Anatase TiO2 Surface Research Articles

Binding group of oligonucleotides on TiO2 surfaces: Phosphate anions or nucleobases?

Although the immobilization of oligonucleotides (nucleic acid) on mineral surfaces is at the basis of different biotechnological applications, an atomistic understanding of the interaction of the nucleic acid components with the titanium dioxide surfaces has not yet been achieved. Here, the adsorption of the phosphate anion, of the four DNA bases (adenine, guanine, thymine, and cytosine) and of some entire nucleotides and dinucleotides on the TiO2 anatase (101) surface is studied through dispersion-corrected hybrid density functional theory (DFT) calculations. Several adsorption configurations are identified for the separated entities (phosphate anion or base) and then considered when studying the adsorption of the entire nucleotides. The analysis shows that both the phosphate anion and each base may anchor the nucleotides to the surface in a collaborative and synergistic adsorption mode. The tendency is that the nucleotides containing the guanine base present the strongest adsorption while those made up with the thymine base have the lowest adsorption energies. Nucleotides based on adenine and cytosine have a similar intermediate behavior. Finally, we investigated the adsorption of competing water molecules to understand whether in the presence of the aqueous solvent, the nucleotides would remain bonded to the surface or desorb.

Oxidation of Anatase TiO2(001) Surface Using Supersonic Seeded Oxygen Molecular Beam.

We investigated the oxidation of oxygen vacancies at the surface of anatase TiO2(001) using a supersonic seeded molecular beam (SSMB) of oxygen. The oxygen vacancies at the top surface and subsurface could be eliminated by the supply of oxygen using an SSMB. Oxygen vacancies are present on the surface of anatase TiO2(001) when it is untreated before transfer to a vacuum chamber. These vacancies, which are stable in the as-grown condition, could also be effectively eliminated by using the oxygen SSMB.

Proton-Coupled Defects Impact O-H Bond Dissociation Free Energies on Metal Oxide Surfaces.

Proton-coupled electron transfer (PCET) reactions on metal oxides require coupling between proton transfer at the solid-liquid interface and electron transfer involving defects at or near the band edge. Herein, hybrid functional periodic density functional theory is used to elucidate the impact of proton-coupled defects on the bond dissociation free energies (BDFEs) of O-H bonds on anatase TiO2 surfaces. These O-H BDFEs are directly related to interfacial PCET thermochemistry. Comparison between geometrically similar O-H bonds associated with different defect types, namely conduction d-band electrons or valence p-band holes, reveals that the BDFEs differ by ∼81 kcal/mol (3.50 eV), comparable to the wide TiO2 band gap. These differences are shown to be determined primarily by differences in electron transfer driving forces, which are analyzed by using band energies and inner-sphere reorganization energies within a Marcus theory framework. These fundamental insights about the impact of proton-coupled defects on PCET thermochemistry at semiconductor surfaces have broad implications for electrocatalysis.

Optimizing the Cosensitization Effect of SQ02 Dye on BP-2 Dye-Sensitized Solar Cells: A Computational Quantum Chemical Study.

Cosensitization of the semiconducting electrode in dye-sensitized solar cells (DSCs), with two or more light-harvesting dyes, is a chemical fabrication method that aims to achieve a panchromatic absorption spectrum emulating that of the solar emission spectrum. In this paper, SQ02 and BP-2 cosensitizers have been investigated, as isolated monomers/dimer and adsorbed monomers/dimer on the TiO2 (101) anatase surface, by employing density functional theory (DFT) and time-dependent DFT calculations. Computed results showed that the dominant electron injection pathway is direct injection from each dye into the conduction band of TiO2. The almost complete spectral overlap between the simulated absorption spectrum of BP-2 and fluorescence emissions of SQ02 implies that excitation energy transfer occurs between cosensitizers via the trivial reabsorption mechanism. However, the results showed very limited unidirectional intermolecular charge transfer (CT) from SQ02 dye to BP-2 dye (0.04 |e-|). Therefore, this study also presents a stepwise molecular engineering of BP-2 dye, aiming at optimizing the cosensitization functionality. First, 14 redesigned dye candidates are reported to identify dyes with photophysical properties matching the requirements for efficient DSCs. Second, the four most promising dyes are shortlisted for testing as cosensitizers with the SQ02 dye. The molecular design factors of cosensitization that need validation are chemical compatibility, availability of CT between cosensitizers, and complementarity of the absorption spectra. This screening suggests the judicious choice of the modeled difluorenyl amine donor-based dye (BP-D4) as a very promising cosensitizer. In particular, the SQ02/BP-D4 dimer showed 10 times larger (0.53 |e-|) unidirectional CT than that of SQ02/BP-2 dimer, in addition to the maximum increased electron population of acceptor moieties upon photoexcitation.

