Mesoporous Ti Research Articles

UV‐Initiated Synthesis of Electroactive High Surface Area Ta and Ti Mesoporous Oxides Composites with Polypyrrole Nanowires within the Pores

AbstractThis paper describes the synthesis and characterization of high surface area mesoporous Ti and Ta oxides with polypyrrole nanowires in the pores. The incorporation of polymer was used to improve the electron conductivity into the channels inside these high surface area (400–1000 m2 g−1) materials in order to exploit surface redox sites for possible pseudocapacitive Li storage. Synthesis was achieved using catalyst‐free UV‐initiated polymerization of vapor‐loaded pyrrole monomer. The best materials showed improved conductivity for both the Ti and Ta oxides as well as improved Li capacity (190 mA h g−1) relative to the pristine material (128 mA h g−1) and superior capacity retention (49 % as compared to 22 %) for the Ti composites. The retention in surface area was also 87 % compared to 49 % reported previously for analogous materials synthesized by catalyst‐initiated methods, which only yielded Li capacities of 170 mA h g−1, further highlighting the superiority of this new photochemical approach.

Mesoporous Ti(0.5)Cr(0.5)N supported PdAg nanoalloy as highly active and stable catalysts for the electro-oxidation of formic acid and methanol.

We report a robust noncarbon Ti0.5Cr0.5N support synthesized by an efficient solid-solid phase separation method. This ternary nitride exhibits highly porous, sintered, and random network structure with a crystallite size of 20-40 nm, resulting in a high specific surface area. It is not only kinetically stable in both acid and alkaline media, but also electrochemically stable in the potential range of fuel cell operation. Two typical anode reactions, formic acid oxidation in acid media and methanol oxidation in alkaline media, are employed to investigate the possibility of Ti0.5Cr0.5N as an alternative to carbon. Bimetallic PdAg nanoparticles (∼4 nm) act as anode catalysts for the two anode reactions. PdAg/Ti0.5Cr0.5N exhibits much higher mass activity and durability for the two reactions than PdAg/C and Pd/C catalyst, suggesting that mesoporous Ti0.5Cr0.5N is a very promising support in both acid and alkaline media.

Mesoporous Ti0.5Nb0.5N Ternary Nitride as a Novel Noncarbon Support for Oxygen Reduction Reaction in Acid and Alkaline Electrolytes

Mesoporous Ti_0.5Nb_0.5N Ternary Nitride as a Novel Noncarbon Support for Oxygen Reduction Reaction in Acid and Alkaline Electrolytes

Hierarchical porous ceramic membrane with energetic ozonation capability for enhancing water treatment

In this work, we proposed a facile method for preparation of hierarchical porous ceramic membrane with energetic catalytic ozonation capability aiming at enhancing the performance of water treatment by using the combined ozone-membrane system. The strategy involved preparation of TiO2 macroporous membrane as a backbone and subsequently coating it with mesoporous Ti–Mn catalyst layer. Scanning electron microscope, transmission electron microscope and nitrogen sorption isotherms characterization demonstrated that the TiO2 membrane was composed of TiO2 nanorods with 200–400nm diameter, 5μm length, and mesoporous Ti–Mn layer was coated on the membrane surface uniformly with the thickness of about 100nm and pore size of 10nm. Energy dispersive X-ray spectroscopy, X-rays photoelectron spectroscopy and X-ray diffractometer showed that Ti–Mn mixed oxide was spread into the inner voids of the membrane to form a hierarchical porous structure. Treating simulated wastewater (aqueous solution of dye Red-3BS and Aniline) it was found that hierarchical porous catalytic membrane exhibited high catalytic ozonation capability which resulted in an enhancement of membrane antifouling, separation and degradation of organic pollutants when the membrane was used as a key device in the combined membrane and ozone system.

