Ti Atoms Research Articles

High-performance quantum anomalous Hall effect in monolayer Ti2Sb2KRb and Ti2Bi2NaK

Quantum anomalous Hall (QAH) insulators are an ideal platform for developing topological electronic devices, but their low observation temperature limits the applications. In this study, based on first-principles calculations, monolayer Ti2Sb2KRb and Ti2Bi2NaK are demonstrated to be QAH insulators with topological gaps 43 and 57 meV, respectively. Their Chern numbers are calculated to be C=−2. The study of electronic structures indicates that the ferromagnetic topological property is induced by the energy band inversion of dxy and dx2−y2 orbitals for Ti atoms near the Dirac cone. Both monolayer Ti2Sb2KRb and Ti2Bi2NaK exhibit a perpendicular magnetic anisotropy, and their Curie temperatures are estimated to be 480 and 478 K, respectively. The ferromagnetic coupling is induced by the small crystal-field splitting energy caused by Sb and Bi atom's large radius. Our study suggests that monolayer Ti2Sb2KRb and Ti2Bi2NaK are promising candidates for room temperature QAH insulators.

Improved performance of epoxy resin coating with the modification of dopamine doped Ti4O7

AbstractIn this paper, a dense and well‐adherent polydopamine‐Ti4O7/epoxy resin (PDA‐Ti4O7/EP) composite coating is successfully prepared. The modified grafting of Ti4O7 by polydopamine (PDA) is achieved through the coordination complexation of unstable catechol groups in PDA with coordination unsaturated Ti atoms in Ti4O7. The potentiodynamic polarization curve and electrochemical impedance spectroscopy test results show that the performance of the composite coating is improved compared with that of the pure epoxy coating, and the composite coating slows down the penetration of electrolytes and aggressive ions and improves the corrosion resistance. The composite coating with 2 wt.% PDA‐Ti4O7 filler shows the best corrosion resistance, and its |Z|0.01 Hz remains above 1011 Ω cm2 after 30 days of immersion in 3.5 wt% NaCl solution. This can be attributed to the good barrier property of PDA‐Ti4O7 filler, which carries NH2 and OH reactive groups, interacting with the resin and matrix to improve the dispersion of the filler and the adhesion of the composite coating. The NH2 group reacts with the epoxy group in the epoxy resin in a ring‐opening reaction, which avoids the agglomeration of the filler and the uniformly dispersed filler fills the pores in the coating due to curing to improve the denseness of the coating and give full play to the barrier property of the filler. At the same time, the hydrogen bonding between the filler and the OH group in the resin and the substrate increases the adhesion of the coating. In addition, the unstable catechol group in PDA chelates with iron ions to further improve the overall corrosion resistance of the coating.Highlights A dense and well‐adherent PDA‐Ti4O7/EP coating is successfully prepared. PDA connect with Ti4O7 through coordination of catechol groups and Ti atom. PDA‐Ti4O7 are chemically bonded to the EP through a ring‐opening reaction. PDA‐Ti4O7 improves the crosslinking density and barrier ability of the coating.

Ferromanganese oxide-functionalized TiO2 for rapid catalytic ozonation of PPCPs through a coordinated oxidation process with adjusted composition and strengthened generation of reactive oxygen species

