Adsorption Of Organic Molecules Research Articles

Adsorption of organic molecules on a melamine-modified porous polymer

Inverse gas chromatography in the infinite dilution regime was used to study the adsorp-tion of organic molecules on a micromesoporous styrene-divinylbenzene copolymer modified with melamine deposited onto its surface in amounts of 10–6, 10–5, 10–4, 10–3, 10–2, and 5•10–2 weight parts. Contributions of different intermolecular interactions and polarity of the samples to adsorption energy values were calculated using LFER and by Dong method. Contributions of methyl group to Helmholtz adsorption energy and to its dispersion compo-nent were determined. The polarity of the modified samples showed a non-linear dependence on the amount of the deposited modifier (pC): at 4 < pC < 6, it increases as the modifier concentration grows, abruptly falls at pC = 3, and does not change with the further decrease in pC. This is probably caused by the formation of melamine intermolecular associates at higher modifier concentrations.

Adsorption of polar organic molecules on sediments: Case-study on Callovian-Oxfordian claystone

The release and transport of anthropogenic organic matter through the geosphere is often an environmental criterion of safety. Sedimentary rocks are widely studied in this context as geological barriers for waste management. It is the case of Callovian-Oxfordian claystone (COx), for which several studies report adsorption of anthropogenic organic molecules. In this study, we evaluated and reviewed adsorption data of polar organic molecules on COx claystone. Experiments were performed on raw claystone, decarbonated and clay fractions. Adsorption isotherms were measured with adsorbates of various polarities: adipate, benzoate, ortho-phthalate, succinate, gluconate, oxalate, EDTA, citrate. A significant adsorption was observed for multidentate polycarboxylic acids as evidenced with phthalate, succinate, oxalate, gluconate, EDTA and citrate (Rd = 1.53, 3.52, 8.4, 8.8, 12.4, 54.7 L kg−1 respectively). Multiple linear regression were performed as a statistical analysis to determine the predictors from these adsorption data. A linear correlation between adsorption data (Rd) and dipole moment (μ) of adsorbates was evidenced (R2 = 0.91). Molecules with a high dipole moment, μ(D) > 2.5, displayed a significant adsorption, Rd≫1 L kg−1. A qualitative correlation can be easily estimated using the water/octanol partition coefficient, Pow, of adsorbates (R2 = 0.77). In this case, two opposite trends were distinguished for polar and apolar molecules. The use of organic carbon content in sediments is relevant for predicting adsorption of apolar compounds, log (Pow)>+1. The oxides/clays contents may be relevant regarding polar molecules, log (apparentPow)<-1. The proposed scheme offers a general methodology for investigation of geo-barriers towards heterogeneous organic plumes.

Tuning the work function of stepped metal surfaces by adsorption of organic molecules

Understanding the binding mechanisms for aromatic molecules on transition-metal surfaces, especially with defects such as vacancies, steps and kinks, is a major challenge in designing functional interfaces for organic devices. One important parameter in the performance of organic/inorganic devices is the barrier of charge carrier injection. In the case of a metallic electrode, tuning the electronic interface potential or the work function for electronic level alignment is crucial. Here, we use density-functional theory (DFT) calculations with van der Waals (vdW) interactions treated with both screened pairwise (vdWsurf) and many-body dispersion (MBD) methods, to systematically study the interactions of benzene with a variety of stepped surfaces. Our calculations confirm the physisorptive character of Ag(2 1 1), Ag(5 3 3), Ag(3 2 2), Ag(7 5 5) and Ag(5 4 4) surfaces upon the adsorption of benzene. The MBD effects reduce the adsorption energies by about 0.15 eV per molecule compared to the results from the DFT + vdWsurf method. In addition, we find that the higher the step density, the larger the reduction of the work function upon the adsorption of benzene. We also study the effect of vdW interactions on the electronic structure using a fully self-consistent implementation of the vdWsurf method in the Kohn–Sham DFT framework. We find that the self-consistent vdWsurf effects increase the work function due to the lowered Fermi level and the increased vacuum level. As a result, the benzene/Ag(2 1 1) system has the lowest work function (3.67 eV) among the five adsorption systems, significantly smaller than the work function of the clean Ag(1 1 1) surface (4.74 eV). Our results provide important insights into the stability and electronic properties of molecules adsorbed on stepped metal surfaces, which could help in designing more appropriate interfaces with low work functions for electron transfer.

Calculating free energies of organic molecules on insulating substrates.

