Adsorption of O2 on TiO2(110): A theoretical study
18 May 1999-Journal of Chemical Physics (American Institute of Physics)-Vol. 110, Iss: 21, pp 10539-10544
TL;DR: In this article, first-principles calculations are carried out with the objective of assigning a chemical identity to the variety of forms of molecular oxygen which are known to exist on a TiO2(110) surface.
Abstract: First-principles calculations are carried out with the objective of assigning a chemical identity to the variety of forms of molecular oxygen which are known to exist on a TiO2(110) surface. Six different geometries and spin configurations of O2 are shown to be stable in the bridging oxygen defect site. The relationship of these results to experimental observations is discussed.
Citations
More filters
[...]
TL;DR: The field of surface science provides a unique approach to understand bulk, surface and interfacial phenomena occurring during TiO2 photocatalysis as mentioned in this paper, including photon absorption, charge transport and trapping, electron transfer dynamics, adsorbed state, mechanisms, poisons and promoters, and phase and form.
Abstract: The field of surface science provides a unique approach to understanding bulk, surface and interfacial phenomena occurring during TiO2 photocatalysis. This review highlights, from a surface science perspective, recent literature that provides molecular-level insights into photon-initiated events occurring at TiO2 surfaces. Seven key scientific issues are identified in the organization of this review. These are: (1) photon absorption, (2) charge transport and trapping, (3) electron transfer dynamics, (4) the adsorbed state, (5) mechanisms, (6) poisons and promoters, and (7) phase and form. This review ends with a brief examination of several chemical processes (such as water splitting) in which TiO2 photocatalysis has made significant contributions in the literature.
1,602 citations
[...]
TL;DR: It is found that the presence of neighboring vacancies can strongly affect the ability of O2 to dissociate, and the implications of this in connection with diffusion of the bridging oxygen vacancies are discussed.
Abstract: The properties of reduced rutile TiO2(110) surfaces, as well as the adsorption, diffusion, and dissociation of molecular oxygen are investigated by means of density functional theory. The O2 molecule is found to bind strongly to bridging oxygen vacancies, attaining a molecular state with an expanded O-O bond of 1.44 A. The molecular oxygen also binds (with somewhat shortened bond lengths) to the fivefold coordinated Ti atoms in the troughs between the bridging oxygen rows, but only when vacancies are present somewhere in the surface. In all cases, the magnetic moment of O2 is lost upon adsorption. The expanded bond lengths reveal together with inspection of electron density and electronic density of state plots that charging of the adsorbed molecular oxygen is of key importance in forming the adsorption bond. The processes of O2 diffusion from a vacancy to a trough and O2 dissociation at a vacancy are both hindered by relative large barriers. However, we find that the presence of neighboring vacancies can strongly affect the ability of O2 to dissociate. The implications of this in connection with diffusion of the bridging oxygen vacancies are discussed.
226 citations
[...]
TL;DR: In this article, first-principles density-functional calculations have been used to study the interaction of molecular oxygen with a partially reduced rutile surface, and the kinetic barriers for conversion between these states have also been calculated.
Abstract: Using first-principles density-functional calculations we have studied the interactions of molecular oxygen with a partially reduced rutile ${\mathrm{TiO}}_{2}$ (110) surface. In agreement with experiments, a number of different ${\mathrm{O}}_{2}$ adsorption states, both molecular and dissociated, have been found. The kinetic barriers for conversion between these states have also been calculated. Based on these results, we analyze the mechanism of oxygen vacancy diffusion, recently observed by Scanning Tunneling Microscopy (STM), and suggest a pathway which does not imply the high oxygen adatom reactivity assumed in the original model.
125 citations
[...]
TL;DR: The electronic structure of the rutile surface after formation of an isolated oxygen vacancy has been studied with density functional (DF) calculations and TiO2 embedded clusters in this article, where restricted and unrestricted open shell wave functions have been analyzed in terms of atomic spin densities and Ti core level shifts.
Abstract: The electronic structure of the rutile(1 1 0) surface after formation of an isolated oxygen vacancy has been studied with density functional (DF) calculations and TiO2 embedded clusters. Restricted and unrestricted open shell wave functions have been analyzed in terms of atomic spin densities and Ti core level shifts. The removal of a neutral oxygen atom from the bridging oxygens of the TiO2(1 1 0) surface results in two unpaired electrons localized at the 3d orbitals of neighboring 5-coordinated Ti atoms. The electronic structure of an O vacancy on the surface of TiO2 is compared with that of the same defect in MgO and SiO2.
110 citations
[...]
TL;DR: In this paper, it was shown that if the surface species formed by oxygen adsorption are restricted to be charge neutral, then oxygen cannot be exothermically adsorbed from the gas phase on the stoichiometric surface.
Abstract: First-principles calculations based on density functional theory in the generalised gradient approximation, together with pseudopotentials and plane-wave basis sets, have been used to investigate the energetics of oxygen adsorption on stoichiometric and weakly and strongly reduced SnO2(1 1 0) surfaces. It is shown that, if the surface species formed by oxygen adsorption are restricted to be charge neutral, then oxygen cannot be exothermically adsorbed from the gas phase on the stoichiometric surface. A variety of molecular and dissociative modes of adsorption are examined on the reduced surface produced by removing all bridging oxygens and on the weakly reduced surface that results from removal of only a fraction of these oxygens, with the adsorbed species being in both the singlet and the triplet states, and we identify a number of modes not discussed before in the literature. We use the calculated adsorption energies to propose a tentative assignment of these adsorption modes to the peaks observed in temperature programmed desorption experiments on the SnO2 and TiO2(1 1 0) surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.