Ferromanganese oxide (MFOx) was first utilized to functionalize TiO2 and an MFOx@TiO2 catalyst was developed for catalytic ozonation for rapid attack of pharmaceutical and personal care products (PPCPs) with adjusted reactive oxygen species (ROSs) composition and strengthened ROSs generation. Unlike Al2O3, which strongly relied on adsorption and was significantly influenced by MFOx loading, synergistic catalytical effects of MFOx and TiO2 were observed, and optimal MFOx doping of 2 wt% and MFOx@TiO2 dosage of 500 ppm were obtained for catalyzing ozonation. In ibuprofen (IBP) degradation, MFOx@TiO2-catalyzed ozonation (MFOx@TiO2/O3) obtained 2.0-, 4.7- and 6.9-folds the kobs of TiO2/O3, MFOx/O3 and bare ozonation (B/O3). Stronger O3 decomposition was observed by MFOx@TiO2 over bare TiO2 with the participation of redox pairs Fe(II)/Fe(III) and Mn(II)/Mn(III)/Mn(IV) and increased surface oxygen vacancies (SOVs) from 9.8 % to 33.7 % was detected. The results revealed that Fe(II), Mn(II) and Mn(III) with low valance accelerated Ti(III) generation from Ti(VI), obtaining an unprecedented high Ti(III) composition occupying 35.3 % of the total Ti atoms. Ti(III) catalyzed the direct reduction of SOVs-O2 to •O2–, and it accelerated the formation of Ti(VI)-OH and Ti(VI)-O which catalyzed O3 decomposition into •O2–. •O2– was found to primarily initiate IBP degradation with nucleophilic addition and dominated over 66 % IBP removal. The enhanced •O2– generation further strengthened •OH and 1O2 production. MFOx@TiO2/O3 obtained 17 %, 21 % and 30 % higher TOC removal over TiO2/O3, MFOx/O3 and B/O3, respectively. Acute toxicity tests confirmed the effective toxicity control of organics by MFOx@TiO2/O3 process (inhibition rate: 10.9 %). Degradation test of atenolol and sulfamethoxazole confirmed the catalytic effects of MFOx@TiO2. MFOx@TiO2 performed strong resistance to water matrix in application test and showed good stability and reusability. The study proposed an effective catalyst for strengthening the ozonation process on PPCPs degradation and provided an in-depth understanding of the mechanisms and characteristics of the MFOx@TiO2 catalyst and MFOx@TiO2/O3 process.

Ab initio molecular dynamics study on the local structures and solid/liquid interface in liquid Al-Ti and Al-B-Ti alloys

High-purity aluminum, owing to its excellent physical and chemical properties, finds extensive applications across various fields. A comprehensive understanding of the local structure of liquid Al-based alloys and the characteristics of solute atoms at the forefront of the solid-liquid interface is highly advantageous for the purification of aluminum. Ab initio molecular dynamics (AIMD) simulations were employed to study the local structures, element interactions and electronic structures in Al-Ti and Al-B-Ti melts, together with the behaviors of Ti atom and B-Ti atom pair at the solid/liquid interface forefront of Al. In the Al-B-Ti ternary melt, there are stronger interactions between B and Ti atoms than those between Al and B atoms as well as between Al and Ti atoms. The introduction of B atoms leads to the disruption of Al-Ti bonds and the formation of B-Ti bonds, thereby altering the state of Ti atoms in the melt and then influencing their diffusion properties. The dynamic process of B-Ti bond formation in the melt has been elucidated. The bond angle distribution function shows that the geometric configuration around Ti atoms in the Al melt undergoes significant changes with the addition of B atoms. A strong hybridization occurs between the 3d orbital of Ti atom and the 2p orbital of B atom. Moreover, a notable charge accumulation between B and Ti atoms, indicates the strong interaction between them. The addition of Ti atom can promote the migration of the Al solid/liquid interface. The B-Ti bond is very stable at the forefront of the Al solid/liquid interface, and the formation of B-Ti bond significantly drag the migration of the Al solid/liquid interface.

Enhancing strength and ductility of extruded Ti-alloy-reinforced Al-Mg-Si composites: Roles of interface nanostructures and chemical bonding

A comprehensive understanding of interface nanostructures and chemical interactions is required for solving the strength-plasticity trade-off dilemma of Al/Ti composites. Continuously Ti-reinforced Al-matrix composites with superior strength and ductility are fabricated via a novel extrusion technique. The unique strain-hardening mechanism of the Al/Ti composite plates at low strains is attributed to the coupling effects of the strong interface constraint potency, the mechanical incompatibility between the soft Al and hard α-Ti, and a large elastic strain of hard α-Ti. Interlocking structures with atomic interdiffusion are observed at the Al/Ti interface. Mechanical and thermal effects induce lattice distortion and atomic superdiffusion, thus resulting in an interfacial intermixing zone with substantial dislocations and misfit strain. These characteristics produce a strong interface constraint effect during tensile, causing superior strain/dislocation hardening and uniform plasticity. Nanoclusters with cubic structures and dispersed dislocations are detected in the three-dimensional (3D) atomic intermixing zone at the Al/TiAl3 interface, accompanied by the aggregation of Mg. The nanostructures with numerous dislocations in the 3D Ti/TiAl3 transition zone feature lattices with partially tetragonal structures and ordered Ti-Al(Si) clusters. Ab initio calculations indicate that the strong chemical interaction between Si and Ti atoms not only improves the interface bonding strength, but also disturbs the lattices and broadens the transition zone. Moreover, the 3D interface transition zones, accompanied by dispersed dislocations, improve the interface constraint potency and hardening capability of the annealed Al/Ti composite plate. This work sheds light on the capability of the extrusion technique to produce fiber-reinforced Al-matrix composites with superior mechanical properties and provides new strategies for improving the chemical bonding strength and interface constraint effect via the interface invasion of specific elements.