Mesoporous Ti–W oxide: synthesis, characterization, and performance in selective hydrogenolysis of glycerol

Mesoporous Ti–W oxides, bearing high surface area, large pore volume, uniform pore size and tunable W/Ti ratios in a wide range (10–40 mol%), were successfully fabricated via an evaporation-induced self-assembly (EISA) strategy. In this approach, the incorporation of W species not only effectively resulted in well-ordered mesoporous structures when calcined below 400 °C but also modified the acidic properties of the obtained oxide composites. The optimal acid amounts (0.47–0.67 mmol g−1 for 400 °C calcinations, 0.25–0.27 mmol g−1 for 500 °C calcinations) were obtained when the W concentration was between 10 and 20 mol%. When calcined at 500 °C, Bronsted acids were generated in Ti90W10-500 and Ti80W20-500. The catalytic performance of these mesoporous solid acids in glycerol hydrogenolysis was studied with a loading of 2 wt% Pt. Pt/Ti100−nWn-500s exhibited high selectivity to 1,3-propanediol (33.5% and 40.3%) and promising catalytic activities (18.4% and 24.2% glycerol conversion) when n is 10 and 20, respectively. This work presents a step forward in the development of highly efficient glycerol hydrogenolysis catalysts and a new understanding of the reaction mechanism of glycerol hydrogenolysis to 1,3-propanediol.

A nanoparticle assembly method for the production of crystalline ordered mesoporous titanium oxide/carbon composites

We demonstrate a simple and reproducible method to prepare thermally stable, crystalline mesoporous Ti oxide/carbon composites. The composites were obtained using titania nanoparticles as inorganic precursors, phenolic resols as carbon sources, and triblock copolymer F127 as a template based on the solvent evaporation-induced self-assembly process. The use of stable titania nanoparticles favored the reproducible preparation of mesoporous Ti–C composites over a wide range of Ti oxide/carbon ratios without the control of atmospheric humidity. Various analysis techniques have been used to investigate the pore structure and crystallinity as a function of synthesis conditions. The resultant composites have an ordered 2D hexagonal mesostructure with high surface areas (200–800 m 2 g −1). In addition to the calcination temperature, the carbon content also has significant effect on the crystalline transformation of titanium species.

Mesoporous Ordered Organosilicas Containing Zr and Ti Species

Periodic mesoporous organosilica materials (PMOs) are the new class of porous and hybrid organic-inorganic materials. They represent exceptional and functional bridged polysilsesquioxanes prepared by sol-gel processing of monomers using triblock copolymers or ionic surfactants as the structure directing agents. By changing the monomer type, various organic functional groups may be incorporated into the framework of PMO materials. Moreover it is possible to introduce heteroatoms in the structure of mesoporous materials via isomorphous substitution of the silicon atoms. In the present study, we report the preparation and characterization of the series of zirconium, titanium and mixture of them, doped mesoporous silica. The PMOs have been synthesized by the hydrolysis and the condensation of bridged silsesquioxane precursors containing two different organic bridging groups ((R’)3Si-CH2-CH2-Si(R’)3, R’ - methoxy or ethoxy). The influence of temperature of synthesis on the structure of PMOs was examined. PMO-Zr and PMO-Zr-Ti were synthesized by employing a zirconyl chloride octahydrate (ZrOCl2•8H2O), titanium isopropoxide, NaCl, bis(trimethoxysilyl)ethane (BTME) as a silica source and triblock copolymer P123 as the structure directing agent while PMO-Ti was prepared using 1,2-bis(triethoxysilyl)ethane (BTESE), titanium isopropoxide, NaOH and cetyltrimethylammonium bromide (CTABr) as a structure directing agent. The resulting materials exhibited well-ordered two-dimensional hexagonal space group p6mm, high surface areas in the range of 700-1100 m2/g. The X-ray photoelectron spectroscopy (XPS) analysis indicated the successful incorporation of heteroatoms into hybrid PMOs and the IR spectra confirmed satisfactory removal of the surfactants.

