Photocatalytic degradation of methylene blue and phenol on Fe-doped sulfated titania

Fe-doped sulfated titania (FST) photocatalysts with high photocatalytic activity were prepared from industrial titanyl sulfate solution and characterized using X-ray diffraction (XRD), thermogravimetry analysis?Cdifferential scanning calorimeter (TGA-DSC), Fourier transform infrared spectroscopy (FT-IR), and nitrogen adsorption?Cdesorption techniques. The photocatalytic activity of the FST photocatalyst was evaluated using the photodegradation of methylene blue (MB) and the photooxidation of phenol in aqueous solutions in the presence of UV irradiation, respectively. The effect of various parameters, such as calcining temperature, calcination time, initial concentration of substrate, amount of catalyst and pH value on the photocatalytic activity of FST photocatalyst was investigated. Among the parameters studied, calcining temperature, initial concentration of substrate, and amount of catalyst have a very similar effect on the activity of FST photocatalyst for both the photodegradation of MB and the photooxidation of phenol, while the others have distinct differences. The optimal calcination conditions were 500?°C, 1.5?h and 650?°C, 2.5?h; the optimal catalyst concentration were 1.0 and 1.2?g?L^?1; the optimal pH values were 8 and 4 for the photodegradation of MB and the photooxidation of phenol, respectively. In addition, the mechanism for the high photocatalytic efficiency of FST photocatalyst has also been put forward.     

Thermodynamic studies of methylene blue adsorption onto Fe-doped sulfated titania

Adsorption equilibrium of methylene blue onto Fe-doped sulfated titania (FST) samples was studied at different temperatures (298, 303, and 308 K). Based on the wavelength scanning from 580 to 760 nm, the wavelength of maximum absorbance of methylene blue was determined to be 666 nm and the corresponding calibration curve can be described by the equation of A = 0.0068 + 0.1514C. The adsorption of methylene blue onto FST samples was conformed to the Langmuir isotherms. The absorption capacity of each FST sample for methylene blue increases with increasing temperature. The increase in the adsorption parameters (q _m, b, and K ₀) and the positive ΔH ^θ reveal the endothermic feature of this adsorption process. The negative ΔG ^θ shows the adsorption of methylene blue onto FST samples can be carried out spontaneously at the examined temperatures. Furthermore, with the calcination temperature increases, the variation in crystallization degree, the surface and the sulfur species will obviously influence the adsorption properties of FST samples and the thermodynamic parameters of this adsorption process.     

Room temperature olefins oligomerization over sulfated titania

Oligomerization reaction was carried out at room temperature using sulfated titania as catalyst. Total isobutene conversion was obtained with high stability for a long period of time. In case of deactivation, total reactivation of the catalyst was reached.     

Effects of urea on the microstructure and photocatalytic activity of bimodal mesoporous titania microspheres

Bimodal mesoporous TiO₂ microspheres with high photocatalytic activity were prepared by a hydrothermal method using titanium sulfate as precursor in the presence of urea. The results indicate that all prepared samples show bimodal pore-size distributions in the mesoporous region: smaller intra-aggregated pores with peak pore diameter of ca. 2 nm and larger inter-aggregated pores with peak pore diameter of ca. 12.5 nm. The molar ratio of urea to Ti(SO₄)₂ (R_u) has an obvious influence on the morphology, microstructure and photocatalytic activity of TiO₂. With increasing R_u, specific surface areas and porosity increase, contrarily, the crystallite size and relative anatase crystallinity decrease. The photocatalytic activity first increases with R_u. At R_u = 2.0, the photocatalytic activity reaches the highest and is obviously higher than that of Degussa P25. With further increasing R_u, the photocatalytic activity decreases. The formation rate of hydroxyl radicals during photocatalysis has a positive correlation with the photocatalytic activity.     

