivatives,m- andp-hydroxy BA, onto SUS316L stainless steel particles of 8–10 μm diameter and under 100 mesh. Adsorption isotherms of these benzoic compounds were determined in the presence of 0.05MNaCl at pH 4 and 30°C. The adsorptions of the these compounds were described well by a Langmuirian model for both adsorbents. When the maximum number of the benzoic compound adsorption sites was expressed on the basis of unit surface area (N, mol/m2), theNvalues were relatively constant, while the greatest value of the affinity (K, ml/μmol) was obtained forp-hydroxy BA, although its value was in the same range as that of the other two adsorbates. Diffuse-reflectance Fourier transform infrared spectra of the fine adsorbent (8–10 μm diameter) after equilibration suggest that the adsorption mainly takes place through the carboxyl group of the adsorbate–stainless steel surface interaction for all adsorbates, whereas concomitant interaction occurs in part with participation of the phenolic hydroxyl group forp-OH BA adsorbate, accounting for the difference in adsorption properties.

The effect of hydrophobic character of drugs and helix-coil transition of kappa-carrageenan on the polyelectrolyte-drug interaction.

The extent of adsorption of different drug molecules to kappa-carrageenan was investigated in order to evaluate the effect of drug hydrophobicity on the adsorption isotherm. Dialysis experiments were used to determine the amount of drug adsorbed to the polyelectrolyte. The amount of drug on both sides of the membrane was determined spectrophotometrically after attaining equilibrium. CMC for the drugs were determined by the dye solubilisation method. It is shown that the small differences in structure between the drug molecules used in this study still leads to considerable difference in adsorption properties, especially the onset of adsorption. It was also found that the slope of the adsorption isotherms among the drug molecules followed the same pattern as the CMC values for drugs. The extent of adsorption of drugs to the helix from of kappa-carrageenan was much higher than to the coil form. These results suggest that the adsorption of charged drug molecules to an oppositely charged polymer is effected not only by the coulombic interactions, but also by the hydrophobicity of the drug. Furthermore, the adsorption of drug molecules to kappa-carrageenan in the helix form is higher than for the coil form because of the shorter distance between the charges and the thereby enhanced hydrophobic interaction between bound drug molecules.

Crystal growth of calcium oxalate hydrates: A comparative kinetics study

The kinetics of crystallization of calcium oxalate mono-, di-, and trihydrates (COM, COD, and COT, respectively) has been studied in calcium oxalate supersaturated solutions, 0.15 M in sodium chloride at 37°C. With COD and COT at relatively high solid/solution ratios, the reaction product for a limited period corresponds to the starting material. The rate of crystallization is proportional to the square of the relative supersaturation for all three hydrate phases with specific rate constants k g (COT) > k g (COM) > k g (COD). At lower solid/solution ratios the crystallization of COD and COT is accompanied by coprecipitation of the thermodynamically more stable COM. The formation of this phase can be suppressed by the addition of polyphosphate which is adsorbed to a greater extent by COM. The differences in adsorption properties of the three hydrates may account for stabilization of COD which has been observed in a number of renal calculi.

Feldionen-Massenspektren organischer Moleküle

The field ion (FI) mass spectra of aliphatic alcohols from methanol to n-decanol are discussed. The influence of the ion emitter geometry and metal was investigated. Tips as well as thin wires were used as FI emitters. The wires consisted of platinum only, whereas platinum, gold and tungsten were used as emitter tip metals. The difference of the FI mass spectra with tip and wire emitters are mainly due to the difference in field strengths, which are usually lower with wires. The differences of the spectra with platinum and gold tips are correlated with differences in adsorption properties of these metals. The main ions in the FI mass spectra of alcohols besides the molecular ions M are: 2M + 1, M + 1, M — 1, M — 2, CnH2n+1 and (CH2)nOH with varying n-values. The mechanisms of formation of these ions are discussed.