Titania Substrate Research Articles

The interaction of size-selected Ru3 clusters with TiO2: depth-profiling of encapsulated clusters.

Ru is a metal of interest in catalysis. Monodisperse Ru3 clusters as catalytic sites are relevant for the development of catalysts because clusters use significantly lower amounts of precious materials for forming active sites due to the small size of the cluster. However, retaining the mono-dispersity of the cluster size after deposition is a challenge because surface energy could drive both agglomeration and encapsulation of the clusters. In the present work Ru3 clusters are deposited by chemical vapor deposition (CVD) of Ru3(CO)12 and cluster source depositions of bare Ru3 onto radio frequency sputter-deposited TiO2 (RF-TiO2) substrates, TiO2(100), and SiO2. When supported on RF-TiO2, bare Ru3 is encapsulated by a layer of titania substrate material during deposition with a cluster source. Ligated Ru3(CO)12 is also encapsulated by a layer of titania when deposited onto sputter-treated RF-TiO2, but only through heat treatment which is required to remove most of the ligands. The titania overlayer thickness was determined to be 1-2 monolayers for Ru3(CO)12 clusters on RF-TiO2, which is thin enough for catalytic or photocatalytic reactions to potentially occur even without clusters being part of the very outermost layer. The implication for catalysis of the encapsulation of Ru3 into the RF-TiO2 is discussed. Temperature-dependent X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and temperature-dependent low energy ion scattering (TD-LEIS) are used to probe how the cluster-surface interaction changes due to heat treatment and scanning transmission electron microscopy (STEM) was used to image the depth of the surface from side-on.

Highly Active under VIS Light M/TiO2 Photocatalysts Prepared by Single-Step Synthesis

A single-step impregnation approach is investigated as a synthetic route for photocatalyst synthesis active under visible light. The as-derived photocatalysts exhibited very high degradation rates towards methylene blue (MB) decolorization under visible light despite the high concentration of the initial MB solution concentration. The TiO2-based photocatalysts were prepared using nitrate precursor compounds for copper and silver; thus, Ag/TiO2 and Cu/TiO2 photocatalysts were prepared. The photocatalyst’s physicochemical properties were determined by XRF, BET, and XRD analysis. The metal nature of the titania substrate, the titania matrix effect, and the metal concentration parameters were studied, while the catalyst concentration in the MB initial solution was optimized.

Phase transformation kinetics of anodic titania nanotube arrays in oxygen-rich atmosphere

Titania substrate and ambient atmosphere are pivotal in influencing the thermal stability of anodic TiO2 nanotube arrays (TNTs) due to anatase-to-rutile phase transition (ATRPT). This paper aimed to investigate detailed relationships between morphology and the crystallite structure and phase kinetics of O2-annealed TNTs with tube length > 10 μm and the inner diameter 60–80 nm. The study shows that below 700 °C, ARPT was very slow, but accelerated above 700 °C as nanotube structures showed signs of dramatic collapse, indicating that the thermal stability became poor. The resulting phase transformation kinetics of the O2-annealed TNTs are described by the general equation Ea= -∂ln(xr)·R/∂(1/T)·1000 , yielding approximate activation energy values of E1 = 150.71 ± 14.67 kJ/mol and E2 = 31.17 ± 1.53 kJ/mol for ARPT at temperatures below and above 600 °C, respectively. The transformation kinetics were found to be dominated by a “feeding effect” and a “size effect”, respectively. These findings serve to provide a useful method for preparing anodic TNTs with anticipant phase composition and thermal stability.

TiO2/ZnO: Type-II Heterostructures for electrochemical crystal violet dye degradation studies

Semiconductor nanomaterials with proper band edge alignments forming “heterostructure” assemblies have significant importance in water splitting, dye degradation, and other electrochemical studies. The formed heterojunction between material phases facilitates fast charge carrier transport and, thereby, improves electrochemical performance in associated processes. Herein, we report a type-II heterostructure combining TiO2 and ZnO nanomaterials for electrochemical crystal violet dye degradation studies. The rationale in choosing the above materials (TiO2, ZnO) in the present study includes stability, lack of toxicity, and high oxidation power, but they also facilitate fast charge carrier movements due to proper band edge alignments, forming a type-II heterostructure assembly. Cyclic voltammetry, combined with ultraviolet-visible analysis, was used to identify the cathodic and anodic peak currents and trace the exact mechanism of dye degradation. The electro-catalytic performance of TiO2/ZnO heterostructured materials fabricated on titania (Ti) substrate show higher performance, in comparison to all individual material interfaces, due to synergistic interaction and synchronized charge transport.

