scholarly journals Computational Study of the Adsorption of Phosphates as Wastewater Pollutant Molecules on Faujasites

Processes ◽  
2021 ◽  
Vol 9 (10) ◽  
pp. 1821
Author(s):  
Luis Fernando Capa-Cobos ◽  
Ximena Jaramillo-Fierro ◽  
Silvia González
Keyword(s):  
Adsorption Energy ◽  
Density Functional ◽  
New Technologies ◽  
Zeolite Y ◽  
Computational Study ◽  
Phosphate Adsorption ◽  
Dihydrogen Phosphate ◽  
Hydrogen Atoms ◽  
Adsorption Activity ◽  
Oxygen Atoms

The adsorption of sodium dihydrogen phosphate (NaH2PO4) onto X- and Y-type faujasite zeolites was computationally studied using the Density Functional Theory (DFT) method. The structures were modeled using the Materials Studio software. The Si/Al ratios for the X- and Y-type zeolite models were 1.2 and 2.5, respectively. The central pore of the zeolite provided a more favorable coordination for adsorbing NaH2PO4. Full molecular optimization and adsorption energy calculations were performed using the VASP code. The adsorption was more effective on zeolite Y, with an adsorption energy of 161 kJ/mol, compared to the zeolite X system, with an adsorption energy of 31.64 kJ/mol. This calculated value for X-type faujasite was found in the interval of the adsorption energy of H2PO4− on hydrated Fe oxide (94.4 kJ/mol) and modified polyether sulfone (22.5 kJ/mol), and the calculated adsorption energy of the molecule on Y-type faujasite coincides with the reported value for this adsorbate on Mg/Ca-modified biochar structures. The molecular conformations of the adsorbate on the two studied models are very different, so the difference between the adsorption energy values of each type of zeolite model is comprehensible. On the one hand, the oxygen atoms of the molecule formed a bidentate complex with the hydrogen atoms of the pore in the X-type faujasite model, and the O-H distance was 1.5 Ǻ. On the other hand, an adsorbed oxygen atom of the phosphate was placed on a hydrogen atom at site II of the Y-type faujasite zeolite, and two of the hydrogen atoms of the phosphate were placed on the oxygen atoms. The Bader analysis results indicated that the negative charge of the phosphate anions was delocalized on the zeolites protons. The hydroxy groups of the phosphate form bonds between their hydrogen atoms and the oxygen atoms of the zeolite porous structure; therefore, we concluded that these sites have an alkaline character. The aim of this study was to include a computational analysis of possible phosphate adsorption mechanisms in faujasite zeolites that can be confirmed by experimental tests, and hence contribute to the generation of new technologies for capturing pollutant molecules in wastewater. The results are in agreement with the experimental information concerning the influence of pH on the adsorption activity of phosphate adsorption on zeolites.

Carbon and silicon substitution in (4, 4) aluminum nitride nanotube — Density functional study of 27Al and 14N electric field gradient tensors

2008 ◽  
Vol 86 (8) ◽  
pp. 745-750 ◽  
Author(s):  
Ahmad Seif ◽  
Mehran Aghaie ◽  
Hossein Aghaie
Keyword(s):  
Density Functional Theory ◽  
Aluminum Nitride ◽  
Density Functional ◽  
Computational Study ◽  
Coupling Constants ◽  
Functional Study ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Aluminum Nitride Nanotube ◽  
Electronic Environments

A computational study at the level of density functional theory (DFT) was performed to investigate the influence of Si and C substitution on the 14N and 27Al quadrupole coupling constants (CQ) in the armchair single-walled aluminum nitride nanotube (SWAlNNT). To this aim, a 1 nm AlNNT consisting of 28 Al and 28 N atoms was considered in which both mouths of the nanotube are capped by hydrogen atoms. Additionally, two other forms of this model of AlNNT were considered in which five Si and five C atoms were substituted in place of the five Al and five N atoms, with two rings in the length of nanotube, like a wire, in the first form; and three Si and three C atoms were substituted in place of three Al and three N atoms as a central ring on the surface of the AlNNT in the second form. The calculated CQ values for three optimized AlNNT systems (raw and Si- and C-substituted) reveal diverse electronic environments in the above-mentioned systems. All the calculations were carried out using the Gaussian 98 software package.Key words: armchair nanotube, density functional theory, nuclear quadrupole resonance.

