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1.
J Phys Condens Matter ; 32(4): 045001, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31585452

RESUMO

Surface interaction through adsorption and dissociation between H2O and metal oxides plays an important role in many industrial as well as fundamental processes. To gain further insights on the interaction, this study performs dispersion-corrected Hubbard-corrected density functional theory calculations in H2O adsorption and dissociation on stoichiometric and nonstoichiometric CuO(1 1 1) surfaces. The nonstoichiometric surfaces consist of oxygen vacancy defect and oxygen-preadsorbed surfaces. This study finds that H2O is chemically adsorbed on the top of Cusub and Cusub-Cusub bridge due to the interaction of its p  orbital with d orbital of Cu. The adsorption is found to be the strongest on the surface with the oxygen vacancy defect, followed by the stoichiometric surface, and the oxygen-preadsorbed surface. The oxygen vacancy increases the reactivity for H2O adsorption and reduces the reaction energy required for H2O dissociation on the surface. However, the surface modification by the oxygen-preadsorbed significantly reduces the barrier energy for H2O dissociation when compared with the other surfaces.

2.
Phys Chem Chem Phys ; 21(36): 20276-20286, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31490485

RESUMO

A DFT study of methanol production via CO2 hydrogenation reactions on clean Ni(111) and Ni(111)-M (M = Cu, Pd, Pt, or Rh) surfaces has been performed. The reaction network of this synthesis reaction has been determined using energy profiles. The competing reaction network between the formate-mediated route and the carboxyl-mediated route is also presented. Both routes are equally possible in mediating the overall synthesis reactions. A simple selectivity analysis based on the energy barrier shows that methanol synthesis is more preferred rather than formic acid (HCOOH) or carbon monoxide (CO) production. A mean-field kinetic analysis is also employed to determine the kinetic performance of all catalytic surfaces. The formate-mediated route is found to be energetically and kinetically more dominant than the carboxyl-mediated route. Cu, Pd, and Pt dopants are successful in increasing the kinetic performance of the clean Ni(111) surface in the formate route and Cu, Pt, and Rh dopants in the carboxyl route.

3.
ChemSusChem ; 2019 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-31270940

RESUMO

Layered double hydroxides (LDHs) containing first-row transition metals such as Fe, Co, and Ni have attracted significant interest for electrocatalysis owing to their abundance and excellent performance for the oxygen evolution reaction (OER) in alkaline media. Herein, the assembly of holey iron-doped nickel-cobalt layered double hydroxide (NiCo-LDH) nanosheets ('holey nanosheets') is demonstrated by employing uniform Ni-Co glycerate spheres as self-templates. Iron doping was found to increase the rate of hydrolysis of Ni-Co glycerate spheres and induce the formation of a holey interconnected sheet-like structure with small pores (1-10 nm) and a high specific surface area (279 m2 g-1 ). The optimum Fe-doped NiCo-LDH OER catalyst showed a low overpotential of 285 mV at a current density of 10 mA cm-2 and a low Tafel slope of 62 mV dec-1 . The enhanced OER activity was attributed to (i) the high specific surface area of the holey nanosheets, which increases the number of active sites, and (ii) the improved kinetics and enhanced ion transport arising from the iron doping and synergistic effects.

4.
J Phys Condens Matter ; 31(36): 365001, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31121574

RESUMO

Due to the increasing demands of new and renewable energy sources by utilising plant oils, uncovering the underlying physico-chemical phenomena at the atomic level responsible for the effective deoxygenation plays a vital role in improving the performance of well-known as well as in looking for the possible new catalysts. This study aims at investigating the adsorption and C-O bonds cleavage of methyl butanoate (MB) over MoS2-based catalyst with various loads of Ni promoters by using first-principles density functional theory (DFT). This study employs surface model that never been used by previous researchers for their investigations of adsorption and bonds cleavage on Ni promoted MoS2-based catalysts. The introduction of nickel into MoS2-based catalyst allows the surface charges when interacts with MB to redistribute in such a way that induces stronger Coulombic attractive forces. This in turn could result in a more stable adsorption configuration. However only in certain Ni-loads will results in the most stable adsorption. Nevertheless the most stable adsorption of MB occurs on M-edge configuration which consists of two Ni atoms, i.e. M-2-Ni-A with adsorption energy at about -2.96 eV. As a comparison, the adsorption energy of MoS2 with the absent of Ni, i.e. M-0-Ni is just -2.79 eV. Since there are three C-O bonds in MB, this study proposes three possible reactions for these bonds to cleave. By using CI-NEB method, the activation energies of those three reaction are calculated. It shows that the presence of Ni with appropriate load could promote C-O bond cleavage, especially in one reaction C-O bond is weaken considerably. Further evaluation on bond dissociation energies of the closest C-C bond to the catalyst surface, M-2-Ni-A shows better reactivity on C-C bond cleavage than M-0-Ni, disregarding of those three reaction routes.

