Titanium Species Research Articles

Synthesis of titania modified silica-pillared clay (SPC) with highly ordered interlayered mesoporous structure for removing toxic metal ion Cr(VI) from aqueous state

Titanium-functionalized silica-pillared clays synthesized through post synthetic route was utilized as adsorbers for the removal of Cr(VI) ions from aqueous solutions under different temperatures and initial concentrations. The starting mesostructured silica-pillared clay is assembled by intragallery ammonia-catalyzed hydrolysis of tetraethoxysilane using cationic surfactant as gallery template, and subsequently, the formed interlayered pore walls were decorated with nano-sized TiO2 particle through organic titanium functionalization process. The kind of structural transformation has been confirmed by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, Fourier transform infrared (FT-IR) analysis, UV–vis diffuse reflectance spectroscopy (DRS), elemental analysis (XRF), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Such results indicate that most of the grafted titanium species was combined with Si–OH on the surface of gallery pores. By changing the concentration of organic titanium source during synthesis, the porous structure system is effected. Under suitable conditions, these materials exhibit high adsorption capacity and efficiency. Qualitative estimates of the thermodynamic parameters showed that the overall adsorption process is spontaneous (ΔG°<0) and endothermic (ΔH°>0). The adsorption isotherms of Cr(VI) on titanium-functionalized silica-pillared clay were best fitted by Redlich–Peterson models. Detail results of thermodynamics and kinetics are also presented.

Waterless TiO2 atomic layer deposition using titanium tetrachloride and titanium tetraisopropoxide

The surface chemistry for TiO2 atomic layer deposition (ALD) typically utilizes water or other oxidants that can oxidize underlying substrates such as magnetic disks or semiconductors. To avoid this oxidation, waterless or oxidant-free surface chemistry can be used that involves titanium halides and titanium alkoxides. In this study, waterless TiO2 ALD was accomplished using titanium tetrachloride (TiCl4) and titanium tetraisopropoxide (TTIP). In situ transmission Fourier transform infrared (FTIR) studies were employed to study the surface species and the reactions during waterless TiO2 ALD. At low temperatures between 125 and 225 °C, the FTIR absorbance spectra revealed that the isopropoxide species remained on the surface after TTIP exposures. The TiCl4 exposures then removed the isopropoxide species and deposited additional titanium species. At high temperatures between 250 and 300 °C, the isopropoxide species were converted to hydroxyl species by β-hydride elimination. The observation of propene gaseous reaction product by quadrupole mass spectrometry (QMS) confirmed the β-hydride elimination reaction pathway. The TiCl4 exposures then easily reacted with the hydroxyl species. QMS studies also observed the 2-chloropropane and HCl gaseous reaction products and monitored the self-limiting nature of the TTIP reaction. Additional studies examined the waterless TiO2 ALD growth at low and high temperature. Quartz crystal microbalance measurements observed growth rates of ∼3 ng/cm2 at a low temperature of 150 °C. Much higher growth rates of ∼15 ng/cm2 were measured at a higher temperature of 250 °C under similar reaction conditions. X-ray reflectivity analysis measured a growth rate of 0.55 ± 0.05 Å/cycle at 250 °C. X-ray photoelectron depth-profile studies showed that the TiO2 films contained low Cl concentrations &amp;lt;1 at. %. This waterless TiO2 ALD process using TiCl4 and TTIP should be valuable to prevent substrate oxidation during TiO2 ALD on oxygen-sensitive substrates.

Preparation of magnetic core/shell structured γ-Fe2O3@Ti-tmSiO2 and its application for the adsorption and degradation of dyes

A core/shell structured γ-Fe2O3@Ti-tmSiO2 nanocomposite with enhanced activity for the degradation of dyes that is capable of fast magnetic separation has been successfully prepared by a sol–gel process followed with calcination. The obtained core/shell structure is composed of a superparamagnetic core with a strong response to external fields, and an outer layer of porous titanium silicate with a tunable porous sizes. The convenient control over the pore size and the thickness of porous silica containing titanium species may make it possible to adsorb and catalyze molecules with different sizes. The presence of porous SiO2 helps to enhance the chemical and thermal stability of γ-Fe2O3 core. It is demonstrated that the core γ-Fe2O3 as a Fenton-like catalyst exhibits good performance, while the Ti4+ existing in the porous shell also gives obvious activity in the degradation of dyes. The composite γ-Fe2O3@Ti-tmSiO2 possesses enhanced activity for the treatment of pollutants in water.