The elastic, electronic, and optical properties of TinO2n-1: Studying of GGA(LDA)+U

Based on the first-principles of density functional theory, the elastic, electronic and optical properties of three titanium suboxides TinO2n-1(n=5，6 and 7) are calculated and analyzed using generalized gradient approximation (GGA+U) and local density approximation (LDA+U) under the pseudopotential of ultra-soft. The results show that all three titanium suboxides are elastically anisotropic, but Ti5O9 has the smallest anisotropy. All the three materials exhibit certain ductility and have certern hardness (∼10 GPa). Electronic structure analysis indicates that Ti5O9, Ti6O11 and Ti7O13 have half-metallic properties, while Ti5O9 also has magnetic property, that is mainly derived from the 3d orbit electrons of Ti atoms. Optical property analysis shows that in the far ultraviolet region (6–12 eV), the reflection coefficient, absorption coefficient and extinction coefficient form resonance.

Role of Cr addition in Ni-based interlayer on strengthening titanium and steel dissimilar bimetallic structures enabled by directed energy deposition with laser beam

For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam (DED-LB), pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work. Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically. The distribution of intermetallic compounds (IMCs) such as β-Ti, Ti2Ni, TiNiFe0.2, Ti2Ni3Si and TiB2 in joints was revealed. The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely. Notably, additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus, leading to fewer IMCs in joints. As a result, both bonding strength and toughness of joints were remarkably improved. The findings emphasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.

Low infrared emissivity and oxidation stability of Ti3C2Tx MXene-based composite with tannic acid

As a novel material with low infrared emissivity, Ti3C2Tx MXene is promising in infrared stealth. However, the problem that MXene is easily oxidized poses a great challenge to its practical applications. In this paper, a tannic acid (TA) enhanced MXene oxidation stability composite film with low infrared emissivity is reported. TA effectively diminishes the pore size within the MXene film and leads to a tight and orderly arrangement of nanosheets, maintaining the low emissivity properties of Ti3C2Tx MXene itself. In addition, TA reacts preferentially with H2O/O2 entering the film to consume the oxidizing source, while also being able to form coordination with Ti atoms for protection against oxidation, resulting in the composite film exhibiting excellent oxidation resistance. Remarkably, there is no formation of TiO2 and the emissivity only rises from 0.16 to 0.18 after 72 h in the humid heat environment. Even after prolonged exposure to 20-day humid heat, it still maintains exceptional infrared emissivity (0.24) and stealth performance (reducing the radiant temperature of the object from 94 °C to 47.4 °C, △T = 46.6 °C). In contrast, the original Ti3C2Tx MXene film has lost its infrared stealth performance after 10-day humid heat (△T = 5.3 °C) with an infrared emissivity of 0.76. This paper provides a new strategy to solve the problem of MXene performance stability in humid and oxidizing environments.

The effect of different transition metal dopants on the magnetic properties of armchair antimonene, phosphorene, and their binary nanoribbons

Binary antimonene-phosphorene, a novel two-dimensional material with a medium band gap, high carrier mobility, and environmental stability, has attracted growing attention due to its wide applications in spintronics. Using density functional theory, we comprehensively investigate and compare the structural and magnetic properties of armchair Sb, P, and binary SbP nanoribbons doped with 3d transition metal atoms (Ti, Cr, Mn, Fe, Co, and Ni) with various concentrations of dopant atoms. We investigated magnetic properties, including magnetic moment, spin polarization, and spin density. It was found that the magnetic properties for single P and Sb nanoribbons do not depend on the substitution position of TM atoms. In contrast, for binary SbP nanoribbons, the substitution of TM atoms in P or Sb positions leads to different behaviors. For example, the magnetization for substitution of Fe and Co atoms in the P position of the binary SbP nanoribbon will be greater than those of the Sb position, but for other impurity atoms, the magnetization of the binary SbP nanoribbon does not strongly depend on the substitution position. The results show that with increasing the number of impurity atoms in the nanoribbon, the magnetic moment increases, except for the nickel atom in the Sb position of the SbP nanoribbon, in which the nanoribbon prefers the ferrimagnetic state. Also, the spin density results show that the magnetism of the doped systems is mainly attributed to the dopant atoms, and the neighboring atoms have a negligible contribution. The findings of antimonene-phosphorene nanoribbons doped with TM atoms may have potential applications in spintronic nanodevices.