The challenges and limitations in calculating free energies and entropies of adsorption and interaction of organic molecules on an insulating substrate are discussed. The adhesion of 1,3,5-tri(4'-cyano-[1,1'-biphenyl]-4-yl)benzene (TCB) and 1,4-bis(4-cyanophenyl)-2,5-bis(decyloxy)benzene (CDB) molecules to step edges on the KCl(001) surface and the formation of molecular dimers were studied using classical molecular dynamics. Both molecules contain the same anchoring groups and benzene ring structures, yet differ in their flexibility. Therefore, the entropic contributions to their free energy differ, which affects surface processes. Using potential of mean force and thermodynamic integration techniques, free energy profiles and entropy changes were calculated for step adhesion and dimer formation of these molecules. However, converging these calculations is nontrivial and comes at large computational cost. We illustrate the difficulties as well as the possibilities of applying these methods towards understanding dynamic processes of organic molecules on insulating substrates.

Adsorption of Phthalates on Activated Carbons in Monosolute Solution and in Mix Within Complex Matrices

Phthalates are considered as dangerous priority pollutants, several effects being attributed to them: foetal deformations, cancers, and endocrine disruptions. Activated carbons are highly efficient materials for the adsorption of numerous organic molecules. Before their use, it is important first to determine both textural and chemical properties and to study kinetics and thermodynamics adsorption, to understand and to optimize the interactions between material and molecules. The aim of this work was to study the kinetics and the adsorption isotherms of three phthalates (dimethylphthalate, diethylphthalate, and diethylhexylphthalate) currently found in industrial effluents, on two different activated carbons. The co-adsorption of these molecules in a synthetic mix and in complex matrices was modeled. The kinetic study and adsorption isotherms of dimethylphthalate and diethylphthalate in monosolute and bisolute were first investigated, followed by a similar study with a mix of the three molecules in complex matrices (surface water (Loire and Loiret Rivers near Orleans city) and municipal wastewater treatment plant outflow). The pseudo-second-order kinetic model was used to determine the kinetic adsorption parameters. The Langmuir equation was used to calculate the surface occupied. Results showed that non-electrostatic interactions are predominant in phthalate adsorption in complex matrices, mainly due to dispersion forces and hydrophobic interactions.

SMALL MOLECULES ADSORBED ON SILICON SURFACES: TWO CASES THROUGH TIME

The adsorption of small organic molecules on silicon surfaces has been long a subject of investigations, as it provides the fundamental basis of silicon-based technologies in many fields. Several approaches were used, both theoretical and experimental, on many types of adsorbate-substrate systems aiming at determining preferential sites and geometries of adsorption, stable configurations, transition barriers, adsorption mechanisms, electronic structures among others. The research efforts, though, did not always bring to conclusive arguments and on some systems investigations are still going on following the evolution of the experimental techniques and computational methods. In this review, two case studies are reported: benzene and methanol on Si(100)2[Formula: see text]1, i.e. examples of a molecular and a dissociative adsorption. The adsorption of benzene on Si(100)2[Formula: see text]1 is still an open case, as it may adsorb in di-[Formula: see text] or tetra-[Formula: see text] bonded configurations, but contrasting evidences have been reported so far, on which of the two is the most stable one and the debate is still open. The adsorption of methanol is less controversial and it is widely accepted it is dissociative with breakage of the O–H at low coverages. But also in this case, investigations are going on to elucidate the adsorption mechanism.

Adsorption of Organic Molecules to van der Waals Materials: Comparison of Fluorographene and Fluorographite with Graphene and Graphite.

Understanding strength and nature of noncovalent binding to surfaces imposes significant challenge both for computations and experiments. We explored the adsorption of five small nonpolar organic molecules (acetone, acetonitrile, dichloromethane, ethanol, ethyl acetate) to fluorographene and fluorographite using inverse gas chromatography and theoretical calculations, providing new insights into the strength and nature of adsorption of small organic molecules on these surfaces. The measured adsorption enthalpies on fluorographite range from −7 to −13 kcal/mol and are by 1–2 kcal/mol lower than those measured on graphene/graphite, which indicates higher affinity of organic adsorbates to fluorographene than to graphene. The dispersion-corrected functionals performed well, and the nonlocal vdW DFT functionals (particularly optB86b-vdW) achieved the best agreement with the experimental data. Computations show that the adsorption enthalpies are controlled by the interaction energy, which is dominated by London dispersion forces (∼70%). The calculations also show that bonding to structural features, like edges and steps, as well as defects does not significantly increase the adsorption enthalpies, which explains a low sensitivity of measured adsorption enthalpies to coverage. The adopted Langmuir model for fitting experimental data enabled determination of adsorption entropies. The adsorption on the fluorographene/fluorographite surface resulted in an entropy loss equal to approximately 40% of the gas phase entropy.

