Anatase TiO2 Surface Research Articles

Effect of carboxylic acid and cyanoacrylic acid as anchoring groups on Coumarin 6 dye for dye-sensitized solar cells: DFT and TD-DFT study

Starting with Coumarin-6 dye, two novel D-π-A organic dyes C6X and C6N have been designed by attaching carboxylic acid and cyanoacrylic acid groups as anchoring groups to Coumarn-6 dye, respectively, to understand their potential use in dye-sensitized solar cells (DSSCs). The electronic structure and photophysical and photovoltaic properties of the novel designed dyes were studied using density functional theory DFT and time-dependent density functional theory TD-DFT with the Becke3-Parameter-Lee–Yang–Parr (B3LYP) functional and the 6-31G (d, p) basis set. Optimized structure and electronic properties (highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital (ELUMO), and energy difference (Eg) between HOMO and LUMO) were calculated showing that C6N has the smallest band gap with the larger absorption region. Density of states (DOS), molecular electrostatic potential (MEP), natural bond orbital (NBO) analysis, non-linear optical (NLO) properties, UV–vis spectra, as well as some crucial parameters affecting the photovoltaic performance of DSSCs, such as light-harvesting efficiency (LHE), electron injection driving force (ΔGinject), dye regeneration driving force(ΔGreg), and the excited state life time(τe), were calculated to study the effect of the anchoring group on the DSSC performance. Additionally, the adsorption of C6X and C6N dyes on the TiO2 anatase (101) surface and the mechanism of electron injection were also investigated using a dye–(TiO2)9 cluster model using TD-B3LYP calculation. The calculated adsorption energies of the dyes suggest a strong adsorption of dyes to a TiO2 surface. The results show that C6N may be theoretically a good candidate as sensitizer of DSSC application.

Na uptake at TiO2 anatase surfaces under electric field control: A first-principles study

Na-ion batteries (NIBs) are promising devices for large-scale energy-storage facilities. Nanostructured TiO2 is an efficient NIB negative electrode, showing good cycling performance and rate capability, but its activity depends on the crystalline facets exposed by anatase nanoparticles. Hence, we propose here a DFT+U study of Na+ adsorption and insertion at (101), (100) and (001)-TiO2 surfaces under the influence of external electric fields, which are simulated by adding a sawtooth-like electrostatic potential to the bare ionic potential. We find that field polarization affects Na+ uptake as well as titania electronic features, promoting redox processes within Ti sublattice, as in battery charge/discharge cycling. Our results highlight the high-energy (001) surface to be the most active, for both directions of external fields, proving its activity to be exerted reversibly. Besides further insights, these outcomes pave the route for further exploration and design of electrode materials by simulation of battery in operando conditions.Graphical

Phenothiazine dye molecular interaction with nanocrystalline TiO2 surface: FTIR and Raman spectroscopy study

Molecular interactions of the organic dye phenothiazine with the active sites on polycrystalline anatase and rutile TiO2 surface has been investigated by IR and Raman spectroscopy. It has been shown that, both for anatase and rutile, the interaction of PTZ with TiO2 surface active sites occurs by a spontaneous electron transfer from PTZ to TiO2 with the formation of the PTZ•+ radical-cations, PTZ2+ dications and reduced Ti3+ ions. At the same time, additional oxygen vacancies OV are created on the TiO2 surface which increases the nonstoichiometry of PTZ-sensitized TiO2 compared with the original samples. The appearance of PTZ•+ radical-cations and reduced Ti3+ ions is a reason for the deep blue color of the obtained TiO2/PTZ samples.

Cover Feature: Elaborated Reaction Pathway of Photothermal Catalytic CO2 Conversion with H2O on Gallium Oxide‐Decorated and ‐Defective Surfaces (Chem. Eur. J. 24/2022)

The elaborate thermodynamic reaction pathways on Ga2O3-decorated and -defective surfaces during photothermal catalytic CO2 conversion with H2O have been established. The basic site generated by Ga2O3 decoration on an anatase TiO2 (101) surface enhances the selective adsorption of CO2, and also balances VO formation and CO2 reduction activity. Surface-defect VO promotes the reaction thermodynamics but tends to be consumed; Ga2O3 helps to keep VO active. Ga2O3 and VO together further decrease the energy barrier of the rate-determining step, thereby promoting C1 production. More information can be found in the Research Article by Y.-W. Zhang et al. (DOI: 10.1002/chem.202104490).

