Water/oxide interfaces are ubiquitous on earth and show significant influence on many chemical pr... more Water/oxide interfaces are ubiquitous on earth and show significant influence on many chemical processes. For example, understanding water and solute adsorption as well as catalytic water splitting can help build better fuel cells and solar cells to overcome our looming energy crisis; the interaction between biomolecules and water/oxide interfaces is one hypothesis to explain the origin of life. However, knowledge in this area is still limited due to the difficulty of studying water/solid interfaces. As a result, research using increasingly sophisticated experimental techniques and computational simulations has been carried out in recent years. Although it is difficult for experimental techniques to provide detailed microscopic structural information, molecular dynamics (MD) simulations have satisfactory performance. In this review, we discuss classical and ab initio MD simulations of water/oxide interfaces. Generally, we are interested in the following questions: How do solid surfaces perturb interfacial water structure? How do interfacial water molecules and adsorbed solutes affect solid surfaces and how do interfacial environments affect solvent and solute behavior? Finally, we discuss progress in the application of neural network potential based MD simulations, which offer a promising future because this approach has already enabled ab initio level accuracy for very large systems and long trajectories.
The kinetics of hydrolysis of dimethyl nitrophenyl phosphate (DMNP), a simulant of the nerve agen... more The kinetics of hydrolysis of dimethyl nitrophenyl phosphate (DMNP), a simulant of the nerve agent Soman, was studied and revealed transition metal salts as catalysts.
Acid/base chemistry is an intriguing topic that still constitutes a challenge for computational c... more Acid/base chemistry is an intriguing topic that still constitutes a challenge for computational chemistry. While estimating the acid dissociation constant (or pKa) could shed light on many chemistry processes, especially in the fields of biochemistry and geochemistry, evaluating the relative stability between protonated and nonprotonated species is often very difficult. Indeed, a prerequisite for calculating the pKa of any molecule is an accurate description of the energetics of water dissociation. Here, we applied constrained molecular dynamics simulations, a noncanonical sampling technique, to investigate the water deprotonation process by selecting the OH distance as the reaction coordinate. The calculation is based on density functional theory and the newly developed SCAN functional, which has shown excellent performance in describing water structure. This first benchmark of SCAN on a chemical reaction shows that this functional accurately models the energetics of proton transfer reactions in an aqueous environment. After taking Coulomb long-range corrections and nuclear quantum effects into account, the estimated water pKa is only 1.0 pKa unit different from the target experimental value. Our results show that the combination of SCAN and constrained MD successfully reproduces the chemistry of water and constitutes a good framework for calculating the free energy of chemical reactions of interest.
Mineral oxide/water interfaces are important for a wide range of industrial, geochemical, and bio... more Mineral oxide/water interfaces are important for a wide range of industrial, geochemical, and biological processes. The reactivity of these interfaces is strongly impacted by the presence of ions. Thus, it is critical to understand how ions alter the interfacial environment. This can be achieved by measuring the changes in the structure and vibrational dynamics of interfacial water induced by the presence of ions in close vicinity to the mineral surface. The α-Al2O3(0001) surface represents a flexible platform to study the effect of ions on interfacial aqueous environments at positive, neutral, and negative surface charges. By using vibrational sum frequency generation (vSFG) in the frequency and time domains, we investigate how monovalent and divalent cations affect the hydrogen bonding environment of the first few layers of interfacial water next to α-Al2O3(0001). Our results indicate that monovalent cations, such as Li+, Na+, K+, and Cs+, appear to have lower binding affinities at the interface compare...
Described is a synthetic method to enhance the electrocatalytic activity of the layered manganese... more Described is a synthetic method to enhance the electrocatalytic activity of the layered manganese oxide, birnessite, for the oxygen evolution reaction (OER) through the development of a Mn/Co/Fe te...