COMPUTATIONAL STUDY OF A CNT-URACIL-CNT COMPOUND

2011 ◽  
Vol 25 (15) ◽  
pp. 1335-1341 ◽  
Author(s):  
MARYAM MIRZAEI ◽  
MOHAMMAD YOUSEFI ◽  
MAHMOUD MIRZAEI
Keyword(s):  
Carbon Nanotubes ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Computational Study ◽  
Dipole Moments ◽  
Coupling Constants ◽  
Modification Process ◽  
Quadrupole Coupling ◽  
Electronic Environments ◽  
Oxygen Atoms

Density functional calculations were performed to investigate the properties of a combination of two representative carbon nanotubes by assistance of the atomic sites of uracil, which is the characteristic nucleobase of RNA. The obtained parameters indicated that the resulting compound exhibit new properties with respect to the original nanotubes and uracil. The effects of the modification process were significant for the dipole moments and conductivity properties of the components as were seen by the significant changes in the new compound. The values of quadrupole coupling constants for the nitrogen and oxygen atoms of the uracil counterpart of the investigated models also indicated the effects of changes of the electronic environments of the components due to the modification process.

Influence of C-Doping on the B-11 and N-14 Quadrupole Coupling Constants in Boron-Nitride Nanotubes: A DFT Study

2007 ◽  
Vol 62 (1-2) ◽  
pp. 56-60 ◽  
Author(s):  
Mahmoud Mirzaei ◽  
Nasser L. Hadipour ◽  
Mohammad Reza Abolhassani
Keyword(s):  
Boron Nitride ◽  
Density Functional ◽  
Computational Study ◽  
Boron Nitride Nanotubes ◽  
Coupling Constants ◽  
Carbon Doping ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Quadrupole Coupling ◽  
C Doping

A computational study at the level of density functional theory (DFT) was carried out to investigate the influence of carbon doping (C-doping) on the 11B and 14N quadrupole coupling constants (CQ) in the (6,0) single-walled boron-nitride nanotube (BNNT). To this aim, a 10 Å length of BNNT consisting of 24 B atoms and 24 N atoms was selected where the end atoms are capped by hydrogen atoms. To follow the purpose, six C atoms were doped instead of three B and three N atoms as a central ring in the surface of the C-doped BNNT. The calculated CQ values for both optimized BNNT systems, raw and C-doped, reveal different electrostatic environments in the mentioned systems. It was also demonstrated that the end nuclei have the largest CQ values in both considered BNNT systems.

A theoretical approach to the energetic stability and geometry of hydrogen and oxygen terminated diamond (100) surfaces

2005 ◽  
Vol 890 ◽  
Author(s):  
Daniel Petrini ◽  
Karin Larsson
Keyword(s):  
Thermodynamic Stability ◽  
Adsorption Energy ◽  
Theoretical Approach ◽  
Surface Coverage ◽  
Hydroxyl Groups ◽  
Hydrogen Atoms ◽  
Energetic Stability ◽  
Oxygen Coverage ◽  
Oxygen Atoms

ABSTRACTThe thermodynamic stability of diamond (100) surfaces as a function of degree of hydrogen and oxygen-related termination coverage has been theoretically studied using DFT techniques. The results show that an exchange of the hydrogen atoms with hydroxyl groups is disfavored, whereas a corresponding exchange with oxygen atoms (in the ketone or ether position) is energetically preferred. The adsorption of up to about 50 % oxygen coverage (ether position) is, however, largely disfavored compared to a fully hydrogen-terminated surface. However, this oxygen termination will be energetically improved as the coverage increases above the 50 % level. The adsorption energy per terminating species (at 100% surface coverage) is −4.13 eV, −4.30 eV, −5.95 eV and 6.21 eV for H, OH, O(ketone) and O(ether) species, respectively.