4-Mercaptobenzoic Acid Adsorption on TiO2 Anatase (101) and TiO2 Rutile (110) Surfaces

The adsorption of 4-mercaptobenzoic acid (4-MBA) on anatase (101) and rutile (110) TiO2 surfaces has been studied using synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy techniques. Photoelectron spectroscopy results suggest that the 4-MBA molecule bonds to both TiO2 surfaces through the carboxyl group, following deprotonation in a bidentate geometry. Carbon K-edge NEXAFS spectra show that the phenyl ring of the 4-MBA molecule is oriented at 70° ± 5° from the surface on both the rutile (110) and anatase (101) surfaces, although there are subtle differences in the electronic structure of the molecule following adsorption between the two surfaces.

Morphological, spectral and toxicological features of new composite material of titanium nanodioxide with nanosilver for use in medicine and biology

The results of this study indicate that titanium dioxide nanoparticles (nano-TiO2) possess adsorptive, photocatalytic, bactericidal, virucidal and fungicidal properties, which are used in antibacterial coating, for air and water disinfection. In parallel with studies of the physicochemical characteristics of titanium dioxide, its toxicological assessment was carried out to prevent possible harmful effects on humans and the biosphere objects, followed by an assessment of the nano-TiO2 hazard class. To enhance these useful properties of nano-TiO2, nanopowders of titanium dioxide and a composite of titanium dioxide were synthesized with a silver (nano-TiO2 /Ag) by way of chemical precipitation of metatitanic acid adding silver nitrate to the composite at 500-600°C. It was stated that the synthesized nanostructures have the following characteristics: anatase crystal structure of TiO2 (anatase, rutile, brookite – natural crystalline modifications of TiO2), the size of Ag nanoparticles is 35-40 nm, TiO2 – 13-20 nm. Nanocomposite has surface defects of the crystal lattice (oxygen vacancies, impurities, excess electrons or holes), silver nanoparticles are localized on the surface of anatase TiO2, which increases adsorptive, photocatalytic, biological and specifically antibacterial properties of the composite material nano-TiO2/Ag. According to the parameters of acute intraperitoneal toxicity, the studied nanocomposite anatase nano-TiO2/Ag was classified as a moderately dangerous substance (material). Nano-TiO2 and TiO2/Ag nanocomposites do not cause local irritation to the skin, yet have a mildly irritating effect on the mucous membrane of the eye, and are also characterized by a weak sensitization effect.

Effect of Bimetallic Dimer-Embedded TiO2(101) Surface on CO2 Reduction: The First-Principles Calculation.

The first-principles calculation was used to explore the effect of a bimetallic dimer-embedded anatase TiO2(101) surface on CO2 reduction behaviors. For the dimer-embedded anatase TiO2(101) surface, Zn-Cu, Zn-Pt, and Zn-Pd dimer interstitials could stably stay on the TiO2(101) surface with a binding energy of about −2.36 eV, as well as the electronic states’ results. Meanwhile, the results of adsorption energy, structure parameters, and electronic states indicated that CO2 was first physically and then chemically adsorbed much more stably on these three kinds of dimer-embedded TiO2(101) substrate with a small barrier energy of 0.03 eV, 0.23 eV, and 0.12 eV. Regarding the reduction process, the highest-energy barriers of the CO2 molecule on the Zn-Cu dimer-embedded TiO2(101) substrate was 0.31 eV, which largely benefited the CO2-reduction reaction (CO2RR) activity and was much lower than that of the other two kinds of Zn-Pt and Cu-Pt dimer-TiO2 systems. Simultaneously, the products CO* and *O* of CO2 reduction were firmly adsorbed on the dimer-embedded TiO2(101) surface. Our results indicated that a non-noble Zn-Cu dimer might be a more suitable and economical choice, which might theoretically promote the designation of high CO2RR performance on TiO2 catalysts.