Titanium species in deactivated HTS-1 zeolite from industrial cyclohexanone ammoxidation process

The types of titanium species and contents in commercialized hollow titanium silicalite (HTS-1) zeolite are essentially related to their ammoxidation performance. XRD and combined TEM methods were used in this study to identify the titanium species in the deactivated HTS-1 zeolite discharged from cyclohexanone ammoxidation unit. Core–shell structure of crystalline–amorphous TiO2 was observed for the first time in the deactivated HTS-1 zeolite. The results of their catalytic activities in phenol hydroxylation are in line with the analysis. This study provided valuable information to understand the deactivation mechanism of HTS-1 zeolite in cyclohexanone ammoxidation.

Narrowing the mesopore size distribution in hierarchical TS-1 zeolite by surfactant-assisted reorganization

Hierarchical TS-1 zeolites exhibiting a uniform mesoporosity were obtained by means of the sequential combination of both bottom-up and top-down synthesis approaches. First, the parent hierarchical TS-1 zeolites were synthesized following the silanization of protozeolitic units procedure, whereby an additional porosity is formed due to the inhibitor crystal growth effect caused by a silanization agent. After that, the materials were subjected to a reorganization hydrothermal alkali treatment in presence of cationic surfactants. Here, the zeolite lattice is locally dissolved, being the nanometric dispersed species reorganized around surfactant micelles. The influence of the reorganization time (15–25h), surfactant molecule length (C10–C18) and textural properties of the starting hierarchical TS-1 zeolite were explored. The reorganized hierarchical TS-1 zeolites so obtained show an uniform mesoporosity around 40Å, in contrast to the more heterogeneous secondary porosity exhibited by the parent hierarchical TS-1 materials, comprised between 10 and 100Å. Nevertheless, a reduction in BET surface area and surface attributed to the secondary porosity was found. Likewise, the materials obtained after the reorganization treatment preserve a high crystallinity degree and Ti leaching is not observed. However, though in the reorganized samples the titanium atoms are mostly in tetrahedral coordination, titanium species with higher coordination number were also detected. The catalytic properties of these materials were tested in cyclohexene (C6H10), dibenzothiophene (DBT) and 2-methylbenzothiophene (2-MBT) oxidation reactions using tert-butylhydroperoxide (TBHP) as oxidizing agent. A beneficial effect of the narrower mesoporosity is observed in the catalytic activity of the reorganized materials compared to that exhibited by the parent zeolites.

Synthesis of thermal stable mesoporous titanosilicates assembled from titanosilicates precursors at high temperature

A series of mesoporous titanosilicates (MTS-9x) are synthesized in an acidic media from titanosilicate precursors with a polymer surfactant (P123) under temperatures ranging from 100 to 180°C. Characterization and analysis show that the hexagonal mesoporous titanosilicates (MTS-9x) contain both primary and secondary structural building units of TS-1 zeolite in their framework, in a manner similar to MTS-9. Furthermore, 29Si NMR spectral analysis suggests that MTS-9180 synthesized at 180°C promotes a higher condensation of Ti-containing silica networks in the mesoporous walls compared to MTS-9100 synthesized at 100°C. The higher synthesis temperature may also be responsible for the increased thermal stability of the four-coordinated titanium species in MTS-9180, which was verified by UV–vis spectral analysis. Catalytic experiments indicate that MTS-9180 shows high hydroxylation activity, regardless of calcination, for both small organic molecules such as phenol and bulky organic molecules such as 2,3,6-trimethylphenol. Moreover, the recycled catalyst retains a high conversion, confirming the high thermal stability of the titanium species.

Crystallization Growth of Titanium Silicalite-1 over Monolithic Cordierite Support

Titanium silicalite-1(TS-1) membranes were prepared on cordierite support by hydrothermal treatment. The TS-1 membranes were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD) and FT-IR, The factor that the ratio of TPA+/Si on influencing TS-1 crystal was investigated and it was indicated that the ratio of TPA+/Si had a strong effect on its morphology. The TS-1 crystal presented ellipsoid when ratio of TPA+/Si was 0.15. However, the morphology of TS-1 crystal changed to coffin-shaped when the ratio of TPA+/Si increased to 0.4. Each lattice plane of TS-1 crystal grew on cordierite support with different speed which was controlled by concentration of structure-directing agent SDA (TPAOH) in precursor solution. The mechanism of TS-1 crystal growth on cordierite support maybe that the TPA+ in the solution attracts silicate species, titanium species to form inorganic-organic composite species, the aggregation the inorganic-organic composite species formed crystal nucleus, the morphologies changed due to the growth rate of different lattice planes.

