Al-doped TiO<Subscript>2</Subscript> mesoporous materials: synthesis and photodegradation properties

Aluminium-doped TiO₂ mesoporous material was successfully fabricated by solid-state reaction with cetyltrimethylammonium bromide as a template agent and tetrabutyl orthotitanate as a precursor. The characteristic results from low-angle and wide-angle X-ray diffraction, high resolution transmission electron microscopy and energy dispersive spectroscopy, N₂ absorption–desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, ultraviolet visible light spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the mesoporous architecture of aluminium-doped TiO₂ was composed of crystal wall and micro-/mesopore formed gradually by the mesopore degradation of anatase TiO₂, and aluminium had been doped into the framework of anatase TiO₂. The mesoporous Al-doped TiO₂ material, not only possessed high thermal stability hexahedral mesostructure, large BET surface area and narrow distribution of pore size, but also showed excellent photodegradation behavior for Congo Red. Furthermore the medium UV–Vis absorption peak of mesoporous aluminium-doped TiO₂ in the range 210–370 nm was the absorption peak of aluminium oxide nanoparticles locating the extraframework of TiO₂. A small quantity of aluminium doped into anatase TiO₂ could obviously improve photodegradation activity, and the photodegradation activity of aluminium-doped TiO₂ was higher than that of pure TiO₂.     

Spray pyrolysis synthesis of mesoporous TiO<Subscript>2</Subscript> microspheres and their post modification for improved photocatalytic activity

Mesoporous TiO₂ microspheres were prepared by spray pyrolysis for photocatalysis. Post modification of TiO₂ by heat treatment was performed to optimize its photocatalytic performance. First, spherical TiO₂ particles with mesoporous structure were synthesized at pyrolysis temperatures of 500, 600, and 700 °C. After characterization by XRD, SEM, and N₂ adsorption, a sample prepared at 500 °C was found to possess desirable properties for photocatalytic performance through post-modification. In methylene blue degradation, mesoporous TiO₂ microspheres synthesized at 500 °C outperformed other microspheres. Furthermore, samples obtained by spray pyrolysis at 500 °C were calcined at various temperatures as a post-modification process. The sample calcined at 350 °C showed improved photocatalytic activity due to optimal anatase crystallinity and surface area.     

One-pot synthesis of bifunctionalized TiO<Subscript>2</Subscript> mesoporous photocatalyst with visible light response

A series of Fe-doped SH/TiO₂ mesoporous photocatalysts have been firstly prepared by one-pot method using P123 as structure-directing agent. This bifunctionalized mesoporous TiO₂ possesses perfect anatase crystal structure and high surface area. The surface area of Fe-doped SH/TiO₂ mesoporous material is 4 times higher than that of P25. Based on the EPR results, it was found that trivalent Fe ions exist at low spin state and substitutes a part of Ti⁴⁺ ions into TiO₂ lattice. Fe-dropping in TiO₂ extends the adsorption band side of the resulting material to about 600 nm. Much high photocatalytic activity in the degradation of phenanthrene was obtained on the bifunctionalized mesoporous TiO₂ under visible light irradiation (λ > 420 nm), which is 6 times higher than that of pristine mesoporous TiO₂. The enhancement in the photocatalytic activity of bifunctionalized TiO₂ is ascribed to the extended absorption to visible light and strong interaction between SH-groups and PHE molecules.     

Preparation and characterization of mesoporous TiO<Subscript>2</Subscript> thin film

Ordered hexagonal mesoporous TiO₂ thin film was prepared by the evaporation-induced self-assembly (EISA) method using triblock copolymer (Pluronic P123) and tetrabutyl orthotitanate (Ti(OBu ⁿ )₄, TBOT) in 1-methoxy-2-propanol (C₄H₁₀O₂, PGME) solvent. The arrangement of mesopores was identified by small-angle X-ray diffraction and transmission electron microscopy (TEM). The well-ordered hexagonal mesoporous TiO₂ had a high specific surface area of 239 m²/g and an average pore size of 6.3 nm. The structure of mesoporous TiO₂ thin film was anatase with a 5.1 nm crystallite. The absorption band shift of the mesoporous TiO₂ toward longer wavelengths as calcined at 350 °C due to the residual carbon.     