Wide-low energy coupled semi-conductor layers of TiO2 – CdX boosting the performance of DSSC

This investigation involves design and fabrication of CdSe overlayer on titania substrate that produces a highly functional DSSC (dye sensitized solar cell) anode using commercial N3 as the sensitizer dye. CdSe nanoparticles were deposited on TiO2 through periodic voltammetry under variable (10 – 130) cycle scans. Matrix morphology and optical parameters of the TiO2 – CdSe fabricated layer were respectively determined by electron microscopy and UV–Visible spectroscopy. Output performance of the cell under illumination was recorded by current density–voltage measurements, transient photo response, electrochemical impedance spectroscopy and incident photon to current conversion efficiency, while chrono-amperometry was used to derive durability of the cell. Remarkable output parameters were obtained for the optimized CdSe – TiO2 photo-anode loaded under 70 cycles showing, 13.29% photo conversion efficiency (PCE) and 15.30 mA cm−2 short circuit current density (JSC) for the operating DSSC. Similar investigations were extended to other chalcogenide NPs (CdTe and CdS) embedded on TiO2 for comparative study, whereby CdSe – TiO2 system was identified as the best performing DSSC anode matrix facilitating electron injection by the concerted effort of aligned energy band levels.

Laser induced formation of copper species over TiO2 nanotubes towards enhanced water splitting performance

We proposed fast and scalable route where the ordered TiO2 nanotubes coated with thin copper layers were annealed by the laser beam of 355 nm wavelength at different fluencies in the range of 15–120 mJ/cm2. As a result, copper species are integrated with the titania substrate and the formed material exhibits unique optical absorption bands in the visible range. Moreover, X-ray photoelectron spectroscopy analysis reveals the formation of Cu2O while the 4+ oxidation state of titanium is preserved. According to the electrochemical results, the material treated by laser exhibits outstanding photoelectrochemical activity comparing to the pristine titania or the one only covered by the thin copper film. In particular, when the fluence of 60 mJ/cm2 was used for the modification of the titania decorated with Cu film, the current density recorded in KOH electrolyte reaches nearly 4.5 mA/cm2 at +2.0 V vs. Ag/AgCl/0.1 M KCl upon visible light.

Ultrathin Chromia on a Hexagonally-Ordered d0 Ferromagnet: Evidence of Interfacial Exchange Bias at the Cr2O3/TiO2-x Interface.

Heterostructures consisting of 10 Å thick chromia films and 50 Å thick titania films display significant exchange bias at and above room temperature. Chromia films ∼10 Å thick were deposited by molecular beam epitaxy (MBE) of Cr at room temperature in ultrahigh vacuum on 50 Å thick TiO2-x(111) films (x < 0.3) also deposited epitaxially by MBE on Al2O3(0001). Cr deposition yields increased Ti(III) formation in the titania substrate and the formation of a Cr2O3 overlayer, without Cr/Ti interfacial mixing, as determined by in situ photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). In situ low-energy electron diffraction (LEED) and XPS data indicate that the chromia overlayer is hexagonally ordered and ∼10 Å thick. Longitudinal and polar magneto-optic Kerr effect (MOKE) measurements at 285-315 K provide evidence of strong exchange bias between the boundary layer magnetization of chromia and the ferromagnetic substrate. These data demonstrate the robust room-temperature interaction of the boundary layer magnetization of a multiferroic antiferromagnet with a d0 ferromagnetic substrate.

