Diego Cortés-Arriagada

Modeling the physisorption of bisphenol A on graphene and graphene oxide

The physisorption of bisphenol A (BPA) on pristine and oxidized graphene was studied theoretically via calculations performed at the PBE-D3 level (including dispersion force corrections). Three stable conformations of BPA on graphene were found. A lying-down configuration was energetically favored because the presence of π–π stacking and dispersion forces increased interactions. In addition, the adsorption of BPA on the edges of graphene oxide was enhanced when adsorption occurred on carboxyl and carbonyl groups, whereas the adsorption strength decreased when adsorption occurred on hydroxyl groups. The highest physisorption strength was obtained on the surface of graphene oxide due to the presence of π–π stacking and dispersion forces (which provided the greatest contribution to the adsorption energy) as well as hydrogen bonds (which provided a smaller contribution), indicating that oxidized graphene is a better candidate than pristine graphene for BPA removal. On the other hand, an increase in electrophilicity was observed after the physisorption of BPA in all systems (with respect to graphene and BPA in their isolated forms), with the adsorbent acting as the electron acceptor. Finally, molecular dynamics simulations performed using the PM6 Hamiltonian showed that the adsorption of BPA on graphene is stable.

Binding of Trivalent Arsenic onto the Tetrahedral Au20 and Au19Pt Clusters: Implications in Adsorption and Sensing

The interaction of arsenic(III) onto the tetrahedral Au20 cluster was studied computationally to get insights into the interaction of arsenic traces (presented in polluted waters) onto embedded electrodes with gold nanostructures. Pollutant interactions onto the vertex, edge, or inner gold atoms of Au20 were observed to have a covalent character by forming metal-arsenic or metal-oxygen bonding, with adsorption energies ranging from 0.5 to 0.8 eV, even with a stable physisorption; however, in aqueous media, the Au-vertex-pollutant interaction was found to be disadvantageous. The substituent effect of a platinum atom onto the Au20 cluster was evaluated to get insights into the changes in the adsorption and electronic properties of the adsorbent-adsorbate systems due to chemical doping. It was found that the dopant atom increases both the metal-pollutant adsorption energy and stability onto the support in a water media for all interaction modes; adsorption energies were found to be in a range of 0.6 to 1.8 eV. All interactions were determined to be accompanied by electron transfer as well as changes in the local reactivity that determine the amount of transferred charge and a decrease in the HOMO-LUMO energy gap with respect to the isolated substrate.

Evaluating the hydrogen chemisorption and physisorption energies for nitrogen-containing single-walled carbon nanotubes with different chiralities: a density functional theory study

The hydrogen adsorption energies for nitrogen-containing carbon nanotubes (N-CNTs) and for bare carbon nanotubes were calculated using the density functional theory methods at the B3LYP/6–31-G(d) level, including dispersion force corrections. The N-CNTs were finite saturated and non-saturated single-walled carbon nanotubes that contained one or more pyrimidine units, the relative positions of which defined the different configurations of the nanotube. The chemisorption of atomic hydrogen to a full exocyclic monolayer of zigzag, armchair, and chiral N-CNTs was studied as a function of the structural parameters. Zigzag N-CNTs of any configuration, with a larger number of nitrogen atoms, a small diameter and a small length, are more reactive compared to chiral and armchair N-CNTs. The presence of nitrogen in the carbon nanotubes enhances their reactivity to chemisorb atomic hydrogen, showing exothermic energy values. In contrast, the physisorption of molecular hydrogen was endothermic for most of the studied saturated N-CNTs, even when including corrections for van der Waals interactions. The endothermicity was greatest for zigzag nanotubes, then decreased for chiral nanotubes and decreased again for armchair nanotubes. In general, the endothermicity decreased for longer nanotubes, which have larger diameters, and a small number of nitrogen atoms. The results of this study suggest that, with saturated bare carbon nanotubes, saturated, and unsaturated N-CNTs could potentially have a higher capacity as hydrogen-storage media than the corresponding unsaturated carbon nanotubes.

The Role of the co-Activation and Ligand Functionalization in Neutral Methallyl Nickel(II) Catalysts for Oligomerization and Polymerization of Ethylene

A detailed quantum chemical study that analyzed the mechanism of ethylene oligomerization and polymerization by means of a family of four neutral methallyl NiII catalysts is presented. The role of the boron co-activators, BF3 and B(C6 F5 )3 , and the position of ligand functionalization (ortho or para position of the N-arylcyano moiety of the catalysts) were investigated to explain the chain length of the obtained polymers. The chain initialization proceeded with higher activation barriers for the ortho-functionalized complexes (≈19 kcal mol-1 ) than the para-substituted isomers (17-18 kcal mol-1 ). Two main pathways were revealed for the chain propagation: The first pathway was favored when using the B(C6 F5 )3 co-activated catalyst, and it produced long-chain polymers. A second pathway led to the β-hydrogen complexes, which resulted in chain oligomerization; this pathway was preferred when the BF3 co-activated catalysts were used. Otherwise, the termination of longer chains occurred via a stable hydride intermediate, which was formed with an energy barrier of about 14 kcal mol-1 for the B(C6 F5 )3 co-activated catalysts. Significant new insights were made into the reaction mechanism, whereby neutral methallyl NiII catalysts act in oligomerization and polymerization processes. Specifically, the role of co-activation and ligand functionalization, which are key information for the further design of related catalysts, were revealed.

Heteroleptic Cu(I) complexes bearing methoxycarbonyl-imidoylindazole and POP ligands – an experimental and theoretical study of their photophysical properties

Four new mixed ligand Cu(I) complexes bearing methoxycarbonyl imidoyl-indazole and bis[2-(diphenylphosphino)-phenyl]ether (POP) ligands were synthesized and characterized by variable-temperature NMR, FT-IR, EA and HRMS. For three of them, the molecular structures were obtained by X-ray diffraction analysis. The electrochemical and absorption–emission properties of all the complexes were investigated by using cyclic voltammetry, UV-Vis spectroscopy, and spectrofluorometric measurements in a CH2Cl2 solution at room temperature and in different solid-state matrices. In addition, quantum chemical computations were performed to gain insight into their electronic and photophysical properties. The complexes showed an MLCT band, which is more influenced by the position of the electron-withdrawing methoxycarbonyl substituent in the indazole ring rather than by the π-extension introduced by the alkene moiety. Besides, all the complexes were found to be weak emitters in the CH2Cl2 solution while they were brighter emitters in the solid-state.