Chitosan based mesoporous Ti–Al binary metal oxide supported beads for defluoridation of water

In the present study, the performance of Ti–Al binary metal oxide supported beads using chitosan template was studied for fluoride removal from drinking water. The adsorbent was synthesized by precipitation method and characterized using FTIR, SEM, XRD and BET. The higher surface area of the synthesized adsorbent 323.83 m 2/g results in a much higher fluoride removal capacity Q max = 2.22 mg g −1 as compared to bare chitosan. Pore size of beads is 42.97 Å, suggesting mesoporous nature of adsorbent. Material works very effectively at all pH except at pH greater than 9. The presence of carbonate and bicarbonate ions showed significant decline in the fluoride removal capacity of adsorbent. The experimental data fitted well to Langmuir adsorption model. The kinetic studies indicate that the system follows the pseudo-second-order and intra-particle diffusion model. Thermodynamic study reveals that the fluoride adsorption by Ti–Al binary metal oxide supported beads is an exothermic and spontaneous process. Alum appears to be the promising regeneration media showing 80% regeneration. The applicability of the adsorbent for fluoride removal was tested in field water collected from the Dhar district in Madhaya Pradesh, India.

Hierarchically Macro-/Mesoporous Ti−Si Oxides Photonic Crystal with Highly Efficient Photocatalytic Capability

Hierarchically macro-/mesoporous Ti-Si oxides photonic crystal (i-Ti-Si PC) with highly efficient photocatalytic activity has been synthesized by combining colloidal crystal template and amphiphilic triblock copolymer. It was found that the thermal stability of mesoporous structures in the composite matrix were improved due to the introduction of silica acting as glue and linking anatase nanoparticles together, and the photocatalytic activity of the i-Ti-Si PCs was affected by the calcination conditions. The influences of photonic and structural effect of the i-Ti-Si PCs on photocatalytic activity were investigated. Photodegradation efficiency of the i-Ti-Si PCs was 2.1 times higher than that of TiO(2) photonic crystals (i-TiO(2) PCs) in the photodegradation of Rhodamine B (RB) dye as a result of higher surface area. When the energy of slow photon (SP) was optimized to the abosorption region of TiO(2), a maximum enhanced factor of 15.6 was achieved in comparison to nanocrystalline TiO(2) films (nc-TiO(2)), which originated from the synergetic effect of SP enhancement and high surface area.

Investigation of the catalytic activities of sulfated mesoporous Ti, Nb, and Ta oxides in 1-hexene isomerization

In the present work, a series of porous transition metal (Ti, Nb, and Ta) oxides with different pore sizes (12–30 Å) were synthesized using a ligand-assisted amine templating approach. The as-synthesized samples were further treated with 1M sulfuric acid and were characterized by nitrogen adsorption/desorption, powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and elemental analysis (EA). The experimental results in the isomerization of 1-hexene were compared with the commercially available zeolites (HY-zeolite and H-ZSM5) and the ion exchange resin Amberlyst 15. The best results were achieved when using C 12H 2SO 4 mesoporous Ta oxide, which possesses a Ho of −8.2 and 19.8 mmol g −1 acid sites. The conversion of 1-hexene to trans/cis 2-isomers reaches 95.89% in 4 h and the ratio of trans/cis isomers reaches up to 3.7 after 6 h, which is very close to their theoretical ratio in thermodynamic equilibrium (3.37) under the same conditions. This conspicuously high selectivity and short reaction time were not detected with the Ta materials synthesized with C 18 or C 6 templates, nor with Ti and Nb materials of any pore size under the same reaction conditions. Temperature-programed desorption (TPD) of ammonia was used to investigate the much higher activity of the Ta materials. The results showed that the Ta materials had a much greater concentration of Brønsted sites in the active Ho range for this reaction than the Nb materials. The unique performance of the C 12H 2SO 4 Ta material was thus attributed to its high BET surface area, increased concentration of effective Brønsted acid sites and optimal pore size for this particular reaction.

