TiO$_2$ and SrTiO$_3$ are well known materials in the field of photocatalysis due to their exceptional electronic structure, high chemical stability, non-toxicity and low cost. However, owing to the wide band gap, these can be utilized only in the UV region. Thus, it's necessary to expand their optical response in visible region by reducing their band gap through doping with metals, nonmetals or the combination of different elements, while retaining intact the photocatalytic efficiency. We report here, the codoping of a metal and a nonmetal in anatase TiO$_2$ and SrTiO$_3$ for efficient photocatalytic water splitting using hybrid density functional theory and \textit{ab initio} atomistic thermodynamics. The latter ensures to capture the environmental effect to understand thermodynamic stability of the charged defects at a realistic condition. We have observed that the charged defects are stable in addition to neutral defects in anatase TiO$_2$ and the codopants act as donor as well as acceptor depending on the nature of doping (p-type or n-type). However, the most stable codopants in SrTiO$_3$ mostly act as donor. Our results reveal that despite the response in visible light region, the codoping in TiO$_2$ and SrTiO$_3$ cannot always enhance the photocatalytic activity due to either the formation of recombination centers or the large shift in the conduction band minimum or valence band maximum. Amongst various metal-nonmetal combinations, Mn$_\textrm{Ti}$S$_\textrm{O}$ (i.e. Mn is substituted at Ti site and S is substituted at O site), S$_\textrm{O}$ in anatase TiO$_2$ and Mn$_\textrm{Ti}$S$_\textrm{O}$, Mn$_\textrm{Sr}$N$_\textrm{O}$ in SrTiO$_3$ are the most potent candidates to enhance the photocatalytic efficiency of anatase TiO$_2$ and SrTiO$_3$ under visible light irradiation.
A series of W, N codoped TiO2 nanotube arrays with different dopant contents were fabricated by anodizing in association with hydrothermal treatment. The samples were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet-visible light diffuse reflection spectroscopy. Moreover, the photocatalytic activity of W and N codoped TiO2 nanotube arrays was evaluated by degradation of methylene blue under visible light irradiation.
We demonstrate experimentally a chemical codoping approach that would simultaneously narrow the band gap and control the band edge positions of oxide semiconductors. Using TiO2 as an example, we show that a sequential doping scheme with nitrogen (N) leading the way, followed by phosphorous (P), is crucial for the incorporation of both N and P into the anion sites. Various characterization techniques confirm the formation of the N-P bonds, and as a consequence of the chemical codoping, the band gap of the TiO2 is reduced from 3.0 eV to 1.8 eV. The realization of chemical codoping could be an im…
In the present work we use TiO2 nanotube arrays, carrying a Pt coating that is optimally dewetted, as a photocatalyst to generate H2. In order to achieve a maximum H2-generation efficiency, on the one hand an ideal thermal dewetting of the Pt layer into nanoparticles is needed that requires an oxygen free heat treatment, and on the other hand an optimal crystallization of the TiO2 nanotubes into anatase with reduced defect density is achieved only by annealing in O2 containing environment. To overcome this issue, we combine adequate reducing and oxidizing conditions in a multiple annealing tre…
In the present work we grow self-organized TiO2 nanotube arrays with a defined and controlled regular spacing between individual nanotubes. These defined intertube gaps allow to build up hierarchical 1D-branched structures, conformally coated on the nanotube walls using a layer by layer nanoparticle TiO2 decoration of the individual tubes, i.e. having not only a high control over the TiO2 nanotube host structure but also on the harvesting layers. After optimizing the intertube spacing, we build host-guest arrays that show a drastically enhanced performance in photocatalytic H2 generation, comp…
Using the hybrid density functional theory and \textit{ab initio} atomistic thermodynamics, we report monodoping of non-metal (N) or metal (Mn) in SrTiO$_3$ can induce visible light absorption, but none of them are suitable to ameliorate the photocatalytic activity. Therefore, in order to achieve enhanced photocatalytic activity of SrTiO$_3$, we have employed codoped Mn and N simultaneously in SrTiO$_3$ to modulate its electronic properties effectively. In the codoped SrTiO$_3$, the recombination of photogenerated charge carriers is suppressed, and the diffusion and mobility are increased owin…
