CO2 and Water Activation on Ceria Nanocluster Modified TiO2 Rutile (110)

10.26434/chemrxiv.5845635 ◽

2018 ◽

Author(s):

Michael Nolan ◽

Stephen Rhatigan

Keyword(s):

Surface Modification ◽

Oxygen Vacancy ◽

Density Functional ◽

Energy Gap ◽

Light Response ◽

Surface Reactivity ◽

Coulomb Interactions ◽

Water Activation ◽

Carrier Separation ◽

The Impact

Surface modification of TiO2 with metal oxide nanoclusters is a strategy for the development of new photocatalyst materials. We have studied modification of the (110) surface of rutile TiO2 with ceria nanoclusters using density functional theory corrected for on-site Coulomb interactions (DFT+U). We focus on the impact of surface modification on key properties governing the performance of photocatalysts, including light absorption, photoexcited charge carrier separation, reducibility and surface reactivity. Our results show that adsorption of the CeO2 nanoclusters, with compositions Ce5O10 and Ce6O12, is favourable at the rutile (110) surface and that the nanocluster-surface composites favour non-stoichiometry in the adsorbed ceria so that reduced Ce ions will be present in the ground state. The presence of reduced Ce ions and low coordinated O sites in the nanocluster lead to the emergence of energy states in the energy gap of the TiO2 host, which potentially enhance the visible light response. We show, through an examination of oxygen vacancy formation, that the composite systems are reducible with moderate energy costs. Photoexcited electrons and holes localize on Ce and O sites of the supported nanoclusters. The interaction of CO2 and H2O is favourable at multiple sites of the reduced CeOx-TiO2 composite surfaces. CO2 adsorbs and activates, while H2O spontaneously dissociates at oxygen vacancy sites.

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A DFT Study of the Impact of Doping on the Electronic and Optical Properties of Indium Nitride Nanocage

10.21203/rs.3.rs-401912/v1 ◽

2021 ◽

Author(s):

Amarjyoti Das ◽

Rajesh Kumar Yadav

Keyword(s):

Optical Properties ◽

Electronic Properties ◽

Density Functional ◽

Chemical Potential ◽

Energy Gap ◽

Indium Nitride ◽

Wavelength Region ◽

Binding Energies ◽

Electronic And Optical Properties ◽

The Impact

Abstract Density functional theory (DFT) calculations are used to investigate the structural, electronic, and optical properties of the significant fullerene-like cage of In12N12 nanoclusters with Zn (group II) and Si (group IV) dopants. In terms of formation energies and binding energies, the structural stability of the nanocages were studied. It has been seen that stability of the structure is slightly increases with the inclusion of doping. The study found that both the dopants significantly reduce the energy gap of the In12N12 nanocluster. The electronic properties of the In12N12 nanocluster seems to be sensitive to dopants, and it could be altered by a specific impurity. Moreover, electronic properties such as density of states (DOS) analysis, dipole moment, HOMO energies, LUMO energies, energy gaps, chemical potential, electron affinity, ionization potential, hardness, and electrophilicity index are also discussed. The optical absorption spectra of pure and doped nanocages were computed using TDDFT formalism. The maximum wavelength of the pure In12N12 nanocage is moved towards higher wavelength region within the infrared region after doping with Zn and Si, indicating a redshift.

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Activation of Water on MnOx-Modified Rutile (110) and Anatase (101) TiO2 and the Role of Cation Reduction

10.26434/chemrxiv.7240823 ◽

2018 ◽

Author(s):

Michael Nolan ◽

Stephen Rhatigan

Keyword(s):

Oxygen Vacancy ◽

Light Absorption ◽

Density Functional ◽

Vacancy Formation ◽

Visible Range ◽

Coulomb Interactions ◽

Carrier Recombination ◽

Oxygen Vacancy Formation ◽

Surface Hydroxyls

Surface modification of titania surfaces with dispersed metal oxide nanoclusters has the potential to enhance photocatalytic activity. These modifications can induce visible light absorption and suppress charge carrier recombination which are vital in improving the efficiency. We have studied heterostructures of Mn4O6 nanoclusters modifying the TiO2 rutile (110) and anatase (101) surfaces using density functional theory corrected for on-site Coulomb interactions (DFT + U). Such studies typically focus on the pristine surface, free of the point defects and surface hydroxyls present in real surfaces. In our study we have considered partial hydroxylation of the rutile and anatase surfaces and the role of cation reduction, via oxygen vacancy formation, and how this impacts on a variety of properties governing the photocatalytic performance such as nanocluster adsorption, light absorption, charge separation and reducibility. Our results indicate that the modifiers adsorb strongly at the surface and that modification extends light absorption into the visible range. MnOx-modified anatase can show an off-stoichiometric ground state, through oxygen vacancy formation and cation reduction spontaneously, and both modified rutile and anatase are highly reducible with moderate energy costs. Manganese ions are therefore present in a mixture of oxidation states. Photoexcited electrons and holes localize at cluster metal and oxygen sites, respectively. The interaction of water at the modified surfaces depends on the stoichiometry and spontaneous dissociation to surface bound hydroxyls is favoured in the presence of oxygen vacancies and reduced metal cations. Comparisons with bare TiO2 and other TiO2-based photocatalyst materials are presented throughout.

