Ti Clusters Research Articles

A Titanium-Based Metal-Organic Framework For Tandem Metallaphotocatalysis.

Metal-organic frameworks (MOFs) have garnered substantial attention for their unique properties, such as high porosity and tunable structures, making them versatile for various applications. This paper constructs photoactive titanium-organic frameworks by combining Ti(IV) clusters and a bipyridine linker. The MOF is synthesized in situ through imine condensation, resulting in NU-2300. Subsequent ex situ nickel salt complexation results in NU-2300-Ni, which is then used for light-mediated carbon-heteroatom cross-couplings. The photophysical properties of the metallaphotocatalyst were investigated by UV-vis and EPR analyses, and both the Ti cluster and the bipyridine linker were found to contribute to successful catalysis, making it a tandem catalyst. The heterogeneous material retained its performance through five cycles of thioetherification. This work contributes not only to MOF synthetic strategies but also to expanding MOF applications as recyclable, tandem metallaphotocatalysts.

Existence state of Ti in diamond-like carbon coatings and its effects on hybrid structure and residual stress: Molecular dynamics simulations

In this study, the modified embedded atom method potential function is selected via the LAMMPS platform and OVITO interface software to describe the interatomic interaction potential, which is used to simulate the existence states of doped Ti in Ti-doped diamond-like coatings as well as their effect on the hybrid structure, hardness, and residual stress of the coatings. The results indicate that Ti atoms preferentially combine with C atoms to form Ti–C bonds, thus rendering it difficult to form metallic Ti clusters. The formation of Ti-C bond clusters with high extent of ordering (nanoc-TiC) in the coating is related to the density (or sp3C fraction) of the coating; the higher the density, the higher is the critical content of Ti (CV-Ti) required to form nanoc-TiC. When the density of the coating ranges from 2.4 to 3.6 g/cm3, the CV-Ti is 2–6 at.%. When the Ti content in the coating is less than CV-Ti, Ti atoms existed only in amorphous Ti–C clusters, which is not conducive to the stability of the sp3C phase and significantly reduces the residual stress and hardness of the coating. When the CV-Ti is exceeded, nanoc-TiC formed and grew until the hybrid C–C bonds in the coating disappeared completely, thus increasing the residual stress of the coating.

Boosting the grain refinement of commercial Al alloys by compound addition of Sc

For decades, Al–Ti–B has been widely used for refining commercial Al alloys. However, the addition of Al–Ti–B master alloys to recycled Al alloys suffers from Si-poisoning and cannot achieve desired refinement and thus final strength-ductility. In this study, a novel grain refiner made of Al–Ti–B-Sc has been developed and its application in refining recycled Al–Si–Cu alloys has been quantified using X-ray computed tomography (XCT). It has been found that the new Al–5Ti–1B-0.8Sc master alloy exceed the performance of Al–5Ti–1B in three aspects: (1) formation of Al3(Sc,Ti) heterogeneous nucleation particles other than Al3Ti; (2) dispersing TiB2 by forming TiB2/Al3(Sc,Ti) clusters and increasing Al melt viscosity; (3) reducing the specific surface area of Al3Ti to improve its high-temperature stability. Surprisingly, the compound addition of Sc has been found to further reduce the grain and Si particle size due to accelerated kinetics of α-Al nucleation and diminished Si poisoning. Therefore, this study proposes not only a new master alloy but also a new grain refinement method, which can effectively increase the tensile strength and elongation of recycled Al alloys up to 433.2 ± 10.5 MPa and 3.0 ± 0.1 %, respectively.

