CO hydrogenation to iso-C4 hydrocarbons over CeO2–TiO2 catalysts

CeO₂–TiO₂ (Ce:Ti = 0.25–9, molar ratio) catalysts were synthesized by a sol–gel method and the catalytic performances were evaluated in the selective synthesis of isobutene and isobutane from CO hydrogenation under the reaction conditions of 673–748 K, 1–5 MPa and 720–3000 h⁻¹. The physical properties, such as specific surface area, cumulative pore volume, average pore diameter, crystal phase and size, of the catalysts were characterized by N₂ adsorption/desorption and XRD. All the CeO₂–TiO₂ composite oxides showed higher surface areas than pure TiO₂ and CeO₂. No TiO₂ phase was detected on the samples of CeO₂–TiO₂ in which TiO₂ contents were in the range of 10–50 mol%. Crystalline Ce₂O₃ was detected in CeO₂–TiO₂ (8:2). The reaction conditions, temperature, pressure and space velocity, had obvious influences on the CO conversion and distribution of the products over CeO₂–TiO₂ (8:2) catalyst.     

Enhanced photocatalytic activity of Ag doped TiO2 nanoparticles synthesized by a microwave assisted method

Pure anatase TiO₂ photocatalyst with different Ag contents was prepared via a controlled and energy efficient microwave assisted method. The prepared material was further characterized by several analytical techniques like X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), surface area measurement (BET), Fourier transform-infrared spectroscopy (FT-IR), diffused reflectance spectroscopy (DRS), and thermogravimetric–differential thermal analysis (TGA–DTA). A 10 nm average crystallite size with nano-crystals of pseudo-cube like morphology was obtained for optimal (0.25 mol%) Ag doped TiO₂. The present research work is mainly focused on the enhancement of degradation efficiency of methyl orange (MO) by doping of Ag in TiO₂ matrix using UV light (365 nm). A 99.5% photodegradation efficiency of methyl orange was achieved by utilizing 0.25 mol% Ag doped TiO₂ (1 g/dm³) at pH=3 within 70 min. Recyclability of photocatalyst was also studied, with the material being found to be stable up to five runs.     

TiO2–SnO2 nanomaterials for gas sensing and photocatalysis

Nanopowders of TiO₂–SnO₂ over a full composition range extending from 100 mol% TiO₂ to 100 mol% SnO₂ are obtained by the sol–gel method from TTIP and SnCl₂·5H₂O precursors of Ti and Sn, respectively followed by calcination at 400 °C. The samples are characterized by means of BET, XRD and TEM. Optical properties of the prepared nanomaterials are studied as well. TEM images indicate that the nanoparticles are regular in shape. The specific surface area, SSA of TiO₂ is 95 m²/g while that of SnO₂ amounts to 129 m²/g. The highest SSA of 156 m²/g is achieved at 20 mol% of TiO₂. Occurrence of rutile, anatase and brookite polymorphic forms depends on the chemical composition of nanopowders. Formation of rutile-type solid solution of TiO₂–SnO₂ over the range of 0–80 mol% TiO₂ is confirmed by Vegard rule applied to lattice constants. Electronic band gap decreases with Ti content from 3.84 eV (100 mol% SnO₂) to 3.18 eV (100 mol% TiO₂).     

Synthesis and Photocatalytic Activity of Anatase TiO2 Nanoparticles-coated Carbon Nanotubes

A simple and straightforward approach to prepare TiO₂-coated carbon nanotubes (CNTs) is presented. Anatase TiO₂ nanoparticles (NPs) with the average size ~8 nm were coated on CNTs from peroxo titanic acid (PTA) precursor even at low temperature of 100 °C. We demonstrate the effects of CNTs/TiO₂ molar ratio on the adsorption capability and photocatalytic efficiency under UV–visible irradiation. The samples showed not only good optical absorption in visible range, but also great adsorption capacity for methyl orange (MO) dye molecules. These properties facilitated the great enhancement of photocatalytic activity of TiO₂ NPs-coated CNTs photocatalysts. The TiO₂ NPs-coated CNTs exhibited 2.45 times higher photocatalytic activity for MO degradation than that of pure TiO₂.     