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Exploring the impact of hydrostatic pressure on the structural, electronic and mechanical properties of ZrNiPb half-Heusler alloy: A DFT approach

International Journal of Modern Physics B ◽

10.1142/s021797921850248x ◽

2018 ◽

Vol 32 (23) ◽

pp. 1850248

Author(s):

M. I. Babalola ◽

B. I. Adetunji ◽

B. E. Iyorzor ◽

A. Yaya

Keyword(s):

Mechanical Properties ◽

Heusler Alloy ◽

Poisson’S Ratio ◽

Density Functional ◽

Energy Gap ◽

Poisson's Ratio ◽

Generalized Gradient ◽

Functional Theory ◽

The Density Functional Theory ◽

The Impact

The structural, electronic, elastic and mechanical properties of ZrNiPb half-Heusler alloy under pressure ranging from 0 to 25 GPa have been studied using the density functional theory within the generalized gradient approximation (GGA). The results of ambient condition were in good agreement with the available theoretical and experimental data. Our electronic structure and density of state results show that ZrNiPb is an indirect bandgap semiconductor half-Heusler alloy with a narrow energy gap of 0.375 eV. Based on the calculated elastic constants (C[Formula: see text], C[Formula: see text] and C[Formula: see text]), Young’s modulus (E), Poisson’s ratio ([Formula: see text]), Shear modulus (G), Zener anisotropy factor (A) and brittle-ductile behaviors under pressure have been discussed. The calculated Poisson’s ratio shows that ZrNiPb undergoes a relatively small volume change during uniaxial deformation. We show that the chemical bonds in ZrNiPb are stronger due to the high value of C[Formula: see text].

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Modification of TiO2 with Metal Chalcogenide Nanoclusters for Hydrogen Evolution

10.26434/chemrxiv.13176773.v1 ◽

2020 ◽

Author(s):

Stephen Rhatigan ◽

Lorenzo Niemitz ◽

Michael Nolan

Keyword(s):

Density Functional Theory ◽

Surface Modification ◽

Hydrogen Evolution ◽

Density Functional ◽

Hydrogen Adsorption ◽

Coulomb Interactions ◽

Free Energies ◽

Functional Theory ◽

Metal Chalcogenide ◽

Adsorption Energies

Using density functional theory, corrected for on-site Coulomb interactions (DFT+U), we have investigated surface modification of TiO2 with metal chalcogenide nanoclusters for hydrogen evolution. The nanoclusters have composition M4X4 (M = Sn, Zn; X = S, Se) and are adsorbed at the rutile (110) surface. The nanoclusters adsorb exothermically, with adsorption energies in the range -3.00 eV to -2.70 eV. Computed density of states (DOS) plots show that cluster-derived states extend into the band-gap of the rutile support, which indicates that modification produces a redshift in light absorption. After modification, photoexcited electrons and holes are separated onto surface and cluster sites, respectively. The free energy of H adsorption is used to assess the performance of metal chalcogenide modified TiO2 as a catalyst for HER. Adsorption of H at nanocluster (S, Se) and surface (O) sites is considered, together with the effect of H coverage. Adsorption free energies at cluster sites in the range (-0.15 eV, 0.15 eV) are considered to be favourable for HER. The results of this analysis indicate that the sulphide modifiers are more active towards HER than the selenide modifiers and exhibit hydrogen adsorption free energies in the active range, for most coverages. Conversely, the adsorption free energies at the selenide nanoclusters are only in the active range at low H coverages. Our results indicate that surface modification with small, dispersed nanoclusters of appropriately selected materials can enhance the photocatalytic activity of TiO2 for HER applications.

