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DOE OSTI2020

Phase Transformations among TiO2 Polymorphs

Polymorphs widely exist in nature and synthetic systems and are well known to determine material properties. Understanding phase transformation mechanisms among polymorphs enables the design of structures and tuning of phases to tailor material properties. However, current understanding is limited due to the lack of direct observations that track the processes and the structural evolution is not known at atomic scale. Here, integrating (semi) in situ transmission electron microscopy and density functional theory, we report atomic structural evolutions of phase transformation from anatase (A) to rutile (R), brookite (B), R-phase, and TiO. Besides the consistent paths with previous reports, we discover several unreported paths, including a [001] direction and (020) plane of anatase to [100]A and (011)R of rutile, respectively, ( , ) and , . Density functional theory analysis elucidates atomic structural evolution during the processes and over 16% of Ti-O bonds break and reform during the processes with energy barriers of ~0.7-1.0 eV per TiO2 formula unit. Under electron-beam irradiation, anatase particles transform into TiO2-R phase or TiO at high or room temperature, respectively. We also reveal the anisotropic nature of electron-beam effect, which is seldom discussed: dependence of crystallographic orientation with respect to electron-beam irradiation direction. Understanding the atomic structural evolution sheds light on interpreting and controlling TiO2 polymorphs and interface structures for various applications. The revealed electron-beam effects in our work provide guidance for in situ transmission electron microscopy studies.

Song, Miao↗

DOE OSTI2019

Structure and enhanced antimicrobial activity of mechanically activated nano TiO2

Titanium dioxide is a photocatalyst, known not only for its ability to oxidize organic contaminants, but also for its antimicrobial properties. In this article, significant enhancement of the antimicrobial activity of TiO2 (up to 32 times) was demonstrated after its activation by ball milling. The antimicrobial activity was analyzed for one fungal and 13 bacterial ATCC strains using the microdilution method and recording the minimum inhibitory concentration (MIC) values. In order to further investigate the correlation between the mechanical activation of TiO2 and its antimicrobial activity, the structure, morphology and phase composition of the material were studied by means of Electron Microscopy, X-ray diffraction and nitrogen adsorption-desorption measurements. UV-Vis diffuse reflectance spectra were recorded and the Kubelka-Munk function was applied to convert reflectance into the equivalent band gap energy (Eg) and, consequently, to investigate changes in the Eg value. X-ray photoelectron spectroscopy was used to analyze the influence of mechanical activation on the Ti 2p and O 1s spectra. The presented results are expected to enable the development of more sustainable and effective advanced TiO2-based materials with antimicrobial properties that could be used in numerous green technology applications.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three TiO2 sheets oriented in the (0, 0, 1) direction. Ti4+ is bonded to six equivalent O2- atoms to form edge-sharing TiO6 octahedra. All Ti–O bond lengths are 1.98 Å. O2- is bonded in a distorted trigonal non-coplanar geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 crystallizes in the monoclinic P2_1/m space group. The structure is two-dimensional and consists of one TiO2 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of Ti–O bond distances ranging from 1.63–1.87 Å. In the second Ti4+ site, Ti4+ is bonded to five O2- atoms to form a mixture of distorted edge and corner-sharing TiO5 trigonal bipyramids. There are a spread of Ti–O bond distances ranging from 1.81–2.00 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted T-shaped geometry to three equivalent Ti4+ atoms. In the second O2- site, O2- is bonded in a single-bond geometry to one Ti4+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to two Ti4+ atoms. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two Ti4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 crystallizes in the orthorhombic Cmm2 space group. The structure is two-dimensional and consists of one TiO2 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded in a distorted single-bond geometry to five O2- atoms. There are a spread of Ti–O bond distances ranging from 1.63–2.09 Å. In the second Ti4+ site, Ti4+ is bonded to four O2- atoms to form corner-sharing TiO4 tetrahedra. There is two shorter (1.81 Å) and two longer (1.86 Å) Ti–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ti4+ atoms. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to two equivalent Ti4+ atoms. In the third O2- site, O2- is bonded in a single-bond geometry to one Ti4+ atom. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 crystallizes in the orthorhombic Cmm2 space group. The structure is two-dimensional and consists of one TiO2 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded in a distorted single-bond geometry to five O2- atoms. There are a spread of Ti–O bond distances ranging from 1.63–2.09 Å. In the second Ti4+ site, Ti4+ is bonded to four O2- atoms to form corner-sharing TiO4 tetrahedra. There is two shorter (1.81 Å) and two longer (1.87 Å) Ti–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ti4+ atoms. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to two equivalent Ti4+ atoms. In the third O2- site, O2- is bonded in a single-bond geometry to one Ti4+ atom. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on TiO2 by Materials Project