The generation of chemical species from gases, noble metals and light interacting with localized ... more The generation of chemical species from gases, noble metals and light interacting with localized surface plasmons represents a new paradigm for achieving low energy sustainable reaction pathways. Here, we demonstrate that the dissociation reaction of H2 meditated by the decay of localized surface plasmons of gold nanoparticles leads to the generation of a new material as detected by a change in the optical properties of the gold nanostructures. The effective permittivity measured by in situ spectroscopic ellipsometry shows a blue-shift of 0.02 eV in the surface plasmon resonance, demonstrating the plausible formation of a metastable gold hydride layer on the surface of nanoparticles following the dissociation of H2. The formation of this gold hydride through the interaction of gold with atomic H is supported by first-principles simulations. These calculations do not indicate a significant charge transfer upon hydrogenation of the (111) surface but rather large Friedel charge oscillations within the gold layer. Moreover, our blue-shift is produced by the formation of a hydride leading to changes in critical band gaps in the electronic structure. For a coverage of 11%, the calculated peak of the imaginary part of the ZZcomponent of the dielectric tensor undergoes a blue shift of 28 nm from a hydrogen free peak at 574 nm. Introduction
Steady-state and time-resolved vibrational sum frequency generation (vSFG) were used to investiga... more Steady-state and time-resolved vibrational sum frequency generation (vSFG) were used to investigate the structure and dynamics of water at the α-Al2O3(0001) surface. The vSFG spectra of the O—H stretch of water next to the Al2O3(0001) surface are blue-shifted compared to the Al2O3(1120) surface, indicating its weaker hydrogen bonding network. Consequently, the vibrational dynamics of the O—H stretch of the neutral Al2O3(0001) surface is two times slower than the neutral Al2O3(1120) surface. Furthermore, the vibrational dynamics of the O—H stretch of water next to charged Al2O3 surfaces is observed to be faster than that in bulk water and at charged SiO2 surfaces, which could be due to (a) fast proton transfer dominating the vibrational relaxation and/or, (b) efficient coupling between the O—H stretch and the bend overtone via the presence of low frequency (∼3000 cm–1) O—H stretching modes. Lastly, the addition of excess ions (0.1 M NaCl) seems to have little to no effect on the time scale of vibrational...
Journal of the American Chemical Society, Feb 8, 2017
We investigated the dependence of the electrocatalytic activity for the oxygen evolution reaction... more We investigated the dependence of the electrocatalytic activity for the oxygen evolution reaction (OER) on the interlayer distance of five compositionally distinct layered manganese oxide nanostructures. Each individual electrocatalyst was assembled with a different alkali metal intercalated between two nanosheets (NS) of manganese oxide to form a bilayer structure. Manganese oxide NS were synthesized via the exfoliation of a layered material, birnessite. Atomic force microscopy was used to determine the heights of the bilayer catalysts. The interlayer spacing of the supported bilayers positively correlates with the size of the alkali cation: NS/Cs(+)/NS > NS/Rb(+)/NS > NS/K(+)/NS > NS/Na(+)/NS > NS/Li(+)/NS. The thermodynamic origins of these bilayer heights were investigated using molecular dynamics simulations. The overpotential (η) for the OER correlates with the interlayer spacing; NS/Cs(+)/NS has the lowest η (0.45 V), while NS/Li(+)/NS exhibits the highest η (0.68...
Utilizing pure amine hydrogen bonding is a novel approach for constructing two-dimensional (2D) n... more Utilizing pure amine hydrogen bonding is a novel approach for constructing two-dimensional (2D) networks. Further, such systems are capable of undergoing structural modifications due to changes in pH. In this study, we designed a 2D network of triaminobenzene (TAB) molecules that by varying the pH from neutral to acidic, form either ordered or disordered structures on Au(111) surface as revealed in scanning tunneling microscopy images. In near-neutral solution (pH ≈5.5), protonation of TAB generates charged species capable of forming H-bonds between amine groups of neighboring molecules resulting in the formation of a 2D supramolecular structure on the electrified surface. At lower pH, due to the protonation of the amine groups, intermolecular hydrogen bonding is no longer possible and no ordered structure is observed on the surface. This opens the possibility to employ pH as a chemical trigger to induce a phase transition in the 2D molecular network of triaminobenzene molecules.