84 citations
References
More filters
[...]
TL;DR: In this article, a semi-empirical exchange correlation functional with local spin density, gradient, and exact exchange terms was proposed. But this functional performed significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
Abstract: Despite the remarkable thermochemical accuracy of Kohn–Sham density‐functional theories with gradient corrections for exchange‐correlation [see, for example, A. D. Becke, J. Chem. Phys. 96, 2155 (1992)], we believe that further improvements are unlikely unless exact‐exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange‐correlation functional containing local‐spin‐density, gradient, and exact‐exchange terms is tested on 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total atomic energies of first‐ and second‐row systems. This functional performs significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
80,847 citations
[...]
TL;DR: In this article, effective core potentials (ECP) have been derived to replace the innermost core electron for third row (K), fourth row (Rb-Ag), and fifth row (Cs-Au) atoms.
Abstract: Ab initio effective core potentials (ECP’s) have been generated to replace the innermost core electron for third‐row (K–Au), fourth‐row (Rb–Ag), and fifth‐row (Cs–Au) atoms The outermost core orbitals—corresponding to the ns2np6 configuration for the three rows here—are not replaced by the ECP but are treated on an equal footing with the nd, (n+1)s and (n+1)p valence orbitals These ECP’s have been derived for use in molecular calculations where these outer core orbitals need to be treated explicitly rather than to be replaced by an ECP The ECP’s for the forth and fifth rows also incorporate the mass–velocity and Darwin relativistic effects into the potentials Analytic fits to the potentials are presented for use in multicenter integral evaluation Gaussian orbital valence basis sets are developed for the (3s, 3p, 3d, 4s, 4p), (4s, 4p, 4d, 5s, 5p), and (5s, 5p, 5d, 6s, 6p) ortibals of the three respective rows
12,824 citations
[...]
TL;DR: In this article, a new coupling of Hartree-Fock theory with local density functional theory was proposed to improve the predictive power of the Hartree−Fock model for molecular bonding, and the results of tests on atomization energies, ionization potentials, and proton affinities were reported.
Abstract: Previous attempts to combine Hartree–Fock theory with local density‐functional theory have been unsuccessful in applications to molecular bonding. We derive a new coupling of these two theories that maintains their simplicity and computational efficiency, and yet greatly improves their predictive power. Very encouraging results of tests on atomization energies, ionization potentials, and proton affinities are reported, and the potential for future development is discussed.
12,447 citations
[...]
TL;DR: In this article, the authors focus on interfacial processes and summarize some of the operating principles of heterogeneous photocatalysis systems, including the electron transfer and energy transfer processes in photocatalytic reactions.
Abstract: In 1972, Fujishima and Honda discovered the photocatalytic splitting of water on TiO{sub 2} electrodes. This event marked the beginning of a new era in heterogeneous photocatalysis. Since then, research efforts in understanding the fundamental processes and in enhancing the photocatalytic efficiency of TiO{sub 2} have come from extensive research performed by chemists, physicists, and chemical engineers. Such studies are often related to energy renewal and energy storage. In recent years, applications to environmental cleanup have been one of the most active areas in heterogeneous photocatalysis. This is inspired by the potential application of TiO{sub 2}-based photocatalysts for the total destruction of organic compounds in polluted air and wastewaters. There exists a vast body of literature dealing with the electron transfer and energy transfer processes in photocatalytic reactions. A detailed description of these processes is beyond the scope of this review. Here, the authors tend to focus on interfacial processes and to summarize some of the operating principles of heterogeneous photocatalysis. In section 2, the authors first look at the electronic excitation processes in a molecule and in a semiconductor substrate. The electronic interaction between the adsorbate molecule and the catalyst substrate is discussed in terms of the catalyzed ormore » sensitized photoreactions. In section 3, thermal and photocatalytic studies on TiO{sub 2} are summarized with emphasis on the common characteristics and fundamental principles of the TiO{sub 2}-based photocatalysis systems. In section 4, they address the research effort in the electronic modification of the semiconductor catalysts and its effect on the photocatalytic efficiency. Several representative examples will be presented including the Schottky barrier formation and modification at metal-semiconductor interfaces. Some concluding remarks and future research directions will be given in the final section. 160 refs.« less
10,191 citations
[...]
TL;DR: In this article, a comparison of several density functional methods for calculating vibrational frequencies is reported, including the local S-VWN (LSDA) functional, the non-local B-LYP and B-VNN functionals, and the hybrid B3-P86 functionals.
Abstract: A comparison of several density functional methods for calculating vibrational frequencies is reported. Methods examined include the local S-VWN (LSDA) functional, the non-local B-LYP and B-VWN functionals and the hybrid B3-LYP and B3-P86 functionals. The split-valence polarized 6-31G∗ basis set has been used in all methods. The computed frequencies were compared with experimental frequencies for a set of 122 molecules (a total of 1066 frequencies). All density functional theory (DFT) methods perform well for the calculation of vibrational frequencies, with overall root mean square errors (34–48 cm−1) significantly less than that reported for the MP2 theory (61 cm−1). The two hybrid functionals (B3-LYP and B3-P86) are more reliable than the S-VWN, B-LYP and B-VWN functionals. Scaling factors recommended for reproducing experimental fundamentals are 0.9833, 0.9940, 0.9820, 0.9613 and 0.9561, for S-VWN, B-LYP, B-VWN, B3-LYP and B3-P86, respectively. The performance of the various DFT methods on the calculation of zero-point energies is compared with experimental results for 24 molecules. Again, the hybrid functionals represent a significant improvement over the local and non-local density functionals.
1,052 citations