scholarly journals Role of Mg Impurity in the Water Adsorption over Low-Index Surfaces of Calcium Silicates: A DFT-D Study

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 665
Author(s):  
Chongchong Qi ◽  
Qiusong Chen ◽  
Andy Fourie
Keyword(s):  
Water Molecule ◽  
Density Functional ◽  
Water Adsorption ◽  
Dissociative Adsorption ◽  
Mg Doping ◽  
Calcium Silicates ◽  
Single Water Molecule ◽  
The Impact ◽  
Mg Doped

Calcium silicates are the most predominant phases in ordinary Portland cement, inside which magnesium is one of the momentous impurities. In this work, using the first-principles density functional theory (DFT), the impurity formation energy (Efor) of Mg substituting Ca was calculated. The adsorption energy (Ead) and configuration of the single water molecule over Mg-doped β-dicalcium silicate (β-C2S) and M3-tricalcium silicate (M3-C3S) surfaces were investigated. The obtained Mg-doped results were compared with the pristine results to reveal the impact of Mg doping. The results show that the Efor was positive for all but one of the calcium silicates surfaces (ranged from −0.02 eV to 1.58 eV), indicating the Mg substituting for Ca was not energetically favorable. The Ead of a water molecule on Mg-doped β-C2S surfaces ranged from –0.598 eV to −1.249 eV with the molecular adsorption being the energetically favorable form. In contrast, the Ead on M3-C3S surfaces ranged from −0.699 eV to −4.008 eV and the more energetically favorable adsorption on M3-C3S surfaces was dissociative adsorption. The influence of Mg doping was important since it affected the reactivity of surface Ca/Mg sites, the Ead of the single water adsorption, as well as the adsorption configuration compared with the water adsorption on pristine surfaces.

scholarly journals Understanding Cement Hydration of Cemented Paste Backfill: DFT Study of Water Adsorption on Tricalcium Silicate (111) Surface

Minerals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 202 ◽  
Author(s):  
Chongchong Qi ◽  
Lang Liu ◽  
Jianyong He ◽  
Qiusong Chen ◽  
Li-Juan Yu ◽  
...  
Keyword(s):  
Water Molecule ◽  
Density Functional ◽  
Cement Hydration ◽  
Cementitious Materials ◽  
Dissociative Adsorption ◽  
Molecular Adsorption ◽  
Cemented Paste Backfill ◽  
Adsorption Mechanisms ◽  
Paste Backfill ◽  
Single Water Molecule

Understanding cement hydration is of crucial importance for the application of cementitious materials, including cemented paste backfill. In this work, the adsorption of a single water molecule on an M3-C3S (111) surface is investigated using density functional theory (DFT) calculations. The adsorption energies for 14 starting geometries are calculated and the electronic properties of the reaction are analysed. Two adsorption mechanisms, molecular adsorption and dissociative adsorption, are observed and six adsorption configurations are found. The results indicate that spontaneous dissociative adsorption is energetically favored over molecular adsorption. Electrons are transferred from the surface to the water molecule during adsorption. The density of states (DOS) reveals the bonding mechanisms between water and the surface. This study provides an insight into the adsorption mechanism at an atomic level, and can significantly promote the understanding of cement hydration within such systems.

scholarly journals DFT Study into the Influence of Carbon Material on the Hydrophobicity of a Coal Pyrite Surface

Molecules ◽  
2019 ◽  
Vol 24 (19) ◽  
pp. 3534 ◽  
Author(s):  
Peng Xi ◽  
Donghui Wang ◽  
Wenli Liu ◽  
Changsheng Shi
Keyword(s):  
Carbon Atom ◽  
Water Molecule ◽  
Density Functional ◽  
Valence Bond ◽  
Covalent Bond ◽  
Point Of View ◽  
Pyrite Surface ◽  
Adsorbed Carbon ◽  
Single Water Molecule ◽  
The Impact

