Synthesis of nanosized TiO2/SiO2 particles using microwave processes and their photocatalytic activity on the decomposition of orange II

The nanosized titania and TiO₂/SiO₂ particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination temperature has been investigated. The major phase of the pure TiO₂ particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO₂/SiO₂ particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO₂/SiO₂ particles decreases as compared to pure TiO₂ at high calcination temperatures. The TiO₂/SiO₂ particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO₂ particles.     

Effects of Heat Treatment on Photocatalytic Property of Sol-Gel Derived Polycrystalline TiO2

Polycrystalline TiO₂ in the bulk form was prepared by hydrothermal treatment of amorphous TiO₂ gel, and its photocatalytic activity for degradation of ethanol and physical properties were investigated after drying and calcination (300–650°C). The maximum photocatalytic activity reached when the polycrystalline TiO₂ was calcinated at temperatures from 300 to 500°C, which was almost the same as for a commercial TiO₂ powder. It was markedly reduced above 600°C. Photocatalytic activity of TiO₂ was affected by crystal growth of anatase, progress of sintering, anatase-rutile transformation and morphology of the polycrystalline TiO₂. It was a characteristic of the polycrystalline TiO₂ prepared in this study that the photocatalytic activity did not vary so much with the calcination temperature in the range of 300–500°C.     

Synthesis and photocatalytic activity for water-splitting reaction of nanocrystalline mesoporous titania prepared by hydrothermal method

Nanocrystalline mesoporous TiO₂ was synthesized by hydrothermal method using titanium butoxide as starting material. XRD, SEM, and TEM analyses revealed that the synthesized TiO₂ had anatase structure with crystalline size of about 8 nm. Moreover, the synthesized titania possessed a narrow pore size distribution with average pore diameter and high specific surface area of 215 m²/g. The photocatalytic activity of synthesized TiO₂ was evaluated with photocatalytic H₂ production from water-splitting reaction. The photocatalytic activity of synthesized TiO₂ treated with appropriate calcination temperature was considerably higher than that of commercial TiO₂ (Ishihara ST-01). The utilization of mesoporous TiO₂ photocatalyst with high crystallinity of anatase phase promoted great H₂ production. Furthermore, the reaction temperature significantly influences the water-splitting reaction.     

Preparation and characterization of highly photoactive nanocrystalline TiO<Subscript>2</Subscript> powders by solvent evaporationinduced crystallization method

Highly photoactive bi-phase nanocrystalline TiO₂ photocatalyst was prepared by a solvent evaporation-induced crystallization (SEIC) method, and calcined at different temperatures. The obtained TiO₂ photocatalyst was characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results show that solvent evaporation can promote the crystallization and phase transformation of TiO₂ at 100°C. When calcination temperatures are below 600°C, the prepared TiO₂ powders show bimodal pore size distributions in the mesoporous region. At 700°C, the pore size distributions exhibit monomodal distribution of the inter-aggregated pores due to the collapse of the intra-aggregated pores. At 100°C, the obtained TiO₂ photocatalyst by this method shows good photocatalytic activity, and at 400°C, its photocatalytic activity exceeds that of Degussa P25. This may be attributed to the fact that the prepared TiO₂ photocatalyst has higher specific surface areas, smaller crystallite size and bimodal pore size distribution.     

Synthesis and Characterization of Photocatalytic Porous Fe3+/TiO2 Layers on Glass

Wet chemical synthesis and preliminary photocatalytical characteristics of titania and Fe(III)-containing TiO₂ layers are presented. A highly stable coating colloids could be prepared under base- as well as acid-catalyzed condensation conditions. Structural properties of the as-prepared wet gels and sintered films were investigated using SEM, TEM, XRD as well as optical absorption spectroscopy, DTA-TG analysis and photomineralisation studies. X-ray amorphous wet titania gel layers start to crystallize at 500°C forming the characteristic anatase phase. In the presence of iron ions (Fe/Ti = 1), nanocrystalline FeTiO₃ ilmenite phase forms. Both TiO₂ and Fe-containing TiO₂ films demonstrate a photocatalytic activity in the process of the photomineralization of dichloroacetic acid.     