Unhindered copper uptake by glutaraldehyde-polyethyleneimine coatings in an artificial seawater model system with adsorbed swollen polysaccharides and competing ligand EDTA

Shortly after a surface is submerged in the sea, a conditioning film is generally formed by adsorption of organic molecules, such as polysaccharides. This could affect transport of molecules and ions between the seawater and the surface. An artificial seawater model system was developed to understand how adsorbed polysaccharides impact copper binding by glutaraldehyde-crosslinked polyethyleneimine coatings. Coating performance was also determined when competed against copper-chelating EDTA. Polysaccharide adsorption and copper binding and distribution were investigated using advanced analytical techniques, including depth-resolved time-of-flight secondary ion mass spectroscopy, grazing incidence X-ray absorption near-edge spectroscopy, quartz crystal microbalance with dissipation monitoring and X-ray photoelectron spectroscopy. In artificial seawater, the polysaccharides adsorbed in a swollen state that copper readily penetrated and the glutaraldehyde-polyethyleneimine coatings outcompeted EDTA for copper binding. Furthermore, the depth distribution of copper species was determined with nanometre precision. The results are highly relevant for copper-binding and copper-releasing materials in seawater.

Can a Photosensitive Oxide Catalyze Decomposition of Energetic Materials?

Organic–inorganic interfaces provide both intrigues and opportunities for designing systems that possess properties and functionalities inaccessible by each individual component. In particular, the electronic, catalytic, and defect properties of inorganic surfaces can significantly affect the adsorption, decomposition, and photoresponse of organic molecules. Here, we choose the formulation of TiO2 and trinitrotoluene (TNT), a highly catalytic oxide and a prominent explosive, as a prototypical example to explore the effect of a catalytic oxide additive on the photosensitivity of energetic materials. We show that whether or not a catalytic oxide additive can help molecular decompositions under light illumination depends largely on the band alignment between the oxide surface and the energetic molecule. For the composite of TiO2 and TNT, the lowest unoccupied molecular orbitals (LUMOs) of TNT merge within the conduction band (CB) of TiO2. As such, no optical transition corresponding to available laser energies is observed. However, oxygen vacancy can lead to electron density transfer from the surface to the energetic molecules, causing an enhancement of the bonding between molecules and surface and a reduction of the molecular decomposition activation barriers. Therefore, when other (than optical) forms of energy (shock, heat, etc.) flow into molecules, molecular decompositions may be triggered more easily.

Competitive Adsorption of Organic Molecules on Clay Rock

The processes governing adsorption of anthropogenic organic molecules on natural systems are complex. The presence of various phases in soils and mudstones may lead to various and simultaneous retention mechanisms. Adsorption experiments were performed on acetic, o-phthalic and citric acids on the Callovo-Oxfordian clay rock. Whereas the retention of inorganic species is dominated by clay minerals, small carboxylic acids were found to sorb on various phases or sites and not necessarily endured competition during co-adsorption. Data will be presented to illustrate the interest of various adsorption protocols to discriminate between mechanisms occurring beside adsorption onto soils and sediments: covalent bounding, chemical perturbation, phase dissolution, bacterial activity, etc..

Emerging investigators series: highly effective adsorption of organic aromatic molecules from aqueous environments by electronically sorted single-walled carbon nanotubes

The use of electronically sorted (i.e. semiconducting or metallic) single-walled carbon nanotubes (SWCNTs) for the removal of organic compounds from aqueous environments is investigated.

From Foundation Stones to Life: Concepts and Results

Systems consisting of mineral surfaces, water, salts and organic molecules are considered to be plausible models of early Earth's prebiotic environments. The probable involvement of clays, highly soluble minerals, sulfides and other minerals at the beginning of life have spurred a number of experimental studies to investigate organic molecule adsorption, polymerization and catalytic reactions of relevance to prebiotic chemistry. This article reviews current ideas in how life originated, summarises experimental results and presents some of the existing challenges that still beset the field of the origins of life.

Removal of sulfur-containing organic molecules adsorbed on inorganic supports by Rhodococcus Rhodochrous spp.