From the macroscopic point of view, the hydrophilicity of symbiotic carbon pyrite is weakened overall compared to that of pure pyrite. It is very important to explain the impact of elemental carbon accreted on a pyrite surface on the surface’s hydrophobicity from the perspective of quantum chemistry. To study the influence of adsorbed carbon atoms on the hydrophilicity of a coal pyrite surface versus a pyrite surface, the adsorption of a single water molecule at an adjacent Fe site of a one-carbon-atom-covered pyrite surface and a carbon atom monolayer were simulated and calculated with the first-principles method of density functional theory (DFT). The water molecules can be stably adsorbed at the adjacent Fe site of the carbon-atom-covered pyrite surface. The hybridization of the O 2p (H2O) and Fe 3d (pyrite surface) orbitals was the main interaction between the water molecule and the pyrite surface, forming a strong Fe–O covalent bond. The water molecule only slightly adsorbs above a C atom on the carbon-atom-covered pyrite and the carbon atom monolayer surfaces. The valence bond between the water molecule and the pyrite surface changed from an Fe–O bond to an Fe–C–O bond, in which the C–O bond is very weak, resulting in a weaker interaction between water and the surface.

scholarly journals Revisiting the reactivity between HCO and CH3 on interstellar grain surfaces

2020 ◽  
Vol 493 (2) ◽  
pp. 2523-2527 ◽  
Author(s):  
J Enrique-Romero ◽  
S Álvarez-Barcia ◽  
F J Kolb ◽  
A Rimola ◽  
C Ceccarelli ◽  
...  
Keyword(s):  
Water Molecule ◽  
Energy Barrier ◽  
Density Functional ◽  
High Energy ◽  
Functional Theory ◽  
Radical Coupling ◽  
High Energy Barrier ◽  
Single Water Molecule ◽  
Complex Organic

ABSTRACT The formation of interstellar complex organic molecules is currently thought to be dominated by the barrierless coupling between radicals on the interstellar icy grain surfaces. Previous standard density functional theory (DFT) results on the reactivity between CH3 and HCO on amorphous water surfaces showed that the formation of CH4 + CO by H transfer from HCO to CH3 assisted by water molecules of the ice was the dominant channel. However, the adopted description of the electronic structure of the biradical (i.e. CH3/HCO) system was inadequate [without the broken-symmetry (BS) approach]. In this work, we revisit the original results by means of BS-DFT both in gas phase and with one water molecule simulating the role of the ice. Results indicate that the adoption of BS-DFT is mandatory to describe properly biradical systems. In the presence of the single water molecule, the water-assisted H transfer exhibits a high energy barrier. In contrast, CH3CHO formation is found to be barrierless. However, direct H transfer from HCO to CH3 to give CO and CH4 presents a very low energy barrier, hence being a potential competitive channel to the radical coupling and indicating, moreover, that the physical insights of the original work remain valid.

Theoretical Insights into the Role of Water Molecule in The Aqueous/Cu(111) Interface during Corrosion Pathway

2014 ◽  
Vol 19 (4) ◽  
pp. 235-240
Author(s):  
Jun Hu ◽  
Xiao-yong Fan ◽  
Chao-Ming Wang
Keyword(s):  
Water Molecule ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Adsorbed Water ◽  
Dipole Interaction ◽  
Hydrogen Atoms ◽  
Functional Theory ◽  
Adsorbed Water Molecule ◽  
The One

The absorption and possible reaction paths during corrosion have been systematically identified at the molecular level by us-ing density functional theory calculations. The results show that the co-adsorbed water molecule has a two-fold impact on the corrosive kinetics process. The one is the solvation effect, where water molecule affects the various reactions through ion dipole interaction, without bond fracture and formation. Another is the H-transfer mediator, where the bond of co-adsorbed water molecule breaks and regenerates in order to transfer hydrogen atoms.