Generalizing Continuum Solvation in Crystal to Nonaqueous Solvents: Implementation, Parametrization, and Application to Molecules and Surfaces.

We present an extension of a generalized finite-difference Poisson-Boltzmann (FDPB) continuum solvation model based on a self-consistent reaction field treatment to nonaqueous solvents. Implementation and reparametrization of the cavitation, dispersion, and structural (CDS) effects nonelectrostatic model are presented in CRYSTAL, with applications to both finite and infinite periodic systems. For neutral finite systems, computed errors with respect to available experimental data on free energies of solvation of 2523 solutes in 91 solvents, as well as 144 transfer energies from water to 14 organic solvents are on par with the reference SM12 solvation model for which the CDS parameters have been developed. Calculations performed on a TiO2 anatase surface and compared to VASPsol data revealed an overall very good agreement of computed solvation energies, surface energies, as well as band structure changes upon solvation in three different solvents, validating the general applicability of the reparametrized FDPB approach to neutral nonperiodic and periodic solutes in aqueous and nonaqueous solvents. For ionic species, while the reparametrized CDS model led to large errors on free energies of solvation of anions, addition of a corrective term based on Abraham's acidity of the solvent significantly improved the accuracy of the proposed continuum solvation model, leading to errors on aqueous pKa of a test set of 83 solutes divided by a factor of 4 compared to the reference solvation model based on density (SMD). Overall, therefore, these encouraging results demonstrate that the generalized FDPB continuum solvation model can be applied to a broad range of solutes in various solvents, ranging from finite neutral or charged solutes to extended periodic surfaces.

Relevance of Dispersion and the Electronic Spin in the DFT + U Approach for the Description of Pristine and Defective TiO2 Anatase.

A density functional theory + U systematic theoretical study was performed on the geometry, electronic structure, and energies of properties relevant for the chemical reactivity of TiO2 anatase. The effects of D3(BJ) dispersion correction and the Hubbard U value over the energies corresponding to the TiO2/Ti2O3 reduction reaction, the oxygen vacancy formation, and transition-metal doping were analyzed to attain an accurate and well-balanced description of these properties. It is suggested to fit the Hubbard correction for the metal dopant atom by taking as reference the observed low spin–high spin (HS) energy difference for the metal atom. PBEsol-D3 calculations revealed a distinct electronic ground state for the yttrium-doped TiO2 anatase surface depending upon the type of doping and interstitial or substitutional defects. Based on the calculations, it was found that a HS state explains the observed ferromagnetism in cobalt-substituted TiO2 anatase. The results presented herein might be relevant for further catalytic studies on TiO2 anatase using a large surface model that would be worthwhile for heterogeneous catalysis simulations.

D-Glucose Adsorption on the TiO2 Anatase (100) Surface: A Direct Comparison Between Cluster-Based and Periodic Approaches.

Titanium dioxide (TiO2) has been extensively studied as a suitable material for a wide range of fields including catalysis and sensing. For example, TiO2-based nanoparticles are active in the catalytic conversion of glucose into value-added chemicals, while the good biocompatibility of titania allows for its application in innovative biosensing devices for glucose detection. A key process for efficient and selective biosensors and catalysts is the interaction and binding mode between the analyte and the sensor/catalyst surface. The relevant features regard both the molecular recognition event and its effects on the nanoparticle electronic structure. In this work, we address both these features by combining two first-principles methods based on periodic boundary conditions and cluster approaches (CAs). While the former allows for the investigation of extended materials and surfaces, CAs focus only on a local region of the surface but allow for using hybrid functionals with low computational cost, leading to a highly accurate description of electronic properties. Moreover, the CA is suitable for the study of reaction mechanisms and charged systems, which can be cumbersome with PBC. Here, a direct and detailed comparison of the two computational methodologies is applied for the investigation of d-glucose on the TiO2 (100) anatase surface. As an alternative to the commonly used PBC calculations, the CA is successfully exploited to characterize the formation of surface and subsurface oxygen vacancies and to determine their decisive role in d-glucose adsorption. The results of such direct comparison allow for the selection of an efficient, finite-size structural model that is suitable for future investigations of biosensor electrocatalytic processes and biomass conversion catalysis.