Surface properties and photocatalytic activity of nanocrystalline titania films

In this work the efficiency and physicochemical details of a thin film produced by help of a microwave assisted sol gel technique is compared to different commercial powders (Degussa P25 and Hombikat UV100) deposited on glass substrates. Furthermore, a supercritical produced TiO₂ powder (SC 134) was included in the comparison.The prepared TiO₂ films were characterized using XRD, XPS, AFM, DSC and DLS. The photocatalytic activity was determined using stearic acid as a model compound. Investigation of the prepared films showed that the Degussa P25 film and the sol–gel film were the most photocatalytic active films. The activity of the films was found to be related to the crystallinity of the TiO₂ film and the amount of surface area and surface hydroxyl groups. Based on the XPS investigation of the films before and after UV irradiation it was suggested that the photocatalytic destruction of organic matter on TiO₂ films proceeds partly through formation of hydroxyl radicals which are formed from surface hydroxyl groups created by interactions between adsorbed water and vacancies on the TiO₂ surface. Furthermore a correlation between the amount of OH groups on the surface of the different TiO₂ films and the photocatalytic activity was found.     

Large-scale preparation of ordered titania nanorods with enhanced photocatalytic activity

A titania layer with ordered nanostructures is expected to be of high photocatalytic activity due mainly to its high specific surface area. In the present work, large-area films with ordered titania nanorods were deposited on titanium substrates through a solution approach. The nanorods, with the phase composition of a mixture of anatase and rutile, grew on top of a condensed anatase interlayer along mainly the rutile [001]-axis. The photocatalytic activity was evaluated by decomposing rhodamine B in water and compared with the general sol-gel derived titania films and a commercial DP-25 titania coating. It is found that the as-deposited titania nanorods exhibited extremely high initial photocatalytic activity but declined to a poor value after the consumption of beneficial oxidative peroxo complexes coordinated to Ti(IV). A subsequent thermal treatment eliminated such complexes but at the same time improved the crystallinity of the titania nanorods. The photocatalytic activity of the thermally treated titania nanorods was stable and significantly higher than that of the sol-gel derived film and commercial DP-25 coating.     

Preparation and photocatalytic activity of multi-modally macro/mesoporous titania

Hierarchically disorder sponge-like macro/mesoporous titania was prepared by adding distilled water dropwise to a coating of tetrabutyl titanate. The results reveal that the un-calcined samples show obvious photocatalytic activity and multi-modal pore-size distribution. With increasing calcination temperatures, the photocatalytic activity and crystallinity increase. At 400°C, the calcined sample shows the highest photocatalytic activity. Further increasing the calcination temperatures results in the decrease of photocatalytic activity due to the drastic decrease of specific surface areas. However, the 600°C-calcined sample exhibits the highest specific photocatalytic activity due to high anatase crystallinity.     

Facile synthesis of spiny mesoporous titania tubes with enhanced photocatalytic activity

We demonstrate here for the first time an original and facile approach to synthesizing a novel TiO(2) tube with a spiny mesoporous wall. The photocatalytic activity of the spiny mesoporous tube was greatly enhanced owing to the superior light reflecting ability of the tubular structure as well as the crosslinked spiny nanosheets.     

Highly porous titania network: fabrication,characterization and photocatalytic activity

Highly porous titania network (CPTN) has been prepared using the protein entrapped cellulose gel as structural template via a template-assisted sol–gel process. The key point toward highly porous titania network lies in the entrapped proteins with template. To elucidate this, the effect of protein loading of template on the structure of final material was investigated. It reveals that high protein loading in cellulose gel gives rise to both large macroporosity and large surface area of final titania network. Specially, highly porous titania network is possessed of bimodal pore system and withstands high compressive pressure over 19 MPa. The highly porous titania network is found to have higher catalytic activity for the photodegradation of methylene blue than its counterpart of commercial P25 and microporous titania one (CTN) that derived from the pure cellulose gel. As a result, the macropores of titania network serve as the leading role in improving the photocatalytic activity. The proposed method might be applied to fabricate other inorganic network with desired macropore structure.     