Preparation and characterization of mesoporous TiO<Subscript>2</Subscript>-pillared titanate photocatalyst

Mesoporous anatase TiO₂-pillared titanate has been successfully prepared by the exfoliation-restacking route. The resulting nanocomposite was characterized by powder X-ray diffraction, scanning electron microscope, thermogravimetric analysis, IR and UV–Vis spectroscopy, specific surface area and porosity measurements. It was revealed that the present nanocomposite exhibits greatly expanded specific surface area (~200 m² g⁻¹) with 2.8- and 6.6-nm-in-diameter mesopore structure, and that there exists an electronic coupling between the host titanate sheets and the guest anatase TiO₂ nanoparticles in the pillared system. The results of degradation of methylene blue under ultraviolet and visible radiation show that the present nanocomposite exhibits much higher photocatalytic activities than that of TiO₂ nanoparticles or layered titanate alone, which are based on the bandgap excitation and the dye sensitization.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hollow spheres and their activity in methylene blue photodecomposition

PSA [poly-(styrene-methyl acrylic acid)] latex particle has been taken into account as template material in SiO₂ hollow spheres preparation. TiO₂-doped SiO₂ hollow spheres were obtained by using the appropriate amount of Ti(SO₄)₂ solution on SiO₂ hollow spheres. The photodecomposition of the MB (methylene blue) was evaluated on these TiO₂-doped SiO₂ hollow spheres under UV light irradiation. The catalyst samples were characterized by XRD, UV-DRS, SEM and BET. A TiO₂-doped SiO₂ hollow sphere has shown higher surface area in comparison with pure TiO₂ hollow spheres. The 40 wt% TiO₂-doped SiO₂ hollow sphere has been found as the most active catalyst compared with the others in the process of photodecomposition of MB (methylene blue). The BET surface area of this sample was found to be 377.6 m²g⁻¹. The photodegradation rate of MB using the TiO₂-doped SiO₂ catalyst was much higher than that of pure TiO₂ hollow spheres.     

Evaluating the ability of separation and adsorption of SO<Subscript>2</Subscript> by nano-CuO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> in high concentrations and moderate temperatures

Nano CuO-Fe₂O₃/TiO₂ adsorbents were made with different compositions of metal oxides using precipitation- desorption method. The adsorbents were applied for adsorption of SO₂ at high concentrations ranging from 10,000 to 30,000 ppm and temperatures between 523 and 627 K. Adsorption experiments were applied for adsorbents in a laboratory fixed bed adsorption column. The adsorption capacity was measured by calculating the area under the adsorption curve using the integral method. The results showed that temperature is the most affecting factor on the adsorption capacity. The highest adsorption capacity was obtained by using 17, 8 and 75 wt% of CuO, Fe₂O₃ and nano TiO₂, respectively. Characteristics of the best sorbent were determined by using Fe-SEM, XRD and nitrogen adsorption-desorption analyses.     

Photo-electrochemical behavior at different wavelengths of electrochemically obtained TiO<Subscript>2</Subscript> nanotubes

The results of an experimental study on the photo electrochemical behavior of nanotubular TiO₂ structures are presented in this work. TiO₂ samples were prepared by electrochemical anodization of Ti foils and submitted to thermal annealing. The influence of the current transient during the anodization, and of the annealing temperature on the photochemical response of the samples at different wavelengths was studied. Different behavior of the samples was observed, which may be attributed to the distributions of defects and to their different sensitivity to the temperature. The analysis of the performance of the samples in absence or in the presence of glycerol, used as hole scavenger, provided more information on the photo-catalytic properties of these structures.     

Two novel hierarchical homogeneous nanoarchitectures of TiO<Subscript>2</Subscript> nanorods branched and P25-coated TiO<Subscript>2</Subscript> nanotube arrays and their photocurrent performances

We report here for the first time the synthesis of two novel hierarchical homogeneous nanoarchitectures of TiO₂ nanorods branched TiO₂ nanotube arrays (BTs) and P25-coated TiO₂ nanotube arrays (PCTs) using two-step method including electrochemical anodization and hydrothermal modification process. Then the photocurrent densities versus applied potentials of BTs, PCTs, and pure TiO₂ nanotube arrays (TNTAs) were investigated as well. Interestingly, at -0.11 V and under the same illumination condition, the photocurrent densities of BTs and PCTs show more than 1.5 and 1 times higher than that of pure TNTAs, respectively, which can be mainly attributed to significant improvement of the light-absorbing and charge-harvesting efficiency resulting from both larger and rougher surface areas of BTs and PCTs. Furthermore, these dramatic improvements suggest that BTs and PCTs will achieve better photoelectric conversion efficiency and become the promising candidates for applications in DSSCs, sensors, and photocatalysis.     

Electrochemical preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> composite film and its high activity toward the photoelectrocatalytic degradation of methyl orange

Uniform TiO₂/SiO₂ composite films were prepared on ITO substrates by electrodeposition, and highly photoelectrocatalytic (PEC) activity of the composite films was observed toward the degradation of methyl orange (MO) in aqueous solutions. It was further found that their PEC activity was dependent on the electrodeposition parameters including deposition time, solution pH and SiO₂ content. Under the optimized condition, the PEC degradation of MO on TiO₂/SiO₂ composite film electrode could be enhanced about 14 times relative to that on neat TiO₂ film electrode. The high PEC activity of the TiO₂/SiO₂ composite film electrode was mainly attributed to the enhancement of the charge separation of photo-generated electron-hole pairs by the dispersion of SiO₂ nanoparticles in the TiO₂ matrix with the aid of the applied electric field.     