Effects of hydroxylation on the acidic and basic strengths of anatase TiO2 surfaces

ABSTRACT Titanium dioxide (TiO2) is one of prototype, water-splitting catalysts, while its catalytic performance is strongly affected by the presence of water molecules or hydroxyl groups on the surface. The adsorption of water on the TiO2(101) and TiO2(001) surfaces at different water/hydroxyl coverages was firstly studied using density functional theory (DFT) calculations. It has been found that the surface hydroxylation state has a significant influence on water adsorption behaviour. On the basis of calculated Gibbs free surface energies as a function of temperature and hydroxylation extent, the fully dehydrated TiO2(101) and TiO2(001) surfaces will be reached at 500 and 1000 K, respectively. In the present work, BF3 and NH3 were used as probe molecules to study the Lewis acidic and Brønsted basic strengths of TiO2(101) and TiO2(001) surfaces under different hydroxylation conditions. As the hydroxyl coverage increases, the Brønsted basic strength becomes stronger while the Lewis acidic strength is weakened. Finally, it is noted that the TiO2 surface is slightly oxidised at low hydroxyl coverage but being reduced at high hydroxyl coverage.

Insights into enhanced O3 adsorption on Ti/ anatase TiO2 (1 0 1) surfaces by positive electric Fields: A theoretical exploration

Enhanced ozone (O3) adsorption at catalyst surfaces is an important prerequisite and key step in enhancing heterogeneous O3 catalysis (catazone) and promoting the production of reactive oxygen species (ROS). This study proposes a new strategy to enhance O3 adsorption via application of a positive electric field. The enhanced mechanism was systematically revealed using first-principles density functional theory calculations. Taking the previously studied Ti/anatase TiO2 (101) electrode as an example, the effects of an electric field strength ranging from 0 V Å−1–1 V Å−1, adsorption site type, and adsorption configuration on the adsorption energy (Eads) were investigated. By resolving the electronic structure changes and orbital composition, the enhanced mechanism of bonding of O3 to the active sites was further elucidated. The results confirmed that the application of a positive electric field significantly increased Eads, and the adsorption sites and configurations played an important role. At 1 V Å−1, Eads was significantly increased by highest value of 179 %, the bimolecular sites such as double water molecules and hydroxyl groups, ≡(H2O)2, ≡(OH)2 achieved high Eads of −4.16 eV, and −3.04 eV, respectively, than the values of −2.58 eV and −2.72 eV for monomolecular sites, ≡H2O or ≡OH, while the bridging configuration attained an Eads value 61.24 % higher than the single-armed configuration. This is mainly because the applied positive electric field can enhance charge enrichment at the adsorption sites by promoting the charge transfer and orbital hybridization between them and the O3 molecules to form new bonds with lower Fermi energy levels, ultimately achieving enhanced O3 adsorption. This theoretical study provides new insights into enhancing O3 adsorption for better catazone and fundamental guidance for subsequent experimental research.

Insight into the Roles of Metal Loading on CO2 Photocatalytic Reduction Behaviors of TiO2.

The photocatalytic reduction of carbon dioxide (CO2) into value-added chemicals is considered to be a green and sustainable technology, and has recently gained considerable research interest. In this work, titanium dioxide (TiO2) supported Pt, Pd, Ni, and Cu catalysts were synthesized by photodeposition. The formation of various metal species on an anatase TiO2 surface, after ultraviolet (UV) light irradiation, was investigated insightfully by the X-ray absorption near edge structure (XANES) technique. CO2 reduction under UV-light irradiation at an ambient pressure was demonstrated. To gain an insight into the charge recombination rate during reduction, the catalysts were carefully investigated by the intensity modulated photocurrent spectroscopy (IMPS) and photoluminescence spectroscopy (PL). The catalytic behaviors of the catalysts were investigated by density functional theory using the self-consistent Hubbard U-correction (DFT+U) approach. In addition, Mott–Schottky measurement was employed to study the effect of energy band alignment of metal-semiconductor on CO2 photoreduction. Heterojunction formed at Pt-, Pd-, Ni-, and Cu-TiO2 interface has crucial roles on the charge recombination and the catalytic behaviors. Furthermore, it was found that Pt-TiO2 provides the highest methanol yield of 17.85 µmol/gcat/h, and CO as a minor product. According to the IMPS data, Pt-TiO2 has the best charge transfer ability, with the mean electron transit time of 4.513 µs. We believe that this extensive study on the junction between TiO2 could provide a profound understanding of catalytic behaviors, which will pave the way for rational designs of novel catalysts with improved photocatalytic performance for CO2 reduction.