Preparation of TiO2 Thin Film Photocatalysts by Dip Coating Using a Highly Viscous Solvent

TiO₂ thin film photocatalysts coated onto soda lime glass were prepared by a dip coating process using a highly viscous solvent. The source of the TiO₂ was tetraisopropyl orthotitanate, and -terpineol was used as the solvent. Two types of thin film preparation procedures based on dip coating (a sol-gel system and thermal decomposition system) were used to prepare the samples. TiO₂ thin films were obtained after calcination at 450°C for 1 hour. The film thickness obtained with a single dipping was proportional to the viscosity of the dip coating solutions. The obtained thin films were transparent with a thickness of 1 m. The crystal form of the obtained photocatalyst films was anatase alone. The thin films were formed with aggregated nano-sized TiO₂ single crystals (7–15 nm). The photocatalytic activity of the TiO₂ thin films, as evaluated by the photooxidation of NO (1 ppm) in dry air, was as high as our previous TiO₂ thin films prepared by the sol-gel method.     

A sol–gel combustion synthesis method for TiO<Subscript>2</Subscript> powders with enhanced photocatalytic activity

TiO₂ photocatalytic powders were synthesized by a sol–gel combustion synthesis method in which urea was used as the fuel and titanyl nitrate was used as the oxidizer. Various fuel-to-oxidizer ratios were studied for their effects on the combustion phenomena and the properties of the synthesized TiO₂. The fuel-to-oxidizer ratio was found to determine the maximum combustion temperature, which in turn affects the specific surface area, crystallite size, and weight fraction of anatase phase of the synthesized TiO₂. The synthesized TiO₂ all contain carbonaceous species and are either pure anatase or anatase–rutile mixed phase in crystalline structure. The photocatalytic activity of the TiO₂ was found to correlate to a certain degree with the specific surface area, crystallite size, weight fraction of anatase phase, and visible and IR absorbances. The mixed phase TiO₂ shows a higher photocatalytic activity than the pure anatase phase TiO₂ when containing a small fraction (<~25 wt%) of rutile phase but a lower phoyocatalytic activity when containing a large fraction (>~25 wt%) of rutile phase. The synthesized TiO₂ all show higher photocatalytic activity than Degussa P25 TiO₂. The enhanced photocatalytic activity was attributed mainly to sensitization by the carbonaceous species and larger amounts of hydroxyl group adsorbed on the TiO₂ surface.     

Microstructure and Photocatalytic Property of SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> Under Various Process Condition

Nanophase silica-titania particles were prepared by two different synthetic routes, namely, sol–gel and hydrothermal processing. The crystallinity and crystallographic phases, particle size and surface area of the materials were controlled by varying the calcination temperature, and/or the ratio of Si to Ti. It was determined by XRD that the crystallite sizes of SiO₂-TiO₂ prepared by sol–gel and hydrothermal processing decreased from 11 to 6 nm and 12 to 9 nm, respectively, as the mole fraction of silica was increased from 0.1 to 0.4. It is proposed that the presence of the amorphous silica suppresses the growth of anatase TiO₂ grains and their phase transformation to rutile. The photocatalytic decomposition rate of 1,4-dichlorobenzene (DCB) in aqueous solution with the sol–gel derived SiO₂-TiO₂ powder prepared at 750 °C was about 10 ± 5% higher than that observed with Degussa P25, whereas the SiO₂-TiO₂ samples prepared by hydrothermal processing at 250 °C showed a slightly lower decomposition rate than P25.     

Characterization and activity of visible light–driven TiO<Subscript>2</Subscript> photocatalysts co<Emphasis Type="Bold">-</Emphasis>doped with nitrogen and lanthanum

Nitrogen and lanthanum co-doped titania photocatalysts were prepared by a modified sol–gel process with urea and lanthanum nitrate doping precursors and characterized by various techniques including XRD, FTIR, TEM, EDS, and UV–Vis DRS. The average crystallite size was ca. 12–15 nm as calculated from XRD patterns, and anatase was the dominant crystalline type in the as-prepared samples. The UV–Vis DRS of the samples revealed significant absorption within the range of 400–500 nm. The optimum composition of N(0.020)La(0.012)TiO₂ exhibited the highest photocatalytic activity for degradation of methyl orange (MO) aqueous solution under simulated sunlight. The percent degradation of MO was ca. 97% for N(0.020)La(0.012)TiO₂ under simulated sunlight irradiation for 9 h. The enhanced photocatalytic activity was ascribed to the synergistic effects of the nitrogen and lanthanum co-doping.     

