Titanium Oxide Clusters Research Articles

Seed‐Mediated Growth of a High‐Nuclearity Titanium‐Oxide Cluster with Enhanced Photocatalytic Activities in CO2/Epoxide Cycloaddition

AbstractA high‐nuclearity titanium‐oxide cluster (TOC), Ti31O52(OiPr)4Bz24 (denoted as Ti31; Bz=PhCO2), was synthesized via a seed‐mediated synthesis method during the solvothermal reaction of the super‐Keggin cluster Ti17O24(OiPr)20 (denoted as Ti17) and Ti(OiPr)4. Single‐crystal X‐ray diffraction analyses indicate that Ti17 acts as a template for the addition of two Ti7O6 rings to form Ti31. The optical absorption edge of Ti31 slightly shifts to 446 nm, relative to the 419 nm absorption edge of Ti17. Ti31 has much better visible‐light response and charge‐separation properties than Ti17, as confirmed by electrochemical impedance, photoluminescence spectroscopy, and transient photocurrent response. Ti31 also shows much better activity and stability than Ti17 in the solar synthesis of cyclocarbonate through CO2/epoxide cycloaddition. This study not only provides a high‐nuclearity member of the TOC family, but also suggests a potential method to enhance the photocatalytic activity of the known TOCs for more efficient solar energy harvesting.

Sub-nm titanium dioxide clusters: efficient photocatalysts for clean SOx conversion under visible light irradiation

Sub-nm titanium dioxide clusters: efficient photocatalysts for clean SOx conversion under visible light irradiation

Case Series: Hepatic and Splenic Titanium Dioxide Deposition in Association With Intravenous Drug Use.

Titanium dioxide is a versatile compound that is found in a variety of consumer products, medical hardware, and pharmaceuticals. Although oral and topical ingestion of this compound is common, intravenous introduction is much less common. We present three cases where significant titanium dioxide deposits were identified in liver and splenic tissue of three decedents, all of whom died of illicit drug overdose in the same geographic area and had fentanyl and its metabolites in blood on postmortem toxicologic testing. At autopsy, liver sections had a granular texture with fine white stippling grossly, and histologic examination of hepatic and splenic tissues showed scattered patches of black granular material with pink birefringence. Energy-dispersive x-ray spectroscopy performed on these tissues revealed the presences of clusters of titanium dioxide. Immunohistochemical staining of both the liver and spleen with CD68 confirmed the titanium dioxide clusters were within macrophages. Intravenous titanium dioxide nanoparticle elimination studies in rats suggest a time sensitive period for this elimination, with a transient period of pigment deposition between 1-58 days following injection. If a time-dependent link between titanium dioxide pigment deposition within tissues and intravenous drug use can be shown, this could be a valuable tool for Pathologists.

Enhancing the photocatalytic performance of a rutile unit featuring a titanium-oxide cluster by Pb2+ doping.

Titanium-oxide clusters (TOCs) are well-defined molecular models for TiO2 materials and provide the opportunity to study the structure-activity relationships of TiO2. Here, we report a new Pb-doped TOC, Ti12Pb2, which resembles a two-layer decker of the {TiTi6} structural units of rutile TiO2 with two Ti4+ ions replaced by two Pb2+ ions. Its electronic structure, photoresponse, and photocatalytic performances were investigated and compared with those of the Ti14 cluster, which is isostructural to Ti12Pb2. Our results indicate that Pb2+ does not affect the electronic structure, but it greatly enhances the photocatalytic activity by improving the charge-separation and interfacial charge-transfer properties of the TOC. The successful synthesis of Ti12Pb2 highlights the roles of closed-shell heterometal ions in the construction of new TOCs. Our mechanism may be an inspiration for understanding the structure-activity relationships of closed-shell heterometal-doped TiO2.

Ligation of Titanium-oxide and {Mo2} Units for Solar CO2 Storage.