Improved suitability as catalyst support and more efficient charge carrier separation of native air-formed TiO2 films by mild laser treatment

The possibility of using native air-formed TiO2 films (N–TiO2) as substrate for platinum deposition and the extent to which the effectiveness of such Pt/TiO2 systems can be improved by a mild laser treatment of the TiO2 support was investigated. Laser-treated titania (LT-TiO2) exhibited homogeneous rough surface and allowed much efficient separation of photogenerated charge carriers. Both N–TiO2 and LT-TiO2 were used as substrates for platinum electrochemical deposition and it was found that the use of the latter enables more uniform distribution and much lower average size of the Pt particles, leading to an enhancement of the electrochemically active specific surface area of ca. 75%. Moreover, the use of a laser-treated titania substrate not only facilitates methanol anodic oxidation overall process but also improves the resistance of the electrocatalyst to deactivation by strong adsorption of intermediates. Upon UV irradiation, Pt/LT-TiO2 electrodes exhibit a strong enhancement of the methanol oxidation current and, importantly, a much better resistance to poisoning.

Hetero-Orientation Epitaxial Growth of TiO2 Splats on Polycrystalline TiO2 Substrate

In the present study, the effect of titania (TiO2) substrate grain size and orientation on the epitaxial growth of TiO2 splat was investigated. Interestingly, the splat presented comparable grain size with that of substrate, indicating the hereditary feature of grain size. In addition, hetero- and homo-orientation epitaxial growth was observed at deposition temperatures below 400 °C and above 500 °C, respectively. The preferential growth of high-energy (001) face was also observed at low deposition temperatures (≤ 400 °C), which was found to result from dynamic nonequilibrium effect during the thermal spray deposition. Moreover, thermal spray deposition paves the way for a new approach to prepare high-energy (001) facets of TiO2 crystals.

Investigation of Ligand-Stabilized Gold Clusters on Defect-Rich Titania

Chemically synthesized atomically precise gold clusters stabilized by triphenylphosphine ligands [Au9(PPh3)8](NO3)3] were deposited onto the surface of titania fabricated via atomic layer deposition. The titania surface was pretreated by heating and sputtering. After deposition of the clusters onto pretreated titania, the samples were heated at 200 °C for 20 min under ultrahigh vacuum and subsequently investigated using metastable-induced electron spectroscopy to study the electronic structure of the outermost layer of the sample and X-ray photoelectron spectroscopy to determine the chemical composition of the surface of the sample. The former study revealed that two reference spectra are needed to explain the electronic structure of the sample. One reference spectrum is related to the titania substrate, while the second spectrum is related to the presence of the Au cluster cores and the ligands removed from the cluster cores. The latter study found that the Au 4f peak is shifted to lower binding energy a...

Self-Sensitized Photocatalytic Degradation of Colorless Organic Pollutants Attached to Rutile Nanorods—Experimental and Theoretical DFT+D Studies

Utilization of visible light by photosensitization of semiconductor photocatalysts via surface attachment of small colorless organic pollutants (COP) is an effective way to stimulate their photocatalytic degradation. Herein, by means of the spectroscopic, photoelectrochemical, spectroelectrochemical, and photocatalytic studies combined with the DFT+D molecular modeling, we show how disubstituted benzene derivatives, like catechol (CAT), salicylic acid (SAL), phthalic acid (PTA), and terephthalic acid (TPA), can tune the photocatalytic properties of rutile nanorods with the dominant (110) termination. We elucidated in a systematic way the COP ligand-binding configurations, the alignment of energy levels, and the charge-transfer pathways from the organic admolecules to the titania substrate. The pDOS structures of the COP@r-TiO2(110) assemblies were interpreted in terms of electronic interactions between the titania photocatalyst and the COP adspecies. It was shown that the appearance of additional states w...

Interface structure between titania and perovskite materials observed by quartz crystal microbalance system

Adsorption of PbI2 onto a titania layer was monitored by a quartz crystal microbalance system in solution. The amount of PbI2 adsorbed on the titania layer increased with an increase in the PbI2 concentration in dimethylformamide (DMF). However, PbI2 remained after being rinsed with DMF, suggesting that PbI2 is rigidly bonded to the surface of the titania. The x-ray photoelectron spectroscopy measurement of PbI2 adsorbed on the titania substrate showed that the Pb compound has a composition of PbI0.33, not PbI2, suggesting that part of the Pb-I reacts with the HO-Ti moieties of titania to form Pb-O-Ti linkages. Trap density as measured by the thermally stimulated current method decreased after PbI2 passivation. Perovskite solar cells consisting of porous titania passivated with PbI2 had a higher efficiency than those without the passivation. It was concluded that PbI2 passivation of porous titania surfaces is one of the crucial approaches for enhancing the efficiency of perovskite solar cells with a scaffold layer of porous titania.