scholarly journals The effect of magnesium ions on triphosphate hydrolysis

2017 ◽  
Vol 89 (6) ◽  
pp. 715-727 ◽  
Author(s):  
Alexandre Barrozo ◽  
David Blaha-Nelson ◽  
Nicholas H. Williams ◽  
Shina C. L. Kamerlin
Keyword(s):  
Transition State ◽  
Metal Ions ◽  
Density Functional ◽  
Reaction Pathway ◽  
Enzymatic Reaction ◽  
Phosphate Ester ◽  
Mechanistic Pathway ◽  
Phosphate Hydrolysis ◽  
The Impact

AbstractThe role of metal ions in catalyzing phosphate ester hydrolysis has been the subject of much debate, both in terms of whether they change the transition state structure or mechanistic pathway. Understanding the impact of metal ions on these biologically critical reactions is central to improving our understanding of the role of metal ions in the numerous enzymes that facilitate them. In the present study, we have performed density functional theory studies of the mechanisms of methyl triphosphate and acetyl phosphate hydrolysis in aqueous solution to explore the competition between solvent- and substrate-assisted pathways, and examined the impact of Mg2+ on the energetics and transition state geometries. In both cases, we observe a clear preference for a more dissociative solvent-assisted transition state, which is not significantly changed by coordination of Mg2+. The effect of Mg2+ on the transition state geometries for the two pathways is minimal. While our calculations cannot rule out a substrate-assisted pathway as a possible solution for biological phosphate hydrolysis, they demonstrate that a significantly higher energy barrier needs to be overcome in the enzymatic reaction for this to be an energetically viable reaction pathway.

Exploring the role of a single water molecule in the tropospheric reaction of glycolaldehyde with an OH radical: a mechanistic and kinetics study

RSC Advances ◽  
2016 ◽  
Vol 6 (35) ◽  
pp. 29080-29098 ◽  
Author(s):  
Ramanpreet Kaur ◽  
Vikas Vikas
Keyword(s):  
Water Molecule ◽  
Hydrogen Abstraction ◽  
Oh Radical ◽  
Kinetics Study ◽  
Single Water Molecule ◽  
Atmospheric Reaction

This work reveals that though a single-water molecule decelerates the atmospheric reaction between the glycolaldehyde and OH radical, however, it facilitates the cis–​trans interconversion along the hydrogen-abstraction pathways.

scholarly journals Isolating the Role of the Node-Linker Bond in the Compression of UiO-66 Metal-Organic Frameworks

2020 ◽  
Author(s):  
Louis Redfern ◽  
Maxime Ducamp ◽  
Megan C. Wasson ◽  
Lee Robison ◽  
Florencia Son ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Density Functional ◽  
Metal Organic Frameworks ◽  
Coordination Bond ◽  
Metal Organic ◽  
Dft Simulations ◽  
The Impact ◽  
Organic Linker

Understanding the mechanical properties of metal–organic frameworks (MOFs) is essential to the fundamental advancement and practical implementations of porous materials. Recent computational and experimental efforts have revealed correlations between mechanical properties and pore size, topology, and defect density. These results demonstrate the important role of the organic linker in the response of these materials to physical stresses. However, the impact of the coordination bond between the inorganic node and organic linker on the mechanical stability of MOFs has not been thoroughly studied. Here, we isolate the role of this node–linker coordination bond to systematically study the effect it plays in the compression of a series of isostructural MOFs, M-UiO-66 (M = Zr, Hf, or Ce). The bulk modulus (i.e. the resistance to compression under hydrostatic pressure) of each MOF is determined by in situ diamond anvil cell (DAC) powder X-ray diffraction measurements and density functional theory (DFT) simulations. These experiments reveal distinctive behavior of Ce-UiO-66 in response to pressures under one GPa. In situ DAC Raman spectroscopy and DFT calculations support the observed differences in compressibility between Zr-UiO-66 and the Ce- analogue. Monitoring changes in bond lengths as a function of pressure through DFT simulations provides a clear picture of those which shorten more drastically under pressure and those which resist compression. This study demonstrates that changes to the node–linker bond can have significant ramifications on the mechanical properties of MOFs.