Stable and 7.7 wt% hydrogen storage capacity of Ti decorated Irida-Graphene from first-principles calculations

Solid-state hydrogen storage is crucial for the widespread applications of hydrogen energy. It is a grand challenge to find appropriate materials that provide high hydrogen density and ambient temperature stability. Herein, we investigated the potential of Ti-decorated Irida-Graphene, a promising effective hydrogen storage system, as a novel hydrogen storage material using first-principles calculation. Irida-Graphene is a two-dimensional isomer of carbon consisting of tri-, hexa-, and octagon rings of carbon. Ti atoms are tightly bounded to the hexagonal rings. Binding energy analysis reveals that a single Ti atom in the primitive unit-cell of Ti-decorated Irida-Graphene is capable to bind up with 5H2 molecules and the average adsorption energy was −0.41 eV/H2. It indicates the gravimetric density of 7.7 wt%. The stability is attributed to Kubas-type interactions and ensured by a 5.0 eV diffusion energy barrier that prevents the Ti–Ti clustering. Further, ab initio molecular dynamics simulations results illustrate that the system remains stable at 600 K, higher than the desorption temperature of 524 K, implying the stability of the system during hydrogen recharge and discharge. The exceptional hydrogen storage performance suggests that Ti-decorated Irida-Graphene is an outstanding candidate for hydrogen storage materials.

Probing the interaction of Ti clusters with isopropanol for ether production: an experimental and computational study

Probing the interaction of Ti clusters with isopropanol for ether production: an experimental and computational study

A novel defect reassembly strategy for NH2-MIL-125(Ti) to enhance the photocatalytic NO removal activity

Photocatalysis technology has been widely used to eliminate typical air pollutants, but its further application is limited by the finite visible light response and severe charge carrier recombination. In this study, through a simple defect reassembly strategy, the carboxyl group of highly photosensitive eosin Y is successfully coordinated with the exposed Ti clusters in the defective NH2-MIL-125(Ti) to improve photocatalytic activity. The results demonstrate that the NO removal rate of the optimal sample (named D-NM-125/EY) is about 62.05%, which is 1.62 times that of the original NH2-MIL-125(Ti). The UV–Vis, PL, and photochemical characterization analysis confirm that the incorporation of eosin Y significantly can enhance the visible light absorption capacity and promote the photogenerated carriers separation, which may be due to that eosin Y can more easily absorb and utilize visible light to produce more photogenerated electron-hole pairs. Combining ESR with in-situ DRIFTS analysis, the possible photocatalytic mechanism is revealed, in which the reactive oxygen species generated in the photocatalytic process are the key factors for the successful degradation of NO into less toxic substances. This study will provide a new strategy for modifying MOFs photocatalysts to solve typical air pollution problems.

Precise Electronic Structures of Amorphous Solids: Unraveling the Color Origin and Photocatalysis of Black Titania

Water splitting through efficient catalysts represents an ultimate solution for carbon neutrality within 40 years. To achieve this goal, amorphous photocatalysts are noted for their promising performances. Among them, the best known is black titania (amorphous TiOx, x ≤ 2). However, despite a large number of studies on black titania, its color origin, structure–property relationship, and photocatalytic mechanism remain a topic of hot debate, largely due to the difficulty to calculate its precise electronic structure. Here, using ab initio molecular dynamics simulations, we report the precise electronic structures of black titania and further reveal the generic evolution pattern of the electronic structures of covalent compounds upon amorphization and reduction. An interesting “disproportionation-like” process resulting in metal clusters of Ti is discovered in heavily reduced amorphous titania, accompanied by oxygen vacancies in different energy states. This study elucidates the workings of amorphous catalysts and offers practical guidance for enhancing their performances.

Transition from chemisorption to physisorption of H2 on Ti functionalized [2,2,2]paracyclophane: A computational search for hydrogen storage

In this work, we studied the hydrogen adsorption-desorption properties and storage capacities of Ti functionalized [2,2,2]paracyclophane (PCP222) using density functional theory and molecular dynamic simulation. The Ti atom was bonded strongly with the benzene ring of PCP222 via Dewar interaction. Subsequently, the calculation of the diffusion energy barrier revealed a significantly high energy barrier of 5.97 eV preventing the Ti clustering over PCP222 surface. On adsorption of hydrogen, the first H2 molecule was chemisorbed over PCP222 with a binding energy of 1.79 eV with the Ti metals. Further addition of H2 molecules, however, exhibited their adsorption over PCP222-Ti through the Kubas-type H2 interaction. Charge transfer mechanism during the hydrogen adsorption was explored by the Hirshfeld charge analysis and electrostatic potential map, and the PDOS, Bader's topological analysis revealed the nature of the interaction between Ti and H2. The PCP222 functionalized with three Ti atoms showed a maximum hydrogen uptake capacity of up to 7.37 wt%, which was fairly above the US-DOE criterion. The practical H2 storage estimation revealed that at ambient conditions, the gravimetric density of up to 6.06 wt% H2 molecules could be usable, and up to 1.31 wt% of adsorbed H2 molecules were retained with the host. The ADMP molecular dynamics simulations assured the reversibility by desorption of adsorbed H2 and the structural integrity of the host material at sufficiently above the desorption temperature (300 K and 500 K). Therefore, the Ti-functionalized PCP222 can be considered as a thermodynamically viable and potentially reversible H2 storage material.