Replication Route Synthesis of Mesoporous Titanium–Cobalt Oxides and Their Photocatalytic Activity in the Degradation of Methyl Orange

Mesoporous Ti–Co oxides were synthesized via a replication route, using a 3-D wormlike mesoporous silica as template and tetra-tert-butyl orthotitanate (TBOT) and Co(NO3)2 as source materials. The prepared materials were characterized by X-ray diffraction (XRD), N2-physisorption, TEM, EDS, and UV/Vis-DRS and found to possess a spherical morphology and a 3-D wormhole-like mesoporous structure, with the average pore size between 4.5 and 16.0 nm. The pore walls consisted mainly of a cobalt-incorporated anatase phase. The Co3+ ions were generated in the replicated mesoporous Co–Ti oxides, via the transfer of electrons from Co2+ to Ti4+ ions. The formation of cobalt-incorporated anatase phase and Co3+ ions were both favored by larger Co/Ti atomic ratios and by relatively low calcination temperatures. The specific surface area decreased and the mesopore sizes increased, with increasing Co/Ti atomic ratio or calcination temperature. The average crystal size of the anatase phase decreased with increasing Co/Ti atomic ratio but increased with increasing calcination temperature. The photocatalytic activity of the replicated mesoporous Co–Ti oxides in the degradation of methyl orange dye was investigated. It was observed that the photocatalytic activity increased with increasing Co/Ti atomic ratio and exhibited a maximum with increasing calcination temperature. With the exception of those prepared at too high calcination temperatures, the replicated mesoporous Co–Ti oxides were much more active than the pure titania. It is concluded that, in addition to a higher diffusion, the cobalt-containing anatase, as the active phase, and the Co3+ ions, as the active sites, are responsible for the high photocatalytic activity of the replicated mesoporous Co–Ti oxide.

Synthesis of Mesoporous TiO2and Its Application to Photocatalytic Activation of Methylene Blue and E. coli

Mesoporous TiO 2 material was synthesized from diblock copolymers with ethylene oxide chains via a sol-gel process in aqueous solution. The properties of these materials were characterized with several analytical techniques including field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), wide angle X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and Barrett-Joyner-Halenda (BJH) analysis. The mesoporous TiO 2 materials calcined at 400°C were found to have specific surface areas 212 m 2 g -1 , average pore sizes 6.2 nm, and their average crystal sizes were found to be 8.2 nm. The photocatalytic activity of mesoporous Ti0 2 was characterized with UV-Vis spectroscopy, and it was found to be 5.8 times higher than that of Degussa P25 TiO 2 (P25). For deactivation of Escherichia coli, mesoporous Ti0 2 also has high photocatalytic inactivity than that of P25. Such a high photocatalytic activity is explained with large surface area and small crystal size with wormhole-like mesoporous structure.

Liquid Phase Epoxidation of Allylic Compounds with Hydrogen Peroxide at Autogenic and Atmospheric Pressure over Mesoporous Ti- MCM-48 Catalyst

AbstractThe epoxidation of allylic compounds: allyl alcohol, methallyl alcohol and methallyl chloride to corresponding epoxides: glycidol, 2-methylglycidol and 2-methylepichlorohydrin with hydrogen peroxide over Ti-MCM-48 catalyst has been studied. The epoxidation was carried out with 30 wt% hydrogen peroxide in methanol as a solvent under autogenic pressure (in autoclave) and at atmospheric pressure in a glass reactor. The optimal technological parameters and regions of advantageous changes of: temperature, the molar ratio allylic compound/H

Visible light absorption of binuclear TiOCo II charge-transfer unit assembled in mesoporous silica