The rutile TiO$_2$ (110) surface reduced by the bridging oxygen vacancy, bridging hydroxyl group or Ti interstitial atom has been investigated by calculating their electronic structures using the density functional theory plus U method. It is found that defect states located in the forbidden band gap can enhance optical absorption. When the surface is highly reduced, the defect states approach the valence band. More importantly, defects induce a substantial up-shift of the conduction band edge, rendering the reduced surface stronger reducibility. The shifts of both conduction and valence band …
The interaction of water with TiO2 is crucial to many of its practical applications, including photocatalytic water splitting. Following the first demonstration of this phenomenon 40 years ago there have been numerous studies of the rutile single-crystal TiO2(110) interface with water. This has provided an atomic-level understanding of the water-TiO2 interaction. However, nearly all of the previous studies of water/TiO2 interfaces involve water in the vapour phase. Here, we explore the interfacial structure between liquid water and a rutile TiO2(110) surface pre-characterized at the atomic lev…
Knowledge of the molecular frontier levels' alignment in the ground state can be used to predict the photocatalytic activity of an interface. The position of the adsorbate's highest occupied molecular orbital (HOMO) levels relative to the substrate's valence band maximum (VBM) in the interface describes the favorability of photogenerated hole transfer from the VBM to the adsorbed molecule. This is a key quantity for assessing and comparing H$_2$O photooxidation activities on two prototypical photocatalytic TiO$_2$ surfaces: anatase (A)-TiO$_2$(101) and rutile (R)-TiO$_2$(110). Using the projec…
Photocatalytic and photovoltaic activity depends on the optimal alignment of electronic levels at the molecule/semiconductor interface. Establishing level alignment experimentally is complicated by the uncertain chemical identity of the surface species. We address the assignment of the occupied and empty electronic levels for the prototypical photocatalytic system of methanol on a rutile TiO2 (110) surface. Using many-body quasiparticle (QP) techniques we show that the frontier levels measured in ultraviolet photoelectron and two photon photoemission spectroscopy experiments can be assigned wi…
TiO2 nanotube arrays grown by anodization were coated with thin layers of polydopamine as visible light sensitizer. The PDA-coated TiO2 scaffolds were used as photocatalyst for selective oxidation of benzyl alcohol under monochromatic irradiation at 473 nm. Benzaldehyde was selectively formed and no by-products could be detected. A maximized reaction yield was obtained in O2-saturated acetonitrile. A mechanism is proposed that implies firstly the charge carrier generation in polydopamine as a consequence of visible light absorption. Secondly, photo-promoted electrons are injected in TiO2 condu…
A systematic study of electronic structure and band gap states is conducted to analyze the mono doping and charge compensated codoping of rutile TiO2 with Rh and Nb, using the DFT+U approach. Doping of rutile TiO2 with Rh atom induces hybridized O 2p and Rh 4d band gap states leading to a red shift of the optical absorption edge, consistent with previous experimental studies. Since Rh mono-doping may induce recombination centers, charge-compensated codoping with Rh and Nb is also explored. This codoping induces an electron transfer from Nb induced states to Rh 4d states which suppresses the fo…
Band alignment effects of anatase and rutile nanocrystals in TiO$_2$ powders lead to an electron hole separation, increasing the photo catalytic efficiency of these powders. While size effects and types of possible alignments have been extensively studied, the effect of interface geometries of bonded nanocrystal structures on the alignment is poorly understood. In order to allow conclusive studies of a vast variety of bonded systems in different orientations, we have developed a new density functional tight binding parameter set to properly describe quantum confinement in nanocrystals. Applyin…
Zr/N co-doped TiO2 nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO2 nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO2 nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO2 were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is…
The efforts in the optimization of the physical and chemical properties related to the photocatalytic efficiency of TiO2 nanoparticles relies mainly on defect engineering strategies, been the structural and the doping the most common ones. The doping of the anatase TiO2 structure with lanthanides elements potentially can turns the TiO2 optical absorption into the visible range increasing drastically its photocatalytic efficiency. Here we show that the processing of TiO2 nanoparticles in oxygen atmosphere and the La doping stabilizes the anatase phase. The La incorporation takes place mainly in…