Accommodation, Accumulation, and Migration of Defects in Ti3SiC2 and Ti3AlC2 MAX Phases

We have determined the energetics of defect formation and migration in Mn+1AXn phases with M = Ti, A = Si or Al, X = C, and n = 3 using density functional theory calculations. In the Ti3SiC2 structure, the resulting Frenkel defect formation energies are 6.5 eV for Ti, 2.6 eV for Si, and 2.9 eV for C. All three interstitial species reside within the Si layer of the structure, the C interstitial in particular is coordinated to three Si atoms in a triangular configuration (C–Si = 1.889 Å) and to two apical Ti atoms (C–Ti = 2.057 Å). This carbon–metal bonding is typical of the bonding in the SiC and TiC binary carbides. Antisite defects were also considered, giving formation energies of 4.1 eV for Ti–Si, 17.3 eV for Ti–C, and 6.1 eV for Si–C. Broadly similar behavior was found for Frenkel and antisite defect energies in the Ti3AlC2 structure, with interstitial atoms preferentially lying in the analogous Al layer. Although the population of residual defects in both structures is expected to be dominated by C interstitials, the defect migration and Frenkel recombination mechanism in Ti3AlC2 is different and the energy is lower compared with the Ti3SiC2 structure. This effect, together with the observation of a stable C interstitial defect coordinated by three silicon species and two titanium species in Ti3SiC2, will have important implications for radiation damage response in these materials.

Generation of a Low‐Valent Titanium Species from Titanatrane and its Catalytic Reactions: Radical Ring Opening of Oxetanes

AbstractTreatment of a titanatrane complex with trimethylsilyl chloride and magnesium powder in tetrahydrofuran generated a low‐valent titanium species. This species catalyzed the radical ring opening of epoxides and oxetanes to produce the corresponding less substituted alcohols. The reagent also catalyzed the deallylation and depropargylation of allylic and propargylic ethers, respectively, to provide the parent alcohols.magnified image

Electron Transfer Process in Fluorescein-Dispersing Titania Gel Films Observed by Time-Resolved Fluorescence Spectroscopy

Transient absorption spectroscopy is generally used to study the photoinduced electron transfer process in the dye–titania systems. Time-resolved fluorescence spectroscopy is more sensitive than transient absorption spectroscopy. Fluorescein-dispersing titania gel films were prepared by a sol–gel process and steam treatment using a titanium alkoxide solution containing fluorescein. The photoinduced electron transfer process in the films was investigated by steady state and time-resolved fluorescence measurements. The fluorescence quenching efficiency increased with an increase in the steam treatment time due to the dye–titania complex formation. The titanium species were coordinated to the carboxylate of the fluorescein species during the steam treatment based on an FTIR analysis. The dye–titania complex formation played an important role in the electron injection from the dye to the titania conduction band.

Synthesis, characterization and photocatalytic activity of mixed oxides derived from ZnAlTi ternary layered double hydroxides

A new series of Ti4+ containing ZnAl-LDHs with varying Zn:Al:Ti (~3:1:0–3:0.5:0.5) ratio were prepared by coprecipitation of homogeneous solution metal salts and characterized by various physicochemical methods. Powder XRD revealed the formation of well crystallized LDH even at the highest Ti4+ content. On thermal treatment at 450°C, the well crystallized LDH precursors yielded mixed oxides with BET surface area in the range 92–118m2/g. UV–vis diffuse reflection spectroscopy (DRS) showed a marginal decrease of band gap energy for calcined ZnAlTi-LDHs in comparison to either ZnO or TiO2-P25. The TEM analyses of a representative sample (as-synthesized and calcined) indicated more or less uniform distribution of titanium species. The derived mixed oxides from titanium containing LDH precursors demonstrated better activity toward photodegradation of methylene blue and rhodamine B than those of a physical mixture of ZnO and TiO2. Moreover, the present work not only provided a first hand understanding about semiconductor properties of ZnAlTi-LDHs but also demonstrated their potential as photocatalysts for degradation of organic pollutants.