The role of Ti in mitigating thermal expansion of silica from molecular dynamics simulations

AbstractMolecular dynamics simulations are performed to investigate the structural response of titania silicate glass to temperature. The coefficient of thermal expansion is computed for two titania silicate glasses with 0 and 10 mol% titania content, the structures of which are presented in terms of radial and angular distributions. Revealed by the different changing rates of intertetrahedra bond angles and bond lengths with respect to the Ti and Si atoms, the glass structures tend to exhibit a nonvectorized expansion process at elevated temperatures, leading to inconsistent expansion rates of the structures in different scales. While the average length of TiO and Si‐O bonds both increases with temperature, the decrease in the coefficient of thermal expansion by the addition of Ti atoms is associated with the different expansion rate of tetrahedra. Arising from the gradual decrease in atomic overlapping, decrease in free volume inside the glass with temperature is also identified.

Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex.

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

First principles study of transition metal (TM = Sc, Ti, V, Cr, Mn) doped penta-BAs5 monolayer for adsorption of CO, NH3, NO, SO2

In this paper, the adsorption capacity of intrinsic penta-BAs5 monolayer on CO, NH3, NO, SO2 and the effect of transition metal doping on gas sensing characteristics are systematically studied by first-principles calculations. Adsorption energy, recovery time, band structure, charge transfer and density of states (DOS) are investigated. The electronic properties and sensing mechanisms under different adsorption systems are expounded. The results showed that the intrinsic penta-BAs5 monolayer had the strongest adsorption capacity for NO and weak sensitivity to CO, NH3 and SO2, which shown strong gas selectivity. Moreover, the recovery time of NO at 380 k was 3.93 s, which was more inclined to be desorption at high temperature. In addition, Sc and Ti doping could selectively improve the adsorption capacity of the intrinsic penta-BAs5 monolayer. The charge transfer of SO2-Sc-BAs5 and CO-Ti-BAs5 were increased by 6.78 and 10.33 times compared with those before doping. The band structure and DOS show that Ti atom and CO have orbital hybridization, which improved the interaction between gases and penta-BAs5. Therefore, intrinsic penta-BAs5, Sc-BAs5 and Ti-BAs5 are suitable for gas sensing and toxic gas monitoring, and have broad application prospects.

Cross‐Scale Synergistic Manipulation of Dielectric Genes in Polymetallic Sulfides from Micropolarization to Macroconductance Toward Wide‐Band Microwave Absorption

AbstractRecently, the design and development of efficient microwave absorbents by facile engineering approaches have attracted much attention. Particularly, some unique structures caused by cross‐scale design are promising in enhancing the absorbing capability toward microwave irradiation. Herein, the cross‐scale design strategy is implemented to enhance the electromagnetic wave absorption performance of polymetallic sulfides (PMS). In PMS, the dipole polarization unit is optimized, and the distribution of electronic states is improved by doping Ti atoms; Meanwhile, the MS/M3S4 homogeneous hetero‐phases interfaces is constructed in PMS using a phase separation strategy; and the conductivity of PMS is modulated by the addition of acetylene black (ACET). The cross‐scale synergy of microwave absorption leads to a significant enhancement of the microwave absorption (MA) performance of PMS/ACET composites. The optimal reflection loss value of Ti‐LES with 10% ACET addition reaches −55.49 dB and the effective absorption bandwidth reaches 6.73 GHz. The 17.5% ACET‐conditioned Ti‐HES achieves a reflection loss of −37.2 dB at a low frequency of 4.8 GHz. This study not only provides a novel strategy for the development of new broadband MA materials but also validates a new idea for the multi‐scale synergistic optimization of MA materials.