HAADF STEM and Ab Initio Calculations Investigation of Anatase TiO2/LaAlO3 Heterointerface

The understanding of the origin of a two-dimensional electron gas (2DEG) at the surface of anatase TiO2 remains a challenging issue. In particular, in TiO2 ultra-thin films, it is extremely difficult to distinguish intrinsic effects, due to the physics of the TiO2, from extrinsic effects, such as those arising from structural defects, dislocations, and the presence of competing phases at the film/substrate interface. It is, therefore, mandatory to unambiguously ascertain the structure of the TiO2/substrate interface. In this work, by combining high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), density functional theory calculations, and multislice image simulations, we have investigated the nature of strainless anatase TiO2 thin films grown on LaAlO3 substrate. In particular, the presence of oxygen vacancies in anatase TiO2 has been proved to stabilize the formation of an extra alloy layer, Ti2AlO4, by means of interface rearrangement. Our results, therefore, elucidate why the growth of anatase TiO2 directly on LaAlO3 substrate has required the deposition of a TiOx extra-layer to have a 2DEG established, thus confirming the absence of a critical thickness for the TiO2 to stabilize a 2DEG at its surface. These findings provide fundamental insights on the underlying formation mechanism of the 2DEG in TiO2/LAO hetero-interfaces to engineer the 2DEG formation in anatase TiO2 for tailored applications.

Nonadiabatic Dynamics of Polaron Hopping and Coupling with Water on Reduced TiO2.

By interplay between first-principles molecular dynamics and nonadiabatic molecular dynamics simulations based on the decoherence-induced surface-hopping approach, we investigate and quantify the mechanisms through which different electron polaron hopping regimes in the reduced anatase TiO2(101) surface influence recombination of photogenerated charge carriers, also in the presence of adsorbed water (H2O) molecules. The simulations reveal that fast hopping regimes promote ultrafast recombination of photogenerated charge-carriers. Conversely, charge recombination is delayed in the presence of slower polaron hopping and even more so if the polaron is pinned at one Ti-site, as typical following adsorption of H2O on the anatase(101) surface. These trends are related to the observed enhancement of the space and energy overlap between conduction band minimum and polaron band gap states, and the ensuing nonadiabatic couplings (NAC) strengths, during a polaronic hop. We expect these insights on the beneficial role of polaron diffusion pinning for the extended lifetime of photoexcitations in TiO2 to sustain ongoing developments of photocatalytic strategies based on this substrate.

Interfacial Adsorption and Electron Properties of Water Molecule/Cluster on Anatase TiO2(101) Surface: Raman and DFT Investigation.

The hydrogen bond network reconstruction at the titanium/water interface was monitored by Raman spectroscopy. In addition, the adsorption properties and the surface electron properties of hydrogen bond cluster (HBC) configurations were analyzed using adsorption energy, work function, Mulliken charge population, and density of states (DOS) by the first-principles method based on density functional theory (DFT). Our results show that the hydrogen bond network of the aqueous solution is reconstructed under the interaction with the anatase TiO2(101) surface with the transformation of the chain and free hydrogen bonds to complex hydrogen bonds. The adsorption energy of a single water molecule and HBC on the anatase TiO2(101) surface are the lowest with the 1-DD-h (-0.851 eV) and 3-D-h-DDA (-1.048 eV) configurations, respectively. Over the long term, artificially regulating the structure of the HBC might be an effective and general way to slow down the metal anodic reaction without surface modification. Furthermore, the surface charge concentrates on the bridging oxygen atom, which will be the active site of the interface reaction. It is helpful to clarify the anodic corrosion reaction mechanism of the titanium spontaneous oxide film/water interface.

