Papers by Keyword: Physisorption

Abstract: Here, the adsorption behavior of the CO₂ molecules on electronic properties of zigzag and armchair ZnO nanotubes (ZnONTs) has been studied at M06-2X/6-31G(d) level of theory. It is found that CO₂ molecules can be physically adsorbed on the nanotubes. Two minima structures A (monodentate) and B (bidentate) were found on the potential energy surface. Inspection of the results shows that in zigzag and armchair nanotubes, the monodentate complex is more stable than bidentate complex. Also, the stability of complexes increases by increasing the number of CO₂ molecules. Comparison of adsorption energies shows that adsorption of CO₂ molecules over zigzag (6, 0) model is stronger than armchair (4,4) model. In this work, the various parameters such as electronic chemical potential (m), hardness (ƞ), softness (S), the maximum amount of electronic charge (DN_max), electrophilicity index (ω), dipole moment and work function were investigated to evaluate the reactivity of structures. It is predicted that the conductivity and reactivity of nanotubes increase upon complexation. Based on the natural bond orbital (NBO) analysis, in all complexes charge transfer occurs from CO₂ molecules to the nanotube. Theory of atoms in molecules (AIM) was also applied to characterize O_CO2… Zn interaction in nanotubes. In addition, the interaction strength is studied through the reduced density gradient (RDG) function. It is predicted that the ZnONTs can be introduced as a favorable candidate in the design and construction of sensors for detecting CO₂ molecules.

Abstract: Hydrogen is the lightest and most abundant element in the universe and an energy carrier. It can be produced from several sources using various methods, such as, electrolysis of water or reforming of hydrocarbons like, natural gas can produce hydrogen in a big plant or fuelling stations. When it is produced using renewable energy sources such as wind, solar, geothermal, or hydroelectric power, it supports the zero emissions approach. Hydrogen powdered electricity generation, whether it is for vehicles, or others, it can be carried out mainly in two ways: burning hydrogen in an internal combustion engine, or reacting hydrogen with oxygen in a fuel cell. Above all, we need to have proper storage facility available at the production and as well as at the utilization site. There are several hydrogen storage technology available such as compressed storage; liquid hydrogen storage; metal hydrides, chemical hydride and by sorption in some porous medium. In this review article, some of the important finding in hydrogen storage materials for physical absorption methods has been discussed.

Abstract: In this study, the interactions between poly (ethylene oxide) (PEO) and lithium-montmorillonite (LiMMT) have been investigated using density functional theory (DFT) calculation. The results of calculations show that the adsorption process of PEO on the LiMMT surface is physisorption with adsorption energy of -0.063 eV. This observation is consistent with the results of our calculations on PES (Potential Energy Surface) and PEC (Potential Energy Curve). The formation of space between PEO and LiMMT are found in range of 3.4 - 4.2 Å which are in good agreement with experimental results.

Abstract: The surface concentrations of organic compounds in a three-component (isopropanol-diethylphthalate-octanol) system were in situ measured using a quartz crystal microbalance. Additionally, the surface concentrations were calculated on the basis of the rate theory, to show that the surface concentration of organic compound was influenced by the other organic compounds. The net situation of airborne organic contamination may change, even when the total amount of organic compounds adsorbed on silicon surface seems to be in a steady state.

Abstract: We have recently disclosed a novel technique for gas analysis based on monitoring the free diffusion-physisorption of the analytes in a microfluidic channel. Equipped with a single general gas sensor, the prototype can recognize variety of gases and gas mixtures. Here, the structural details of the fabricated prototype are given. The performance of the prototype is demonstrated by presenting analysis results obtained for a number of pure and mixed gaseous analytes.

Abstract: In this work, novel types of colored, organic and water based paints have been developed. These paints can be produced less expensively and have equivalent or better properties compared to existing paints in the market. These new paints use organic nanocrystalline dyes (about 10 nm in size), which produce the various colors by absorption. The results are achieved with pigment composites containing nano-Cu-phthalocyanine (CuPC) pigment crystallites and finely precipitated and ground micro Al(OH)3 distance-holder (“spacer”) disks.

Abstract: The removal of trichloroethylene (TCE) from water using activated carbon fibers (ACF) and activated carbon (AC) was investigated. Adsorption, as an efficient process to remove TCE from water was chosen; in particular with ACF and AC as adsorbents. The results showed that physisorption play important roles for adsorption of TCE onto activated carbon fibers, while the less important chemisorption. Langmuir and Freundlich models were then employed to correlate the equilibria data. The Langmuir model best described the AC adsorption isotherm of TCE, with R2 0.9942. Freundlich model best fitted the ACF adsorption isotherm of TCE, with R2 0.9978.

Abstract: Density functional theory calculations of hydrogen storage capacity for different organometallic structures have been carried out. Complexes involving Sc, Ti and V bound to C4H4, C5H5, C5F5 and B3N3H6 molecules have been considered, and all present a hydrogen storage capability limited by the 18-electron rule. In order to stabilize the complexes, which the 18-electron rule is not completed, additional ligands are considered, namely -H, -CH3, -NH2, -OH and -F. These ligands affect the H2-metal bond; particularly the back donation effect from the metal atom to the * antibonding state of H2 and then its H2 storage capacity.

Abstract: With scanning tunneling microscopy (STM), the intramolecular conformational and intermolecular ordering aspects have been investigated of a variety of organic molecules physisorbed at the liquid-solid interface. By balancing the interplay between intramolecular and intermolecular interactions (hydrogen bonding), leading to control of the molecular conformation, foldamers were created which order into well-defined two-dimensional crystals. The nature of the hydrogen bonding groups in conjugated oligomers leads to the formation of infinite stacks and cyclic multimers, expressing the chiral nature of the molecules.

Abstract: We review some recent investigations on prototypical SiC-based interfaces, as obtained from first-principles molecular dynamics. We discuss the interface with vacuum, and the role played by surface reconstruction in SiC homoepitaxy, and adatom diffusion. Then we move to the description of a buried, highly mismatched semiconductor interface, the one which occurs between SiC and Si, its natural substrate for growth: in this case, the mechanism governing the creation of a network of dislocations at the SiC/Si interface is presented, along with a microscopic description of the dislocation core. Finally, we describe a template solid/liquid interface, water on SiC: based on the predicted structure of SiC surfaces covered with water molecules, we propose (i) a way of nanopatterning cubic SiC(001) for the attachment of biomolecules and (ii) experiments to reveal the local geometry of adsorbed water.