Ti Clusters Research Articles

Structure identification of Ti(iv) clusters in low-temperature TiO2 crystallization: creating high-surface area brush-shaped rutile TiO2

We demonstrate for the first time a controlled reaction of Cl-coordinating Ti(iv) clusters in low-temperature hydrolysis (27 °C) to create large-surface area rutile TiO2 crystals.

Diffusion and retention of hydrogen in vanadium in presence of Ti and Cr: First-principles investigations

We systemically investigated diffusion and retention of hydrogen (H) in vanadium (V) in presence of Ti/Cr and determined the stability of Hn clusters and Hn-vacancy clusters (n = 1–6) near Cr/Ti using first-principles calculations. H prefers a tetrahedral site near Ti than other interstitial sites. H-Cr interactions have a weak repulsion contrarily H-Ti interactions have a weak attraction. Kinetically, H diffusion barrier decreases towards Ti, while it increases towards Cr. Ti and Cr block H mobility in V alloys. Moreover, Hn Ti clusters are quite stable while HnCr clusters are less stable. Ti enhances H retention by acting as a trapping site for multiple H atoms in similar with vacancy, and a Ti atom can trap at least six H atoms. The stability of H-vacancy-Cr/Ti complexes and vacancy-Cr/Ti trapping for multiple H atoms are discussed. The findings are valuable for understanding the mechanism of H bubble nucleation and H embrittlement under irradiation.

Aerobic oxidation of alcohols in visible light on Pd-grafted Ti cluster

The titanium cluster with the reduced band gap has been synthesized having the palladium nanoparticles over the surface, which not only binds to the atmospheric oxygen but also catalyzes the oxidation of alcohols under visible light.

Recent Advances in the Preferential Thermal-/Photo-Oxidation of Carbon Monoxide: Noble Versus Inexpensive Metals and Their Reaction Mechanisms

Preferential oxidation (PROX) of CO is applicable because of its low cost, ease of implementation, and low loss of H2 during purification. Mo–SiO2 and Cr–SiO2 photocatalysts utilized charge separation at metal=O bonds, and the PROX selectivity of CO was high. The CO PROX rates using semiconductor-based photocatalysts were comparable to those of photocatalysts (380 μmol h−1 g cat −1 ) and were also selective (100 %). These photocatalysts are advantageous because they do not activate H2 in comparison to noble metal catalysts. Below 473 K using noble metals, Ru, Rh, Pt, or Au supported on reducible metal oxides exhibited excellent CO thermal-PROX rates of ~4900 μmol h−1 g cat −1 ; however, the CO PROX selectivity of ~48 % was insufficient because of H2 activation on noble metals in nature. CO adsorbed onto TiO2 and O2 was stabilized at the interface between a Ti site and an Au atom. Weakly adsorbed water increased the effective number of active sites by stabilizing Au–OOH or Au–COOH. The PROX rates of CO using Au/TiO2-based catalysts under dark conditions increased under UV–visible light by the effect of charge separation and surface plasmon resonance and the promoted electron transfer to the adsorbed O2. In the case of CuO–CeO2 catalysts, CO adsorbed onto CuO and reacted with lattice O atoms at the boundary between CuO and CeO2 to form CO2 at an O vacancy, which was subsequently filled with an O2 molecule. The combination of Cu or Co with a reducible metal oxides also provided performance comparable to or higher than that of CuO–CeO2 owing to adequate standard reduction potential for Cu2+, Co3+, Mn3+/4+, and Ce4+. Finally, binary metal–organic framework consisting of oxyhydroxide Ti clusters interlinked by organic ligands and Cu oxyhydroxide ligands showed superior CO PROX performance (76 % conversion and 99 % selectivity) to that achieved using CuO–CeO2 owing to effective dispersion of Cu–O–Ti connection in microporous crystallites. Further progress is needed to alleviate the activity loss in the presence of moisture and/or CO2 based on suggestions that steric hindrance of some types of microporous crystallites would suppress the blocking of moisture or CO2.

Revealing the Multibonding State between Hydrogen and Graphene-Supported Ti Clusters

Hydrogen adsorption on graphene-supported metal clusters has brought much controversy due to the complex nature of the bonding between hydrogen and metal clusters. The bond types of hydrogen and graphene-supported Ti clusters are experimentally and theoretically investigated. Transmission electron microscopy shows that Ti clusters of nanometer-size are formed on graphene. Thermal desorption spectroscopy captures three hydrogen desorption peaks from hydrogenated graphene-supported Ti clusters. First principle calculations also found three types of interaction: Two types of bonds with different partial ionic character and physisorption. The physical origin for this rests on the charge state of the Ti clusters: when Ti clusters are neutral, H2 is dissociated, and H forms bonds with the Ti cluster. On the other hand, H2 is adsorbed in molecular form on positively charged Ti clusters, resulting in physisorption. Thus, this work clarifies the bonding mechanisms of hydrogen on graphene-supported Ti clusters.