Surface-Induced Desolvation of Hydronium Ion Enables Anatase TiO2 as an Efficient Anode for Proton Batteries.

Hydrogen ion is an attractive charge carrier for energy storage due to its smallest radius. However, hydrogen ions usually exist in the form of hydronium ion (H3O+) because of its high dehydration energy; the choice of electrode materials is thus greatly limited to open frameworks and layered structures with large ionic channels. Here, the desolvation of H3O+ is achieved by using anatase TiO2 as anodes, enabling the H+ intercalation with a strain-free characteristic. Density functional theory calculations show that the desolvation effects are dependent on the facets of anatase TiO2. Anatase TiO2 (001) surface, a highly reactive surface, impels the desolvation of H3O+ into H+. When coupled with a MnO2 cathode, the proton battery delivers a high specific energy of 143.2 Wh/kg at an ultrahigh specific power of 47.9 kW/kg. The modulation of the interactions between ions and electrodes opens new perspectives for battery optimizations.

Adsorption of CO molecules on anatase TiO2(001) loaded with noble metals M (M = Ir/Pd/Pt): A study from DFT calculations

The structure and electronic behaviour of anatase TiO2(001) surface loaded with noble metal atoms M (Ir, Pd and Pt) are systematically investigated by first-principles calculations. Meanwhile, the adsorption behaviour of CO on M-loaded anatase TiO2 is also studied. The results show that Ir and Pt atoms are more likely to be adsorbed on the O2 C (T1) site, while Pd atom is more easily adsorbed at the Ti5 C (T3) site. Among all of the considered systems, the formation energy of Pd/TiO2 (−2.500 eV) is the lowest one followed with Pt/TiO2 (−4.552 eV) and Ir/TiO2 (−6.298 eV). The adsorption mechanism of CO on the anatase TiO2(001) surface is studied by choosing the most stable configurations. The order of adsorption energy is CO/TiO2 (−1.065 eV) >CO/Pd/TiO2 (−2.535 eV) >CO/Pt/TiO2 (−3.326 eV) >CO/Ir/TiO2 (−3.593 eV). This theoretical study shows the adsorption mechanism of CO on the anatase TiO2(001) and provides guidelines for further exploring the adsorption material with excellent adsorption capacity.

Photothermal Catalysis for Selective CO2 Reduction on the Modified Anatase TiO2 (101) Surface

Photothermal Catalysis for Selective CO₂ Reduction on the Modified Anatase TiO₂ (101) Surface

Enhanced low-temperature activity and selectivity for the ammoxidation of 2,6-dichlorotoluene using V-Ti-O nanocomposite synthesized by one-step hydrothermal method

V-Ti-O nanocomposite was synthesized via a one-step hydrothermal decomposition of oxalate-vanadium and -titanium complex solution. Various characterization results have showed that the V-Ti-O product is composed of numerous nanoparticles with sizes of around 10–20 nm which aggregate and result in clusters. The nanostructures exhibit great specific surface area of 90.2 m2 g−1. Vanadium is tetracoordinated and disperses in polymeric species on the surface of anatase TiO2, meanwhile partial V4+ substituting Ti4+ ions are doped into anatase TiO2 lattice, which promotes the redox properties. The catalytic performance of the as-obtained V-Ti-O nanomaterial was tested in the ammoxidation of 2,6-dichlorotoluene to 2,6-dichlorobenzonitrile. The results have demonstrated that the V-Ti-O nanostructure exhibits unprecedented low-temperature activity of 330 °C with the yield of 2,6-dichlorobenzonitrile reaching up to 84%.

Migration and oxidation of vanadium atom and dimer supported on anatase TiO2(1 0 1) surface

The migration and oxidation of single V atom and V2 dimer on the anatase TiO2(1 0 1) surface are systematically studied based on density functional theory (DFT) calculations. For a single V atom, migration on the surface is almost impossible at room temperature while diffusion between surface and subsurface is easy in ultra-high vacuum (UHV) conditon. Without O attraction, single V atom prefers to stay at subsurface interstitial sites. But in oxygen condition, the subsurface interstitial V atom will easily diffuse to the surface and be oxidized into VOn (n = 1–3) monomers. The V2 dimer is dynamically stable on the TiO2(1 0 1) surface and favors to be embedded in the surface layer in UHV condition. However, it can be easily decomposed and oxidized into VOn monomers in the condition of O2. Our results offer an deep insight for the formation mechanism of sublayer vadanium oxides on TiO2 support, and will be instructive for synthesizing desired VOx/TiO2 catalysts.