Solid acidities of SiO2–TiO2/montmorillonite composites synthesized under different pH conditions

SiO₂–TiO₂/montmorillonite composites were prepared under acidic, neutral and basic conditions and the solid acidity of the resulting composites were determined. All the SiO₂/TiO₂ ratio of the colloidal particles was set at 10 but the resulting SiO₂/TiO₂ ratios were significantly richer in TiO₂. The XRD patterns of the acidic composite showed expanding and broadening of the (001) reflection by intercalation of colloidal SiO₂–TiO₂ particles, but the neutral and basic composites showed only broadening of the reflections and no intercalation. The specific surface areas of the acidic, neutral and basic composites (375, 237 and 247 m²/g, respectively) were much larger than of montmorillonite (6 m²/g). The average pore sizes were about 4, 15 and 50 nm, and the amounts of solid acidic sites measured by the NH₃-TPD were 178, 95 and 86 µmol/g for the acidic, neutral and basic composites, respectively. The solid acid amount of the acidic composite was twice that of a commercial catalyst, K-10, (85 µmol/g) and much higher than the guest phase SiO₂–TiO₂ gel (16 µmol/g) or the host phase montmorillonite (6 µmol/g). The TPD peak temperatures reflect the acid strength, and were similar in all the samples, ranging from 175° to 200 °C.     

Characterization of Au/MnO x /TiO2 for Photocatalytic Oxidation of Carbon Monoxide

The Au/MnO _x /TiO₂ catalyst was used for the photocatalytic oxidation of carbon monoxide. The catalytic activity of Au/MnO _x /TiO₂ with low concentration of manganese (3–7 mol%) was much higher than that of Au/TiO₂. The surface of Au/MnO _x /TiO₂ was characterized by XPS and Raman spectroscopy. While the main state of manganese in 13.8 mol% MnO _x /TiO₂ was Mn⁴⁺ species, Mn³⁺ was the dominant species in the samples with below 6.5 mol% manganese. Raman spectroscopy revealed that the interaction between the MnO _x and TiO₂ form Mn–O–Ti species in which the state of manganese was Mn³⁺. The Au particles also interacted with both MnO _x and TiO₂ to modify the surface of them. In the case of the Au species, low loading of manganese produced the metallic Au⁰ and perimeter interfacial Au^δ+, whereas high loading showed the coexistence of three components which were metallic Au⁰, perimeter interfacial Au^δ+, and oxidic Au³⁺. The catalytic active component was the metallic Au⁰ and perimeter interfacial Au^δ+ species, which were dispersed on TiO₂ and Mn³⁺/TiO₂.     

Preparation, Characterization and Photocatalytic Activities of F-doped TiO2 Nanotubes

F-doped TiO₂ nanotubes were prepared by impregnation method. The prepared catalysts were characterized by XRD, TEM, and XPS. The photocatalytic activity of F-doped TiO₂ nanotubes was evaluated through the photodegradation of aqueous methyl orange. The experiments demonstrated that the F-doped TiO₂ nanotubes calcined at 300 °C possessed the best photocatalytic activity. Compared with pure TiO₂ nanotubes, the doping with F⁻ significantly enhanced the photocatalytic efficiency. The high photocatalytic activity was ascribed to several beneficial effects produced by F-doping: creation of oxygen vacancies, presence of Ti³⁺, and so on. An erratum to this article can be found at     

Significantly improved dielectric properties of TiO2 ceramics through acceptor-doping and Ar/H2 annealing

The acceptor-doped rutile TiO₂ ceramics, x mol% M₂O₃-(1-x) mol% TiO₂ (M = Al³⁺, Ga³⁺, and In³⁺), were prepared by solid state reaction method. The influence of Ar/H₂ annealing on the structural and dielectric properties of the ceramics were systematically investigated. Our results reveal that the dielectric properties of the ceramics can be significantly improved by the Ar/H₂ annealing. Ga³⁺ is found to be the most suitable dopant with the best doping level of 5 mol%. Excellent dielectric properties of colossal and flat dielectric permittivity (~1.2 × 10⁵ (@1 kHz and 25 °C), low dielectric loss (~0.1), and good frequency stability were achieved over the temperature range of -70–150 °C in the Ar/H₂-annealed 5 mol% Ga₂O₃-95 mol% TiO₂ ceramic. This approach of acceptor-doping and Ar/H₂ annealing leads to two thermally activated relaxations in the sample. The low-temperature relaxation is argued to be a Maxwell-Wagner relaxation caused by frozen electrons, while the high-temperature relaxation is a glass-transition-like relaxation associated with the freezing process of the electrons. This work highlights that engineering low-temperature Maxwell-Wagner relaxation paves a new way other than the frequently used acceptor-donor dual doping to design superior dielectric properties in the TiO₂ system.     