Grafting of Co II(NCCH 3) 2Cl 2 onto mesoporous Ti–MCM-41 silica in acetonitrile solution affords binuclear Ti–O–Co II sites on the pore surface under complete replacement of the precursor ligands by interactions with anchored Ti centers and the silica surface. The Co II ligand field spectrum signals that the Co centers are anchored on the pore surface in tetrahedral coordination. FT-infrared action spectroscopy using ammonia gas adsorption reveals Co–O–Si bond modes at 831 and 762 cm −1. No Co oxide clusters are observed in the as-synthesized material. The bimetallic moieties feature an absorption extending from the UV into the visible to about 600 nm which is attributed to the Ti IV–O–Co II → Ti III–O–Co III metal-to-metal charge-transfer (MMCT) transition. The chromophore is absent in MCM-41 containing Ti and Co centers isolated from each other; this material was synthesized by grafting Co II onto a Ti–MCM-41 sample with the Ti centers protected by a cyclopentadienyl ligand. The result indicates that the appearance of the charge-transfer absorption requires that the metal centers are linked by an oxo bridge, which is additionally supported by XANES spectroscopy. The MMCT chromophore of Ti–O–Co II units has sufficient oxidation power to serve as visible light electron pump for driving multi-electron transfer catalysts of demanding uphill reactions such as water oxidation.

Hydrogen Storage in Chemically Reducible Mesoporous and Microporous Ti Oxides

Chemically reducible micro- and mesoporous Ti oxides with controlled pore sizes from 12 to 26 A were synthesized. The hydrogen storage and adsorption capacity at 77 K was tested as a function of surface area, pore size, and reducing agent. Surprisingly, the oxidation state of the surface Ti species had an even greater effect on the storage densities than surface area or pore size. For example, the 12 A material reduced with bis(toluene) Ti possesses a surface area of less than 300 m2/g, but absorbs up to 4.94 wt % and 40.46 kg/m3 of H2 reversibly at 77 K and 100 atm. This volumetric storage capacity is higher than that of AX-21, which has a much higher surface area. The H2 binding enthalpies increased from 4.21 kJ/mol to 8.08 kJ/mol as the surface oxidation state of the Ti decreased. These results suggest that a Kubas-type sigma H2 complex may be involved and that further tuning of the H2 binding enthalpies through use of appropriate organometallic reagents may achieve even higher storage levels at more moderate temperature.

Catalytic Characterization of Mesoporous Ti–Silica Hollow Spheres

Titanium–silica hollow spheres (TSHS) with a mesoporous shell were synthesized using an inverse multiple oil–water–oil (O/W/O) emulsion. These novel materials show interesting potential for catalysis. Excellent catalytic performance was found in the epoxidation of cyclohexene with tert-butylhydroperoxide. The investigation of the titanium environment by UV–vis, Raman and FTIR spectroscopy showed that at low Ti loading only isolated species are present and catalytic measurements demonstrated that these species are the active sites for this reaction. At higher loading Ti–O–Ti microdomains are present and they do not exhibit any significant catalytic activity.

Solid-State 23Na and 7Li NMR Investigations of Sodium- and Lithium-Reduced Mesoporous Titanium Oxides

Mesoporous titanium oxide synthesized using a dodecylamine template was treated with 0.2, 0.6, and 1.0 equiv of Li- or Na-naphthalene. The composite materials were characterized by nitrogen adsorption, powder X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric analysis, and solid-state 23Na and 7Li NMR spectroscopy. In all cases the wormhole mesoporosity was retained as evidenced by BET surface areas from 400 to 700 m(2)/g, Horvath-Kawazoe pore sizes in the 20 Angstroms range, and a lack of hysteresis in the nitrogen adsorption isotherms. Variable-temperature conductivity studies show that the Li-reduced materials are semiconductors, with conductivity values 3 orders of magnitude higher than those of the Na-reduced materials. Electrochemical measurements demonstrate reversible intercalation/deintercalation of Li+ ions into pristine mesoporous Ti oxides with good cycling capacity. Solid-state 23Na NMR reveals two distinct Na environments: one corresponding to sodium ions in the mesoporous channels and the other corresponding to sodium ions intercalated into the metal framework. 23Na NMR spectra also indicate that the relative population of the framework site increases with increased reduction levels. Solid-state 7Li NMR spectra display a single broad resonance, which increases in breadth with increased reduction levels, though individual resonances inferring the presence of channel and framework Li species are not resolved. Comparisons of the lithium chemical shifts with published values suggests an "anatase-like structure" with no long-range order in the least-reduced samples but a "lithium titanate-like structure" with no long-range order in the higher reduced materials.

