6 research outputs found
CO<sub>2</sub> Capture by TiO<sub>2</sub> Anatase Surfaces: A Combined DFT and FTIR Study
In
this work, by combining FTIR results with periodic DFT calculations,
we highlight the role of different anatase surface sites in the CO<sub>2</sub> adsorption and in the subsequent reactions. It is shown that
CO<sub>2</sub> is mainly adsorbed in linear form at the (101) surface,
while the formation of a variety of surface carbonates is occurring
at the (001) one. The role of coadsorbed water in the formation of
surface bicarbonates is also investigated. All the structures identified
by FTIR spectroscopy were modeled by DFT, and the adsorption geometries
and the energy of formation for the surface species were carefully
analyzed. For the most stable structures we also performed the calculation
of the vibrational frequencies that were compared with the FTIR data
Surface Properties of ZnS Nanoparticles: A Combined DFT and Experimental Study
Carbon
monoxide adsorption on nanosize ZnS has been investigated
by FTIR spectroscopy and periodic DFT calculations. FTIR experiments
show that CO adsorption on the zinc sulfide nanoparticles gives rise
to a single main νÂ(CO) band indicating that the majority of
the exposed sites are on the same surface. Computed adsorption energies
(−0.244/–0.207 eV for the low and high coverage, respectively)
and stretching frequencies (2182/2172 cm<sup>–1</sup>) of CO
adsorbed at the most stable (110) ZnS surface are in excellent agreement
with observations (νÂ(CO) = 2190/2168 cm<sup>–1</sup>).
CO is weakly bound to the Zn<sup>2+</sup> Lewis acid surface site
mainly through electrostatic interaction and a small contribution
from σ donation. The strength of surface Lewis sites in ZnS
is lower with respect to ZnO
Ab Initio Simulation of ZnO/LaMnO<sub>3</sub> Heterojunctions: Insights into Their Structural and Electronic Properties
Layered oxide heterostructures
show interesting properties that
encompass those of the standalone moieties; hence, a detailed understanding
of the interface is key to the development and use of such materials.
In this work, we have performed quantum-chemical ab initio calculations
to give a complex description of structural and electronic properties
of epitaxial growth ZnO/LaMnO<sub>3</sub> (ZnO/LMO) interfaces. The Crystal code, which uses a local (Gaussian) basis set, is used
to design and characterize ZnO/LMO heterostructures including (112Ì…0)
and (101Ì…0) nonpolar overlayers of ZnO on LMO(001), supported
from simpler formulation to hybrid functionals of density functional
theory. The applied structural models and coincidence cells are described
and illustrated in detail. We discuss the impact of different termination
of LMO through stability (computed strain and adhesion energies) and
structural and electronic properties (density of states and 3D charge
density differences). The ZnO(112Ì…0) overlayer shows the lesser
structural distortion and the most stable configuration with LaO termination
of LMO. These important findings enable us to propose novel hybrid
composites for electrochemical devices
Systematic Life Cycle Environmental Impact Comparison of Alternative Synthetic Strategies for Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene
The need for more environmentally sustainable MXene syntheses
was
ranked by the MXene community among the top research challenges for
the upcoming decades. This means that both well-established synthetic
protocols and newly proposed ones need to be assessed and compared
in terms of their associated environmental impacts. Despite the various
number of existing synthetic methods for MXenes, only one synthesis
of Ti3C2Tx has been
assessed from an environmental perspective, by applying the life cycle
assessment (LCA) methodology. This work proposes for the first time
a systematic life cycle environmental impact comparison among seven
different synthetic pathways of the same Ti3C2Tx MXene. Starting from the first reported
synthesis, the further approaches assessed differ in terms of MAX
phase precursors, etching, and delamination procedures adopted. An
uncertainty analysis was also performed to determine the reliability
of the obtained results, which were also used in conjunction with
those related to the measured bulk electrical conductivity of the
MXene produced together with the obtained density values of opportunely
prepared Ti3C2Tx freestanding films. This allows accounting for the necessary different
quality of the obtained products, highlighting the better trade-off
solutions between low environmental impacts, high electrical conductivity,
and low weight of the potentially developed Ti3C2Tx MXene-based devices
Stability and Formation of the Li<sub>3</sub>PS<sub>4</sub>/Li, Li<sub>3</sub>PS<sub>4</sub>/Li<sub>2</sub>S, and Li<sub>2</sub>S/Li Interfaces: A Theoretical Study
Solid electrolytes
have shown superior behavior and many
advantages
over liquid electrolytes, including simplicity in battery design.
However, some chemical and structural instability problems arise when
solid electrolytes form a direct interface with the negative Li-metal
electrode. In particular, it was recognized that the interface between
the β-Li3PS4 crystal and lithium anode
is quite unstable and tends to promote structural defects that inhibit
the correct functioning of the device. As a possible way out of this
problem, we propose a material, Li2S, as a passivating
coating for the Li/β-Li3PS4 interface.
We investigated the mutual affinity between Li/Li2S and
Li2S/β-Li3PS4 interfaces by
DFT methods and investigated the structural stability through the
adhesion energy and mechanical stress. Furthermore, a topological
analysis of the electron density identified preferential paths for
the migration of Li ions
Work Function of Oxide Ultrathin Films on the Ag(100) Surface
Theoretical calculations of the work function of monolayer
(ML)
and bilayer (BL) oxide films on the Ag(100) surface are reported and
analyzed as a function of the nature of the oxide for first-row transition
metals. The contributions due to charge compression, charge transfer
and rumpling are singled out. It is found that the presence of empty
d-orbitals in the oxide metal can entail a charge flow from the Ag(100)
surface to the oxide film which counteracts the decrease in the work
function due to charge compression. This flow can also depend on the
thickness of the film and be reduced in passing from ML to BL systems.
A regular trend is observed along first-row transition metals, exhibiting
a maximum for CuO, in which the charge flow to the oxide is so strong
as to reverse the direction of rumpling. A simple protocol to estimate
separately the contribution due to charge compression is discussed,
and the difference between the work function of the bare metal surface
and a Pauling-like electronegativity of the free oxide slabs is used
as a descriptor quantity to predict the direction of charge transfer