Synthesis of visible-light reactive TiO2−xNy photocatalyst by mechanochemical doping

Yellowish TiO_2−xN_y was prepared by a novel mechanochemical nitrogen-doping method. The samples were prepared by a high-energy ball milling of P25 titania with different nitrogen sources such as hexamethylenetetramine, urea or ammonium carbonate, followed by calcination in air at 400 °C. The high mechanical energy accelerated the phase transformation of anatase to rutile, while the existence of the nitrogen reagents tended to block the transformation. The calcination treatment slightly increased the crystallinity of the prepared titania. The prepared powders possessed two absorption edges at around 400 and 540 nm and showed an excellent photocatalytic ability for the oxidation of nitrogen monoxide under visible light irradiation. Under the irradiation of visible light with wavelengths of >510 nm, nitrogen monoxide could be continuously removed by the nitrogen doped titania prepared from the P25 titania-hexamethylenetetramine mixture, while the powders prepared using urea and ammonium carbonate as nitrogen sources showed lower activities. This mechanochemical technique might be widely useful for doping oxides with nonmetallic elements.     

High temperature stability and photocatalytic activity of nanocrystalline anatase powders with Zr and Si co-dopants

TiO₂ nanopowders doped by Si and Zr were prepared by sol–gel method. The effects of Si and Zr doping on the structural, optical, and photo-catalytic properties of titania nanopowders have been studied by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and UV–Vis absorption spectroscopy. XRD results suggest that adding impurities has a significant effect on anatase phase stability, crystallinity, and particle size of TiO₂. Titania rutile phase formation in ternary system (Ti–Si–Zr) was inhibited by Zr⁴⁺ and Si⁴⁺ co-doped TiO₂ in high temperatures (500–900 °C) and 36 mol% anatase composition is retained even after calcination at 1,000 °C. The photocatalyst activity was evaluated by photocatalytic degradation kinetics of aqueous methylen orange under visible radiation. The results show that the photocatalytic activity of the 20 %Si and 15 %Zr co-doped TiO₂ nanopowders have a larger degradation efficiency than pure TiO₂ under visible light.     

单斜与锐钛矿双晶相TiO2/MWNTs复合材料的制备及其可见光光催化活性

以超强耐酸碱的表面活性剂-丁基封端脂肪醇聚氧乙烯醚作为晶型调节剂,利用钛酸丁酯和氢氧化钠的水热反应制备了单斜相与锐钛矿相双晶相TiO2/多壁碳纳米管(简称MWNTs)复合材料,并考察了复合材料的可见光光催化活性。结果显示:MWNTs的加入可调控TiO2的晶相组成,增强TiO2的光催化活性,其中含5%MWNTs的样品具有较高的催化降解效率;随煅烧温度的升高,样品的光催化活性大幅提升。其机理归因于(1)促进单斜相和锐钛矿相双晶相结构的形成;(2)碳纳米管优良的导电作用及碳纳米管/TiO2间的异质结效应;(3)高温下碳纳米管分解产生的碳元素掺杂作用。     

单斜与锐钛矿双晶相TiO2/MWNTs复合材料的制备及其可见光光催化活性

以超强耐酸碱的表面活性剂-丁基封端脂肪醇聚氧乙烯醚作为晶型调节剂,利用钛酸丁酯和氢氧化钠的水热反应制备了单斜相与锐钛矿相双晶相TiO₂/多壁碳纳米管(简称MWNTs)复合材料,并考察了复合材料的可见光光催化活性。结果显示:MWNTs的加入可调控TiO₂的晶相组成,增强TiO₂的光催化活性,其中含5%MWNTs的样品具有较高的催化降解效率;随煅烧温度的升高,样品的光催化活性大幅提升。其机理归因于(1)促进单斜相和锐钛矿相双晶相结构的形成;(2)碳纳米管优良的导电作用及碳纳米管/TiO₂间的异质结效应;(3)高温下碳纳米管分解产生的碳元素掺杂作用。     