Water/oxide interfaces are ubiquitous on earth and show significant influence on many chemical pr... more Water/oxide interfaces are ubiquitous on earth and show significant influence on many chemical processes. For example, understanding water and solute adsorption as well as catalytic water splitting can help build better fuel cells and solar cells to overcome our looming energy crisis; the interaction between biomolecules and water/oxide interfaces is one hypothesis to explain the origin of life. However, knowledge in this area is still limited due to the difficulty of studying water/solid interfaces. As a result, research using increasingly sophisticated experimental techniques and computational simulations has been carried out in recent years. Although it is difficult for experimental techniques to provide detailed microscopic structural information, molecular dynamics (MD) simulations have satisfactory performance. In this review, we discuss classical and ab initio MD simulations of water/oxide interfaces. Generally, we are interested in the following questions: How do solid surfaces perturb interfacial water structure? How do interfacial water molecules and adsorbed solutes affect solid surfaces and how do interfacial environments affect solvent and solute behavior? Finally, we discuss progress in the application of neural network potential based MD simulations, which offer a promising future because this approach has already enabled ab initio level accuracy for very large systems and long trajectories.
The kinetics of hydrolysis of dimethyl nitrophenyl phosphate (DMNP), a simulant of the nerve agen... more The kinetics of hydrolysis of dimethyl nitrophenyl phosphate (DMNP), a simulant of the nerve agent Soman, was studied and revealed transition metal salts as catalysts.
Acid/base chemistry is an intriguing topic that still constitutes a challenge for computational c... more Acid/base chemistry is an intriguing topic that still constitutes a challenge for computational chemistry. While estimating the acid dissociation constant (or pKa) could shed light on many chemistry processes, especially in the fields of biochemistry and geochemistry, evaluating the relative stability between protonated and nonprotonated species is often very difficult. Indeed, a prerequisite for calculating the pKa of any molecule is an accurate description of the energetics of water dissociation. Here, we applied constrained molecular dynamics simulations, a noncanonical sampling technique, to investigate the water deprotonation process by selecting the OH distance as the reaction coordinate. The calculation is based on density functional theory and the newly developed SCAN functional, which has shown excellent performance in describing water structure. This first benchmark of SCAN on a chemical reaction shows that this functional accurately models the energetics of proton transfer reactions in an aqueous environment. After taking Coulomb long-range corrections and nuclear quantum effects into account, the estimated water pKa is only 1.0 pKa unit different from the target experimental value. Our results show that the combination of SCAN and constrained MD successfully reproduces the chemistry of water and constitutes a good framework for calculating the free energy of chemical reactions of interest.
Mineral oxide/water interfaces are important for a wide range of industrial, geochemical, and bio... more Mineral oxide/water interfaces are important for a wide range of industrial, geochemical, and biological processes. The reactivity of these interfaces is strongly impacted by the presence of ions. Thus, it is critical to understand how ions alter the interfacial environment. This can be achieved by measuring the changes in the structure and vibrational dynamics of interfacial water induced by the presence of ions in close vicinity to the mineral surface. The α-Al2O3(0001) surface represents a flexible platform to study the effect of ions on interfacial aqueous environments at positive, neutral, and negative surface charges. By using vibrational sum frequency generation (vSFG) in the frequency and time domains, we investigate how monovalent and divalent cations affect the hydrogen bonding environment of the first few layers of interfacial water next to α-Al2O3(0001). Our results indicate that monovalent cations, such as Li+, Na+, K+, and Cs+, appear to have lower binding affinities at the interface compare...
Described is a synthetic method to enhance the electrocatalytic activity of the layered manganese... more Described is a synthetic method to enhance the electrocatalytic activity of the layered manganese oxide, birnessite, for the oxygen evolution reaction (OER) through the development of a Mn/Co/Fe te...