Bonding states of hydrogen for supported Ti clusters on pristine and defective graphene

To determine whether graphene-supported Ti clusters can synergistically store hydrogen through Kubas and spillover effect, we systematically investigate the growth pattern of Tin (n = 1–10) clusters on pristine and defective graphene and analyze multiple types of bonding states of hydrogen in detail. For pristine graphene, the most stable Tin (n = 1–10) clusters are the quasi-planar structure except for supported Ti4 and Ti5. The Ti dissociation energies and the binding energy of Tin clusters gradually increase with increasing n, which indicates that larger Tin clusters tend to form. Efficient spillover will occur on single-site Ti Catalysts at low hydrogen concentration due to the lower hydrogen spillover energy barrier (3.05 eV), while the energy barrier of hydrogen migration from Tin (n = 2–7) clusters to graphene on the cluster is 5.34–6.82 eV. The Ti: H ratio is a maximum of 1:8 for the single-site Ti catalyst, while decreases with the Tin cluster increases. Therefore, the pristine graphene-supported Ti nanoclusters are more suitable as substrates for hydrogen adsorbent rather than spillover. The introduced defects make Tin clusters have three-dimensional conical configurations from n = 4. Ti3 and Ti6 are the most stable clusters. Moreover, the migration energy barriers of H atoms on them decrease from 6.54 eV to 6.82 eV–4.32 eV and 3.42 eV, respectively. Our results explain recent experimental phenomena [Appl Phys Lett 2015; 106: 083,901. ACS Energy Lett 2022; 7 (7): 2297–2303] in depth at the molecular level.

Geometrical and magnetic properties of small titanium and chromium clusters on monolayer hexagonal boron nitride.

Magnetic clusters on an insulating substrate are potential candidates for spin-based quantum devices. Here we investigate the geometric, electronic, and magnetic structures of small Ti and Cr clusters, from dimers to pentamers, adsorbed on a single-layer hexagonal boron nitride (h-BN) sheet within the framework of density functional theory. The stable adsorption configurations of the Ti clusters and Cr clusters composed of the same number of atoms are found to be totally different from each other. The difference in their bonding mechanisms has been revealed by the density of states and the charge density difference of the corresponding adsorption systems. While chemical bonds are formed between the Ti atoms and the supporting sheet, the Cr clusters are found in the physisorption state on the substrate. In addition, it is shown that the h-BN sheet is energetically favorable for building three-dimensional Ti clusters. These findings support the use of h-BN as a suitable decoupling substrate for manipulation of quantum spin states in small transition metal (TM) clusters and fabrication of devices based on them.

Structural evolution and electronic properties of neutral and anionic TiASil (A = Sc, Ti; l ≤ 12): relatively stable TiASi4 as a structural unit.