Two Mo-Ti-mixed oxide clusters, Ti6Mo4 and Ti4Mo4, which contain the {Mo2V} unit commonly observed in many polyoxomolybdates, were successfully synthesized. The introduction of a {Mo2V} dopant into a titanium-oxide cluster (TOC) results in a red shift of the absorption edge, hence leading to a substantial enhancement of visible-light absorption. The band gap electron transition mainly involves the ligand-to-metal charge transfer (LMCT, benzoate-to-Mo) and MoV d-d transition. Both clusters show favorable visible-light responsiveness and charge-separation efficiency. Both serve as heterogeneous photocatalysts and exhibit excellent catalytic activity in CO2/epoxide cycloadditions under very mild conditions. The mechanism study suggests that the catalytically active sites are mainly MoV, and the photogenerated electrons and holes are both involved. Ti6Mo4 exhibits better photocatalytic activity than Ti4Mo4, demonstrating the crucial role of the titanium-oxide core, which corresponds to improved light absorption and charge-separation efficiency. Our findings highlight the potential of the {Mo2V} unit in constructing Mo-Ti-mixed oxide clusters with interesting topologies and excellent solar-light-harvesting activity.

Divalent Heterometal Doped Titanium-Oxide Cluster Polymers: Structures, Photoresponse, and Photocatalysis.

Five cluster polymers based on heterometal-doped titanium-oxide cluster (TOC) monomers are reported. The monomers feature Ti10-oxide cluster cores and are connected to the divalent closed-shell heterometal anchors by salicylate ligands. The Sr2+, Ba2+, and Pb2+ dopants cause the monomers to bind head-to-head and generate linear chains, while the Ca2+ and Cd2+ lead to head-to-tail connections and zigzag chains. The cluster polymers are responsive to visible-light up to 565 nm and photo-catalytically active in both H2 evolution and CO2/epoxide cycloaddition reactions. The photo-absorption, photo-charge separation, and photocatalytic properties of the cluster polymers are dependent on the heterometal dopants in order Cd > Pb > Ba > Sr > Ca. Heterometals serve as the catalytic sites in the cluster polymers, which depending on the contribution of the pCB bottom, facilitate photo-charge separation and interfacial charge transfer, further enhancing catalytic activity. The tunable compositions and topologies of the cluster polymers shown herein may inspire the design and synthesis of more multidimensional functional metal-oxide cluster materials for a variety of applications in the future.

Synthesis, Structure and Light‐Driven H2 Production of a {Ti21} Titanium‐Oxo Cluster Featuring Pentagonal {Ti(Ti5)} Motifs

AbstractPentagonal {Ti(Ti5)} motifs play a crucial role during the assembly of novel titanium‐oxide clusters (TOCs), whose development is still in its infancy. In this work, an unprecedented TOC [(CH3)2NH2]2[Ti21O29(OiPr)12(DMF)6(SO4)8] ({Ti21}) based on {Ti(Ti5)} motifs had been obtained under hydrothermal conditions. It possesses ‘fused’ dimeric {Ti11} as well as trimeric {Ti12} subunits featuring unexpected bonding modes based on pentagonal {Ti(Ti5)} motifs. Furthermore, {Ti21} exhibits good water and solvent tolerance. As an atomically precise TOCs‐based semiconductor photocatalyst, {Ti21} exhibits appreciable photocatalytic hydrogen evolution activity with an optimal hydrogen generation rate of 191.94 μmol/g/h under UV/Vis light. This work provides significant advances and favorable models for the further synthesis of TOCs with unique structure and functionality.

Lead-Decorated Titanium Oxide Compound with a High Performance in Catalytic CO2 Insertion to Epoxides.

The CO2 cycloaddition to epoxides is an efficient method for CO2 capture and storage, important not only for reducing greenhouse gas emission but also for producing cyclic carbonates, which are valuable industrial materials. In this study, we report a novel high-nuclearity titanium oxide cluster (TOC) inlayed with main-group element Pb2+, H2Ti16Pb9O24(SA)18(DMF)10(OH2)2 (denoted as 1; SA = salicylate; DMF = N,N-dimethylformamide), which has the property of visible-light absorption and has shown high catalytic activities for cycloadditions of CO2 under visible-light irradiation. The cluster was synthesized in a high yield in a facial solvothermal process. Its structure and electronic structure were characterized by single-crystal X-ray diffraction, density functional theory calculations, and complementary techniques. The cycloaddition reactions were performed under solvent-free conditions. While the catalytic activity due to the Lewis acidity was moderate, visible-light irradiation further folded the reaction rates. The turnover number reached 3400 with a turnover frequency of 120 h-1. Mechanism studies indicated a synergistic effect of the Lewis acidity and photogenerated charge carriers. The performance of 1 in reversible I2 uptake was also investigated. This study demonstrates the high potential of heterometal-decorated TOCs in the cost-effective and efficient CO2 cycloaddition reaction under mild conditions.