Photovoltaic efficiency on dye-sensitized solar cells (DSSC) assembled using Ga-incorporated TiO2 materials

This study examined the photoelectric conversion efficiency of DSSC (dye-sensitized solar cell) when nanometer sized Ga (0.25, 0.50, and 1.00 mol%)–TiO₂ prepared using a hydrothermal method was employed as a working electrode material. The particle sizes observed in the transmission electron microscopy images were <20 nm in all samples. However, with increasing Ga concentration, the size increased and the shapes transformed to a stick form. The absorption band was slightly blue-shifted upon the incorporation of gallium ions, but the intensity of the photoluminescence (PL) curves of the Ga-incorporated TiO₂ was significantly smaller, with the smallest case being the 0.50 mol% Ga–TiO_2, which was related to recombination between the excited electrons and holes. When Ga–TiO₂ was applied in DSSC, the energy conversion efficiency was enhanced considerably compared to that using pure TiO₂; it was approximately 4.57% with the N3 dye under 100 mW/cm² of simulated sunlight. These results are in agreement with an electrostatic force microscopy (EFM) study showing that the electrons were transferred rapidly to the surface of Ga–TiO₂ film, compared with that on a pure TiO₂ film.     

Shock-consolidated TiO2 bulk with pure anatase phases fabricated by explosive compaction using underwater shockwave

Titanium dioxide (TiO₂) bulk with pure anatase phases was fabricated by an explosive compaction technique using an underwater shockwave. Dynamic shock pressure of 6 GPa was used to consolidate anatase TiO₂ powders. Its microstructural, crystalline structural and photocatalytic characteristics were observed and measured by various techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and photocatalytic activity measurement system. It was confirmed that the relative density of anatase TiO₂ compact is about 96% (3.73 g/cm³) of the theoretical density (3.89 g/cm³) and a strong surface bonding between particles is formed by a shock energy. In X-ray diffraction analysis, high purity anatase phases, broadened peaks due to lattice defects and decreased crystallite size were found. For the photocatalytic activities, the anatase TiO₂ compact was quite excellent compared to the commercial sintered TiO₂ bulk.     

Photo-catalytic degradation of Rhodamine B on C-, S-, N-, and Fe-doped TiO2 under visible-light irradiation

C-, S-, N-, and Fe-doped TiO₂ photocatalysts were synthesized by a facile sol–gel method. The structure and properties of catalysts were characterized by N₂ desorption–adsorption, X-ray diffraction (XRD), UV–vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Results revealed that the surface area of the multi-doped TiO₂ was significantly increased and the crystallite size was smaller than the pure TiO₂ obtained by a similar route. Compared with TiO₂, the peak position in doped-TiO₂ XRD patterns was slightly shifted, which could be attributed to the distortion by the substitution of carbon, nitrogen, and sulfur dopants for some oxygen atoms and Fe³⁺ for Ti⁴⁺ in the lattice of TiO₂. These substitutions were confirmed by XPS. In addition, these dopants were responsible for narrowing the band gap of TiO₂ and shifting its optical response from ultraviolet (UV) to the visible-light region. The photocatalytic reactivities of these multi-doped TiO₂ catalysts were investigated by degrading Rhodamine B (RB) in aqueous solution under visible-light irradiation (λ > 420 nm). It was found out that the reactivity was significantly enhanced and the catalyst doped with nitrogen, carbon, sulfur, and 0.3 wt% iron had the highest photocatalytic activity.     

Low Temperature Preparation and Characterization of N-doped and N-S-codoped TiO2 by Sol–gel Route

This paper reports a new method to prepare the N-doped and N-S-codoped anatase TiO₂ photocatalysts at 100 °C. The as-prepared photocatalysts were characterized by means of XRD, Raman spectra, TEM, BET, UV–Vis diffuse reflectance spectra (DRS) and XPS. The results showed that the N-doping and N-S-codoping extended the absorbance spectra of TiO₂ into visible region with different extent. The BET surface area of the N-S-codoped TiO₂ photocatalysts was high up to 245 m²g⁻¹. The results of degradation of methyl orange (MO) solution showed that the N-doped and N-S-codoped TiO₂ photocatalysts exhibited higher photocatalytic activity than that of Degussa P-25 and the as-prepared pure TiO₂ under visible irradiation. This property can be attributed to the results of synergetic effects of absorption in the visible light region, red shift in adsorption edge, good crystallization and large surface area of the as-prepared N-doped or N-S-codoped TiO₂.     