Titanium-mediated reductive cross-coupling reactions of imines with terminal alkynes: An efficient route for the synthesis of stereodefined allylic amines

Low-valency titanium species, generated in situ by using Ti(OiPr)4/2 c-C5H9MgCl reagent, react with imines to give a titanium-imine complex that can couple with terminal alkynes to provide azatitanacyclopentenes with excellent regioselectivity. Stereodefined allylic amines are obtained in good yields after hydrolysis or iodonolysis of the corresponding azatitanacyclopentenes. When ethynylcyclopropane is used as the coupling partner to react with imines in this reaction, the initially generated allylic amine undergoes an unexpected 1,3-amino migration on silica gel during the column chromatography.

Finding the “Missing Components” during the Synthesis of TS-1 Zeolite by UV Resonance Raman Spectroscopy

The catalytic performance of TS-1 zeolite greatly depends on the types of titanium species and their concentrations in the zeolite. Coupled with UV/vis spectroscopy, we present a UV resonance Raman spectroscopic investigation on the evolution of the titanium species during the crystallization of TS-1 zeolite. It is found that a small portion of Ti species leaches from the solid phase into the liquid phase. The “missing” Ti species in addition to the framework Ti species during the assembly process of TS-1 is identified as isolated “TiO6” species, due to the resonance Raman effect excited at 266 nm. The formation mechanisms of framework Ti species in TS-1 and the relation with the isolated “TiO6” species during the synthesis process are clarified. A synthetic strategy was designed to increase the concentration of the framework titanium by a factor of 1.5 for the actual synthesis of TS-1 zeolite.

Nanocomposites of poly(ε-caprolactone) doped with titanium species

Organic–inorganic hybrid nanocomposites were prepared via in situ sol–gel process. The organic phase is a biodegradable polymer, poly(e-caprolactone) (PCL), while the tetrabutyl titanate (TBT, Ti(OBu)4) was used as inorganic precursor. Synthesis parameters like acidity medium and precursor amount were investigated in order to assess their influence on hybrid properties. The obtained nanocomposites were characterised by thermal analysis, spectroscopic techniques, transmission electronic microscopy (TEM) and X-ray diffraction to gather information on the structure of the nanocomposites. Mechanical properties and biodegradability were also evaluated. A reaction mechanism based on Fourier transform infrared spectroscopy and NMR results was proposed using methyl acetate as model compound. TEM micrographs of the nanocomposites show a fine good nanoparticles dispersion. Acidic conditions and 10 wt% of precursor lead to a nanocomposite with higher mechanical properties and biodegradability than PCL.

Direct synthesis of Mn-Ti-SBA-15 catalyst for the oxidation of ethylbenzene

Bimetallic Mn-Ti-SBA-15 materials were prepared by direct hydrothermal method with appropriate pH adjustment. The materials were characterized by low and wide angle XRD, N2 sorption studies, DRSUV-Vis, XPS, ESR, SEM and TEM. The XRD and BET results clearly demonstrated the incorporation of manganese and titanium species in the SBA-15 framework without affecting the mesoscopic nature of the material. The oxidation state and coordination environment of the active sites were confirmed by DRSUV-Vis, XPS and ESR. The results revealed that Mn2+ is in octahedral geometry whereas Mn3+ and Ti4+ are in tetrahedral coordination in the SBA-15 framework. The O1s XPS spectrum well established the framework incorporation of manganese and titanium species. The catalytic activity of Mn-Ti-SBA-15 materials was evaluated in the oxidation of ethylbenzene with TBHP as the oxidant under optimized reaction condition. It was found that Mn-Ti-SBA-15(50) catalyst showed high catalytic activity with a rate constant of 7.155 × 10−3 min−1. The synergetic effect of Mn2+/Mn3+ and Ti4+ sites in Mn-Ti-SBA-15 is a promising catalyst for the oxidation of ethylbenzene and other alkylbenzenes.

Dimerization of xanthene dyes in sol–gel titania films

Dye-dispersing titania gel films were prepared by the sol–gel method using titanium alkoxide solutions containing xanthene dyes, i.e., fluorescein, eosin Y, rhodamine 110, and rhodamine 123. Dimerization of the xanthene dyes in the films, depending on their concentrations, and their photoinduced electron transfer processes to the titania gels were investigated using spectroscopic and photoelectric techniques. The dye having a higher dimerization constant in solution formed a higher amount of the dimer in the titania gel. There was only a slight difference between the photoelectric conversion efficiencies of the monomer and dimer. The titanium species were coordinated to the carboxylate of the dyes. The dimers as well as the monomers were encapsulated in the narrow spaces of the gel films and strongly interacted with the surrounding titania matrix in the dye-dispersing titania gel films. The dye having a more nucleophilic carboxylate oxygen could easily form the coordination complex with the titanium species. The dye–titania interaction played an important role in the electron injection from the dye to the titania conduction band.