The Ti environment in natural hibonite: XANES spectroscopy and computer modelling

The local atomic structure around Ti in Ti-bearing hibonite (CaAl12O19) was studied using X-ray absorption near-edge structure (XANES) spectroscopy and computer modelling. Structural models of the direct substitution of Al by Ti3+, Al by Ti4+ charge balanced by the coupled substitution of Mg2+ for Al, and small Ti clusters were considered. The Ti K-XANES spectra of natural hibonite with different Ti concentration were recorded. Theoretical Ti K- XANES spectra for structural models of hibonite were calculated. It was shown that the theoretical Ti K-XANES spectra for a model with Ti at the five-coordinated M2 site are in agreement with the experimental XANES spectra of hibonite with low concentrations of Ti, while the theoretical spectra for a structural model of clustered Ti are in agreement with the experimental spectra of hibonite with higher Ti contents.

Structures and Electronic Properties of TinV (n = 1-16) Clusters: First-Principles Calculations.

Structures and electronic properties of TinV (n = 1-16) clusters have been investigated using density functional theory with the generalized gradient approximatio. The calculations have shown that the TinV clusters favor compact spherical structures having similar conformations to the pure Tin clusters. The results show that the vanadium atom remains on the surface when n ⩽ 8 and n = 16, while for n = 9-15, it occupies the endohedral position. The Ti6V, Ti12V, and Ti14V clusters are found to be more stable than their neighbors, consistent with pure Tin clusters that have the same size. Additionally Ti4V has been found to be also magic, consistent with recent reports of B- and Al-doped Ti clusters. Small TinV (n ⩽ 4) clusters exhibit a transition from metallic-like to semimetallic electronic structure, while for n = 5 onward, no significant changes are observed compared with pure Tin clusters.

Co-sputtered metal and polymer nanocomposite films and their electrical responses for gas sensing application

Titanium and polytetrafluoroethylene (Ti–PTFE) nanocomposite thin films were successfully fabricated on glass substrates using a combination of dc and rf magnetron sputtering. When the Ti–PTFE composites were prepared at below the percolation threshold i.e. 27% metal volume filling (F), Ti clusters with the average sizes of 7±2nm were found. As the Ti content was increased above the percolation threshold (F=62%), the connecting regions of Ti were formed within the polymer matrix and the electrical property changed rapidly from insulator-like to metal-like properties. The Ti–PTFE composites prepared near the percolation threshold showed the electrical response to different volatile organic compounds (VOCs). The sensitivity significantly depended upon the VOCs concentrations. These composites devices showed the presence of distinct chemical bonds of CC, CCF, CF and CF2 and TiF in TiO2 on the surface as investigated by X-ray photoelectron spectroscopy (XPS) while the surface morphology, characterized by atomic force microscopy (AFM) presented the root mean square (RMS) surface roughness of 13.3nm. Cross-section transmission electron microscopy (TEM) images of the device revealed Ti clusters dispersed in PTFE matrix with particle sizes varied between 10nm and 30nm.

Chemoselective Claisen–Schmidt bis-substitutional condensation catalyzed by an alkoxy-bridged dinuclear Ti(IV) cluster

The highly efficient and chemoselective α,α′-bis-substitution of alkanones is important in organic synthesis. Herein, a dimeric titanium cluster, Ti2Cl2(OPri)6·2HOPri (Ti2), is used in the Claisen–Schmidt condensation reaction, for the selectively activation of symmetrical ketones containing α,α′-methylene groups and production of α,α′-bis-substituted alkanones in high efficiency and chemoselectivity. The high efficiency and chemoselectivity can be extended to a variety of typical alkanones and aromatic aldehydes. Both of the oxo-bridged dimeric motif of Ti2 and the ionic Ti–Cl bond are responsible for the high efficiency and chemoselectivity.

Ti(iv) nanoclusters as a promoter on semiconductor photocatalysts for the oxidation of organic compounds

Ti(IV) clusters act to accelerate the photocatalytic oxidation of organic compounds.