Zn-doped TiO2 nanoparticles for glutamate sensors

TiO₂ has been widely used in catalysis because of its superior catalytic properties. The enhancement of catalytic performance can generally be achieved through doping. In the present study, Zn-doped TiO₂ nanoparticles (at a Zn doping level of 2.5, 5, and 10 mol%) were synthesized by the solution combustion technique and characterized to examine their potential usage in sensor applications. The bandgap energies and electrocatalytic activities of the synthesized nanoparticles were microstructurally investigated. The results revealed the presence of anatase nanoparticles with average sizes of 9–14 nm, which agglomerated into clusters with sizes in the range of 78–107 nm. The Zn concentrations did not significantly affect the chemical compositions, but the particles exhibited slight refinement with an increase in the Zn dopant. Narrower bandgaps were observed in the nanoparticles with higher Zn concentrations. The electrocatalytic activities were evaluated by cyclic voltammetry and found that TiO₂ nanoparticles with 2.5 mol% Zn had the most prominent activities. Sensitivity, measured in glutamate solutions with concentrations between 0.001 and 1000 mM ranged from 2.47 to 7.20 × 10^?6 mA mM^?1 cm^?2, which were comparable with those reported by other researchers. The TiO₂ nanoparticles with 2.5 mol% Zn exhibited fair selectivity and reusability. The oxidation peak current degraded by 12.5%, after 200 cycles of measurement in glutamate solution. The results suggested that TiO₂ nanoparticles doped with 2.5 mol% Zn are potential candidates for glutamate-sensing applications.     

Effect of silica on the microstructure and photocatalytic properties of titania

A series of TiO₂/SiO₂ composite with different Ti/Si ratios were prepared by sol–gel technique. The samples were characterized by different analytical techniques such as XRD, FT-IR, BET and XPS. Grain size of anatase TiO₂ calculated using Scherrer's formula was found to be in the range of 2.1–8.7 nm, and the content of anatase phase in TiO₂ ranges from 45% to 40.1%. The photocatalytic properties on methyl orange (MO) solution were also studied. The degradation rate of the composite is much higher than that of the pure TiO₂ in the same conditions.     

Properties of sol-gel SnO2/TiO2 electrodes and their photoelectrocatalytic activities under UV and visible light illumination

A visible light active binary SnO₂-TiO₂ composite was successfully prepared by a sol-gel method and deposited on Ti sheet as a photoanode to degrade orange II dye. Titanium and SnO₂ can promote the development of rutile phase of TiO₂ and inhibit the formation of anatase phase of TiO₂. Formation of SnO₂ crystalline is insignificant even when the calcination temperature increases to 700 °C. Heterogenized interface between SnO₂ and TiO₂ inhibits growth of TiO₂ linkage and leads to the particle-filled surface morphology of SnO₂-containing films. The carbonaceous, Ti-O-C bonds and Ti³⁺ species are likely to account for the photoabsorption and photoelectrocatalytic (PEC) activity under visible light illumination. The electrode with 30% SnO₂ exhibits higher photocurrent when compared with those in the region of 0-50%. The 600 °C-calcined SnO₂-TiO₂ electrode indicates higher activity when compared with those at 400, 500, 700 and 800 °C. PEC degradation of orange II follows the Langmuir-Hinshelwood model and takes place much effectively in a solution of pH 3.0 than those in pH 7.0 and pH 11.0.     

Fabrication of high performance silicon nitride ceramics with TiO2 additive by annealing process

The high performance Si₃N₄ ceramic was prepared firstly for TiO₂, Y₂O₃ and MgO as pressureless sintering additives. Si₃N₄ ceramic with relative density of 99.6% and flexural strength of 785 ± 23.3 MPa could be obtained with 3 mol% TiO₂ and sintered at 1800 °C for 2 h. After annealing at 1700 °C, the facture toughness of sample of 1 mol% TiO₂ increased from 8.31 ± 0.28 MPa m^1/2 to 9.84 ± 0.16 MPa m^1/2. The flexural strength of sample of 2 mol% TiO₂ increased from 707 ± 26 MPa to 981 ± 16 MPa, thermal conductivity increased from 57.8 W/(m·K) to 68.49 W/(m·K). The XRD results showed that the ratio of I₁₀₁/I₂₁₀ and grain height reached to 1.84 and 5 μm of the sample of 3 mol% TiO₂, respectively. The present investigation revealed that the three-dimensional array of highly oriented crystalline Si₃N₄ micro rods could be prepared which array on the homogeneous substrates by using TiO₂ as agent. This phenomenon may propose a method that the mechanical properties the Si₃N₄ ceramics added TiO₂ can be improved significantly after annealing process.     