Photochemical silver nanoparticles deposition on sol–gel TiO2 for plasmonic properties utilization

This paper shows investigations on silver nanoparticles deposition using simple photochemical method on sol–gel coated titania. The influence of titania substrate, silver precursor concentration, light intensity and irradiation time are considered as a factors determining the microstructure. The average diameter of the particles and surface coverage are calculated from SEM microstructure investigations and confirmed by AFM imaging. The crystalline phase in titania layers were determined by TEM and Raman spectroscopy. The optical measurements of absorbance and absorption were shown indicating that there was no absorption of the light used in experiment even though deposition of nano silver was confirmed. Finally, the plasmonic properties were simulated for the model particles by finite difference time domain method. Possible application of obtained structure was proposed.

Phosphine-stabilised Au₉ clusters interacting with titania and silica surfaces: the first evidence for the density of states signature of the support-immobilised cluster.

Chemically made, atomically precise phosphine-stabilized clusters Au9(PPh3)8(NO3)3 were deposited on titania and silica from solutions at various concentrations and the samples heated under vacuum to remove the ligands. Metastable induced electron spectroscopy was used to determine the density of states at the surface, and X-ray photoelectron spectroscopy for analysing the composition of the surface. It was found for the Au9 cluster deposited on titania that the ligands react with the titania substrate. Based on analysis using the singular value decomposition algorithm, the series of MIE spectra can be described as a linear combination of 3 base spectra that are assigned to the spectra of the substrate, the phosphine ligands on the substrate, and the Au clusters anchored to titania after removal of the ligands. On silica, the Au clusters show significant agglomeration after heat treatment and no interaction of the ligands with the substrate can be identified.

Effect of a Gold Cover Layer on the Encapsulation of Rhodium by Titanium Oxides on Titanium Dioxide(110)

The present study focuses on the thermal behavior of continuous rhodium thin films (∼10 nm) deposited on a TiO2(110) substrate at 300 K and covered by a continuous ultrathin gold film (∼1 nm), applying scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and low-energy ion scattering (LEIS) techniques. This arrangement facilitated a rather clear-cut investigation into the effect of the Au cover layer on the well-known encapsulation/decoration of Rh by TiOx, since the contribution of the titania substrate to the XPS and LEIS spectra could be avoided. Upon annealing a monometallic Rh film, the diffusion of Ti and O from the TiO2(110) substrate on top of the Rh film is essentially complete up to 850 K, leading characteristically to the formation of a “pinwheel” encapsulation layer with a TiO1.2 stoichiometry. The dewetting of the Rh film does not take place up to 950 K. Upon annealing of the Rh film in the presence of a continuous Au cover layer, the diffusion/accumulation of O was co...

Periodic DFT+D Molecular Modeling of the Zn-MOF-5(100)/(110)TiO2 Interface: Electronic Structure, Chemical Bonding, Adhesion, and Strain

Electronic structure, bonding characteristics, adhesion, and stress energy of the Zn-MOF-5(100)/(110) rutile interface were modeled by using periodic DFT+D calculations, corroborated by simulation of high resolution transmission electron microscopy (HR-TEM) images. Adjustment of the flexible metal–organic framework (MOF) moiety to the rigid rutile substrate was achieved within a supercell comprised of (1 × 1) Zn-MOF-5 and (4 × 9) TiO2 units. It was shown that binding of the Zn-MOF-5 layer takes place via bidentate 1,4-benzenedicarboxylate (BDC)–titania bridges. A coherent interface can be formed with the minimal periodicity along the [11̅0] direction defined by nine Ti5c adsorption sites (9 × 2.96 Å = 26.64 Å) and two consecutive linkers of the Zn-MOF-5 chain (2 × 12.94 Å = 25.88 Å). The MOF part is tuned to the oxide substrate by tilting the BDC linkers by 10° and twisting around their long axis by 34°. The resultant lattice strain of the Zn-MOF-5 layer was equal to ε[001] = 0.31% and ε[11̅0] = 2.86%, and the associated stress energy to σtotal = 4.8 eV. Pronounced adhesion energy of the Zn-MOF-5 layer deposited on the rutile surface (−0.33 eV/nm2) stems from the sizable dispersion (−0.39 eV/nm2) contribution, counterbalancing the unfavorable lattice strain and bonds distortion components. The calculated density of states structure of the Zn-MOF-5(100)/(110)TiO2 interface revealed that it can be described as an electronically coupled, staggered (Type II) charge injection system, where a photoinduced electron may be directly transferred from the Zn-MOF-5 moiety to the conduction band of the titania substrate.