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is trigonal omega-like structured and crystallizes in the orthorhombic Pmmn space group. The structure is two-dimensional and consists of two TiO2 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form edge-sharing TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.91–2.07 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form edge-sharing TiO6 octahedra. There are a spread of Ti–O bond distances ranging from 1.97–1.99 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ti4+ atoms. In the second O2- site, O2- is bonded in a distorted T-shaped geometry to three Ti4+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ti4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

TiO2 Nanocrystal-Framed Li 2 TiSiO 5 Platelets for Low-Voltage Lithium Battery Anode

Titanium-based anode materials are attracting considerable attention for use in high-performance lithium-ion batteries, but the compromised energy density caused by high voltage plateaus and unsatisfactory capacities severely retards their practical applications. Herein, a molten-salt synthesis of Li 2 TiSiO 5 crystalline platelets and a subsequent selective facet modification by in situ growth of TiO 2 nanocrystal frames are facilely achieved. The discharge voltage plateau at around 0.5 V renders the Li 2 TiSiO 5 anode safe compared with graphite and confers a high energy density compared with zero-strain Li 4 Ti 5 O 12 anode. With the optimized size, structure, and content of modified TiO2 nanocrystals associated with the exposed (001) plane of Li 2 TiSiO 5 , the Li 2 TiSiO 5 -based anodes can deliver a capacity of above 300 mAh g -1 , enhanced rate performance, and a capacity retention of 66% after 10 000 cycles. In situ X-ray diffraction and ex situ transmission electron microscopy have demonstrated the structural stability of the anodes upon charge/discharge. Further theoretical calculation reveals 3D migration paths of Li + ions in Li 2 TiSiO 5 . The selective modification of in situ grown TiO2 nanocrystals on certain facets of crystallites opens a new door for the development of electrode materials possessing superior electrochemical properties.

anodes↗

DOE OSTI2018

The role of hydrothermal conditions in determining 1D TiO2 nanomaterials bandgap energies and crystal phases

Highlights: • Application of hydrothermal method for 1D TiO2 synthesis. • Varying hydrothermal synthesis conditions on 1D TiO2 crystal phase, size and SSA. • Effects on crystal phase, size and SSA on bandgap. - Abstract: One-dimensional TiO{sub 2} nanostructure synthesized using a hydrothermal method showed significant differences in the bandgap energies and crystal phase properties under different synthesis conditions. The objectives of this study were to evaluate the effect of the hydrothermal reaction conditions on the bandgap energy and to optimize the reaction conditions using a 3-factor 3-level Box Behnken design. The factors investigated include temperature, NaOH concentration and TiO{sub 2} concentration (BBD). A quadratic response surface model predicted optimum conditions for the maximum and minimum bandgap energy. The BBD analysis and other statistical tools provided evidence showing the temperature and NaOH concentration significantly affected the 1D TiO{sub 2} bandgap energy. Pure anatase was associated with a higher bandgap energy, whereas the biphasic anatase-rutile and anatase-TiO{sub 2}-B phases were linked with decreasing the bandgap energy. In addition, the crystal size and specific surface area (SSA) impact on the bandgap energy was due to the size quantization effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2020

Binding of Formic Acid on Anatase TiO2(101)

The adsorption of formic acid (FA) and the formation of formate species on metal oxide surfaces are of great interest in catalysis. Formic acid is used to probe the adsorption properties of surface sites and formates are common intermediates in many catalytic reactions. Here we focus on the interaction of FA with a prototypical anatase TiO2(101) surface by using a combination of scanning tunneling microscopy (STM), infrared reflection absorption spectroscopy (IRAS), electron stimulated desorption (ESD), and density functional theory (DFT) to assess the coverage dependent evolution of different FA-derived surface species at low temperatures (80–240 K). We find that isolated FA adsorbs at 80 K in both monodentate (MD) and bidentate (BD) configurations on top of undercoordinated Ti sites (Ti5c). The MD form is likely deprotonated and readily converts upon annealing to bridging BD on two neighboring Ti5c sites. DFT calculations show that molecularly-bound MD FA is metastable and readily converts into a deprotonated state in the proximity of subsurface oxygen vacancy. The stability of the MD species increases as the availability of the paired Ti5c sites for BD formation diminishes at high coverages. Upon surface saturation, a mixed configuration of alternating bidentate and monodentate species with coverage of 2/3 FA/Ti5c represents the most favorable configuration. This is in contrast with the adsorption of FA on rutile TiO2(110) and many other oxides, where bidentate formate species dominate. Y.W., A.D., G.A.K., R.R., N.G.P., and Z.D. were supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Division of Chemical Sciences, Geosciences and Biosciences (CSGB) under FWP 47319. B.W. and A.S. acknowledge the support of DOE BES, CSGB Division under Award DESC0007347. The experimental studies were performed in EMSL, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for DOE by Battelle. The authors also acknowledge computational resources from the TIGRESS high-performance computer center at Princeton University.