The formaldehyde adsorption on anatase TiO2 (2 1 1) surface

The adsorption behaviors of formaldehyde (CH2O) molecule on anatase TiO2 (2 1 1) surface are studied by the first-principles method. Besides monodentate and bidentate adsorption configurations, there is an interesting found that both stable bidentate adsorption involved surface bridging O22 atom will induce a surface bond breaking. The π bond of formaldehyde is also opening. Combination of these two ingredients produces the most stable adsorption. Moreover, those two configurations are essentially the same just oxygen atom of molecule OF and the surface O22 interchanged. Furthermore, their bonding properties are analyzed in detail through the density of state. It is revealed that covalent and ionic bonding coexist in the oxygen atoms involved in adsorption.

Structure and Band Alignment of InP Photocatalysts Passivated by TiO2 Thin Films

Composite materials made by a low-band-gap semiconductor covered by a thin oxide layer are increasingly used in solar cells and photocatalysis. InP/TiO2 heterojunctions show high efficiency because of visible light absorption by the InP component and an efficient migration of photogenerated electrons toward TiO2. The passivating TiO2 film also guarantees stability in humid environments. In this work, we investigate the nature of InP/TiO2 by means of density functional theory calculations, showing that due to strong interface chemical bonds, the formation of an InP/TiO2 junction is a favorable process. Irrespective of the anatase TiO2 surface in contact with InP, (101) or (001), the system behaves as a type II junction, where the TiO2 band edges are lower in energy than InP ones, providing a rationalization for the observed electron–hole separation. We also considered explicitly the role of the TiO2 thin layer thickness, finding that a favorable junction is retained for every thickness of the titania passivating film. The highest efficiency is predicted for film thicknesses of 2–3 nm as this provides a good compromise between favorable band edge alignment and efficient transfer of the photogenerated electrons to the surface.

Synthesis, Characterization and Visible-Light Photocatalytic Activity of Solid and TiO2-Supported Uranium Oxycompounds.

In this study, various solid uranium oxycompounds and TiO2-supported materials based on nanocrystalline anatase TiO2 are synthesized using uranyl nitrate hexahydrate as a precursor. All uranium-contained samples are characterized using N2 adsorption, XRD, UV–vis, Raman, TEM, XPS and tested in the oxidation of a volatile organic compound under visible light of the blue region to find correlations between their physicochemical characteristics and photocatalytic activity. Both uranium oxycompounds and TiO2-supported materials are photocatalytically active and are able to completely oxidize gaseous organic compounds under visible light. If compared to the commercial visible-light TiO2 KRONOS® vlp 7000 photocatalyst used as a benchmark, solid uranium oxycompounds exhibit lower or comparable photocatalytic activity under blue light. At the same time, uranium compounds contained uranyl ion with a uranium charge state of 6+, exhibiting much higher activity than other compounds with a lower charge state of uranium. Immobilization of uranyl ions on the surface of nanocrystalline anatase TiO2 allows for substantial increase in visible-light activity. The photonic efficiency of reaction over uranyl-grafted TiO2, 12.2%, is 17 times higher than the efficiency for commercial vlp 7000 photocatalyst. Uranyl-grafted TiO2 has the potential as a visible-light photocatalyst for special areas of application where there is no strict control for use of uranium compounds (e.g., in spaceships or submarines).

The effect of shape and size of 1D and 0D titanium oxide nanorods in the photocatalytic degradation of red amaranth toxic dye

In this work, the effect of layered TiO2 anatase nanorod preparation and application were systematically analyzed. The nanoparticles were widely characterized and applied in the photocatalytic degradation of red amaranth toxic dye. The nanorod morphology changed with the type of acid treatment; they decreased in length and diameter with the increase in acid concentration. The use of HCl induced a preferential growth of (101) planes, while HNO3 favored the formation of the (004) face. Likewise, the HCl acid treatment allowed the incorporation of small quantities of Cl− ions on the surface of TiO2 anatase, impacting the activity positively. Otherwise, the presence of surface nitrogen was not detected when treated with nitric acid. The characterization and activity result allowed us to propose structure–activity correlations with morphology and Cl− ions. It was revealed that the Na removal enhanced reactivity revealing to the enhanced crystallinity of TiO2 nanorods is responsible for the photocatalytic activity results. We conclude that these nanomaterials are suitable as catalysts for the degradation of dye pollutants in water if a fine-tuning is done with acid solutions.