5.
Spectrochim Acta A Mol Biomol Spectrosc ; 171: 112-125, 2017 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-27497289

RESUMO

This study reports the novel spectroscopic investigations and enhanced the electron transfers of Citrus reticulata and Musa acuminata fruit peels as the photosensitizers for the dye-sensitized solar cells. The calculated TD-DFT-UB3LYP/6-31+G(d,p)-IEFPCM(UAKS), experiment spectra of ultra-violet-visible spectroscopy, and Fourier transform infrared spectroscopy studies indicate the main flavonoid (hesperidin and gallocatechin) structures of the dye extracts. The optimized flavonoid structures are calculated using Density functional theory (DFT) at 6-31+G(d,p) level. The rutinosyl group of the hesperidin pigment (Citrus reticulata) will be further investigated compared to the gallocatechin (Musa acuminata) pigment. The acidity of the dye extract is treated by adding 2% acetic acid. The energy levels of the HOMO-LUMO dyes are measured by a combined Tauc plot and cyclic voltammetry contrasted with the DFT data. The electrochemical impedance spectroscopy will be performed to model the dye electron transfer. As for the rutinosyl group presence and the acidic treatment, the acidified Citrus reticulata cell under continuous light exposure of 100mW·cm-2 yields a short-circuit current density (Jsc) of 3.23mA/cm2, a photovoltage (Voc) of 0.48V, and a fill factor of 0.45 corresponding to an energy conversion efficiency (η) of 0.71% because the shifting down HOMO-LUMO edges and the broadening dye's absorbance evaluated by a combined spectroscopic and TD-DFT method. The result also leads to the longest diffusion length of 32.2µm, the fastest electron transit of 0.22ms, and the longest electron lifetime of 4.29ms.


Assuntos
Produtos Biológicos/química , Citrus/química , Corantes/química , Frutas/química , Musa/química , Teoria Quântica , Energia Solar , Espectroscopia Dielétrica , Técnicas Eletroquímicas , Elétrons , Modelos Moleculares , Nanopartículas/química , Nanopartículas/ultraestrutura , Espectrofotometria Ultravioleta , Espectroscopia de Infravermelho com Transformada de Fourier , Termodinâmica , Titânio/química , Difração de Raios X
6.
J Phys Condens Matter ; 24(47): 475506, 2012 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-23110845

RESUMO

The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H(2)O/Li-MMT.

7.
J Nanosci Nanotechnol ; 11(4): 2793-801, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-21776634

RESUMO

The absorption of lithium in montmorillonite [LiSi8(Al3Mg)O20(OH)4] was investigated using Density Functional Theory (DFT). The final position of lithium after absorption was found to be in good agreement with an experimental observation where lithium atom migrated from the interlayer into the vacant octahedral site of montmorillonite. The lithium absorbed on montmorillonite was held together by a very strong attraction between ions and exhibited an insulating behavior as depicted from the density of states curve. Due to the presence of lithium in the octahedral site of montmorillonite, the OH group reoriented itself perpendicular to the ab plane and an electron of lithium was transferred in order to compensate the existing net charge of montmorillonite caused by isomorphous substitutions. Relative small charge transfer was observed between lithium and montmorillonite.


Assuntos
Bentonita/química , Lítio/química , Lítio/isolamento & purificação , Modelos Químicos , Absorção , Simulação por Computador , Eletricidade Estática
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