Enhanced photocatalytic activity of bimodal mesoporous titania powders by C60 modification

In this work, fullerene modified TiO(2) nanocomposites (denoted as C(60)/TiO(2)) with low C(60) loadings (0-1.5 wt.%) have been prepared by a simple hydrothermal method using tetrabutylorthotitanate (TBOT, Ti(OC(4)H(9))(4)) as the titanium precursor. The as-prepared C(60)/TiO(2) nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, UV-visible spectrophotometry, nitrogen adsorption, and X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy. The formation of hydroxyl radicals (˙OH) on the surface of UV-illuminated TiO(2) is probed by photoluminescence using terephthalic acid as a probe molecule. Our results have demonstrated that C(60) molecules can be dispersed as a monolayer onto bimodal mesoporous TiO(2)via covalent bonding. The photocatalytic oxidation rate of gas-phase acetone over C(60)/TiO(2) nanocomposites is greater than that over pure TiO(2), commercial Degussa P25 (P25) and C(60)-TiO(2) counterparts prepared by simple impregnating mixing. In particular, 0.5 wt.% C(60)/TiO(2) nanocomposites show the greatest photocatalytic activity with the rate constant k exceeding that of P25 by a factor of 3.3. Based on the results of the current study, we propose that C(60) molecules doped onto TiO(2) act as "electron acceptors" responsible for the efficient separation of photogenerated charge carriers and the enhancement of photocatalytic activity. The proposed mechanism for the observed photocatalytic performance of C(60)/TiO(2) nanocomposites is further corroborated by experiments on hydroxyl radical and transient photocurrent response.     

Synthesis of iron-containing nitrogen-doped titania by hydrothermal method and its photocatalytic activity

By a hydrothermal method, iron and nitrogen co-doped TiO₂ and iron oxide impregnated nitrogen-doped TiO₂ were prepared. The obtained Fe and N co-doped TiO₂ showed mixed anatase, rutile, and brookite phases, and high specific surface areas above 160 m²/g. The Fe co-doping was proved to be effective to enhance the visible light absorption ability; however, the photocatalytic activity in deNO _x experiment decreased due to the increase in the amount of lattice vacancy. On the other hand, the photocatalytic activity of N-doped TiO₂ was improved by the impregnation of iron oxide.     

Mesoporous titania photocatalyst: effect of relative humidity and aging on the preparation of mesoporous titania and on its photocatalytic activity performance

Mesoporous TiO₂ has been synthesized by the sol–gel method, using a nonionic triblock copolymer P123 as surfactant template under acidic conditions. The as-prepared samples were characterized by thermogravimetry–differential thermal analysis (TG–DTA), nitrogen absorption–desorption (BET), field emission scanning electron microscopy, and transmission electron microscopy. The photocatalytic activity of the mesoporous TiO₂ was evaluated by degradation of methylene blue under high-intensity UV light irradiation; the amount of methylene blue was measured by UV–visible spectroscopy. TG–DTA analysis revealed that the surfactant had been removed partly in as-synthesized samples. BET analysis proved that all the samples retained mesoporosity with a narrow pore-size distribution (4.5–6.3 nm) and high surface area (103–200 m²/g). All calcined mesoporous TiO₂ had high photocatalytic activity in the photodegradation of methylene blue.     

Influence of phosphate modification on the surface properties of sulfated titania

The effect of increasing phosphate loading on the bulk and surface properties of sulfated titania was investigated by thermogravimetry, X-ray diffraction, laser Raman spectroscopy and FT-IR spectroscopy. The acid properties of the material were probed by low-temperature FT-IR spectroscopy of adsorbed CO. Monophosphate species in varying symmetries and protonation states were detected on the surface of the sulfated titania at low loadings. These condensed with formation of surface polyphosphates with increasing loading. Phosphate blocks weak Lewis acid sites and partially displaces sulfate groups. While the acid, properties of phosphate-free sulfated titania are dominated by Lewis acid sites, the phosphated samples also developed Brønsted acid sites due to the presence of POH groups on the surface.     