Density functional theory study of Mo-doped M@(BN)48 (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) clusters

The structure and magnetic properties of Mo-doped M@(BN)48 (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) clusters were calculated at BPW91/LanL2DZ level. The magnetic nature of the clusters M@(BN)48 significantly changed when doping with Mo atom, except for Co@(BN)48. Only the magnetic moment for the CrMo@(BN)48 cluster was decreased to zero. Thus, M@(BN)48 clusters can be selected as the model system to detect Mo atom by the change of the magnetic moment.

Nearly Perfect Spin Filter Based on a Wire of Half-Metallic(η5−C5H5)Ti(η8−C8H8)TiUnits

Applications in spintronics require components that create or preserve pure spin currents. The authors' calculations show that a nanowire built from organometallic (\ensuremath{\eta}${}^{5}$- C${}_{5}$H${}_{5}$)Ti(\ensuremath{\eta}${}^{8}$-C${}_{8}$H${}_{8}$)Ti clusters is half-metallic, with 100% spin polarization near the Fermi level in its electronic structure. They predict that such a wire coupled to gold electrodes should be multifunctional, which seems quite promising for devices---especially considering that these clusters can actually be prepared in the laboratory.

Green Synthesis and Radial Breathing Modes inTiNanoparticles

This work presents the synthesis of metallic nanoparticles of titanium. The extract from the nopal (Opuntia ficus-indica) plant was used as the redactor agent. The results of transmission electronic microscopy (TEM) show that nanoparticles have a sphere-like shape with an approximate diameter of 1–4 nm. The presence of Ti in these particles was corroborated by energy dispersive X-ray spectroscopy (EDS). Optical properties were detected with the presence of absorption bands centered in 295 nm and 355 nm, similar to those reported in the literature. Two Raman bands centered at 359 cm-1and 404 cm-1were observed after the synthesis of titanium nanoparticles. Afterwards, structural and vibrational parameters of small clusters of Ti ( Tin, n = 3–13) were analyzed by the density functional theory (DFT) at the B3LYP level of approximation combined with the basis set LANL2DZ. Radial breathing modes (RBMs) were detected in the vibrational spectrum of each cluster, placed around 298–387 cm-1.

Electronic and structural properties of Ti9XO20 (X=Ti, C, si, Ge, Sn and pb) clusters: A DFT study

The electronic and structural properties of Ti9XO20 (X=Ti, C, Si, Ge, Sn and Pb) clusters have been obtained in the density functional theory (DFT) framework. The changes in the bond length, binding energy, frontier orbitals, and electronic potential have been fully analyzed when one titanium atom in the (TiO2)10 cluster is replaced by elements with four valence electrons. When one titanium atom is substituted by one carbon atom, a charge excess among the guest and the surrounding oxygen atoms is generated, which is approximately 1.5 times that of the pristine case, and this structure has been shown to be the most stable among the studied systems. In addition, the Ti10O20–Cd2 and Ti9CO20–Cd2 clusters exhibit HOMO–LUMO gaps that have decreased by 0.58 and 2.12eV, respectively, with respect to the bare cases.

Mixed-Metal Oxo Clusters Structurally Derived from Ti6O4(OR)8(OOCR')8.

The mixed-metal oxo clusters FeTi5O4(OiPr)4(OMc)10 (OMc = methacrylate), Zn2Ti4O4(OiPr)2(OMc)10, Cd4Ti2O2(OAc)2(OMc)10(HOiPr)2, [Ca2Ti4O4(OAc)2(OMc)10]n, and [Sr2Ti4O4(OMc)12(HOMc)2]n were obtained from the reaction of titanium alkoxides with the corresponding metal acetates and methacrylic acid. Their structures are derived from Ti clusters with the composition Ti6O4(OR)8(OOCR′)8. The Ca and Sr derivatives consist of chains of condensed clusters.

Modification of microstructure and hardness for Cu–Ti alloy by means of energetic ion beam irradiation

Cu–Ti alloys were irradiated with5.4MeV Al ions, 7.3MeV Fe ions, 10MeV I ions, and 16MeV Au ions at room temperature and the Vickers microhardness was measured. The hardness once increases by the irradiation with a low fluence, and then it remains almost constant even with increasing the ion fluence. The change in hardness was well correlated with the density of energy deposited through the elastic collisions and not the electronic excitation. The observation of atom probe tomography (APT) did not show any Ti clusters in the irradiated specimens. This result suggests that not Ti clusters but lattic defects (interstitial atoms, vacancies and/or their aggregates) contributed to the increase in hardness of Cu–Ti alloys.

Robust molecular crystals of titanium(IV)-oxo-carboxylate clusters showing water stability and CO2 sorption capability.