A Computational Study on Structural and Electronic Properties of 1-(4-Chlorophenyl)-2-{[5-(4-Chlorophenyl)-1,2,3-Oxadiazol-2-Yl]Sulfanyl}Ethanone

2019 ◽  
Vol 892 ◽  
pp. 1-7
Author(s):  
Pek Lan Toh ◽  
Montha Meepripruk ◽  
Rosfayanti Rasmidi
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Molecular System ◽  
Population Analysis ◽  
Atomic Charge ◽  
Dft Method ◽  
Basis Sets ◽  
Hydrogen Atoms ◽  
Mulliken Population ◽  
Total Energies

In this paper, a first principle Density Functional Theory (DFT) method was conducted to study the geometric and electronic structures of 1-(4-chlorophenyl)-2-{[5-(4-chlorophenyl) -1,3,4-oxadiazol-2-yl] sulfanyl} ethanone, C16H10Cl2N2O2S. Using B3LYP level of theory with four basis sets of 6-31G**, 6-31++G**, 6-311G**, and 6-311++G**, the equilibrium structure of the title molecule was used to determine the total energies, Frontier molecular orbital’s energies, Mulliken atomic charges, and others. The computed findings present that four total energies obtained are close to each other, with the corresponding values of-59716.06 eV, -59709.42 eV, -59708.56 eV, and-59716.51 eV, respectively for B3LYP/6-31G**, B3LYP/6-31++G**, B3LYP/6-311G**, and B3LYP/6-311++G** methods. The calculated HOMO-LUMO energy gaps were predicted in the range of 4.001 eV - 4.089 eV. In this study, the atomic charge values of molecular system were also determined using Mulliken Population Analysis (MPA) approach. For DFT/B3LYP/6-311G** level of calculation, the computed results show that the atom of C8 accommodates the highest negative charge in the title molecular system. All the oxygen, nitrogen, and chloride atoms are having negative charges, whereas all the hydrogen atoms are having positive charges. In addition, the dipole moment value was also determined to be 1.4758 Debye by employing DFT/B3LYP/6-311G** level of theory.

Proton Acidity and Proton Mobility in ECR-40, a Silicoaluminophosphate That Violates Löwenstein’s Rule

2019 ◽  
Author(s):  
Michael Fischer
Keyword(s):  
Density Functional ◽  
Water Clusters ◽  
Computational Study ◽  
Acid Catalyst ◽  
Ab Initio Molecular Dynamics ◽  
Brønsted Acidity ◽  
Hydrothermal Route ◽  
Proton Mobility ◽  
Brönsted Acidity ◽  
A Minor

<p>The silicoaluminophosphate zeotype ECR-40, which has the MEI topology, contains linkages of AlO<sub>4</sub> tetrahedra via a common oxygen atom, thereby violating the famous “Löwenstein’s rule”. Due to the proven existence of Al-O-Al linkages in this material, it constitutes an ideal model system to study the acidity and mobility of protons associated with such unusual linkages. In addition, their properties can be directly compared to those of protons associated with more common Si-O-Al linkages, which are also present in ECR-40. In this work, static density functional theory (DFT) calculations including a dispersion correction were employed to study the preferred proton sites as well as the Brønsted acidity of the framework protons, followed by DFT-based ab-initio molecular dynamics (AIMD) to investigate the proton mobility in guest-free and hydrated ECR-40. Initially, two different proton arrangements were compared, one containing both H[O6] protons associated with Al-O-Al linkages and H[O10] protons at Si-O-Al linkages, the other one containing only H[O10] protons. The former model was found to be thermodynamically favoured, as a removal of protons from the Al-O-Al linkages causes a local accumulation of negative charge. Calculations of the deprotonation energy showed a moderately higher Brønsted acidity of the H[O10] protons, at variance with previous empirical explanations, which attributed the exceptional performance of ECR-40 as acid catalyst to the presence of Al‑O‑Al linkages. The AIMD simulations (<i>T</i> = 298 K) delivered no appreciable proton mobility for guest-free ECR-40 and for low levels of hydration (one H<sub>2</sub>O per framework proton). Under saturation conditions, framework deprotonation occurred, leading to the formation of protonated water clusters in the pores. Pronounced differences between the two types of framework protons were observed: While the H[O10] protons were always removed from the Si-O-Al linkages, the Al-O-Al linkages remained mostly protonated, but deprotonation did occur to a minor extent. The observation of a degree of framework deprotonation of Al-O-Al linkages differs from the findings reported in a recent computational study of hydrated aluminosilicate zeolites with such linkages (Heard et al., <i>Chem. Sci.</i> <b>2019</b>, <i>10</i>, 5705), pointing to an influence of the overall framework composition. Further inspection of the AIMD results showed that a coordination of water molecules to framework Al atoms occurred in many cases, especially in the vicinity of the Al-O-Al linkages, sometimes resulting in a pronounced modification of the linkages through additional bridging oxygen atoms. Given the changes in the local structure, it can be expected that such modified linkages are especially prone to break upon dehydration. Thus, in addition to elucidating the deprotonation behaviour of protons associated with different types of linkages, the calculations also provide insights into possible reasons for the instability of Al-O-Al linkages, clarifying why Löwenstein’s rule is mostly obeyed in materials that are formed via a hydrothermal route.</p>