Simulated photoelectron spectroscopy was conducted to investigate the structural evolution and electronic properties of TiASil (A = Sc, Ti; l ≤ 12) clusters and their anions via the Perdew-Burke-Enzerhof scheme and extensive cluster search using the ABCluster software. The results revealed that the ground-state structures of the TiASil (A = Sc, Ti) clusters generally exhibited similar configurations except for the Ti2Si3, ScTiSi3, and TiScSi10 clusters. Furthermore, the TiASil clusters exhibited an adsorptive evolution pattern, and the TiASi4 unit was considered the basic constituent framework of the structure, excluding several distortions and minor changes. With the increase in the cluster size, the lowest-energy structures varied from the exohedral to the cage structures of the single-metal atom at the center. Regarding the second energy difference data, the neutral TiASi4 clusters exhibited better stability among the neutral and anionic TiASil (A = Sc, Ti; l ≤ 12) clusters. Furthermore, the chemical bonding in the TiASi4 clusters was analyzed by molecular orbitals (MOs), highest occupied MO-lowest unoccupied MO gaps, and adaptive natural density partitioning analyses for the best Ti2Si4 cluster especially, and the results were combined with the natural population analysis data. The hybridization of the spd orbital of the metal atoms, eight localized bonds, and four delocalized bonds may primarily account for the relative stabilities of the neutral, square bipyramidal structure of Ti2Si4. Thus, the TiASi4 clusters may be assembled as the basic units of silicon-based semiconductor clusters of large-size neutral and anionic TiASil.

Photoactivation of titanium-oxo cluster [Ti6O6(OR)6(O2C t Bu)6]: mechanism, photoactivated structures, and onward reactivity with O2 to a peroxide complex.

The molecular titanium-oxo cluster [Ti6O6(OiPr)6(O2C t Bu)6] (1) can be photoactivated by UV light, resulting in a deeply coloured mixed valent (photoreduced) Ti (iii/iv) cluster, alongside alcohol and ketone (photooxidised) organic products. Mechanistic studies indicate that a two-electron (not free-radical) mechanism occurs in this process, which utilises the cluster structure to facilitate multielectron reactions. The photoreduced products [Ti6O6(OiPr)4(O2C t Bu)6(sol)2], sol = iPrOH (2) or pyridine (3), can be isolated in good yield and are structurally characterized, each with two, uniquely arranged, antiferromagnetically coupled d-electrons. 2 and 3 undergo onward oxidation under air, with 3 cleanly transforming into peroxide complex, [Ti6O6(OiPr)4(O2C t Bu)6(py)(O2)] (5). 5 reacts with isopropanol to regenerate the initial cluster (1) completing a closed cycle, and suggesting opportunities for the deployment of these easily made and tuneable clusters for sustainable photocatalytic processes using air and light. The redox reactivity described here is only possible in a cluster with multiple Ti sites, which can perform multi-electron processes and can adjust its shape to accommodate changes in electron density.

Oxidation and hydrogenation of monolayer MoS2 with compositing agent under environmental exposure: The ReaxFF Mo/Ti/Au/O/S/H force field development and applications

An atomistic modeling tool is essential to an in-depth understanding upon surface reactions of transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), with the presence of compositing agents, including Ti and Au, under different environmental exposures. We report a new ReaxFF reactive force field parameter set for Mo, Ti, Au, O, S, and H interactions. We apply the force field in a series of molecular dynamics (MD) simulations to unravel the impact of the Ti dopant on the oxidation/hydrogenation behaviors of MoS2 surface. The simulation results reveal that, in the absence of Ti clusters, the MoS2 surface is ruptured and oxidized at elevated temperatures through a process of adsorption followed by dissociation of the O2 molecules on the MoS2 surface during the temperature ramp. When the MoS2 surface is exposed to H2O molecules, surface hydrogenation is most favored, followed by oxidation, then hydroxylation. The introduction of Ti clusters to the systems mitigates the oxidation/hydrogenation of MoS2 at a low or intermediate temperature by capturing the O2/H2O molecules and locking the O/H-related radicals inside the clusters. However, OH− and H3O+ are emitted from the Ti clusters in the H2O environment as temperature rises, and the accelerating hydrogenation of MoS2 is consequently observed at an ultra-high temperature. These findings indicate an important but complex role of Ti dopants in mitigating the oxidation and hydrogenation of MoS2 under different environmental exposures. The possible mechanisms of oxidation and hydrogenation revealed by MD simulations can give an insight to the design of oxidation resistant TMDs and can be useful to the optical, electronic, magnetic, catalytic, and energy harvesting industries.