scholarly journals Isolating the Role of the Node-Linker Bond in the Compression of UiO-66 Metal-Organic Frameworks

2020 ◽  
Author(s):  
Louis Redfern ◽  
Maxime Ducamp ◽  
Megan C. Wasson ◽  
Lee Robison ◽  
Florencia Son ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Density Functional ◽  
Metal Organic Frameworks ◽  
Coordination Bond ◽  
Metal Organic ◽  
Dft Simulations ◽  
The Impact ◽  
Organic Linker

Understanding the mechanical properties of metal–organic frameworks (MOFs) is essential to the fundamental advancement and practical implementations of porous materials. Recent computational and experimental efforts have revealed correlations between mechanical properties and pore size, topology, and defect density. These results demonstrate the important role of the organic linker in the response of these materials to physical stresses. However, the impact of the coordination bond between the inorganic node and organic linker on the mechanical stability of MOFs has not been thoroughly studied. Here, we isolate the role of this node–linker coordination bond to systematically study the effect it plays in the compression of a series of isostructural MOFs, M-UiO-66 (M = Zr, Hf, or Ce). The bulk modulus (i.e. the resistance to compression under hydrostatic pressure) of each MOF is determined by in situ diamond anvil cell (DAC) powder X-ray diffraction measurements and density functional theory (DFT) simulations. These experiments reveal distinctive behavior of Ce-UiO-66 in response to pressures under one GPa. In situ DAC Raman spectroscopy and DFT calculations support the observed differences in compressibility between Zr-UiO-66 and the Ce- analogue. Monitoring changes in bond lengths as a function of pressure through DFT simulations provides a clear picture of those which shorten more drastically under pressure and those which resist compression. This study demonstrates that changes to the node–linker bond can have significant ramifications on the mechanical properties of MOFs.

scholarly journals Local Distortions in a Prototypical Zeolite Framework Containing Double Four-Ring Cages: The Role of Framework Composition and Organic Guests

2020 ◽  
Author(s):  
Michael Fischer ◽  
Linus Freymann
Keyword(s):  
Density Functional ◽  
Zeolite Framework ◽  
Functional Theory ◽  
Organic Structure ◽  
Judicious Choice ◽  
Dynamics Simulations ◽  
The Impact ◽  
Local Distortions ◽  
Framework Composition

<p>Cube-like double four-ring (<i>d4r</i>) cages are among the most frequent building units of zeolites and zeotypes. In materials synthesised in fluoride-containing media, the fluoride anions are preferentially incorporated in these cages. In order to study the impact of framework composition and organic structure-directing agents (OSDAs) on the possible occurrence of local distortions of fluoride-containing <i>d4r</i> cages, density functional theory (DFT) calculations and DFT-based molecular dynamics simulations were performed for AST-type zeotypes, considering four different compositions (SiO<sub>2</sub>, GeO<sub>2</sub>, AlPO<sub>4</sub>, GaPO<sub>4</sub>) and two different OSDA cations (tetramethylammonium [TMA] and quinuclidinium [QNU]). All systems except SiO<sub>2</sub>-AST show significant deformations, with a pyritohedron-like distortion of the <i>d4r</i> cages occurring in GeO<sub>2</sub>- and GaPO<sub>4</sub>-AST, and a displacement of the fluoride anions towards one of the corners of the cage in AlPO<sub>4</sub>- and GaPO<sub>4</sub>-AST. While the distortions occur at random in TMA-containing zeotypes, they exhibit a preferential orientation in systems that incorporate QNU cations. </p><p>In addition to providing detailed understanding of the local structure of a complex host-guest system on the picosecond timescale, this work indicates the possibility to stabilise ordered distortions through a judicious choice of the OSDA, which might enable a tuning of the material’s properties.</p>

Sign in / Sign up

Export Citation Format

Share Document