H2O splitting on Run/TiO2(101) surface: Lowered energy barrier due to charge transfer at interface

Metal-support interactions have been explored as an effective method to improve the photocatalytic activity in heterogeneous catalysis. In this study, first-principles calculations confirmed that H2O can be split on Ru8 cluster decorated anatase TiO2(101) surface (denoted as Ru8/TiO2(101)), whose adsorption energy (Eads) and energy barrier (Eb) are lower than H2O on isolated Ru8 cluster, due to significant charge transfer from Ru8 cluster to TiO2(101). Compared with Ru8/TiO2(101), single Ru atom decorated TiO2(101) has higher Eads with H2O, manifesting better catalytic property. The similar dissociation process of H2O on isolated Ru8 cluster and Ru8/TiO2(101) indicated that we can study the molecule/cluster in detail firstly, and then apply it to molecule/cluster/surface, which will save much computing resource.

Coating Ag on an Anatase TiO2 Surface and Adsorption on a 3-Aminopropyltrimethoxysilane-Modified Al or Glass Surface

In this study, Ag–TiO2 was synthesized by reducing AgNO3. AgNO3 and anatase TiO2 nanoparticles (NPs) were boiled with sodium citrate, resulting in the reduction of Ag. Ag was used to coat the anatase TiO2 NP surfaces. At this stage, the assembly reaction on the anatase TiO2 surface was incomplete. The acidity with pH 4 or less was subsequently adjusted using dilute HCl. After processing, Ag was distributed over the entire surface of anatase TiO2. Furthermore, the synthesized Ag–TiO2 could be adsorbed on an Al or glass surface using 3-aminopropyltrimethoxysilane. Al plates were used to create a substrate exhibiting surface-enhanced Raman scattering activity, and Raman intensity was measured for pyridine. Ag remained stable on the TiO2 surface for over five months. The proposed method, which is cost effective and simple, can be used to prepare materials for studying the environment and so on.

Photocatalytic Nitrogen Reduction by Ti3C2 MXene Derived Oxygen Vacancy‐Rich C/TiO2

AbstractIn this work, oxygen vacancy‐rich C/TiO2 (OV‐C/TiO2) samples are prepared by a one‐step calcination approach using Ti3C2 MXene as the precursor, and used for the photocatalytic N2 reduction. The NH3 yields of all the prepared OV‐C/TiO2 samples exceed those achieved on commercial anatase TiO2 and P25, with both H2O and CH3OH as the proton sources. Among them, the OV‐C/TiO2‐600 offers the remarkable NH3 synthesis rates, which are 41.00 µmol g−1 h−1 (with H2O as the proton source) and 84.00 µmol g−1 h−1 (with CH3OH as the proton source). The photocurrent and fluorescence spectra show that OV‐C/TiO2‐600 exhibit the highest generation/separation rate and longest lifetime of photocarriers among all the prepared samples. ESR and TPD experiments confirm much more efficient chemisoption of N2 on the surface of the prepared OV‐C/TiO2‐600 than that on the surface of the commercial anatase TiO2. Moreover, DFT calculations further demonstrate that N2 conversion to NH3 through a Gibbs free energy release leading alternating pathway with a low energy barriers, on the oxygen vacancy on TiO2 surface.

D-[formula omitted]-A dye attached on TiO2(101) and TiO2(001) surfaces: Electron transfer properties from ab initio calculations

The stability, electronic, and transfer properties of a photo-sensitizer donor-(π-bridge)-acceptor (D-π-A) zinc-porphyrin dye adsorbed on anatase TiO2(101) and TiO2(001) surfaces are studied by periodic density functional theory calculations, including the screened hybrid functional. We also study the dye adsorption on the TiO2(101) surface with an oxygen vacancy. Our results show that the deprotonated dye attaches strongly on surface Ti5c atoms forming both bidentate bridging and chelating linkage modes. The protonated dye is found stable on pristine TiO2(101), forming the monodentate linkage mode. However, on TiO2(001) and defective TiO2(101), the monodentate mode stabilizes after a spontaneous dye deprotonation. The electronic band structure of the TiO2-dye assemblies shows the dye lowest-unoccupied molecular-orbital resonant with TiO2 conduction bands, exhibiting a strong hybridization, where the electron injection potentials are calculated around 1 eV for all systems under study. This high value, together with the favorable electronic coupling, suggest a fast electron injection from the dye into the semiconductor as experimentally reported. Moreover, the electronic properties of TiO2-dye assemblies show similarities independent of the adsorption modes or the surface characteristic, suggesting that the high efficiency of anatase TiO2-based dye sensitized solar cell resides largely in its favorable electron injection properties.