Selectivity of Ru-rich Ru-Ti-O oxide surfaces in parallel oxygen and chlorine evolution reactions

The electrocatalytic behaviour of single-phase Ru1-xTixO2 materials was studied to outline general trends controlling the selectivity of oxide-based anodes in parallel oxygen evolution and chlorine evolution reactions. Materials with x ranging between 0 and 0.2 were prepared by spray freeze freeze drying approach. Prepared materials show a non-homogeneous distribution of Ti in the structure with dominant clustering of the Ti along the (001) direction. For materials with x higher than 0.1 the dominant linear clustering of Ti along the z-axis changes, including Ti clustering also along (111) direction. Prepared materials are active in both oxygen evolution and chlorine evolution reactions. The Ti has a pronounced effect on the selectivity of the prepared materials. Ti presence affects the selectivity of the prepared materials in a complex manner. Materials featuring a low Ti content (x∼0.05) retain a preference for oxygen evolution reaction even in presence of chlorides and are more selective for oxygen evolution than pure RuO2. The selectivity towards chlorine evolution increases with increasing Ti content and, apparently, also with clustering of Ti along the (111) direction. The selectivity towards chlorine evolution may be related to the tendency of the prepared catalysts to evolve the oxygen via lattice oxygen evolution reaction (LOER) reflecting the ability of the catalyst surface to form active sites under operando conditions.

Cluster-type analogue memristor by engineering redox dynamics for high-performance neuromorphic computing

Memristors, or memristive devices, have attracted tremendous interest in neuromorphic hardware implementation. However, the high electric-field dependence in conventional filamentary memristors results in either digital-like conductance updates or gradual switching only in a limited dynamic range. Here, we address the switching parameter, the reduction probability of Ag cations in the switching medium, and ultimately demonstrate a cluster-type analogue memristor. Ti nanoclusters are embedded into densified amorphous Si for the following reasons: low standard reduction potential, thermodynamic miscibility with Si, and alloy formation with Ag. These Ti clusters effectively induce the electrochemical reduction activity of Ag cations and allow linear potentiation/depression in tandem with a large conductance range (~244) and long data retention (~99% at 1 hour). Moreover, according to the reduction potentials of incorporated metals (Pt, Ta, W, and Ti), the extent of linearity improvement is selectively tuneable. Image processing simulation proves that the Ti4.8%:a-Si device can fully function with high accuracy as an ideal synaptic model.

Guerbet coupling of methanol catalysed by titanium clusters

Alcohol coupling, also known as the Guerbet reaction, is a potentially important process to increase the value of short chain hydrocarbons. We present here an insight of C-C bond formation in the coupling of methanol to higher alcohols by Ti clusters. We have synthesized Ti13 clusters by laser ablation in methanol, and studied the catalysis for methanol coupling reactions using high resolution mass spectroscopy and also density-functional theory calculations. The experimental findings concurs with the calculated kinetic- and thermodynamic- allowed reaction pathways, helping to understand the catalytic mechanism of alcohols conversion chemistry on the transition metal catalysts.

The effect of Ti content on age hardening and mechanical properties of uranium-titanium alloys

The effect of Ti content on age hardening and the resulting mechanical properties are described for γ-quenched U-Ti alloys containing 0.3 to 2.0 wt.%Ti. Age hardening occurs between ∼250 and ∼450°C. Overaging occurs at higher temperatures by cellular decomposition. Age hardening kinetics suggest that different mechanisms occur depending on Ti content and initial microstructure. Strengthening in α′a acicular martensites begins by the formation of Ti clusters which evolve into thin U2Ti disc shaped precipitates and later mature into continuous U2Ti rods beginning at peak hardness. The mechanism of hardening in α′b banded martensite is more elusive, as significant hardening occurs where atomic mobility is lower than that required for precipitate formation, similar to that reported for age hardening in α′′b banded martensite in U-6%Nb. The activation energy for aging varies with Ti content and microstructure. In fully martensitic alloys containing 0.75 to 2.0%Ti it is in the vicinity of ∼44 kcal/mole (184 kJ/mole). But it is lower in alloys containing less than 0.6%Ti where quenched microstructures are less than fully martensitic. Tensile ductility is high prior to aging, decreases with age hardening, is effectively zero at peak hardness, and remains low in overaged conditions. Attractive combinations of strength and ductility are best obtained in alloys containing 0.6 to 1.0%Ti which have been partially aged to fractional hardening levels no greater than ∼0.6. This corresponds to the very early stages of aging, associated with clustering and the earliest stages of U2Ti disc formation. Alloys containing 0.45%Ti or less are not as responsive to age hardening. Alloys containing 1.5 and 2.0%Ti can be aged to higher strengths, but extreme quench rate sensitivity prevents them from being effectively heat treated in realistic section thicknesses.

