Adsorption Of Nonpolar Molecules Research Articles

Influence of Defects in Boron Nitride Nanotubes in the Adsorption of Molecules. Insights from B3LYP-D2* Periodic Simulations

The adsorption of H2O, NH3 and HCOOH as polar molecules and C6H6 and CH4 as non-polar ones on a series of zig-zag (6,0) single-walled boron nitride nanotubes (BNNTs) both being defect-free (P_BNNT) and containing defects at the nanotube walls has been studied by means of B3LYP-D2* periodic calculations. We focused on defects derived from monovacancies of B (N-rich_BNNT) and N (B-rich_BNNT) atoms and also on Stone-Wales defects (SW_BNNT). The adsorption of polar molecules with defective BNNTs is generally based on dative interactions and H-bonding, and their adsorption energies strongly depend on the type of BNNT. N-rich_BNNT is the most reactive nanotube towards adsorption of polar molecules, as in all cases deprotonation of the polar molecules is spontaneously given upon adsorption. The strength in the adsorption energies is followed by B-rich_BNNT, SW_BNNT and P_BNNT. Adsorption of non-polar molecules is mainly dictated by dispersion interactions, and, accordingly, the adsorption energies are almost constant for a given molecule irrespective of the type of nanotube.

Physisorption vs. chemisorption of probe molecules on boron nitride nanomaterials: the effect of surface curvature

The adsorption of H2O, NH3 and HCOOH as polar probe molecules and C6H6 and CH4 as non-polar ones on a series of zig-zag (n,0) single-walled boron nitride nanotubes (BNNTs) and on a boron-nitride mono-layer (BNML) has been studied by means of B3LYP-D* periodic calculations. Computed electrostatic potential maps for the pristine BN nanomaterials indicate that the smaller the radius, the larger the polar character. Polar molecules are found to be strongly chemisorbed on small radius BNNTs by means of dative interactions between electron donor atoms of the molecules and B atoms of the BNNTs, H-bonding, as well as dispersive forces. Remarkably, for HCOOH interacting with the (4,0) BNNT, this dative interaction is accompanied by a proton transfer to the nanotube. The corresponding computed adsorption energies decrease sharply with increasing tube radius, gradually approaching the values for physisorption on the BNML. Adsorption of non-polar molecules, mainly dictated by π-stacking (C6H6) and CH-π (CH4) dispersion interactions, is found to be energetically more favorable when physisorbed on large radius BNNTs, the most stable adducts being formed on the BNML.

Effect of the molecular interactions on the separation of nonpolar mixtures using Cu-BTC metal–organic framework

We report an investigation on the adsorption of nonpolar molecules using the copper(II) benzene-1,3,5-tricarboxylate metal–organic framework (Cu-BTC) by means of molecular simulations. This metal–organic framework is formed by small, tetrahedral cages of 5Å in diameter and by large cages of 11 and 13Å in diameter. We focus on the effect that the molecular interactions adsorbents–adsorbates and adsorbates–adsorbates exert on the adsorption that takes place inside the tetrahedral cages. The study is carried out for simple gases modeled as spherical pseudoatoms and for their mixtures. These mixtures are composed by molecules of argon – that are accessible to the tetrahedral cages – and by hypothetic molecules with sigma Lennard–Jones parameters that span from 3.6Å (sigma defined for the molecule of argon) to 4.66Å (sigma defined for the molecule of carbon tetrafluoride). When the value of sigma is low enough to allow the molecule to enter the tetrahedral cages, we observe that it competes with argon for the adsorption in these cavities. This competition is enhanced for the molecules with the largest values of the sigma Lennard–Jones parameter.

The New Mechanism of Physical Adsorption on Solid Surface. I. Adsorption of Nonpolar Molecules

AbstractA phenomenological theory of a new type of physical adsorption is constructed. The mechanism of the adsorption is due to softening of one of the energy levels of an nonmonoatomic molecule. This mode‐softening occurs due to the interaction of the molecule with the adsorbent surface. It is shown, that the nonlinear polarizabilities of a molecule and solid can play an essential role in forming of the adsorption potential.