Sites for CO 2 activation over amine-functionalized mesoporous Ti(Al)-SBA-15 catalysts

Activation of CO 2 and its utilization in the synthesis of chloropropene and styrene carbonates over functionalized, mesoporous SBA-15 solids, have been investigated. The surface basicity of SBA-15 was modified with nitrogen-based organic molecules of varying basicity viz., alkyl amines (–NH 2), adenine (Ade), imidazole (Im) and guanine (Gua). The surface of SBA-15 was also functionalized with Ti 4+ and Al 3+ species. The acid–base properties of these modified SBA-15 materials were investigated by temperature-programmed desorption (TPD) and diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy. NH 3 and pyridine were used as probe molecules for acid sites, while CO 2 was used to characterize the basic sites. CO 2 was activated at the basic amine sites forming surface carbamate species (IR peaks: 1609 and 1446 cm −1). The latter reacted further with epoxides adsorbed on the acid sites forming cyclic carbonates. A correlation between the intensity of the IR peak at 1609 cm −1 and cyclic carbonate yield has been observed. The cyclic carbonate yields were higher when both the acid and base functionalities were present on the surface. The Ti- and Al-SBA-15 functionalized with adenine exhibited the highest catalytic activity and selectivity. There is an optimal dependence (“volcanic plot”) of the yield of cyclic carbonates on the desorption temperature, T max(CO 2) in the TPD experiments. These solid catalysts were structurally stable up to 473 K and could be recycled for repeated use. In addition to density, the strength and type of amine sites play a crucial role on CO 2 activation and utilization.

Heterogeneous oxidation of pyrimidine and alkyl thioethers in ionic liquids over mesoporous Ti or Ti/Ge catalysts.

Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity.

Eu이 도핑된 LiGdF4의 Down-conversion을 이용한 염료감응형 태양전지의 효율 향상

Down-conversion of Eu<TEX>$^{3+}$</TEX> doped LiGdF<TEX>$_4$</TEX> (LGF) for increasing the cell efficiency on dye-sensitized Ti <TEX>$O_2$</TEX> solar cells has been studied. The dye sensitized solar cell (DSC) consisting of mesoporous Ti <TEX>$O_2$</TEX> electrode deposited on transparent substrate, an electrolyte containing I<TEX>$^{[-10]}$</TEX> /I<TEX>$_3$</TEX><TEX>$^{[-10]}$</TEX> redox couple, and Pt counter electrode is a promising alternative to the inorganic solar cell. The structure of DSC is basically a sandwich type, viz., FTO glass/Ru-red dye-absorbed Ti <TEX>$O_2$</TEX>/iodine electrolyte/sputtered Pt/FTO glass. The cell without down converter had open circuit potential of approximately 0.66 Volt, the short circuit photocurrent density of 1.632 mA/<TEX>$\textrm{cm}^2$</TEX>, and fill factor of about 50 ％ at the excitation wavelength of 550 nm. In addition, 5.6 mW/<TEX>$\textrm{cm}^2$</TEX> incident light intensity beam was used as a light source. From this result, the calculated monochromatic efficiency at the wavelength of 550 nm of this cell was about 9.62 ％. The incident photon to current conversion efficiency (IPCE) of N3 used as a dye in this work is about 80 ％ at around 590 nm and 610 nm, which is the emission spectrum of Eu<TEX>$^{3+}$</TEX> doped LGF, results in efficiency increasing of DSC.C.