Preparation and Characterization of Bismuth Doped TiO2 Thin Films

A series of Bismuth-doped titanium oxide (Bi-doped TiO₂) thin films on glass substrates have been prepared by sol-gel dip coating process. The prepared catalysts were characterized by XRD and XPS. The photocatlytic activity of the thin film catalysts was evaluated through the photodegradation of aqueous methyl orange under UV illumination. The experiments demonstrated that the Bi-doped TiO₂ prepared was anatase phase. The doped bismuth was in the 3⁺ oxidation state. The presence of Bi significantly enhanced the photocatalytic activity of TiO₂ films. At calcination temperature of 500°C, with doping concentration of 2 wt %, Bi-doped TiO₂ thin film showed the highest photocatalyic activity.     

The influence of titanium dioxide phase composition on dyes photocatalysis

A comparative study of TiO₂ powders prepared by sol–gel methods is presented. Titanium tetraisopropoxide was used as the precursor for the sol–gel processes. The effects of the annealing treatment on phase, crystallite size, porosity and photodegradation of dyes (methyl orange and methylene blue) were studied. The phase structure, microstructure and surface properties of the films were characterized by using X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). The X-ray diffraction was used for crystal phase identification, for the accurate estimation of the anatase–rutile ratio and for the crystallite size evaluation of each polymorph in the samples. It was found that the only TiO₂ anatase phase of the synthesized TiO₂ develops below 500 °C, between 600 and 800 °C the anatase coexist with rutile and above 800 °C only the rutile phase was found in the samples. Attention has been paid not only to crystal structures, but also to the porosity, the particle size and the photocatalytic properties. However, the annealing temperature was found to have significant influence on the photocatalytic properties. Different TiO₂ doctor blade thin films were obtained mixing the sol gel powder (100% anatase) and TiO₂ Aldrich with TiO₂ Degussa P25. The surfactant (Triton X100 or sodium dodecyl sulfate) affects the packing density of the particles during deposition and the photocatalytic degradation efficiency of the dyes. The photocatalytic degradation kinetics of methyl orange and methylene blue using TiO₂ thin film were investigated.     

Effect of synthesis conditions on the preparation of titanium dioxides from peroxotitanate solution and their photocatalytic activity

Nanosized TiO₂ particles were prepared by the hydrothermal method from the amorphous powders which were precipitated in an aqueous peroxotitanate solution. The physical properties of the nanosized TiO₂ particles prepared were investigated. We also examined the activity of TiO₂ particles as a photocatalyst on the decomposition of orange II. The titania sol can be successfully crystallized to the anatase phase through hydrothermal aging at temperatures higher than 160°C. The particle size increases from 18 to 26 nm as the synthesis temperature increases from 140 to 200°C. Titania particles prepared at 180°C show the highest activity, and titania particles calcined at 400°C show also the highest activity on the photocatalytic decomposition of orange II.     

Aerosol-assisted synthesis of mesoporous titania nanoparticles with high surface area and controllable phase composition

Mesoporous titania nanoparticles (denoted as MTN) with high surface area (e.g., 252 m² g⁻¹) were prepared using tetrapropyl orthotitanate (TPOT) as a titania precursor and 10–20 nm or 20–30 nm silica colloids as templates. Co-assembly of TPOT and silica colloids in an aerosol-assisted process and immediate calcination at 450 °C resulted in anatase/silica composite nanoparticles. Subsequent removal of the silica colloids from the composite by NaOH solution created mesopores in the TiO₂ nanoparticles with pore size corresponding to that of silica colloids. Effects of silica colloids’ contents on MTN porosity and crystallites’ growth at a higher calcination temperature (e.g., 1000 °C) were investigated. Silica colloids suppressed the growth of TiO₂ crystallites during calcination at a higher calcination temperature and controllable contents of the silica colloids in precursor solution resulted in various atomic ratios of anatase to rutile in the calcinated materials. The mesostructure and crystalline structure of these titania materials were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), differential thermal analysis (DTA)-thermo-gravimetric analysis (TGA), and N₂ sorption.     