Cr-Ti Mixed Oxide Molecular Cages: Synthesis, Structure, Photoresponse, and Photocatalytic Properties.

The solvothermal reaction of titanium isopropoxide and chromate in the presence of benzoate produced two novel host-guest clusters encapsulating Cs+ or H3O+, (H3O)@Ti7Cr14 and Cs@Ti7Cr14. The most remarkable feature is that the Ti7O7 ring is concentrically embraced by a Cr14O14 ring to form a rigid Ti7Cr14 host. ESI-MS and 133Cs NMR revealed that the overall framework structures are preserved, whereas the benzoate ligands on the two clusters may be labile in solutions. Both (H3O)@Ti7Cr14 and Cs@Ti7Cr14 exhibit good UV-vis light-responsive properties and photocatalytic activities, with absorption edges extending up to 780 nm. Cs@Ti7Cr14 is an effective visible-light-responsive photocatalyst in both the heterogeneous methylene dye degradation and homogeneous CO2 cycloaddition reaction under mild conditions like room temperature and 1 bar of CO2. According to the mechanism studies, Cs+, as a rigid guest, can significantly improve the photogenerated charge separation efficiency of the Ti7Cr14 host, thereby improving its interface charge separation properties, photocurrent, and photocatalytic activities. Our findings not only provide new members of heterometallic titanium oxide clusters to enrich the metal oxide cluster family but also open up new possibilities for their photoresponses, which may play an important role in solar energy harvesting for sustainable chemistry.

In-situ formation of Au nanoparticles with surface plasmon resonance confined in the framework of Cu ions doped NH2-MIL-125(Ti) to enhance photocatalytic hydrogen production and NO removal

A novel bifunctional photocatalyst Au@NML-(Cu/Ti) was fabricated to improve the photocatalytic performance of hydrogen production and NO removal, in which the Cu ion was first doped into the titanium oxide clusters of NH2-MIL-125(Ti) (NML) via a convenient method, and uniformly dispersed gold nanoparticles with surface plasmon resonance effect in-situ generated under the constraint of NML-(Cu/Ti) framework. The introduction of copper ions reduced the band gap of NML and accelerated the charge separation rate. Moreover, the NML-(Cu/Ti) framework could prevent the Au nanoparticles agglomeration as far as possible via confinement effect to obtain highly dispersed gold nanoparticles in very small size, which can effectively improve the atom utilization efficiency for enhancing photocatalytic performance. The photocatalytic hydrogen production of Au@NML-(Cu/Ti) was 5193.4 μ mol·g−1, which was 11.8 times that of the original NML. Meanwhile, the NO removal rate of Au@NML-(Cu/Ti) was about 25.6% higher than that of the pristine NML. Moreover, the photocatalytic NO oxidation process was also monitored by in-situ DRIFTS, which indicates Au@NML-(Cu/Ti) could realize the effective oxidation of NO. These results showed that the synergistic combination of central metal cluster modification of MOFs with surface plasma resonance provided a feasible strategy for improving photocatalytic hydrogen production and NO removal.

Copper(II)-Doped Two-Dimensional Titanium-Based Metal-Organic Frameworks toward Light-Driven CO2 Reduction to Value-Added Products.

Recently, metal-organic framework (MOF)-based photocatalysts for an efficient CO2 reduction reaction have drawn wide attention in multidisciplinary fields and sustainable chemistry. In this work, a series of Cu2+-doped two-dimensional Ti-based MOFs were fabricated by a facile in situ solvothermal method. Cu2+ ions were doped in equal proportions and uniformly dispersed in the crystal structure of the MOF matrix. Interestingly, the doping content of Cu2+ ions and the photocatalytic performance displayed an obvious volcanic relationship, the medium-concentration Cu2+-doped sample (T1-2Cu) held the greatest activity with 100% carbonaceous product (CH4 and CO) formation, and the CH4 production rate was 3.7 μmol g-1 h-1 with 93% electron selectivity. The band structure, local electronic structure, carrier separation kinetics, and CO2 adsorption studies demonstrated that the excellent photocatalytic activity of T1-2Cu benefited from the appropriate amount of Cu2+ ion doping: (1) a doping amount of 2 atom % optimized the conduction band position of the MOF substrate and endowed T1-2Cu with strong reduction potential in thermodynamics, (2) doping Cu2+ ions tuned the local electronic environment around titanium oxide clusters and optimized the generation, separation, and migration processes of photoinduced carriers, and (3) the introduction of Cu2+ ions also provided more accessible active sites and more probabilities for the adsorption and activation of CO2 reactants.