The adsorption of nonpolar molecules into lipid bilayer membranes

Thermodynamic considerations show that the adsorption of nonpolar molecules into lipid bilayer membranes should depend upon the curvature of the membranes. Estimations of the differences in adsorption of a small n-alkane between a planar phospholipid bilayer and liposomal vesicles have been attempted. For spherical multilamellar liposomes exposed to saturated solutions of alkane in water the adsorption is calculated to be 17-65% of the value for the planar bilayer, depending on the assumptions in the model.

Adsorption of n-Alkanes by Wyoming Montmorillonite

MUCH is known about the interlamellar adsorption of both inorganic and organic cations and polar organic molecules by clay minerals, but there is little information about the interlamellar adsorption of non-polar saturated hydrocarbons by expansible clays. Indeed, there seems to be little or no positive evidence for such adsorption. MacEwan1 found no interlamellar adsorption of n-hexane or n-heptane by montmorillonite after boiling the mineral in the organic liquids and he concluded that polar or polarizable groups are necessary to cause penetration and separation of montmorillonite sheets and hence the formation of complexes. Similarly, Barshad2 stated that the lack of expansion in montmorillonite on treatment with saturated aliphatic hydrocarbons was attributable to their non-polar nature. It was thus to be expected that adsorption of non-polar molecules like n-hexane would occur only on external surfaces as a result of “dispersion” or London-Van der Waals forces.

Adsorption of nonpolar molecules with various electron shell structures on different types of adsorbents

1. The nitrogen adsorption in the monomolecular surface-filling range on barium sulfate samples baked at 400–500° is much greater than the argon adsorption. 2. In contrast with argon, when nitrogen is adsorbed on polar and ionic adsorbents there is, in addition to the electrokinetic and electrostatic induced interaction, an interaction between the electrostatic surface field and the adsorbed nitrogen molecules which have a large quadrupole moment.

Adsorption of nonpolar molecules with different electron shell structures on adsorbents of various types

1. The adsorption of benzene vapor in the monomolecular surface filling range is much greater than the adsorption of n-hexane vapor on barium sulfate samples. The difference in adsorption increases as the baking temperature is raised and thus is not caused by hydration of the surface but by the ionic structure of the surface. 2. In contrast with hexane, when benzene is adsorbed on barium sulfate, interaction in addition to electrokinetic shows up principally between the surface electrostatic field and the π-electron bonds of the benzene molecule. 3. Comparing the adsorptions of benzene and n-hexane on various adsorbents shows that the effect of this additional interaction is determined by the chemical structure of the adsorbent surface layer.

Adsorption of N‐Butane by Kaolinite and Montmorillonite: Phase Changes in the Monolayer Region

AbstractThe adsorption of n‐butane by Ca‐kaolinite and Ca‐montmorillonite, using high vacuum technique, was studied to determine the nature of the differences that occur during the adsorption of nonpolar molecules by clay minerals. The adsorption is described in terms of a 2‐dimensional mobile film with the spreading pressure, ϕ, calculated by the integrated Gibbs equation. At surface coverages of < 4%, the adsorbed films on both surfaces can be described as an ideal 2‐dimensional gas, i.e., ϕA = kT, where A is the molecule area, k is Boltzman's constant, and T is the absolute temperature. Throughout the monolayer region, adsorption of n‐butane could be described as either a perfect or imperfect gaseous film. The ϕA — ϕ curves show that a transition from a liquid expanded to a liquid intermediate phase occurs in the imperfect gas region of both clay systems. The differences noted in the nature of the phase changes on both surfaces coupled with the isosteric heats of adsorption is explained on the basis that kaolinite is essentially nonporous and has a homogeneous surface, whereas the presence of capillary pores dominates the adsorption of n‐butane by montmorillonite.