The generation of chemical species from gases, noble metals and light interacting with localized ... more The generation of chemical species from gases, noble metals and light interacting with localized surface plasmons represents a new paradigm for achieving low energy sustainable reaction pathways. Here, we demonstrate that the dissociation reaction of H2 meditated by the decay of localized surface plasmons of gold nanoparticles leads to the generation of a new material as detected by a change in the optical properties of the gold nanostructures. The effective permittivity measured by in situ spectroscopic ellipsometry shows a blue-shift of 0.02 eV in the surface plasmon resonance, demonstrating the plausible formation of a metastable gold hydride layer on the surface of nanoparticles following the dissociation of H2. The formation of this gold hydride through the interaction of gold with atomic H is supported by first-principles simulations. These calculations do not indicate a significant charge transfer upon hydrogenation of the (111) surface but rather large Friedel charge oscillations within the gold layer. Moreover, our blue-shift is produced by the formation of a hydride leading to changes in critical band gaps in the electronic structure. For a coverage of 11%, the calculated peak of the imaginary part of the ZZcomponent of the dielectric tensor undergoes a blue shift of 28 nm from a hydrogen free peak at 574 nm. Introduction
Steady-state and time-resolved vibrational sum frequency generation (vSFG) were used to investiga... more Steady-state and time-resolved vibrational sum frequency generation (vSFG) were used to investigate the structure and dynamics of water at the α-Al2O3(0001) surface. The vSFG spectra of the O—H stretch of water next to the Al2O3(0001) surface are blue-shifted compared to the Al2O3(1120) surface, indicating its weaker hydrogen bonding network. Consequently, the vibrational dynamics of the O—H stretch of the neutral Al2O3(0001) surface is two times slower than the neutral Al2O3(1120) surface. Furthermore, the vibrational dynamics of the O—H stretch of water next to charged Al2O3 surfaces is observed to be faster than that in bulk water and at charged SiO2 surfaces, which could be due to (a) fast proton transfer dominating the vibrational relaxation and/or, (b) efficient coupling between the O—H stretch and the bend overtone via the presence of low frequency (∼3000 cm–1) O—H stretching modes. Lastly, the addition of excess ions (0.1 M NaCl) seems to have little to no effect on the time scale of vibrational...
Journal of the American Chemical Society, Feb 8, 2017
We investigated the dependence of the electrocatalytic activity for the oxygen evolution reaction... more We investigated the dependence of the electrocatalytic activity for the oxygen evolution reaction (OER) on the interlayer distance of five compositionally distinct layered manganese oxide nanostructures. Each individual electrocatalyst was assembled with a different alkali metal intercalated between two nanosheets (NS) of manganese oxide to form a bilayer structure. Manganese oxide NS were synthesized via the exfoliation of a layered material, birnessite. Atomic force microscopy was used to determine the heights of the bilayer catalysts. The interlayer spacing of the supported bilayers positively correlates with the size of the alkali cation: NS/Cs(+)/NS > NS/Rb(+)/NS > NS/K(+)/NS > NS/Na(+)/NS > NS/Li(+)/NS. The thermodynamic origins of these bilayer heights were investigated using molecular dynamics simulations. The overpotential (η) for the OER correlates with the interlayer spacing; NS/Cs(+)/NS has the lowest η (0.45 V), while NS/Li(+)/NS exhibits the highest η (0.68...
Utilizing pure amine hydrogen bonding is a novel approach for constructing two-dimensional (2D) n... more Utilizing pure amine hydrogen bonding is a novel approach for constructing two-dimensional (2D) networks. Further, such systems are capable of undergoing structural modifications due to changes in pH. In this study, we designed a 2D network of triaminobenzene (TAB) molecules that by varying the pH from neutral to acidic, form either ordered or disordered structures on Au(111) surface as revealed in scanning tunneling microscopy images. In near-neutral solution (pH ≈5.5), protonation of TAB generates charged species capable of forming H-bonds between amine groups of neighboring molecules resulting in the formation of a 2D supramolecular structure on the electrified surface. At lower pH, due to the protonation of the amine groups, intermolecular hydrogen bonding is no longer possible and no ordered structure is observed on the surface. This opens the possibility to employ pH as a chemical trigger to induce a phase transition in the 2D molecular network of triaminobenzene molecules.
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Papers by Eric Borguet