Highly ordered TiO2 nanotube arrays (TNAs) codoped with V and N were synthesized by electrochemical anodization in association with hydrothermal treatment. The samples were characterized by field emission scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The photocurrent and photocatalytic activity of codoped TiO2 nanotube arrays were investigated under visible light irradiation. Moreover, the production of hydroxyl radicals on the surface of visible light-irradiated samples is detected by a photoluminescence technique using terephthalic acid (TA) as a probe…
Titanium dioxide is a photocatalytic substance of great practical importance. However, with its bandgap in the ultraviolet (UV) regime, native forms (undoped) of TiO2 generally exhibits poor photocatalytic activities under visible light. Here we report a facile one-step low-temperature method to treat native TiO2 with NaH in a solution-based protocol. The NaH treatment effectively induces the Ti(III) species and oxygen vacancies into the TiO2 host lattice, and enables the bandgap of TiO2 to be conveniently adjusted from the UV region to the red end of the visible spectrum. The modified TiO2 ex…
"Black" TiO2 has gained increasing interest because of its outstanding properties and promising applications in a wide range of fields. Among the outstanding features of the material is that certain synthesis processes lead to the formation of an intrinsic co-catalytic center and thus enable noble-metal free photocatalytic H2 generation. In this work, we report "grey TiO2" by an appropriate hydrogenation treatment exhibits excellent photocatalytic hydrogen. In this case, by the employment of thermally stable and high-surface-area TiO2 nanoparticles as well as mesoporous particles as the hydrog…
We investigate the photocatalytic performance of nanocomposites prepared in a one-step process by liquid-phase exfoliation of graphite in the presence of TiO$_2$ nanoparticles (NPs) at atmospheric pressure and in water, without heating or adding any surfactant, and starting from low-cost commercial reagents. The nanocomposites show enhanced photocatalytic activity, degrading up to 40$\%$ more pollutants with respect to the starting TiO$_2$-NPs. In order to understand the photo-physical mechanisms underlying this enhancement, we investigate the photo-generation of reactive species (trapped hole…
Photocatalytic $H_2$ evolution reactions on pristine TiO$_2$ is characterized by low efficiencies due to trapping and recombination of charge carriers, and due to a sluggish kinetics of electron transfer. Noble metal (mainly Pt, Pd, Au) nanoparticles are typically decorated as cocatalyst on the TiO$_2$ surface to reach reasonable photocatalytic yields. However, owing to the high cost of noble metals, alternative metal cocatalysts are being developed. Here we introduce an approach to fabricate an efficient noble metal free photocatalytic platform for $H_2$ evolution based on alloyed NiCu cocata…
Gold-decorated TiO$_2$ nanotubes were used for the photocatalytic abatement of Hg(II) in aqueous solutions. The presence of dewetted Au nanoparticles induces a strong enhancement of photocatalytic reduction and scavenging performances, with respect to naked TiO$_2$. In the presence of chlorides, a massive formation of Hg2Cl2 nanowires, produced from Au nanoparticles, was observed using highly Au loaded photocatalysts to treat a 10 ppm Hg(II) solution. EDS and XPS confirmed the nature of the photo-produced nanowires. In the absence of chlorides and/or at lower Hg(II) starting concentrations, th…
Effective co-catalysts are of key importance for photocatalytic H2 generation from aqueous environments. An attractive co-catalyst candidate are AuPt (metastable) alloys due to the synergistic electronic and chemical interaction of the constituents in the charge transfer and H2 evolution process. Here we introduce the fabrication of AuPt alloy nanoparticles with nanoporosity (pore size of 2-5 nm) fabricated on spaced TiO2 nanotubes. By dewetting a layered AgAuPt coating, we form AuPtAg alloy nanoparticles. From these alloys, Ag can selectively be dissolved leading to the desired nanoporous AuP…
Surface fluorination of TiO$_2$ (F-TiO$_2$) has complicate photocatalytic behavior in degradation of organic compounds. This work attempts to establish an elegant scenario based on the band model to understand this behavior. Density functional theory (DFT) calculations show that fluorination of the rutile TiO$_2$(110) surface (F-TiO$_2$${110}$) results in the falling of band edges. The falling of valence band edge (VBE) facilitates production of free $\cdot$OH radicals, whereas the falling of conduction band edge (CBE) lowers the reducing power of photo-electrons and inhibits reductive reactio…