To remove dibenzothiophene (DBT) and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT) adsorbed on alumina, silica and sepiolite through biodesulfurization (BDS) using Rhodococcus Rhodochrous spp., that selectively reduce sulfur molecules without generating of gaseous pollutants. The adsorption of DBT and 4,6-DMDBT was affected by the properties of the supports, including particle size and the presence of surface acidic groups. The highest adsorption of both sulfur-containing organic molecules used particle sizes of 0.43-0.063mm. The highest percentage removal was with sepiolite (80% for DBT and 56% for 4,6-DMDBT) and silica (71% for DBT and 37% for 4,6-DMDBT). This is attributed to the close interaction between these supports and the bacteria. Biodesulfurization is effective for removing the sulfur-containing organic molecules adsorbed on inorganic materials and avoids the generation of gaseous pollutants.

Thermodynamics of the adsorption of organic molecules on graphitized carbon black modified with a monolayer of 5-hydroxy-6-methyluracil

Thermodynamic characteristics of the adsorption of alkanes, alcohols, arenes, and esters on graphitized carbon black with a deposited monolayer (0.17%) of 5-hydroxy-6-methyluracil are studied by means of inverse gas chromatography at infinite dilution. It is established that size effects (violation of the additivity of molar changes in internal energy and the entropy of adsorption for pairs of molecules of one homologous series that differ by one methyl group) are observed when organic molecules are adsorbed on the surface of the resulting adsorbent. The size effects are similar to those observed when 1% 5-hydroxy-6-methyluracil is deposited on graphitized carbon black. It is concluded that the observed violation of additivity is associated with cavities in the supramolecular structure.

MODELING STYRENE HYDROGENATION KINETICS USING PALLADIUM CATALYSTS

Abstract - The high octane number of pyrolysis gasoline (PYGAS) explains its insertion in the gasoline pool. However, its use is troublesome due to the presence of gum-forming chemicals which, in turn, can be removed via hydrogenation. The use of Langmuir-Hinshelwood kinetic models was evaluated for hydrogenation of styrene, a typical gum monomer, using Pd/9%Nb 2 O 5 -Al 2 O 3 as catalyst. Kinetic models accounting for hydrogen dissociative and non-dissociative adsorption were considered. The availability of one or two kinds of catalytic sites was analyzed. Experiments were carried out in a semi-batch reactor at constant temperature and pressure in the absence of transport limitations. The conditions used in each experiment varied between 16 – 56 bar and 60 – 100 oC for pressure and temperature, respectively. The kinetic models were evaluated using MATLAB and EMSO software. Models using adsorption of hydrogen and organic molecules on the same type of site fitted the data best. Keywords

Ionic complexation and adsorption of small organic molecules on calcium silicate hydrate: Relation with their retarding effect on the hydration of C3S

The ion complexing power and the adsorption of set-retarders such as sugar derivatives (d-glucitol, d-gluconate…), amino-carboxylates and phosphonates (EDTA, EDTMP, …) on C-S-H were identified and compared. The complexation equilibria of the predominant calcium and/or hydroxide complex and its relative constant were determined after measuring the solubilizing effect of the molecules in suspensions buffered by portlandite. The adsorption of the molecules on C-S-H as well as their possible complexation with silicate ions in solution were also investigated. All the molecules studied are shown to complex calcium and/or hydroxide ions but only amino-phosphonates, d-gluconate and d-glucitol complex silicate ions. They all adsorb on portlandite and C-S-H but to different extents. These organic compounds are also revealed to be sensitive to the presence of calcium counter-ions at the surface of C-S-H. Finally, the relation between their ionic complexing powers, adsorption properties and retarding effects on the hydration of C3S are discussed.

Functional Group Adsorption on Calcite: I. Oxygen Containing and Nonpolar Organic Molecules

Considerable interest in calcite crystallization has prompted many studies on organic molecule adsorption. However, each study has explored only a few compounds, using different methods and conditions, so it is difficult to combine the results into a general model that describes the fundamental mechanisms. Our goal was to develop a comprehensive adsorption model from the behavior of a range of organic compounds by exploring how common functional groups interact with calcite and the effects of various side groups and hydrogen on adsorption. We used density functional theory, with semiempirical dispersion corrections (DFT-D2), to determine adsorption energy on calcite {10.4} for nonpolar (benzene, ethane, and carbon dioxide) and oxygen containing polar molecules (water, methanol, ethanol, phenol, formic acid, acetic acid, propanoic acid, benzoic acid, formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, dimethyl ether, acetone, and furan). From the adsorption energies, within the transition state theo...

