Search

Anatase/rutile constituting TiO2 thin films were prepared by sputter deposition, and the influence of the post-annealing step with a narrow window at 200 °C revealed a gaining factor of 5 in H2 production. An in-depth analysis of the photocatalytic performance revealed the dominant role of intermediate states rather than the heterocrystalline nature and the mesoscale structure. Structural, chemical and optical investigations based on scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible spectroscopy and photoluminescence supported by ab initio calculation correlated the H2 production with the dual presence of OH− and Ti3+ defects in the form of titanium interstitial atoms. In addition, steady-state photoluminescence measurements determined the chemically active role of ethanol, commonly used as a hole scavenger, in inducing deep hole traps upon dissociation on the surface. These results give new directions for the design of TiO2 based photocatalytic systems for light-driven H2 production through water splitting, guided by a detailed description of defects present on the electronic structure and their chemical identification. [ABSTRACT FROM AUTHOR]

We perform first-principles calculations to explore the electronic, thermodynamic and dielectric properties of two-dimensional (2D) layered, alkaline-earth hydroxides Ca(OH) 2 and Mg(OH) 2 . We calculate the lattice parameters, exfoliation energies and phonon spectra of monolayers and also investigate the thermal properties of these monolayers, such as the Helmholtz free energy, heat capacity at constant volume and entropy as a function of temperature. We employ Density Functional Perturbation Theory (DFPT) to calculate the in-plane and out-of-plane static dielectric constant of the bulk and monolayer samples. We compute the bandgap and electron affinity values using the HSE06 functional and estimate the leakage current density of transistors with monolayer Ca(OH) 2 and Mg(OH) 2 as dielectrics when combined with HfS 2 and WS 2 , respectively. Our results show that bilayer Mg(OH) 2 (EOT∼0.60 nm) with a lower solubility in water offers higher out-of-plane dielectric constants and lower leakage currents than does bilayer Ca(OH) 2 (EOT∼0.56 nm). Additionally, the out-of-plane dielectric constant, leakage current and EOT of Mg(OH) 2 outperform bilayer h-BN. We verify the applicability of Anderson's rule and conclude that bilayers of Ca(OH) 2 and Mg(OH) 2 , respectively, paired with lattice-matched monolayer HfS 2 and WS 2 , are effective structural combinations that could lead to the development of innovative multi-functional Field Effect Transistors (FETs). [ABSTRACT FROM AUTHOR]

Pyrazine‐linked hybrid ultramicroporous (pore size <7 Å) materials (HUMs) offer benchmark performance for trace carbon capture thanks to strong selectivity for CO2 over small gas molecules, including light hydrocarbons. That the prototypal pyrazine‐linked HUMs are amenable to crystal engineering has enabled second generation HUMs to supersede the performance of the parent HUM, SIFSIX‐3‐Zn, mainly through substitution of the metal and/or the inorganic pillar. Herein, we report that two isostructural aminopyrazine‐linked HUMs, MFSIX‐17‐Ni (17=aminopyrazine; M=Si, Ti), which we had anticipated would offer even stronger affinity for CO2 than their pyrazine analogs, unexpectedly exhibit reduced CO2 affinity but enhanced C2H2 affinity. MFSIX‐17‐Ni are consequently the first physisorbents that enable single‐step production of polymer‐grade ethylene (>99.95 % for SIFSIX‐17‐Ni) from a ternary equimolar mixture of ethylene, acetylene and CO2 thanks to coadsorption of the latter two gases. We attribute this performance to the very different binding sites in MFSIX‐17‐Ni versus SIFSIX‐3‐Zn. [ABSTRACT FROM AUTHOR]

[Display omitted] • Full coverage with water is exothermic for both perfect and defective surfaces. • A subsurface oxygen vacancy enhances dissociation of water up to 67% coverage. • During enhanced dissociation, vacancy migrates to the surface and is annihilated. • Dissociation is endothermic at full coverage as vacancy migration is hindered. • Vacancy shows no catalytic effect on dissociation at full coverage. Titanium (IV) oxide is a reference photocatalytic material for a number of chemical processes of interest in the energy transition, including the reduction of water into hydrogen gas. Density functional theory calculations have previously revealed that the decomposition into hydrogen and hydroxyl ions could be catalyzed by a subsurface oxygen vacancy (V O). However, these theoretical investigations have been carried out with models considering only isolated water molecules. We investigate the role of the subsurface V O at different levels of coverage up to full monolayer (ML) coverage. We observe that migration of the vacancy concomitantly to water decomposition is mandatory to obtain an exothermic pathway. Furthermore, the migration of the V O only occurs in the presence of an under-coordinated surface oxygen atom. As coverage and decomposition increase, surface oxygen atoms are saturated which inhibit further migration of the subsurface V O ; hence the V O shows no catalytic effect on the splitting of water into hydrogen and hydroxyl ions at full water coverage. [ABSTRACT FROM AUTHOR]

Anatase/rutile constituting TiO 2 thin films were prepared by sputter deposition, and the influence of the post-annealing step with a narrow window at 200 °C revealed a gaining factor of 5 in H 2 production. An in-depth analysis of the photocatalytic performance revealed the dominant role of intermediate states rather than the heterocrystalline nature and the mesoscale structure. Structural, chemical and optical investigations based on scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-visible spectroscopy and photoluminescence supported by ab initio calculation correlated the H 2 production with the dual presence of OH - and Ti 3+ defects in the form of titanium interstitial atoms. In addition, steady-state photoluminescence measurements determined the chemically active role of ethanol, commonly used as a hole scavenger, in inducing deep hole traps upon dissociation on the surface. These results give new directions for the design of TiO 2 based photocatalytic systems for light-driven H 2 production through water splitting, guided by a detailed description of defects present on the electronic structure and their chemical identification.