Due to their characteristic geometry, TiO$_2$ nanotubes (TNTs), suitably doped by metal-substitution to enhance their photocatalytic properties, have a high potential for applications such as clean fuel production. In this context, we present a detailed investigation of the magnetic, electronic, and optical properties of transition-metal doped TNTs, based on hybrid density functional theory. In particular, we focus on the $3d$, the $4d$, as well as selected $5d$ transition-metal doped TNTs. Thereby, we are able to explain the enhanced optical activity and photocatalytic sensitivity observed in…
This paper reports on a new and swift hydrothermal chemical route to prepare titanate nanostructures (TNS) avoiding the use of crystalline TiO2 as starting material. The synthesis approach uses a commercial solution of TiCl3 as titanium source to prepare an amorphous precursor, circumventing the use of hazardous chemical compounds. The influence of the reaction temperature and dwell autoclave time on the structure and morphology of the synthesised materials was studied. Homogeneous titanate nanotubes with a high length/diameter aspect ratio were synthesised at 160^{\circ}C and 24 h. A band gap…
Reduced titanium dioxide has recently attracted large attention, particularly for its unique co-catalyst-free H$_2$ heterogeneous photocatalytic application. The enhanced photocatalytic activity of the reduced TiO$_2$ was previously ascribed to the introduction of point crystal defects (mainly Ti$_3^+$ centers), which result in the formation of intrinsic co-catalytic centers and enhanced visible light absorption. In this work, we systematically investigate the effect of different defects in the TiO$_{2-x}$ lattice on photocatalytic H$_2$ evolution. To introduce different types of defects, ther…
In this paper, we report on the co-doping nitrogen and sulfur has been achieved in the TiO2 nanotube array films by treatment with thiourea and calcination under vacuum at 500 °C for 3 h. The samples were characterized by scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectroscopy. XPS spectra revealed that N might coexist in the forms of NTiO and NOTi, S was incorporated into the lattice of TiO2 through substituting oxygen atoms in the N + S co-doped TiO2 nanotube array films. XRD patterns indicated tha…
Au nanoparticles at the TiO$_2$ surface can enhance the photocatalytic H$_2$ generation performances owing to their electron transfer co-catalytic ability. Key to maximize the co-catalytic effect is a fine control over Au nanoparticle size and placement on the photocatalyst, in relation to parameters such as the TiO$_2$ morphology, illumination wavelength and pathway, and light penetration depth in the photocatalyst. Here we present an approach for site-selective intrinsic-decoration of anodic TiO$_2$ nanotubes (TNs) with Au nanoparticles: we produce, by Ti and Au co-sputtering, Ti-Au alloy la…
The band gap of SrTiO$_{3}$ retards its photocatalytic application. Regardless narrowing the band gap of the anion doped SrTiO$_{3}$, the anion doping structures have low photoconversion efficiency. The co-cation dopings are used to modify the band gap and band edges positions of SrTiO$_{3}$ to enhance the photocatalyitic properties by extending the absorption to longer visible-light. Using density functional calculations with the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional for exchange-correlation, the crystal and electronic structures as well as the optical properties of the mono and c…
Visible light-driven production of fuels and value-added chemicals is currently one of the most intensely investigated research topics across various scientific disciplines, due to its potential to ease the World s dependence on fossil fuels. In this perspective, we recapitulate some of the main features of dye-sensitized photocatalytic systems aimed at solar H$_2$ production, focusing in particular on TiO$_2$-based three-component assemblies with organic sensitizers. Relevant aspects include the structural and electronic properties of the sensitizers, the nature of the semiconductor and the h…
Self-organized V-N co-doped TiO2 nanotube arrays (TNAs) with various doping amount were synthesized by anodizing in association with hydrothermal treatment. Impacts of V-N co-doping on the morphologies, phase structures, and photoelectrochemical properties of the TNAs films were thoroughly investigated. The co-doped TiO2 photocatalysts show remarkably enhanced photocatalytic activity for the CO2 photoreduction to methane under ultraviolet illumination. The mechanism of the enhanced photocatalytic activity is discussed in detail.