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Modification of TiO2 with Metal Chalcogenide Nanoclusters for Hydrogen Evolution

10.26434/chemrxiv.13176773 ◽

2020 ◽

Author(s):

Stephen Rhatigan ◽

Lorenzo Niemitz ◽

Michael Nolan

Keyword(s):

Density Functional Theory ◽

Surface Modification ◽

Hydrogen Evolution ◽

Density Functional ◽

Hydrogen Adsorption ◽

Coulomb Interactions ◽

Free Energies ◽

Functional Theory ◽

Metal Chalcogenide ◽

Adsorption Energies

Using density functional theory, corrected for on-site Coulomb interactions (DFT+U), we have investigated surface modification of TiO2 with metal chalcogenide nanoclusters for hydrogen evolution. The nanoclusters have composition M4X4 (M = Sn, Zn; X = S, Se) and are adsorbed at the rutile (110) surface. The nanoclusters adsorb exothermically, with adsorption energies in the range -3.00 eV to -2.70 eV. Computed density of states (DOS) plots show that cluster-derived states extend into the band-gap of the rutile support, which indicates that modification produces a redshift in light absorption. After modification, photoexcited electrons and holes are separated onto surface and cluster sites, respectively. The free energy of H adsorption is used to assess the performance of metal chalcogenide modified TiO2 as a catalyst for HER. Adsorption of H at nanocluster (S, Se) and surface (O) sites is considered, together with the effect of H coverage. Adsorption free energies at cluster sites in the range (-0.15 eV, 0.15 eV) are considered to be favourable for HER. The results of this analysis indicate that the sulphide modifiers are more active towards HER than the selenide modifiers and exhibit hydrogen adsorption free energies in the active range, for most coverages. Conversely, the adsorption free energies at the selenide nanoclusters are only in the active range at low H coverages. Our results indicate that surface modification with small, dispersed nanoclusters of appropriately selected materials can enhance the photocatalytic activity of TiO2 for HER applications.

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Modeling the Physical Properties of ZnO Nanoparticles with Selective Hydrogen Using DFT

International Journal of Nanoscience ◽

10.1142/s0219581x21500113 ◽

2020 ◽

pp. 2150011

Author(s):

Bilal K. Al-Rawi ◽

Safaa M. H. Aljanabi

Keyword(s):

Bond Length ◽

Vibration Frequency ◽

Zno Nanoparticles ◽

Density Functional ◽

Energy Gap ◽

Frequency Function ◽

Functional Theory ◽

Nanoparticle Surface ◽

Homo And Lumo ◽

The Impact

The impact of hydrogen on the conductivity and vibration for zinc oxide (ZnO) nanoparticles had implicated for nanoscale optoelectronic units. Infrared reflectance spectra for ZnO hydrogen-annealed nanoparticles were calculated at incidence. The theory of density functional theory is applied to the reflectance model and absorption spectra. There is an agreement between both the model suggesting that the nanoparticles have inhomogeneous carriers’ concentrations and the experimental results. A significant decrease in carrier concentration resulted from exposure to oxygen for several hours, according to the adsorption on the nanoparticle surface of negative oxygen molecules. Also, the density of states in deferent wurtzoid’s size has been studied. The experimental energy gap values of bulk ZnO, HOMO and LUMO levels as a function of the total Zn and O atoms number in ZnOH diamondoids were determined, as well as the bond length in deferent wurtzoid’s size where the experimental ZnO bond length at 1.9767 Å has been calculated. The tetrahedral angles in deferent wurtzoid’s size were studied, deferent wurtzoid’s size Reduced mass as a vibration frequency function and force constant as a function of vibrational frequency in deferent wurtzoid’s size were determined. A good result for infrared as a vibration frequency function in deferent wurtzoid’s size has been found, as well as Raman as a vibration frequency function in deferent wurtzoid’s size.

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Activation of Water on MnOx-Modified Rutile (110) and Anatase (101) TiO2 and the Role of Cation Reduction

10.26434/chemrxiv.7240823.v1 ◽

2018 ◽

Author(s):

Michael Nolan ◽

Stephen Rhatigan

Keyword(s):

Oxygen Vacancy ◽

Light Absorption ◽

Density Functional ◽

Vacancy Formation ◽

Visible Range ◽

Coulomb Interactions ◽

Carrier Recombination ◽

Oxygen Vacancy Formation ◽

Surface Hydroxyls

Surface modification of titania surfaces with dispersed metal oxide nanoclusters has the potential to enhance photocatalytic activity. These modifications can induce visible light absorption and suppress charge carrier recombination which are vital in improving the efficiency. We have studied heterostructures of Mn4O6 nanoclusters modifying the TiO2 rutile (110) and anatase (101) surfaces using density functional theory corrected for on-site Coulomb interactions (DFT + U). Such studies typically focus on the pristine surface, free of the point defects and surface hydroxyls present in real surfaces. In our study we have considered partial hydroxylation of the rutile and anatase surfaces and the role of cation reduction, via oxygen vacancy formation, and how this impacts on a variety of properties governing the photocatalytic performance such as nanocluster adsorption, light absorption, charge separation and reducibility. Our results indicate that the modifiers adsorb strongly at the surface and that modification extends light absorption into the visible range. MnOx-modified anatase can show an off-stoichiometric ground state, through oxygen vacancy formation and cation reduction spontaneously, and both modified rutile and anatase are highly reducible with moderate energy costs. Manganese ions are therefore present in a mixture of oxidation states. Photoexcited electrons and holes localize at cluster metal and oxygen sites, respectively. The interaction of water at the modified surfaces depends on the stoichiometry and spontaneous dissociation to surface bound hydroxyls is favoured in the presence of oxygen vacancies and reduced metal cations. Comparisons with bare TiO2 and other TiO2-based photocatalyst materials are presented throughout.