A comparative study on characterization and photocatalytic activities of gadolinium–boron codoped and mono-doped TiO2 nanoparticles

Gadolinium?Cboron codoped and mono-doped TiO₂ nanoparticles were prepared using a sol?Cgel method, and tested for photocatalytic activity by the UV light after a further calcination process. For comparison, a pure TiO₂ sample was also prepared and tested under the same conditions. The prepared catalysts were characterized by X-ray diffraction, scanning electron microscope, and UV?CVis spectra. The photocatalytic activity of the samples was evaluated through the photo-degradation of three different dyes under UV light. The experiments demonstrated that the gadolinium?Cboron codoped TiO₂ (Gd?CB?CTiO₂) sample calcined at 500?°C possessed the best photocatalytic activity, and the photodegradation rate of the Reactive Brilliant Red K2G aqueous solution could reach to 95.7% under UV irradiation for 80?min. The results showed that Gd?CB?CTiO₂ has smaller crystallite size and higher photocatalytic activity than that of mono-doped TiO₂ samples and undoped TiO₂.     

Synthesis of high surface area nanocrystalline anatase-TiO2 powders derived from particulate sol-gel route by tailoring processing parameters

Stabilised titania sols were prepared using an additive free particulate sol-gel route, via electrostatic stabilisation mechanism, with various processing parameters. Peptisation temperature, 50°C and 70°C, and TiO₂ concentration, 0.1, 0.2 and 0.4 molar, were chosen as processing parameters during sol preparation. Results from TiO₂ particle size and zeta potential of sols revealed that the smallest titania hydrodynamic diameter (13 nm) and the highest zeta potential (47.7 mV) were obtained for the sol produced at the lower peptisation temperature of 50°C and lower TiO₂ concentration of 0.1 M. On the other hand, between the sols prepared at 70°C, smaller titania particles (20 nm) and higher zeta potential (46.3 mV) were achieved with increasing TiO₂ concentration up to 0.4 M. X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) results of produced powders annealed at different temperatures showed that the 300°C annealed powder made from 0.1 M sol prepared at 50°C was a mixture of anatase and brookite, corresponding to a major phase of anatase (∼95% estimated), with the smallest average crystallite size of 1.3 nm and the highest specific surface area (SSA) of 193 m²/g. Furthermore, increasing TiO₂ concentration up to 0.4 molar for the sols prepared at 70°C resulted in decreasing the average crystallite size (1.9 nm at 300°C) and increasing SSA (116 m²/g at 300°C) of the powders annealed at different temperatures. Anatase-to-rutile phase transformation temperature was increased with decreasing peptisation temperature down to 50°C, whereas TiO₂ concentration had no effect on this transition. Anatase percentage increased with decreasing both peptisation temperature and TiO₂ concentration. Such prepared powders can be used in many applications in areas from photo catalysts to gas sensors.     

Solar active nano-TiO2 for mineralization of Reactive Red 120 and Trypan Blue: 1st Nano Update

Nano-TiO₂ was synthesized by sol–gel method. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) images, transmission electron microscope (TEM), BET surface area measurement and DRS analysis. The formation of anatase phase nano-TiO₂ was confirmed by XRD measurements and its crystalline size is found to be 15.2 nm. SEM images depict the crystalline nature of prepared TiO₂. The BET surface area of prepared TiO₂ is found to be 86.5 m² g^?1 which is higher than that of commercially available TiO₂–P25. The photocatalytic activity of prepared anatase phase TiO₂ has been tested for the degradation of two azo dyes: Reactive Red 120 (RR 120) and Trypan Blue (TB) using solar light. The photocatalytic activity of nano-TiO₂ is higher than TiO₂–P25 under solar light. The mineralization of dyes has been confirmed by chemical oxygen demand (COD) measurements.