In this study, we investigate noble metal free photocatalytic water splitting on natural anatase single crystal facets and on wafer slices of the [001] plane before and after these surfaces have been modified by high pressure hydrogenation (HPH) and hydrogen ion-implantation. We find that on the natural, intact low index planes photocatalytic H$_2$ evolution (in absence of noble metal co-catalyst) can only be achieved when the hydrogenation treatment is accompanied by the introduction of crystal damage, such as simple scratching, miscut in the wafer or by implantation damage. X-ray reflectivit…
A literature-grounded scientific reasoning framework for defect-engineered TiO$_{2}$ photocatalysts
National Centre for Nuclear Research, NOMATEN CoE（国家核研究中心，NOMATEN中心）；Military University of Technology, Institute of Applied Physics, Solid State Physics Department（军事科技大学，应用物理研究所，固体物理系）
Titanium dioxide materials have been studied intensively and extensively due to photocatalytic applications. A long-standing open question is the energy band alignment of rutile and anatase TiO2 phases, which can affect the photocatalytic process in the composite system. There are basically two contradictory viewpoints about the alignment of these two TiO2 phases supported by respective experiments: 1) straddling type and 2) staggered type. In this work, our DFT plus U calculations find that the perfect rutile (110) and anatase (101) surfaces have the straddling type band alignment, whereas th…
Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. We perform $G_0W_0$ calculations to determine the coverage dependence of the level alignment for a prototypical photocatalytic interface: 1/2 and 1 monolayer (ML) intact and dissociated CH$_3$OH on rutile TiO$_2$(110). We find changes in the wavefunction's spatial distribution, and a consequent renormalization of the quasiparticle energy levels, as a function of CH$_3$OH coverage and dissociation. Our results sug…
Copper dopants are varyingly reported to enhance photocatalytic activity at titanium dioxide surfaces through uncertain mechanisms. In order to interpret how copper doping might alter the performance of titanium dioxide photocatalysts in aqueous media we applied density functional theory methods to simulate surface units of doped anatase (101) planes. By including van der Waals interactions, we consider the energetics of adsorbed water at anatase surfaces in pristine and copper doped systems. Simulation results indicate that copper dopant at anatase (101) surfaces is most stable in a 2+ oxidat…
Self-standing TiO$_2$ nanotube layers in the form of membranes are fabricated by self-organizing anodization of Ti metal and a potential shock technique. The membranes were then decorated by sputtering different Pt amounts i) only at the top, ii) only at the bottom or iii) at both top and bottom of the tube layers. The Pt-decorated membranes are transferred either in tube top up or in tube top down configuration onto FTO slides and investigated after crystallization as photocatalysts for H$_2$ generation using either front or back-side light irradiation. Double-side Pt-decoration of the tube m…
As an appealing concept for developing next-generation solar cells, intermediate-band solar cells (IBSCs) promise to drastically increase the quantum efficiency of photovoltaic conversion. Yet to date, a standing challenge lies in the lack of materials suitable for developing IBSCs. Recently, a new doping approach, termed non-compensated n-p codoping, has been proposed to construct intermediate bands (IBs) in the intrinsic energy band gaps of oxide semiconductors such as TiO$_2$. We explore theoretically the optimal quantum efficiency of IBSCs based on non-compensated n-p codoped TiO$_2$ under…
In the present work, a simple strategy is used to thermally oxidize TiN nanopowder (ca. 20 nm) to an anatase phase of a TiO2:Ti3+:N compound. In contrast to the rutile phase of such a compound this photocatalyst provides photocatalytic activity for hydrogen evolution under AM1.5 conditions - this without the use of any noble metal co-catalyst. Moreover the photocatalyst is active and stable over extended periods of time (tested for 4 months). Importantly, to achieve successful conversion to the active anatase polymorph, sufficiently small starting particles of TiN are needed. The key factor fo…