Effects of pH and temperature on photocatalytic activity of PbTiO3 synthesized by hydrothermal method

PbTiO₃ photocatalyst was synthesized successfully by facile hydrothermal method. The effects of the hydrothermal reaction temperatures and the pH values of the systems on the photocatalytic activities of PbTiO₃ were investigated in detail. The photocatalytic activities of samples were evaluated by the degradation of methyl orange (MO) aqueous solution under simulated solar irradiation. The as-obtained PbTiO₃ sample exhibits anisotropical growth along the (0 0 1) plane, and its photocatalytic activity is about 3 times higher than that of PbTiO₃ prepared by precipitation method. Moreover, the as-prepared PbTiO₃ has high stability during photocatalytic oxidation process, and does not cause secondary pollution.     

A sonochemical approach to hierarchical porous titania spheres with enhanced photocatalytic activity

A novel sonochemical approach has been developed to prepare hierarchical porous titania spheres in the presence of a triblock copolymer; it was found that textural meso- and macro-porosity could enhance the photocatalytic activity of mesoporous TiO2.     

Great enhancement of photocatalytic activity of nitrogen-doped titania by coupling with tungsten oxide

The TiO2-N-x%WO3 composite photocatalysts were prepared by introducing WO3 into nitrogen-doped TiO2. The composite catalysts present much higher photocatalytic activity than TiO2 and nitrogen-doped TiO2 under both ultraviolet and visible light irradiation. Diffuse reflectance UV-vis spectra, XPS analysis, and IR spectra show that the coordinated nitrogen species (or N-metal-O linkages) may contribute to the visible light photocatalytic activity. WO3 coupling increases the active nitrogen species and thus enhances the visible light activity of the composite photocatalysts. The superior activity of TiO2-N-x%WO3 composite photocatalysts upon UV light irradiation can be rationalized in terms of efficient charge separation and high adsorption affinity of WO3.     

Phase-compositional control and visible light photocatalytic activity of nitrogen-doped titania via solvothermal process

Nitrogen-doped titania nanoparticles consisted of pure anatase, rutile and brookite phases were successfully prepared by a solvothermal process in TiCl₃-HMT (hexamethylenetetramine, C₆H₁₂N₄)-alcohol mixed solution. The powders were yellow or beige and showed excellent visible light absorption and photocatalytic ability for the oxidative destruction of nitrogen monoxide under irradiation of visible light of wavelength >510 nm.     

Hydrothermal synthesis and catalytic properties of superacid sulfated titania

The micromorphology and catalytic properties of nanocrystalline TiO₂/SO₄²⁻ superacid systems prepared by a conventional sol-gel process, as well as hydrothermal (HT) and microwave-hydrothermal (MW-HT) processes, were analyzed. The samples prepared by the HT process have no developed surfaces and, as a consequence, have no high reactivity in isobutylene oligomerization. The TiO₂/SO₄²⁻ samples prepared by single-step MW-HT synthesis in their morphologic, acid, and catalytic properties are competitive with the systems prepared by the conventional multistage sol-gel process.     

Synthesis of a new magnetic nano-island titania photocatalyst and investigation of its photocatalytic activity

In this study, a new magnetic nano-island titania photocatalyst (Fe₃O₄@SiO₂·TiO₂) was designed and fabricated. Precipitation, sol-gel, and hydrothermal methods were utilized to synthesize the magnetite, silica shell, and titania islands, respectively. Characterization of the synthesized catalyst was carried out by XRD, EDS, FTIR, SEM, TEM, and VSM analysis. The TEM analysis revealed that the overall size of the catalyst is about 490 nm, and titania island on the magnetic core was about 50 nm. VSM analysis showed that the photocatalyst has a fantastic paramagnetic property with magnetic saturation of 52 emu g^?1. Furthermore, photocatalytic activity of the synthesized catalyst was evaluated in the removal of p-nitrophenol as a typical pollutant of nitro-aromatic compounds such that its degradation and mineralization efficiency were obtained at 82 and 45% after 100 and 200 min of the process, respectively, using 100 ppm of the photocatalyst in pH = 6.5.