Density Functional Theory Molecular Simulations Research Articles

Metal-organic frameworks based on pyrazolates for the selective and efficient capture of formaldehyde

Indoor air pollution is one of the major threads in developed countries, notably due to high concentrations of formaldehyde, a harmful molecule difficult to eliminate. Addressing this purification challenge while adhering to the principles of sustainable development requires the use of innovative, advanced sustainable materials. Here we show that by combining state-of-the-art spectroscopic techniques with density-functional theory molecular simulations, we have developed an advantageous mild chemisorption synergistic mechanism using porous metal (III or IV) pyrazole- di-carboxylate based metal-organic framework (MOF) to trap formaldehyde in a reversible manner, without incurring significant energy penalties for regeneration. A straightforward, environmentally friendly, and scalable synthesis protocol was established for the porous, water-stable aluminum pyrazole dicarboxylate known as Al-3.5-PDA or MOF-303, capable of functioning as a highly efficient and reusable filter. It demonstrates selectivity and high storage capacity for formaldehyde under conditions typical of severe indoor use, such as in housing or vehicle cockpits, including varying VOC mixtures and concentrations, humidity, and temperature, without any accidental release. Furthermore, we have successfully regenerated this sorbent using a simple domestic protocol, ensuring the material reusability for at least 10 cycles.

Organo cationic dyes adsorption on charged nano-clay: Revealing dual mechanisms through GCS modeling and DFT molecular simulations

This study investigates the adsorption mechanisms of organic cationic dyes, specifically malachite green (MG) and toluidine blue (TB), on sodium montmorillonite clay (Na-MMC). Using montmorillonite sourced from the Nador deposit in Northern Morocco, we aim to model cation exchange with the Gouy-Chapman-Stern (GCS) model. The adsorption capacities are found to be 192.5 meq/100 g for TB and 175.8 meq/100 g for MG at room temperature and uncontrolled pH. X-ray diffraction (XRD) analysis was employed to determine the interlayer spacing of the montmorillonite, contributing to the understanding of adsorption mechanisms. GCS modeling provided insight into the adsorption constants for both dyes, alongside parameters related to the solid/solution interface such as the amount adsorbed per layer, ion concentration in the solution, and clay surface potential. These findings confirmed a significant affinity between the dyes and the clay, aligning with the literature. Moreover, Density Functional Theory (DFT) simulations indicated a stronger affinity of toluidine blue for negatively charged surfaces compared to other dyes.

Trio of improvements allows for fast, realistic molecular simulations of electrochemical systems

Removing three approximations from classical Density Functional Theory molecular simulations of processes in electrochemical devices improves accuracy without sacrificing speed.

Characterization of metal-free D-(π-A)2 organic dye and its application as cosensitizer along with N719 dye for efficient dye-sensitized solar cells

The optical, electrochemical and density functional theory molecular simulation of a metal-free D-(π-A)2, i.e., 3,3′-(5,5′-(9-hexyl-9H-carbazole-3,6-diyl)bis(thiophene-5,2-diyl))bis(2-cyanoacrylic acid) denoted as D has been investigated. A stepwise cosensitization of D with N719 dye is adopted to enhance the power conversion efficiency of dye-sensitized solar cells. The metal-free dye possesses strong absorption in the 370–450 nm wavelength range and effectively overcomes the competitive light absorption by I 3 − /I −. The N719/D cosensitized dye-sensitized solar cell shows a power conversion efficiency of about 7.24 %, which is higher than the dye-sensitized solar cells based on either N719 (5.78 %) or D (3.95 %) sensitizers. The improved power conversion efficiency of the cosensitized dye-sensitized solar cell is attributed to the combined enhancement of both short-circuit photocurrent and open-circuit voltage. The short-circuit photocurrent improvement is attributed to the increase in the both light-harvesting efficiency of the cosensitized photoanode and charge collection efficiency of the dye-sensitized solar cell. However, the open-circuit voltage is improved due to better adsorption and surface coverage of TiO2 on cosensitization and an associated reduction in the back electron recombination with increased electron lifetime. These effects are analyzed using electrochemical impedance spectroscopy and dark current–voltage measurements of the dye-sensitized solar cells.

Density functional theory molecular simulation of thiophene adsorption on MoS 2 including microwave effects

Hydrodesulfurization (HDS) is an important catalytic process in the oil industry used to remove sulfur from petroleum fractions, thus producing cleaner fuels. Molybdenum sulfide catalysts are extensively used in this process. In particular, thiophene adsorption, a first step of HDS process, is a prototype system for theoretical investigations. In this work, density functional theory (DFT) calculations of thiophene adsorption on MoS 2, using a Mo 16S 32 cluster, were done. A distributed multipole analysis provided values of charges, dipole and quadrupole moments on atomic sites of the thiophene molecule and the Mo 16S 32 cluster, before and after adsorption. Harmonic vibrational frequencies were also computed. These data were used to discuss the adsorption process and to qualitatively investigate patterns of microwave absorption on this system, a possible way of accelerating the rate of HDS process. It was verified that permanent site dipoles would be the main effect responsible for dielectric heating. In particular, the distributed multipole analysis presented appreciable values of the permanent dipole moment values at atomic sites of the cluster active region and at the adsorbed thiophene. These results indicate differential heating properties at the atomic level when microwave heating is used, which are theoretically shown here for the first time. Therefore, theoretical evidences on the existence of hot spots are provided, which were only previously implied experimentally.