Effects of Ti on the solidification and crystallization behavior of nanocomposite permanent material under different cooling rates

Effects of Ti on the crystallization behavior, phase composition, microstructure and magnetic properties of Nd2Fe14B/α-Fe dual-phase nanocomposite permanent magnet materials in different states were studied, respectively. The results show that Ti could affect the solidification and crystallization behavior of dual-phase nanocomposite materials by regulating the cooling rate during the rapid solidification process. When the cooling rate is slow, part of Ti atoms enters the soft magnetic phase α-Fe, and part forms the TiFe2 phase around the hard magnetic phase. Exchange coupling is enhanced. The maximum energy product and the remanence of the alloy are 10.54 MGOe and 8.34 kGs, respectively. When the cooling rate faster, Ti can stabilize another ferromagnetic ThMn12-type phase with a low coercivity and maximum energy product, which should be avoided. When the cooling rate is fast enough to form amorphous, Ti and Fe preferentially combine to form the TiFe2 phase during crystallization, which selectively inhibits the growth of the hard magnetic phase and the precipitation of the soft magnetic phase, resulting in a significant enhancement of coercivity to 12.82 kOe. By regulating the mechanism of Ti in the solidification and crystallization process, nanocomposite permanent magnet materials with varying magnetic characteristics can be obtained, offering a flexible approach to tailoring their performance according to specific application requirements.

Study on hydrogen desorption of ZrCoH3 promoted by doping Hf and Ti with DFT

This work aims to provide new insights into the hydrogen evolution of ZrCoH3. The transition metal elements Hf and Ti are designed to be added to ZrCoH3 by occupying Co atoms, Zr atoms, and interstitial sites. The effects of Hf and Ti atoms on the hydrogen evolution of ZrCoH3 are investigated through a first-principles study. The results show that the doping of Hf and Ti atoms can effectively improve the hydrogen desorption ability of ZrCoH3, which is related to the weak Co–H covalent interaction in the doping system, metallic properties, and the formation of Hf/Ti–H bonds. Hf atom doping has the best catalytic effect on the dehydrogenation of ZrCoH3, and the Hf atom can easily enter the ZrCoH3 body to form the Zr16Co16HfH48 compound. Although the Zr15Co16HfH48 compound has a low hydrogen dissociation energy and exhibits good hydrogen desorption performance, it requires a high energy cost when Hf occupies the Zr site in practical applications. When doped with the same element, the occupancy energy and hydrogen dissociation energy are inversely related. The hydrogen dissociation energy of ZrCoH3 is negatively correlated with the electronegativity of the dopant atom, namely, the lower the electronegativity of the dopant atom, the smaller the hydrogen dissociation energy of the system. This study confirms by simulation calculations that the use of low electronegativity metals to recombine with ZrCoH3 is an effective way to achieve ZrCoH3 destabilization.

On double-layer and reverse discharge creation during long positive voltage pulses in a bipolar HiPIMS discharge

Time-resolved Langmuir probe diagnostics at the discharge centerline and at three distances from the target ( 35mm , 60mm , and 100mm ) was carried out during long positive voltage pulses (a duration of 500μs and a preset positive voltage of 100V ) in bipolar high-power impulse magnetron sputtering of a Ti target (a diameter of 100mm ) using an unbalanced magnetron. Fast-camera spectroscopy imaging recorded light emission from Ar and Ti atoms and singly charged ions during positive voltage pulses. It was found that during the long positive voltage pulse, the floating and the plasma potentials suddenly decrease, which is accompanied by the presence of anode light located on the discharge centerline between the target center and the magnetic null of the magnetron’s magnetic field. These light patterns are related to the ignition of a reverse discharge, which leads to the subsequent rise in the plasma and the floating potentials. The reversed discharge is burning up to the end of the positive voltage pulse, but the plasma and floating potentials have lower values than the values from the initial part of the positive voltage pulse. Secondary electron emission induced by the impinging Ar+ ions to the grounded surfaces in the vicinity of the discharge plasma together with the mirror configuration of the magnetron magnetic field are identified as the probable causes of the charge double-layer structure formation in front of the target and the ignition of the reverse discharge.