Recognition of Water-Induced Double-Edged Sword Effects in Photocatalytic Selective Oxidation of Toluene on Titanium Dioxide Clusters with Density Functional Theory Calculations.

Recently, water promotion effects in the selective oxidation of benzyl alcohol to benzaldehyde have been experimentally recognized and identified. However, the effects of water on the photocatalytic selective oxidation of toluene into benzaldehyde remain elusive. In this work, the Ti3O9H6 clusters in different solvents (water and toluene solvent) are used to study the water-induced effects in photocatalytic oxidation reactions in kinetics and thermodynamics using density functional theory (DFT) calculations. In addition, the influences of the OH groups on catalysts (Ti-OH bonds) from photocatalytic water splitting are also considered. The results clearly demonstrate the water-induced double-edged sword effects in the photocatalytic selective oxidation of toluene. We expect that our work can not only shed light on the mechanisms of photocatalytic selective oxidation of toluene into benzaldehyde and other activation reactions of sp3 C-H bonds but also design and modulate highly efficient photocatalysts.

Integrating CdS and Titanium Oxide Clusters with Molecular Redox Catalysts into Metal‐Organic Frameworks Promoting Photocatalytic Efficient H2 Evolution

AbstractA new quaternary crystalline catalyst was obtained by a mixed hydrothermal method of integrating inorganic semiconductors, titanium oxide cluster (TOC) and molecular redox centers orderly into metal organic framework (MOF) materials. It shows a hydrogen production rate 3711.53 μmol g−1 h−1 under visible light irradiation, exceeds most of the same type of catalyst reported in recent years, and a favorable stability with. The excellent performance of the CdS/TOC/UiO‐67‐bpy/Co composites due to efficient promotion of photo‐induced carrier separation and migration, and offering abundant active sites for generating hydrogen. This work will help to guide the preparation of new efficient and stable photocatalysts and promote the effective conversion of solar energy to chemical energy.

Oxygen Deficiencies in Titanium Oxide Clusters as Models for Bulk Defects.

TD-DFT calculations were performed on neutral TinO2n, TinO2n-1, and TinO2n-2 clusters, where n ≤ 7. Calculations show the TinO2n clusters are closed shell systems containing empty d orbitals and that the partially filled d orbitals of the suboxide clusters have a profound effect on their structural, electronic, and topological properties. The low energy photoexcitations of TinO2n clusters are all O-2p to Ti-3d transitions, while the open-shell suboxide clusters are all characterized by d-d transitions that occur at a much smaller optical gap. Upon low energy photoabsorption, the localization of the hole is accompanied by a local bond elongation, i.e., polaron formation, whereas d-electrons are generally delocalized around the cluster. The properties of the clusters, including the oxygen binding energies and structures, were calculated to account for the variation in relative populations found in experimental cluster distributions. Several TinO2n-2 clusters contain higher symmetry which is reflected in their relative stability. In particular, the tetrahedral symmetry of Ti4O6 inhibits charge carrier localization and therefore exhibits higher stability.

New picolinate-functionalized titanium-oxide clusters: syntheses, structures and photocatalytic H2 evolution.

Two nanosized titanium-oxide clusters (TOCs), Ti12(μ2-O)14(μ3-O)4PA16 (1; PA = 2-picolinate) and Ti12(μ2-O)18PA18 (2) were synthesized by using 2-picolinic acid and Ti(OiPr)4 in one-pot reactions. Their structures were determined using single-crystal X-ray diffractometry. Although both have the same core composition of Ti12O18, 1 exhibited superior H2 evolution activity of up to 180 μmol h-1 g-1, which is nearly eight times faster than 2. Mechanism studies revealed that 1 could induce the assembly of 2.3 nm PtNPs into 10-30 nm supra-nanoparticle structures, which contributed to the increased H2 evolution rate.