Mechanisms of the ammonia oxidation by hydrogen peroxide over the perfect and defective Ti species of TS-1 zeolite

The catalytic performances of titanium species in TS-1 zeolite for the hydroxylamine formation have been investigated using the density functional theory with the ONIOM scheme. The reaction process for making hydroxylamine is divided into two steps: (i) the H2O2 decomposition over the Ti species to produce the peroxo titanium species and (ii) the NH3 oxidation over the generated oxidizing species. Our results indicated that defective Ti species in the TS-1 zeolite are the dominant catalytic sites for H2O2 decomposition rather than perfect Ti species, leading to the formation of ≡Ti-OOH species as oxygen-donating intermediates for NH3 oxidation reaction. The energetic profiles for the ammonia oxidation over the ≡TiOOH species and the catalytic effect from water were fully investigated, consisting of three proposed mechanisms. The most favored pathway was found to be: the adsorption of ammonia (NH3/η(1)≡TiOOH) → ammonia oxide complex (NH3O/≡TiOH) → hydrated-titanium-oxyamine species (H2O/≡TiONH2) → hydroxylamine product (NH2OH/≡TiOH), in which the highest energy barrier is 16.3 kcal mol(-1). Besides the hydrolysis of titanium-oxyamine species, the hydroxylamine was also generated through the second H2O2 decomposition over the titanium-oxyamine species whereas the activation energy for this step was slightly decreased to be 15.7 kcal mol(-1).

La Loaded TiO2Encapsulated Zeolite Y Catalysts: Investigating the Characterization and Decolorization Process of Amaranth Dye

Lanthanide ions loaded TiO2encapsulated into Y zeolite catalysts were synthesized and used in sonocatalytic degradation of Amaranth dye in aqueous solution. The support zeolite Y was modified by different loading of Ti and La species using ion exchange method. The sonocatalytic reaction condition was carried out at 10 mg/L initial dye concentration, original pH, 1.5 g/L of catalyst loading with low ultrasonic frequency of 40 KHz. Different characterization techniques were used to reveal the physicochemical characteristics of the catalysts. Successful loading of TiO2and La/TiO2into zeolite Y was achieved. The framework of zeolite Y remained unchanged after the loading of TiO2. Titanium species was bound to the framework of zeolite through Ti–O–Si bonds through isomorphous substitution of Si in the zeolite. The ultrasonic degradation of Amaranth dye was enhanced by the TiO2encapsulation with a maximum degradation efficiency of 50% after 120 min of reaction. However, the activity of the catalyst decreased after the loading of lanthanum. This decrease was attributed to the poor contact between the metal crystallites located on the external surface and the titanium encapsulated into cages of zeolite Y.

Synthesis, characterization and application of MTS-9 with different content of titanium

Heteroatom of Ti is effectively incorporated into the framework of ordered mesoporous silica materials in strong acidic media by a two-step procedure. The synthesized samples (designated as MTS-9) are characterized by many methods. Results indicate that MTS-9 synthesized maintains mesoporous structure, and MTS-9 (Si/Ti=53) possesses the more tetrahedrally coordinated titanium species. The catalysts are applied for oxidation of propene and styrene in methanol with hydrogen peroxide as the oxidant. As the ratio of Si to Ti is below 53, the increase of titanium content benefits to the formation of benzaldehyde.

A novel route for preparation of Ti-containing mesoporous silica with high catalytic performance by using a molecular precursor tetrakis(tris-tert-butoxysiloxy)titanium

Mesoporous silica containing isolated Ti with variable Si/Ti ratios was prepared by pyrolysis of a mixture of tetrakis(tris-tert-butoxysiloxy)titanium (TS4) and tetraethoxysilane (TEOS) through a hard template method. TEOS plays two roles as a silica source and solvent. TS4 works as a catalyst for the hydrolysis of TEOS. Titanium species are found to be isolated in the silica frameworks, supported by DR-UV-vis, FT-IR, ESR, and XPS. The mesoporous structure was verified by XRD, N2 adsorption, and SEM. The results of the catalytic performance for the oxidation reaction of cyclohexene using tert-butoxy hydrogen peroxide (TBHP) as oxidant show that high conversion (29%) of cyclohexene and selectivity (98%) of cyclohexene oxide are realized for the Ti-containing mesoporous silica with Si/Ti ratios of 28 and 51.