Wang, Yang↗

DOE OSTI2024

Photoreversible Color-Switching Cu-Doped TiO2 Nanoparticles for High-Contrast Rewritable Printing

Light-printable rewritable paper that can be used multiple times has attracted extensive attention because of its potential benefits in reducing environmental pollution and energy consumption. Developing rewritable paper with high black-to-colorless contrast, lasting legibility, and a fast response is fascinating but challenging. Here, we integrate the redox chemistry of Cu2+ ions into photoreductive TiO2 nanoparticles to produce Cu-doped TiO2 nanoparticles capable of highly photoreversible switching between colorless and black with excellent contrast and color stability. Incorporating such nanoparticles into hydroxyethyl cellulose produces a rewritable paper with the same appearance as that of conventional paper. More importantly, it demonstrates great features promising for practical applications, including high black-to-colorless contrast, fast light-printing (<20 s), long legible time (>3 days), high reversibility (>50 cycles), high resolution (90 μm), and large scale (A4 size) applicability.

Wang, Wenshou↗

DOE OSTI2019

Influence of crystalline order and defects on the absolute work functions and electron affinities of TiO2- and SrO-terminated n-SrTiO3(001)

We establish how the detailed structure and composition of the terminal layer of n-SrTiO3 (001) determine key surface electronic properties. We have measured and calculated from first principles the absolute work functions and electron affinities of bulk SrNb0.01Ti0.99O3(001) with both TiO2 and nominally SrO terminal planes. The match between theory and experiment is excellent at 4.6(1) eV for the TiO2 termination if an ideal, bulk-truncated surface structure is assumed. In contrast, the ideal SrO-termination leads to a calculated work function that is ~1.3 eV lower than the experimental value of 3.6(1) eV. We show that this discrepancy is associated with defects on the SrO surface that serve as electron scavengers. These defects deplete the concentration of itinerant electrons in the subsurface region and increase the negative charge density on the surface, thus increasing the work function. Several different surface defect configurations were modeled; the ones that yield the best agreement with experiment involve Sr vacancies in the terminal layer along with OH–/H– pairs or O22– occupying anion sites adjacent to the Sr vacancies.

Chambers, Scott A.↗

DOE OSTI2020

Aqueous Phase Aldol Condensation of Formaldehyde and Acetone on Anatase TiO2(101) Surface: A Theoretical Investigation

A mechanistic understanding of catalytic reactions at solid-liquid interface is limited both experimentally and theoretically but attracts much interest. Using density functional theory calculations (DFT) and ab initio molecular dynamics (AIMD) simulations, we investigated the effect of liquid water on a-H abstraction, C-C coupling, and dehydration steps of aldol condensation of formaldehyde and acetone on an anatase TiO2(101) surface. The existence of the aqueous phase lowered the Gibbs energy of activation of dehydration step pronouncedly from 187 to 74 kJ/mol through proton transfer mechanism, making the hydrogenation pathway more favorable in the aqueous phase. In contrast, a mixed route prevails in the vapor phase. This work provides insights into the effect of the bulk water through a proton transfer mechanism on the dehydrogenation, C-C coupling, and dehydration

anatase TiO2, formaldehyde and acetone, aldol cond↗

DOE OSTI2026

Anharmonic TiO2 Phonons

Single Crystal ARCS data of TiO2 at several temperatures

36 MATERIALS SCIENCE↗

DOE OSTI2024

Nanoporous Tio2 Water Training Data

Data and input files used to train a Deep Potential (DP) model for the nanoporous TiO2-water interface. The DeepMD-kit code was used to train the DP. Information about data format, and how to use DeepMD-kit can be found at https://docs.deepmodeling.com/projects/deepmd/en/master/

08 HYDROGEN↗

DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is Rutile structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ti4+ is bonded to six equivalent O2- atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles are 49°. There is four shorter (1.96 Å) and two longer (2.00 Å) Ti–O bond length. O2- is bonded in a distorted trigonal planar geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is zeta iron carbide-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Ti4+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 51–52°. There are a spread of Ti–O bond distances ranging from 1.88–2.13 Å. O2- is bonded in a distorted trigonal planar geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