We systematically investigated native defects and reconstructions of TiO2 anatase (101) using USPEX and VASP codes. For lightly reduced samples, the coverage of O vacancies at surface depends on its concentration in bulk, while Ti interstitials prefer to dissolve in bulk. Atomic configurations of reconstructed TiO2 anatase (101) structures were given for severe reduced samples at the first time. Increasing the reduction degree, the Fermi level can be modulated in the whole bandgap. For O-rich samples, due to the indirect-to-direct bandgap transition and bandgap narrowing, O interstitials are r…
Titanium dioxide has been extensively studied in recent decades for its important photocatalytic application in environmental purification. The search for a method to narrow the optical band-gap of TiO2 plays a key role for enhancing its photocatalytic application. The optical band gap of epitaxial rutile and anatase TiO2 thin films deposited by helicon magnetron sputtering on sapphire and on SrTiO3 substrates was correlated to the lattice constants estimated from HRTEM images and SAED. The optical band-gap of 3.03 eV for bulk-rutile increased for the thin films to 3.37 on sapphire. The band g…
Molybdenum and nitrogen co-doped $TiO_2$ nanotube arrays (TNAs) were prepared by anodizing in association with hydrothermal treatment. As-prepared Mo and N co-doped TNAs were characterized by field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and ultraviolet-visible light diffuse reflection spectroscopy. Besides, the photocatalytic activity of Mo and N co-doped TNAs for the degradation of methylene blue (denoted as MB) under visible light irradiation was evaluated. It was found that N in co-doped TNAs coexists in the forms of N-Ti-O and N-O-Ti, whi…
We use density functional theory (DFT) calculations to investigate structural models consisting of anatase TiO2(101) slabs covered by reduced overlayers formed by (101) crystallographic shear planes (CSPs). Ab initio thermodynamics supports the stability of these structures under a wide range of experimental conditions. The overlayers are found to have Ti2O3 stoichiometry with a crystal structure different from the known corundum-like Ti2O3 (here denoted α-Ti2O3) phase. DFT calculations predict this new "csp-Ti2O3" phase to be energetically close to α-Ti2O3 and to have also a similar band gap.…
This paper reviews and summarizes the recent first-principles theoretical studies of the structural stability, electronic structure, optical and magnetic properties of nonmetal-doped TiO$_2$. The first section presents a comparison study of the structural stability for X-anion and X-cation doped TiO$_2$ (X=B, C, Si, Ge, N, P, As, Sb, S, Se, Te, F, Cl, Br, and I), which reveals that the sites of nonmetal dopants (i.e., at O sites or at Ti sites) in TiO$_2$ are determined by the growth condition of doped TiO$_2$ and the dopants' electronegativities. The next section reviews the electronic struct…
SrTiO$_3$ is a highly efficient photocatalyst for the overall water splitting reaction under UV irradiation. However, an atomic-level understanding of the active surface sites responsible for the oxidation and reduction reactions is still lacking. Here we present a unified experimental and computational account of the photocatalytic activity at the SrO- and TiO$_2$- terminations of aqueous-solvated [001] SrTiO$_3$. Our experimental findings show that the overall water-splitting reaction proceeds on the SrTiO$_3$ surface only when the two terminations are simultaneously exposed to water. Our si…
Black TiO2 with/without noble metal has been proposed for visible photocatalyst, still leaving poor catalyst efficiency. Alternatively, phase-mixed TiO2 such as anatase and rutile has been commonly used for visible catalysts with the inevitable inclusion of noble metal. Here, we perform a noble metal-free visible photocatalyst blue TiO2 with type-II band-aligned ordered anatase/disordered rutile structure, via phase-selective reduction with alkali metals. The changed band alignment in this heterostructure was identified by absorption and ultraviolet photoemission spectroscopy, which was furthe…
Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. Standard density functional theory (DFT) based methods have proven unable to provide a quantitative description of this level alignment. This requires a proper treatment of the anisotropic screening, necessitating the use of quasiparticle (QP) techniques. However, the computational complexity of QP algorithms has meant a quantitative description of interfacial levels has remained elusive. We provide a systematic …
Doping is one of the most common strategies for improving the photocatalytic and solar energy conversion properties of TiO$_2$, hence an accurate theoretical description of the electronic and optical properties of doped TiO$_2$ is of both scientific and practical interest. In this work we use many-body perturbation theory techniques to investigate two typical n-type dopants, Niobium and Hydrogen, in TiO$_2$ rutile. Using the GW approximation to determine band edges and defect energy levels, and the Bethe Salpeter equation for the calculation of the absorption spectra, we find that the defect e…
Titanium dioxide (TiO$_2$) plays a central role in the study of artificial photosynthesis, owing to its ability to perform photocatalytic water splitting. Despite over four decades of intense research efforts in this area, there is still some debate over the nature of the first water monolayer on the technologically-relevant anatase TiO$_2$ (101) surface. In this work we use first-principles calculations to reverse-engineer the experimental high-resolution X-ray photoelectron spectra measured for this surface in [Walle et al., J. Phys. Chem. C 115, 9545 (2011)], and find evidence supporting th…
Atomic and electronic structures of TiO_2(110) surface with possible adsorptional, substitutional and interstitial Au or Pt elemental impurities at full and one-sixth monolayer concentrations were investigated by density functional theory calculations using the projector augmented wave approach within the plane wave method. Relative thermodynamic stabilities of such phases have been discussed by means of their surface free energies. Our results suggest that tunable photocatalytic activity can be achieved on Pt atom admixed rutile (110) surface at low coverages.
The novel concept of non-compensated n-p codoping has made it possible to create tunable intermediate bands in the intrinsic band gap of TiO2, making the codoped TiO2 a promising material for developing intermediate band solar cells (IBSCs). Here we investigate the quantum efficiency of such IBSCs within two scenarios - with and without current extracted from the extended intermediate band. Using the ideal equivalent circuit model, we find that the maximum efficiency of 57% in the first scenario and 53% in the second are both much higher than the Shockley-Queisser limit from single gap solar c…
Electronic properties and atomic structures of W, N, S, W/N, and W/S dopings of anatase TiO_2 have been systematically investigated using the density functional theory (DFT). The exchange and correlation effects have been treated with Heyd, Scuseria and Ernzerhof (HSE) hybrid functional. Mixing traditional semi-local and non-local screened Hartree-Fock (HF) exchange energies, the HSE method corrects the band gap and also improves the description of anion/cation derived gap states. Enhanced charge carrier dynamics, observed for W/N codoped titania, can partly be explained by the passivative mod…
Nanotubed titanic acid (H2Ti2O4(OH)2) was prepared from nanotubed sodium titanate (Na2Ti2O4(OH)2) by an ion exchange reaction in a pH=1 HCl solution. The effect of annealing temperature on the morphology, structure and photocatalytic behavior of nanotubed H2Ti2O4(OH)2 was studied by means of TEM, XRD, DTG, DSC, BET and ESR. The results showed that nanotubed H2Ti2O4(OH)2 is thermally unstable. Its dehydration consists of two steps. In the first-step dehydration, single-electron-trapped oxygen vacancies (SETOVs) were generated. Accompanying the second-step dehydration, the transition of crystal …