Functional Group Adsorption on Calcite: II. Nitrogen and Sulfur Containing Organic Molecules

Sulfur and nitrogen are two common constituents of natural and synthetic organic molecules, especially in systems where organisms play a role. There is evidence in the literature that nitrogen and sulfur containing functional groups have an influence on adsorption of organic molecules to calcite surfaces. The purpose of this work was to investigate the interaction of these functional groups with CaCO3 and to explore how adsorption is affected by various side groups and the H atom. First, we used density functional theory with semiempirical dispersion corrections (DFT-D2) to determine the energy of adsorption on the dominant calcite face, {10.4} for molecules containing nitrogen (ammonia, methylamine, ethylamine, aniline, hydrogen cyanide, acetonitrile, propionitrile, benzonitrile, dimethylamine, pyrrole, trimethylamine, and pyridine) and sulfur (hydrogen sulfide, methanethiol, ethanethiol, thiophenol, dimethyl sulfide, and thiophene). Second, based on the determined adsorption energies, we predicted desor...

Asphaltene adsorption on quartz sand in the presence of pre-adsorbed water

Background and hypothesisIn the oil industry, asphaltenes are known for their tendency to aggregate in solution and to deposit on surfaces, with both properties being connected with operational problems associated with recovery, production and refining. Interactions involving asphaltenes and other crude oil components have been a major aspect of investigation in attempting to understand the full nature of these problems. Water is implicated in asphaltene behavior in solution, for example, where it has been found to delay the deposition of asphaltene aggregates. At interfaces, there is evidence that water-in-crude oil emulsion stability is enhanced through asphaltene-water interactions, and there have been a few reports that asphaltene adsorption on mineral surfaces is reduced in the presence of water. We consider the latter aspect, because the instances of reduced adsorption to date have not attempted to quantify the effect. Previous studies showed that vapor-phase adsorption of organic molecules is reduced in the presence of pre-adsorbed water and we were interested to determine whether the same is true for liquid-phase adsorption of asphaltenes. ExperimentsThe surface of quartz sand was controlled by pre-adsorption of water from different relative humidity (RH) environments as the water adsorption isotherm is known from previous studies. These pre-conditioned sand samples were used as substrates for the adsorption from toluene solutions of n-heptane-precipitated asphaltenes (C7A) from an Athabasca oil sands bitumen. To supplement the adsorption behavior, atomic force microscopy (AFM) images were taken of the resultant sand grains at 0 and 80% RH, and low-field NMR was used to estimate the sand wettability. FindingsAsphaltene adsorption on sand is sensitive to surface-adsorbed water, with ∼4-fold reduction in adsorption when increasing the RH from 0 to 100%. This is in general agreement with previous vapor-phase adsorption of small organic molecules, and is therefore believed to be the first demonstration of the effect of pre-adsorbed water on adsorption from solution. Asphaltene adsorption as a function of RH is the converse of literature water adsorption isotherm data. Three asphaltene adsorption regions have been tentatively identified based on water adsorption behavior and the literature interpretation of water structure on quartz: the highest asphaltene adsorption occurs at very low RH, decreasing to a near-constant value in the range ∼40–80% RH, followed by a rapid decrease beyond 80% RH. Further analysis strongly suggests that asphaltene adsorption decreases linearly with the thickness of the adsorbed water film. The effects of RH on asphaltene adsorption are also reflected in AFM images and NMR wettability results.

Van der Waals molecular interactions in the organic functionalization of graphane, silicane, and germanane with alkene and alkyne molecules: a DFT-D2 study.

Density functional theory with the addition of a semi-empirical dispersion potential was applied to the conventional Kohn-Sham energy to study the adsorption of alkene and alkyne molecules on hydrogen-terminated two-dimensional group IV systems (graphane, silicane, and germanane) by means of a radical-initiated reaction. In particular, we investigated the interactions of acetylene, ethylene, and styrene with those surfaces. Although we had studied these systems previously, we included van der Waals interactions in all of the cases examined in the present work. These forces, which are noncovalent interactions, can heavily influence different processes in molecular chemistry, such as the adsorption of organic molecules on semiconductor surfaces. This unified approach allowed us to perform a comparative study of the relative reactivities of the various organic molecule/surface systems. The results showed that the degree of covalency of the surface, the lattice size, and the partial charge distribution (caused by differences in electronegativity) are all key elements that determine the reactivity between the molecules and the surfaces tested in this work. The covalent nature of graphane gives rise to energetically favorable intermediate states, while the opposite polarities of the charge distributions of silicane and germanane with the organic molecules favor subsequent steps of the radical-initiated reaction. Finally, the lattice size is a factor that has important consequences due to steric effects present in the systems and the possibility of chain reaction continuation. The results obtained in this work show that careful selection of the substrate is very important. Calculated energy barriers, heats of adsorption, and optimized atomic structures show that the silicane system offers the best reactivity in organic functionalization.