The effect of doping with pt impurity on ti clusters: a density functional theory study

Transition metal nanoclusters have been greatly investigated in various areas such as catalysis, energy conversion and sensing due to their unique chemical, optical, structural, and electronic properties. Doping monometallic clusters with other metals offer the opportunity to enhance these properties. Extensive work has been done on late transition metal clusters i.e., noble and platinum metals. However, less work has been done on titanium metal clusters. The structural properties of TiN-1Pt (N = 2 – 16) clusters have been investigated using the density functional theory method with the PBEsol exchange-correlation functional. Our results showed that the binding energies for both systems decrease with cluster size N. The Ti12Pt cluster was found to be more enhanced in comparison with pure Ti revealed by the binding energy, relative stability and dissociation energy. Furthermore, binding, relative stability and dissociation energies were found to be enhanced as compared to the energies for Ti monometallic clusters.

Structures, and electronic and spectral properties of single-atom transition metal-doped boron clusters MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni).

A theoretical study of geometrical structures, electronic properties, and spectral properties of single-atom transition metal-doped boron clusters MB24− (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) is performed using the CALYPSO approach for the global minimum search, followed by density functional theory calculations. The global minima obtained for the MB24− (M = Sc, Ti, V, and Cr) clusters correspond to cage structures, and the MB24− (M = Mn, Fe, and Co) clusters have similar distorted four-ring tubes with six boron atoms each. Interestingly, the global minima obtained for the NiB24− cluster tend to a quasi-planar structure. Charge population analyses and valence electron density analyses reveal that almost one electron on the transition-metal atoms transfers to the boron atoms. The electron localization function (ELF) of MB24− (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) indicates that the local delocalization of MB24− (M = Sc, Ti, V, Cr, and Ni) is weaker than that of MB24− (M = Mn, Fe, and Co), and there is no obvious covalent bond between doped metal and B atoms. The spin density and spin population analyses reveal that open-shell MB24− (M = Ti, Cr, Fe, and Ni) has different spin characteristics which are expected to lead to interesting magnetic properties and potential applications in molecular devices. The polarizability of MB24− (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) shows that MB24− (M = Mn, Fe, and Co) has larger first hyperpolarizability, indicating that MB24− (M = Mn, Fe, and Co) has a strong nonlinear optical response. Hence, MB24− (M = Mn, Fe, and Co) might be considered as a promising nonlinear optical boron-based nanomaterial. The calculated spectra indicate that MB24− (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) has different and meaningful characteristic peaks that can be compared with future experimental values and provide a theoretical basis for the identification and confirmation of these single-atom transition metal-doped boron clusters. Our work enriches the database of geometrical structures of doped boron clusters and can provide an insight into new doped boron clusters.

The Microstructure in an Al–Ti Alloy Melt: The Wulff Cluster Model from a Partial Structure Factor

In the present work, the Wulff cluster model—which has been proven to successfully describe pure metals, homogeneous alloys, and eutectic alloys—has been extended to complex binary Al80Ti20 alloys, containing intermetallic compounds. In our model, the most probable structure in metallic melts should have the shape determined by Wulff construction within the crystal structure inside, and the cluster’s size could be measured by pair distribution function. For Al80Ti20 binary alloy, three different types of clusters (Al cluster, Al3Ti cluster, and Ti cluster) were proposed. Their contributions in XRD results are investigated by a comparison with the partial XRD pattern. Ti–Ti and Al–Ti partial structural factors are completely contributed by a pure Ti cluster and an Al3Ti cluster, respectively. Al–Al partial structural factor is contributed not only by a pure Al cluster but is also related to part of the Al3Ti cluster. The simulated XRD curve shows a good agreement with the experimental partial I(θ), including the peak position, width, and relative intensity.