In-situ measurements of reconstructed anatase TiO2(001) surface by variable-temperature STM

The catalytic performance of metal oxide surface mainly depends on its atomic surface structure, which usually changes under various treatment conditions and during catalytic reactions. Therefore, it is quite important to acquire the atomic geometries of the surfaces under different treatments for further understanding the catalytic mechanisms in the surfaces with complicated reconstructions. Here, we report the investigation on the evolution of surface geometries of the Ar+-ion-sputtered anatase TiO2(001) films followed by heating treatments at various temperatures, characterized using variable-temperature scanning tunneling microscopy. Our experimental results reveal the different surface morphologies at different heating temperatures. During the heating treatment, the migrations of O atoms from the bulk to the surface of TiO2(001) play an important role in the reoxidation of the Ti2+ and Ti3+ states for the formation of (1×4) reconstruction. The atomic-resolution images of the ridges show asymmetric features, which well support the fully oxidized structural model of the reconstructed TiO2(001)-(1×4) surface.

Reply to the 'Comment on "Real-time atomistic simulation of the Ostwald ripening of TiO2 supported Au nanoparticles"' by V. P. Zhdanov, Nanoscale, 2022, 14, DOI: 10.1039/D1NR05352C.

Dr Zhdanov argues that the model in our Nanoscale paper cannot prove the Au dimer as the primary species in the Ostwald ripening of Au nanoparticles on TiO2. We would like to point out that the relative stability of the monomer and dimer of Au has been greatly changed on the substrate compared to the gas phase. Thus, the conclusion of the original paper is solid, as proved by not only the simulations but also the further density functional theory calculations, and relevant discussions in the main text.

Interaction of KRSR Peptide with Titanium Dioxide Anatase (100) Surface: A Molecular Dynamics Simulation Study.

Due to its tensile strength and excellent biocompatibility, titanium (Ti) is commonly used as an implant material in medicine and dentistry. The success of dental implants depends on the formation of a contact between the oxidized surface of Ti implant and the surrounding bone tissue. The adsorption of proteins and peptides to the implant surface allows the bone-forming osteoblast cells to adhere to such modified surfaces. Recently, it has been observed that tetrapeptide KRSR (Lys-Arg-Ser-Arg) functionalization could promote osteoblast adhesion to implant surfaces. This may facilitate the establishment of an efficient bone-to implant contact and improve implant stability during the healing process. GROMACS, a molecular dynamics software package was used to perform a 200 ns simulation of adsorption of the KRSR peptide to the TiO2 (anatase) surface in an aqueous environment. The molecule conformations were mapped with Replica Exchange Molecular Dynamics (REMD) simulations to assess the possible peptide conformations on the anatase surface, and the umbrella sampling method was used to calculate the binding energy of the most common conformation. The simulations have shown that the KRSR peptide migrates and attaches to the surface in a stable position. The dominant amino acid residue interacting with the TiO2 surface was the N-terminal charged lysine (K) residue. REMD indicated that there is a distinct conformation that is taken by the KRSR peptide. In this conformation the surface interacts only with the lysine residue while the ser (S) and arg (R) residues interact with water molecules farther from the surface. The binding free energy of the most common conformation of KRSR peptide to the anatase (100) surface was ΔG = −8.817 kcal/mol. Our result suggests that the N-terminal lysine residue plays an important role in the adhesion of KRSR to the TiO2 surface and may influence the osseointegration of dental implants.

Density Functional Theory Study of Metal and Metal-Oxide Nucleation and Growth on the Anatase TiO2(101) Surface

Experimental studies have shown the possible production of hydrogen through photocatalytic water splitting using metal oxide (MOy) nanoparticles attached to an anatase TiO2 surface. In this work, we performed density functional theory (DFT) calculations to provide a detailed description of the stability and geometry of MxOy clusters M = Cu, Ni, Co, Fe and Mn, x = 1–5, and y = 0–5 on the anatase TiO2(101) surface. It is found that unsaturated 2-fold-coordinated O-sites may serve as nucleation centers for the growth of metal clusters. The formation energy of Ni-containing clusters on the anatase surface is larger than for other M clusters. In addition, the Nin adsorption energy increases with cluster size n, which makes the formation of bigger Ni clusters plausible as confirmed by transition electron microscopy images. Another particularity for Ni-containing clusters is that the adsorption energy per atom gets larger when the O-content is reduced, while for other M atoms it remains almost constant or, as for Mn, even decreases. This trend is in line with experimental results. Also provided is a discussion of the oxidation states of M5Oy clusters based on their magnetic moments and Bader charges and their possible reduction with oxygen depletion.