A series of new Ti(IV)-oxo clusters supported by carboxylate ligands are synthesized by solvothermal reactions, and their crystal structures and gas sorption properties are studied in detail. Depending on the reaction medium, two types of Ti6O6 clusters are formed with benzoate-derived ligands whose 2- or 4-position is substituted by a hydrophobic moiety. The molecular packing structures of these Ti clusters are found stable against water- and heat-treatments. Gas sorption studies reveal that a dense-packed Ti-carboxylate cluster can adsorb almost the same number of CO2 molecules as the one with considerable intermolecular voids in the packing structure. The effect of benzoate substituents on the gas sorption behavior is discussed.

Phase evolution and alloying mechanism of titanium aluminide nanoparticles

The evolution of phase composition of titanium aluminide nanoparticles synthesized by the flow-levitation method was systematically investigated by adjustment of the evaporating temperature of the mixed metallic droplet and the X-ray diffraction spectrum. Their alloying mechanism was analyzed according to the variation of phase composition. ε(h, l)-TiAl3, γ-TiAl and α2-Ti3Al phases are gradually formed in TiAl alloy nanoparticles with the increasing of evaporating temperature of the mixed droplet. The alloying reaction is possible to perform between the small clusters of Ti and Al during the cooling process with high cooling rate. And the alloying mechanism can be explained based on the Gibbs free energy of alloying reaction of Ti and Al small clusters.

Titanium embedded cage structure formation in Al(n)Ti+ clusters and their interaction with Ar.

Recently, Ar physisorption was used as a structural probe for the location of the Ti dopant atom in aluminium cluster cations, Al(n)Ti(+) [Lang et al., J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. As an experiment result, the lack of Ar complexes for n > nc determines the cluster size for which the Ti atom is located inside of an Al cage. To elucidate the decisive factors for the formation of endohedrally Al(n)Ti(+), experimentalists proposed detailed computational studies as indispensable. In this work, we investigated, using the density functional theory, the structural and electronic properties of singly titanium doped cationic clusters, Al(n)Ti(+) (n = 16-21) as well as the adsorption of an Ar atom on them. The first endohedral doped cluster, with Ti encapsulated in a fcc-like cage skeleton, appears at nc = 21, which is the critical number consistent with the exohedral-endohedral transition experimentally observed. At this critical size the non-crystalline icosahedral growth pattern, related to the pure aluminium clusters, with the Ti atom in the surface, changes into a endohedral fcc-like pattern. The map of structural isomers, relative energy differences, second energy differences, and structural parameters were determined and analyzed. Moreover, we show the critical size depends on the net charge of the cluster, being different for the cationic clusters (nc = 21) and their neutral counterparts (nc = 20). For the Al(n)Ti(+) · Ar complexes, and for n < 21, the preferred Ar adsorption site is on top of the exohedral Ti atom, with adsorption energy in very good agreement with the experimental value. Instead, for n = 21, the Ar adsorption occurs on the top an Al atom with very low absorption energy. For all sizes the geometry of the Al(n)Ti(+) clusters keeps unaltered in the Ar-cluster complexes. This fact indicates that Ar adsorption does not influence the cluster structure, providing support to the experimental technique used. For nc = 21, the smallest size of endohedral Ti doped cationic clusters, the Ar binding energy decreases drastically, whereas the Ar-cluster distance increases substantially, point to Ar physisorption, as assumed by the experimentalists. Calculated Ar adsorption energies agree well with available experimental binding energies.

On the limits to Ti incorporation into Si using pulsed laser melting

Fabrication of p-Si(111) layers with Ti levels well above the solid solubility limit was achieved via ion implantation of 15 keV 48Ti+ at doses of 1012 to 1016 cm−2 followed by pulsed laser melting using a Nd:YAG laser (FWHM = 6 ns) operating at 355 nm. All implanted layers were examined using cross-sectional transmission electron microscopy, and only the 1016 cm−2 Ti implant dose showed evidence of Ti clustering in a microstructure with a pattern of Ti-rich zones. The liquid phase diffusivity and diffusive velocity of Ti in Si were estimated to be 9 × 10−4 cm2/s and (2 ± 0.5) × 104 m/s, respectively. Using these results the morphological stability limit for planar resolidification of Si:Ti was evaluated, and the results indicate that attaining sufficient concentrations of Ti in Si to reach the nominal Mott transition in morphologically stable plane-front solidification should occur only for velocities so high as to exceed the speed limits for crystalline regrowth in Si(111).