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Nanostructured ZnO–X Alloys with Tailored Optoelectronic Properties for Solar-energy Technologies

MRS Proceedings ◽

10.1557/opl.2013.1134 ◽

2013 ◽

Vol 1558 ◽

Author(s):

Maofeng Dou ◽

Clas Persson

Keyword(s):

First Principles ◽

Density Functional ◽

Alloy Composition ◽

Energy Gap ◽

Band Gap Energy ◽

Optoelectronic Properties ◽

Gap Energy ◽

Energy Technologies ◽

Small Distortion ◽

The Impact

ABSTRACTAlloying ZnO with isovalent compounds allows tailoring the material’s optoelectronic properties. In this work, we theoretically analyze the ZnO-based alloys ZnO–X ≡ (ZnO)1−x(X)x where X = GaN and InN, employing a first-principles Green’s function method GW0 based on the density functional approach. Since the alloy compounds are isovalent to ZnO, we find relatively small distortion of the crystalline structure, however, nanocluster structures are expected to be present in the alloy. ZnO–X reveal intriguing optoelectronic properties. Incorporating GaN or InN in ZnO strongly narrows the energy gap. The band gap energy is reduced from Eg = 3.34 eV in intrinsic ZnO to ∼2.17 and ∼1.89 eV in ZnO–X by alloying ZnO with 25% GaN and InN, respectively. Moreover, clustering enhances the impact on the electronic structure, and the gap energy in ZnO–InN is further reduced to 0.7–1.5 eV if the 25% compound contains nanoclusters. The dielectric function ε2(ω) varies weakly in ZnO–GaN with respect to alloy composition, while it varies rather strongly in ZnO–InN. Hence, by properly growing and designing ZnO–X, the alloy can be optimized for a variety of novel integrated optoelectronic nano-systems.

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Structure, Stability and Water Adsorption on Ultra-Thin TiO2 Supported on TiN

10.26434/chemrxiv.8425367.v1 ◽

2019 ◽

Author(s):

Jose Julio Gutierrez Moreno ◽

Marco Fronzi ◽

Pierre Lovera ◽

alan O'Riordan ◽

Mike J Ford ◽

...

Keyword(s):

Density Functional ◽

Water Adsorption ◽

Chemical Potential ◽

Energy Gap ◽

Molecular Water ◽

Structure Stability ◽

Ambient Conditions ◽

Rutile Structure ◽

The Stability ◽

The One

Interfacial metal-oxide systems with ultrathin oxide layers are of high interest for their use in catalysis. In this study, we present a density functional theory (DFT) investigation of the structure of ultrathin rutile layers (one and two TiO2 layers) supported on TiN and the stability of water on these interfacial structures. The rutile layers are stabilized on the TiN surface through the formation of interfacial Ti–O bonds. Charge transfer from the TiN substrate leads to the formation of reduced Ti3+ cations in TiO2. The structure of the one-layer oxide slab is strongly distorted at the interface, while the thicker TiO2 layer preserves the rutile structure. The energy cost for the formation of a single O vacancy in the one-layer oxide slab is only 0.5 eV with respect to the ideal interface. For the two-layer oxide slab, the introduction of several vacancies in an already non-stoichiometric system becomes progressively more favourable, which indicates the stability of the highly non-stoichiometric interfaces. Isolated water molecules dissociate when adsorbed at the TiO2 layers. At higher coverages the preference is for molecular water adsorption. Our ab initio thermodynamics calculations show the fully water covered stoichiometric models as the most stable structure at typical ambient conditions. Interfacial models with multiple vacancies are most stable at low (reducing) oxygen chemical potential values. A water monolayer adsorbs dissociatively on the highly distorted 2-layer TiO1.75-TiN interface, where the Ti3+ states lying above the top of the valence band contribute to a significant reduction of the energy gap compared to the stoichiometric TiO2-TiN model. Our results provide a guide for the design of novel interfacial systems containing ultrathin TiO2 with potential application as photocatalytic water splitting devices.

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