Effects of anatase TiO2 morphology and surface fluorination on environmentally relevant photocatalytic reduction and oxidation reactions

Aiming at clarifying the interplay on TiO2 photoactivity between particle morphology and surface fluorination, the photocatalytic performance of anatase nanocrystals, characterized by a pseudo-spherical shape or a nanosheet structure, is investigated in both a reduction and an oxidation reaction, either in the absence or in the presence of added fluoride anions. Cr(VI) photocatalytic reduction is strongly favored by a large exposure of anatase {001} facets; however, surface fluorination leads in this case to a morphology-independent photoactivity decrease, due to the decreased adsorption of the reaction substrate. More interestingly, a beneficial synergistic effect between the platelet-like anatase morphology and TiO2 surface fluorination is clearly outlined in Rhodamine B photocatalytic degradation, possibly resulting from the intrinsic ability of fluorinated {001} anatase facets of boosting •OH radical mediated oxidation paths, due to their larger amount of surface –OH groups, as revealed using Fourier-transform infrared spectroscopy.

Evolution of atomic and electronic structures of Cun (n = 2–10) clusters supported on anatase TiO2(1 0 1) surface

Based on extensive structural search and density functional theory (DFT) calculations, the atomic and electronic structures of of Cun (n = 2–10) clusters supported on anatase TiO2(101) surface (denoted as Cun/A(101)) are systematically studied. The atomic structures exhibit obvious hereditary feature, i.e. most of the low-energy structures of larger clusters can be obtained by adding additional Cu atoms onto those of smaller clusters. Small sized clusters (n ≤ 6) prefer to quasi planar structures while large sized clusters (n > 6) prefer to complex three-dimensional structures. The thermodynamic stabilities of the supported Cun clusters are investigated by calculating the binding energies, second order energy difference, adsorption energies and nucleation energies. It is found that Cu3/A(101), Cu5/A(101), and Cu8/A(101) are particularly stable and Cu3, Cu5 and Cu9 clusters would be stabilized by the substrate mostly. All these Cun clusters can introduce in-gap states and reduce the band gaps according to the calculated density of states. Supported Cun clusters play the role of electron donor, resulting in partial oxidation state Cuδ+ and zero valence state Cu0.

First-Principles Modeling of Protein/Surface Interactions. Polyglycine Secondary Structure Adsorption on the TiO2 (101) Anatase Surface Adopting a Full Periodic Approach.

Computational modeling of protein/surface systems is challenging since the conformational variations of the protein and its interactions with the surface need to be considered at once. Adoption of first-principles methods to this purpose is overwhelming and computationally extremely expensive so that, in many cases, dramatically simplified systems (e.g., small peptides or amino acids) are used at the expenses of modeling nonrealistic systems. In this work, we propose a cost-effective strategy for the modeling of peptide/surface interactions at a full quantum mechanical level, taking the adsorption of polyglycine on the TiO2 (101) anatase surface as a test case. Our approach is based on applying the periodic boundary conditions for both the surface model and the polyglycine peptide, giving rise to full periodic polyglycine/TiO2 surface systems. By proceeding this way, the considered complexes are modeled with a drastically reduced number of atoms compared with the finite-analogous systems, modeling the polypeptide structures at the same time in a realistic way. Within our modeling approach, full periodic density functional theory calculations (including implicit solvation effects) and ab initio molecular dynamics (AIMD) simulations at the PBE-D2* theory level have been carried out to investigate the adsorption and relative stability of the different polyglycine structures (i.e., extended primary, β-sheet, and α-helix) on the TiO2 surface. It has been found that, upon adsorption, secondary structures become partially denatured because the peptide C═O groups form Ti-O═C dative bonds. AIMD simulations have been fundamental to identify these phenomena because thermal and entropic effects are of paramount importance. Irrespective of the simulated environments (gas phase and implicit solvent), adsorption of the α-helix is more favorable than that of the β-sheet because in the former, more Ti-O═C bonds are formed and the adsorbed secondary structure results less distorted with respect to the isolated state. Under the implicit water solvent, additionally, adsorbed β-sheet structures weaken with respect to their isolated states as the H-bonds between the strands are longer due to solvation effects. Accordingly, the results indicate that the preferred conformation upon adsorption is the α-helix over the β-sheet.