S-scheme enhanced photocatalysis on titanium oxide clusters functionalized with soluble perylene diimides

We demonstrate that S-scheme photocatalysis of a hybrid system can promote the performance of photo-Fenton reaction under sunlight. Highly efficient charge-carrier separation can be achieved owing to a dispersion of TOC-PDI-POSS on the g-C3N4 surface.

Syntheses, structures and ligand binding modes of titanium-oxide complexes of 2-picolinate.

Six titanium-oxide clusters (TOCs) comprised of 6-19 Ti atoms all of which are of nanometer size were synthesized with the functionalization of 2-picolinate (PA). Their structures were determined by single-crystal X-ray diffraction and a few complementary spectroscopic techniques. The binding modes of PA on the surface of the TOCs were analyzed and found to be limited to only one binding mode, that is, PA acts as a bidentate ligand through both pyridyl-N and the carboxylate-O. UV-vis diffuse reflection spectra and electron paramagnetic resonance spectra indicate the ligand-to-metal charge transfer (LMCT) through the N-Ti bond. However, the LMCT band in the visible light region (400-600 nm) is very weak. Hence, picolinates do not bring about intense visible light absorption to TOCs. The binding mode of PA on the TOC surfaces and the LMCT revealed herein may be inspiring for studies on classical picolinate/TiO2-based dye-sensitized solar cells.

A Mesoporous Lead-Doped Titanium Oxide Compound with High Performance and Recyclability in I2 Uptake and Photocatalysis.

A three-dimensional (3D) mesoporous material with an atomically precise structure, Ti16Pb5O16(C6H5CO2)2(OCH3)40 (Ti16Pb5), comprised of a novel high-nuclearity Pb-doped titanium oxide cluster (TOC), was synthesized. Ti16Pb5 exhibited a surface area of 45 m2 g-1 and a pore diameter of 3.5 nm. It exhibited an uptake capacity of I2 of ≤2.2 g g-1 in vapor, and the performance was maintained after seven uptake-release cycles. Ti16Pb5 also showed a high adsorption ratio and capacity (93% and 3.1 g g-1) in hexane. The characterization data, including Fourier transform infrared, Raman, and powder X-ray diffraction, suggested the lattice structure of Ti16Pb5 was rigid and I2 was accommodated in the pores of Ti16Pb5. To the best of our knowledge, this is the first example of using a TOC in I2 adsorption. In addition, Ti16Pb5 showed excellent activity and recyclability in visible-light degradation of dye pollutants and photocurrent generation. Our structural analysis suggested the alkoxide ligands within the channels of Ti16Pb5 build up a confined polar environment and thereby facilitate I2 accommodation, and meanwhile, the improved performances and stabilities of Ti16Pb5 are correlated with its cluster-based, 3D hierarchical structure.

Effect of oxidation on excited state dynamics of neutral TinO2n-x (n < 10, x < 4) clusters.

Excited state lifetimes of neutral titanium oxide clusters (TinO2n-x, n < 10, x < 4) were measured using a sequence of 400nm pump and 800nm probe femtosecond laser pulses. Despite large differences in electronic properties between the closed shell stoichiometric TinO2n clusters and the suboxide TinO2n-x (x = 1-3) clusters, the transient responses for all clusters contain a fast response of 35fs followed by a sub-picosecond (ps) excited state lifetime. In this non-scalable size regime, subtle changes in the sub-ps lifetimes are attributed to variations in the coordination of Ti atoms and localization of charge carriers following UV photoexcitation. In general, clusters exhibit longer lifetimes with increased size and also with the addition of O atoms. This suggests that the removal of O atoms develops stronger Ti-Ti interactions as the system transitions from a semiconducting character to a fast metallic electronic relaxation mechanism.

Assembly of Interlocked Superstructures with a Titanium Oxide Molecular Ring in Water.

[2]Catenane, [2]rotaxane, and [2]pseudorotaxane based on a cyclic titanium oxide cluster, [Ti8O8(SO4)16]16- (Ti8), and cyclic/linear alkylammonium cations are reported. Their syntheses, structures, spectroscopy, and stability in water were studied. These molecules were synthesized from and remained intact upon redissolution in acidic water. Hence, the cluster Ti8 is a promising metal oxide ring that can be used as an inorganic analogue of crown ether to assemble inorganic-organic hybrid mechanical interlocked supramolecular assemblies in water.