Computational Study on the Kinetics and Mechanisms of Unimolecular Reactions of (Z)-(Z)-N-(λ5-phosphanylidene) Formohydrazonic Formic Anhydride: Intramolecular aza-Wittig Reaction in Competition with Mumm Rearrangement

2020 ◽  
Vol 17 (11) ◽  
pp. 884-889
Author(s):  
Somayeh Mirdoraghi ◽  
Hamed Douroudgari ◽  
Farideh Piri ◽  
Morteza Vahedpour
Keyword(s):  
Rate Constants ◽  
Density Functional ◽  
Wittig Reaction ◽  
Computational Study ◽  
Single Step ◽  
Low Energy ◽  
Coupled Cluster ◽  
Unimolecular Reaction ◽  
Single Step Reaction ◽  
Good Agreement

For (Z)-(Z)-N-(λ5-phosphanylidene) formohydrazonic formic anhydride, Aza-Wittig reaction and Mumm rearrangement are studied using both density functional and coupled cluster theories. For this purpose, two different products starting from one substrate are considered that are competing with each other. The obtained products, P1 and P2, are thermodynamically favorable. The product of the aza-Wittig reaction, P1, is more stable than the product of Mumm rearrangement (P2). For the mentioned products, just one reliable pathway is separately proposed based on unimolecular reaction. Therefore, the rate constants based on RRKM theory in 300-600 K temperature range are calculated. Results show that the P1 generation pathway is a suitable path due to low energy barriers than the path P2. The first path has three steps with three transition states, TS1, TS2, and TS3. The P2 production path is a single-step reaction. In CCSD level, the computed barrier energies are 14.55, 2.196, and 10.67 kcal/mol for Aza-Wittig reaction and 42.41 kcal/mol for Mumm rearrangement in comparison with the corresponding complexes or reactants. For final products, the results of the computational study are in a good agreement with experimental predictions.

Magnetic Volume Effect of Hydrogen Diffusion in Palladium

2020 ◽  
Vol 310 ◽  
pp. 29-33
Author(s):  
Sarantuya Nasantogtokh ◽  
Xin Cui ◽  
Zhi Ping Wang
Keyword(s):  
Transition Metal ◽  
Density Of States ◽  
Density Functional ◽  
Hydrogen Diffusion ◽  
Magnetic Moments ◽  
Interstitial Site ◽  
Volume Effect ◽  
Face Centered Cubic ◽  
Hydrogen Atoms ◽  
Octahedral Interstitial Site

The electronic and magnetic properties of palladium hydrogen are investigated using first-principles spin-polarized density functional theory. By studying the magnetic moments and electronic structures of hydrogen atoms diffusing in face-centered cubic structure of transition metal Pd, we found that the results of magnetic moments are exactly the same in the two direct octahedral interstitial site-octahedral interstitial site diffusion paths-i.e. the magnetic moments are the largest in the octahedral interstitial site, and the magnetic moments are the lowest in saddle point positions. We also studied on the density of states of some special points, with the result that the density of states near the Fermi level is mainly contributed by 4d electrons of Pd and the change of magnetic moments with the cell volume in the unit cell of transition metal Pd with a hydrogen atom.

scholarly journals Computational Study of the Electron Spectra of Vapor-Phase Indole and Four Azaindoles

Molecules ◽  
2021 ◽  
Vol 26 (7) ◽  
pp. 1947
Author(s):  
Delano P. Chong
Keyword(s):  
Density Functional Theory ◽  
Vapor Phase ◽  
Density Functional ◽  
Computational Study ◽  
Geometry Optimization ◽  
The Other ◽  
Functional Theory ◽  
Electron Spectra

After geometry optimization, the electron spectra of indole and four azaindoles are calculated by density functional theory. Available experimental photoemission and excitation data for indole and 7-azaindole are used to compare with the theoretical values. The results for the other azaindoles are presented as predictions to help the interpretation of experimental spectra when they become available.

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