Improving the electrochemistry and microstructure of nickel electrode by deposition on anodized titanium substrate for the electrocatalytic oxidation of methanol and ethanol

The electrodeposition process of nickel and the substrate used for the electrodeposition can be improved to obtain an effective catalyst for methanol oxidation. Thus, nanoparticles of nickel have been uniformly electrodeposited on the surface of previously anodized titanium at 5 V during 1 h. The optimized microstructure has been studied by using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The XPS and argon-ion etching experiments have revealed the composition profile of the titanium/titania/nickel thin film electrode. Metallic Ni is detected by XRD. The nickel particles dispersed in a porous TiO2 substrate have great catalytic activity for methanol oxidation in basic solution and through the redox couple NiO(OH)/Ni(OH)2. The optimized titania substrate yields to electrodes (crystalline titanium/amorphous titania/nanocrystalline nickel) with higher catalytic activity than non-anodized metallic titanium (titanium/nickel). However, further oxidation and thickening of the titania film drives to poorer electrochemical behavior. The SEM and EDS results show that the nickel particles exhibit certain tendency to agglomerate and to form spherical particles of around 2 μm. This electrode material also is active to oxidize ethanol, but this activity is poorer.

Combined Nanofibers of Carbon Nanotube, Titania and Polymer Substrate for Oxidation of Toluene and Isopropyl Alcohol

Combined Nanofibers of Carbon Nanotube, Titania and Polymer Substrate for Oxidation of Toluene and Isopropyl Alcohol

Atomic Structure and Special Reactivity Toward Methanol Oxidation of Vanadia Nanoclusters on TiO2(110)

We have grown highly controlled VOx nanoclusters on rutile TiO2(110). The combination of photoemission and photoelectron diffraction techniques based on synchrotron radiation with DFT calculations has allowed identifying these nanostructures as exotic V4O6 nanoclusters, which hold vanadyl groups, even if vanadium oxidation state is formally +3. Our theoretical investigation also indicates that on the surface of titania, vanadia mononuclear species, with oxidation states ranging from +2 to +4, can be strongly stabilized by aggregation into tetramers that are characterized by a charge transfer to the titania substrate and a consequent decrease of the electron density in the vanadium 3d levels. We then performed temperature programmed desorption experiments using methanol as probe molecule to understand the impact of these unusual electronic and structural properties on the chemical reactivity, obtaining that the V4O6 nanoclusters can selectively convert methanol to formaldehyde at an unprecedented low temperature (300 K).

Atomistic simulations of thiol-terminated modifiers for hybrid photovoltaic interfaces

Small aromatic molecules such as benzene or pyridine derivatives are often used as interface modifiers (IMs) at polymer/metal oxide hybrid interfaces. We performed a theoretical investigation on prototypical thiol-terminated IMs aimed at improving the photovoltaic performances of poly(3-hexylthiophene)/TiO2 devices. By means of first-principles calculations in the framework of the density functional theory we investigate 3-furanthiol (3FT), 4-mercaptobenzoicacid (4MB), and 6-isoquinolinethiol (6QT) molecules. We discuss the role of these molecules as modifiers alternative to 4-mercaptopyridine (4MP) which has recently shown to induce a large improvement in the overall power conversion efficiency of mesoporous films of TiO2 infiltrated by poly(3-hexylthiophene). The IMs investigated are expected to keep the beneficial features of 4MP giving at the same time the possibility to further tune the interlayer properties (e.g., its thickness, stability, and density). Dense interlayers of 6QT turn out to be slightly unstable since the titania substrate induces a compressive strain in the molecular film. On the contrary, we predict very stable films for both 3FT and 4MB molecules, which makes them interesting candidates for future experimental investigations.