Thermal self-crosslink after etching for regulated preparation of Ti3C2 type MXene membrane and its preliminary gas separation

We present an innovative methodology for the synthesis of MXene membranes through a dual-stage process involving etching and subsequent thermal self-crosslinking. A molar ratio of 1 (Al3+):9 (F−) using HCl/LiF was employed to convert raw Ti3AlC2 (MAX phase) into MXene within 48 h at 40 °C. This procedure predominantly yielded monolayers distinguished by diameters exceeding 500 nm, elevated crystallinity and a high overall yield. Advanced characterization techniques, including FESEM, TEM, HRTEM, AFM, XPS, and FTIR, were utilized. Instrumental analysis confirmed the formation of MXene exhibiting a single-flake morphology with diameters exceeding 500 nm. These monolayers were intact and continuous, with smooth peripheries and a uniform thickness of 2.1 nm. The surfaces were predominantly composed of carbon (C), oxygen (O), and titanium (Ti) atoms, interconnected by chemical bonds such as C–Ti–O, C–Ti–OH, C–C, C–O, and Ti–O. In the subsequent phase, vacuum filtration facilitated the assembly of a self-supporting MXene membrane. Thermal treatment at 170 °C for 30 h resulted in the reinforcement of C–Ti–O bonds within the nanosheets, increasing their prevalence to 43.14 % and 19.47 %, respectively. This thermal regulation reduced the interlayer d-spacing from 4.33 to 3.54 Å, which significantly improved the gas separation efficiency beyond the Knudsen diffusion limit, as demonstrated by the αH2/CF4 value exceeding 23.0.

Oxygen Defects Containing TiN Films for the Hydrogen Evolution Reaction: A Robust Thin-Film Electrocatalyst with Outstanding Performance.

Density functional theory (DFT) calculations of hydrogen adsorption on titanium nitride had previously shown that hydrogen may adsorb on both titanium and nitrogen sites with a moderate adsorption energy. Further, the diffusion barrier was also found to be low. These findings may qualify TiN, a versatile multifunctional material with electronic conductivity, as an electrode material for the hydrogen evolution reaction (HER). This was the main impetus of this study, which aims to experimentally and theoretically investigate the electrocatalytic properties of TiN layers that were processed on a Ti substrate using reactive ion sputtering. The properties are discussed, focusing on the role of oxygen defects introduced during the sputtering process on the HER. Based on DFT calculations, it is shown that these oxygen defects alter the electronic environment of the Ti atoms, which entails a low hydrogen adsorption energy in the range of -0.1 eV; this leads to HER performances that match those of Pt-NPs in acidic media. When a few nanometer-thick layers of Pd-NPs are sputtered on top of the TiN layer, the performance is drastically reduced. This is interpreted in terms of oxygen defects being scavenged by the Pd-NPs near the surface, which is thought to reduce the hydrogen adsorption sites.

Effects of silanol defects and Ti site location within Ti-MWW on alkene epoxidation with aqueous hydrogen peroxide

Catalytic reaction kinetics and thermodynamics within zeolites respond to the physical properties of the framework through noncovalent interactions with solvents. Here, we demonstrate that rates of alkene epoxidations depend sensitively upon the topological location of Ti atoms and the density of silanol ((SiOH)x) defects in hydrothermally synthesized Ti-MWW catalysts. Turnover rates for 1-hexene epoxidation do not change systematically with (SiOH)x density unlike previous reports for other zeolite framework. Site-averaged turnover rates on Ti-MWW catalysts with the greatest portion of Ti sites located in sinusoidal channels exceed those on materials with most Ti in supercages by a factor of 40-fold. These differences appear to reflect free energy contributions and compensation between activation enthalpies and entropies, induced by the structural organization of solvent molecules that responds differently to the topological locations of active sites and the presence of defects.

Unveiling the pressure-driven metal–semiconductor–metal transition in the doped TiS2

Abstract Conventional theories expect that materials under pressure exhibit expanded valence and conduction bands, leading to increased electrical conductivity. Here, we report the electrical properties of the doped 1T-TiS2 under high pressure by electrical resistance investigations, synchrotron x-ray diffraction, Raman scattering and theoretical calculations. Up to 70 GPa, an unusual metal–semiconductor–metal transition occurs. Our first-principles calculations suggest that the observed anti-Wilson transition from metal to semiconductor at 17 GPa is due to the electron localization induced by the intercalated Ti atoms. This electron localization is attributed to the strengthened coupling between the doped Ti atoms and S atoms, and the Anderson localization arising from the disordered intercalation. At pressures exceeding 30.5 GPa, the doped TiS2 undergoes a re-metallization transition initiated by a crystal structure phase transition. We assign the most probable space group as P212121. Our findings suggest that materials probably will eventually undergo the Wilson transition when subjected to sufficient pressure.