Hydrothermal synthesis of nanotubes based on (Mg,Fe,Co,Ni)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> hydrosilicates

Hydrosilicate nanotubes of the variable composition (Mg,Fe,Co,Ni)₃Si₂O₅(OH)₄ with a chrysotile structure have been synthesized under hydrothermal conditions at temperatures of 250–450°C and pressures of 30–100 MPa in media of different compositions. The conditions and ranges of formation of nanotubular hydrosilicates of the compositions under investigation have been determined. It has been demonstrated that the type of cation of the octahedral layer in the chrysotile structure has a decisive effect on the physicochemical conditions, mechanism, and rate of formation of nanotubes, as well as on their structure, morphology, and sizes.     

Dye sensitized CO<Subscript>2</Subscript> reduction over pure and platinized TiO<Subscript>2</Subscript>

TiO₂ thin and thick films promoted with platinum and organic sensitizers including novel perylene diimide dyes (PDI) were prepared and tested for carbon dioxide reduction with water under visible light. TiO₂ films were prepared by a dip coating sol–gel technique. Pt was incorporated on TiO₂ surface by wet impregnation [Pt(on).TiO₂], or in the TiO₂ film [Pt(in).TiO₂] by adding the precursor in the sol. When tris (2,2′-bipyridyl) ruthenium(II) chloride hexahydrate was used as sensitizer, in addition to visible light activity towards methane production, H₂ evolution was also observed. Perylene diimide derivatives used in this study have shown light harvesting capability similar to the tris (2,2′-bipyridyl) ruthenium(II) chloride hexahydrate.     

Facile synthesis of TiO<Subscript>2</Subscript>/ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite by sol-gel auto combustion method for superior visible light photocatalytic efficiency

Photocatalytic composite materials having photon absorption capability in the range of visible light were synthesized by loading TiO₂ (5, 10, 15, and 20 wt%) on ferrite nanocomposites by sol-gel auto-combustion method. The synthesized nanocomposites were analyzed using X-ray diffraction, Transmission electron microscopy, diffuse reflectance spectroscopy and N₂ adsorption techniques. The generation of photo active hydroxyl radicals for all the synthesized composites was found higher under the irradiation of red LED (RLED irradiation) which was confirmed by degradation of rhodamine B dye under irradiation of RLED. Photocatalytic activity of the synthesized nanocomposites was also carried out under irradiation of ultraviolet (UVLED) and blue (BLED) light emitting diodes, which is comparatively less than for the reaction under red LED irradiation. The operational parameters like catalyst amount, pH and concentration of dye solution were studied and ESI-MS degradation pathway is proposed by analyzing the degraded samples.     

Adsorption of thallium cations on RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> electrodes

The electrochemical ion-exchange properties of RuO₂–TiO₂ film electrodes with different composition have been studied in acidic and alkaline media. Thallium-cation uptake has been observed only from the latter and its extent was found to be a function of electrode potential and composition. At potentials near 0.0 V (RHE), the amount of adsorbed Tl⁺ exhibited a maximum, and decreased with increasing potential, reaching a broad minimum in the range 0.4–0.8 V. A further increase in the electrode potential, above about 1.0 V, led to an increase of adsorbed thallium species, essentially due to deposition of a few layers of Tl(III) hydroxide. In fact, the release of the latter species was found to be much slower than that of thallium ions adsorbed at 0.0 V. For the latter, in turn, the double injection/ejection mechanism, currently accepted to explain the charge-storage in oxide electrodes, seems to be confirmed. The high Γ values attained at 0.0 V indicate that the large ionic radius of Tl⁺ does not prevent its diffusion through the thinner pore texture of the oxide coatings, possibly because of its poor hydration, related with lower charge density at the ion surfaces.     

Ni<Superscript>2+</Superscript> reduction under solar irradiation over CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> catalysts

The photo-electrochemical characterization of the hetero-system CoFe₂O₄/TiO₂ was undertaken for the Ni²⁺ reduction under solar light. The spinel CoFe₂O₄ was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 V_SCE) is more cathodic than the potential of Ni²⁺/Ni couple (-0.6 V_SCE), thus leading to a feasible nickel photoreduction. TiO₂ with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni²⁺ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni²⁺ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10^-2 min^-1 according to the Langmuir-Hinshelwood model.     

Combustion of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Al thermit mixtures in steel tubes

Explored was the combustion of Fe₂O₃/TiO₂/Al thermit mixtures in steel tubes upon variation in green composition and with special emphasis on the dependence of combustion temperature T _c and burning velocity U on reaction heat Q. Special attention was given to incompleteness of combustion for compositions with low Q.