Uniform dispersion of CuO nanoparticles on mesoporous TiO2 networks promotes visible light photocatalysis

Here, we focus our efforts on synthesizing a uniform dispersion of CuO nanoparticles on mesoporous TiO₂ networks for the first time. H₂PtCl₆ was added through a photocatalytic reaction to produce 0.5% Pt/CuO–TiO₂ nanocomposites. XRD patterns confirmed that the prepared TiO₂ formed the anatase phase. TEM images showed close contacts between CuO and TiO₂ with 5–10 nm particle sizes. One of the advantages of the synthesized mesoporous CuO–TiO₂ nanocomposites was the high pore volume (0.540 cm³ g⁻¹) and large surface area (300 m² g⁻¹). The H₂ evolution over the mesoporous 3 wt% CuO–TiO₂ nanocomposites using a glucose hole scavenger [10 vol%] was determined to be ~13000 μmol/g, a value that was 1300 times greater than that of mesoporous TiO₂. The H₂ evolution rate was increased by up to 1300 and 20 times for 3 wt% CuO–TiO₂ and 0.1 wt% CuO–TiO₂ nanocomposites, respectively, compared with that of mesoporous TiO₂. The increase in H₂ evolution over mesoporous CuO–TiO₂ nanocomposites was explained by the increased light harvesting capacity, high glucose molecule diffusion and efficient charge carrier separation. Moreover, the construction of a heterostructure with a p–n CuO–TiO₂ heterojunction expedited the separation of charge carriers and promoted the evolution of H₂. In addition, H₂ evolution was substantially increased by the synergistic effects of Pt and CuO on the mesoporous TiO₂ networks. Photoelectrochemical and photoluminescence measurements were employed to prove the H₂ evolution mechanism over the CuO nanoparticles deposited on the mesoporous TiO₂ networks.     

Titania-silica composites with less aggregated particles

Less aggregated titania-silica composite was developed by a versatile and reproducible method using relatively cheap precursors. The final product has more suitable properties than the conventional materials. The composite was synthesized by using sodium silicate, as a silica precursor, and freshly prepared TiOCl₂ as a titania source. The final product was obtained after subsequent calcination for 5 h at 300 to 1000 °C. The primary particles of the composite, as examined by SEM technique, are generally less aggregated. The XRD patterns for the calcined samples indicate the presence of TiO₂ and there is a significant increase of peak intensity as the calcination temperature increases. EDS and XPS analyses confirmed the formation of pure composite rich in Ti, Si, and O. Nitrogen physisorption studies reveal that the composite is mesoporous and have large BET surface area (~ 375 m²/g). A simple experiment of photoreduction of methyl orange under solar radiation was attempted to demonstrate the reliability and improvement of titania-silica composite in practice. It was found out that its efficiency is high as compared to P-25 TiO₂ under solar light. The results demonstrate that composite with desirable properties for various applications can be obtained via the present route.     

Effects of TiO2 doping on the defect chemistry and thermo-physical properties of Yb2O3 stabilized ZrO2

Yb₂O₃ stabilized ZrO₂ (YbSZ) doped with different TiO₂ contents were produced, and their phase structure, thermal conductivities and thermal expansion coefficients were investigated. A new solid-solution model is proposed, i.e. Ti⁴⁺ would take the interstitial sites when its content is below a critical value (≤2.5 mol%) and then substitute for Zr⁴⁺. The abnormal lattice volume and thermo-physical properties of 2.5 mol% TiO₂ doped YbSZ, and the positive effects of TiO₂ doping on the thermal conductivity at moderate doping level are consistent with the new defect model. However, monoclinic phase is formed when the TiO₂ content reaches to 10 mol% and its content increases with doping content, which have negative influence on the thermo-physical properties. Considering the comprehensive properties, 10 mol% TiO₂ doped YbSZ is considered as a promising thermal barrier coating ceramic.     

Synthesis of TiO2–Ag nanocomposite with sol–gel method and investigation of its antibacterial activity against E. coli

TiO₂–Ag nanocomposite was prepared by the sol–gel method and an azeotropic distillation with benzene was used for dehydration of the gel. Because of gel dehydration by distillation method a nanopowder with a surface area of 230 m²/g was produced which decreased to 80 m²/g after calcination. TEM micrographs and XRD patterns showed that spherical nanosized Ag particles (≈ 10 nm) were deposited among TiO₂ particles. The antibacterial activity of calcined powder at 300 and 500 °C was studied in the presence and in the absence of UV irradiation against Escherichia coli as a model for Gram-negative bacteria. The antibacterial tests confirmed the powder calcined at 300 °C possessed more antibacterial activity than the pure TiO₂, amorphous powder and the powder calcined at 500 °C under UV irradiation. In the absence of UV, the reduction in viable cells was observed only with calcinated powder at 300 °C.