Synthesis Of TiO2 Powders Research Articles

Photocatalytically active titanium dioxide nanopowders: Synthesis, photoactivity and magnetic separation

Two approaches were used to obtain nanocrystalline titanium dioxide (TiO2) photocatalyst powders. Firstly, low-temperature synthesis method and secondly liquid flame spraying. The structural properties of the produced powders were determined with X-ray diffraction, transmission electron microscopy and nitrogen adsorption tests. The photocatalytic properties of the powders were studied with methylene blue (MB) discoloration tests. After discolorations tests, TiO2 was coagulated with magnetite particles using FeCl3·6 H2O at a fixed pH value. Magnetic separation of coagulated TiO2 and magnetite was carried out by a permanent magnet. The obtained results showed that the particle size of the powders synthesized at low-temperature was very small and the specific surface area high. The phase content of the powder was also shown to depend greatly on the acidity of the synthesis solution. Powder synthesized by liquid flame spraying was mixture of anatase and rutile phases with essentially larger particle size and lower specific surface area than those of low-temperature synthesized powders. The MB discoloration test showed that photocatalytic activity depends on the phase structure as well as the specific surface area of the synthesized TiO2 powder. The magnetic separation of TiO2–magnetite coagulate from solution proved to be efficient around pH:8.

Photocatalytic inactivation of Gram-positive and Gram-negative bacteria by reactive plasma processed nanocrystalline TiO2 powder

Nanocrystalline TiO2 powder is synthesized using a novel reactive plasma process in which the precursor TiH2 powder is oxidized through thermal plasma in-flight route to generate nanocrystalline TiO2 powder. The synthesized powder consists of nano-sized TiO2 particles, both anatase and rutile phases, in which anatase is the predominant phase. An additional feature of the plasma synthesized TiO2 powder is the higher surface concentration of Ti3+ state and hydroxyl group that enhance its photocatalytic activity. The photocatalytic inactivation of Gram-positive Enterococcus and Gram-negative Klebsiella bacteria is studied using the plasma synthesized TiO2 nanopowder with 365 nm ultraviolet (UV) light. The mechanism behind the photocatalytic disinfection of bacteria is discussed. The plasma synthesized TiO2 nanopowder catalyst is found effective in killing Enterococcus and Klebsiella. The results corroborated that the plasma synthesized TiO2 powder can be used for waste water treatment and water purification.

Iron–sulfur codoped TiO2 anatase nano-materials: UV and sunlight activity for toluene degradation

Iron and sulfur single- and co-doped TiO2 nanocrystals were prepared and characterized by a multitechnique approach. The presence of sulfur affected drastically the crystal size of anatase as well as other morphological characteristics such as BET surface area, pore volume and pore size. Significant differences were also detected on the isolated OH species concentration as a function of sulfur content. On the contrary, X-ray absorption spectroscopy (XAFS) showed that sulfur did not alter substantially the structural and electronic properties of Fe on TiO2. The photocatalytic activity of the synthesized TiO2 powders was studied in the gas-phase oxidation of toluene. The trials showed that the co-doped S/Fe-TiO2 nanomaterials have enhanced photo-activity compared to the reference single-doped Fe-TiO2 under both sunlight and UV-light irradiation. This is not however the case if compared with the single S-doped materials. Sulfur additionally modifies the selectivity of toluene photo-oxidation toward partial oxidation products. The partial vs. total oxidation yield ratio increased with increasing S content in both co-doped S/Fe-TiO2 or single-doped S-TiO2 series and was attributed to differences in surface properties related to both S-containing and OH entities.

Comparison of Sonochemistry Method and Sol-Gel Method for the Fabrication of TiO<sub>2</sub> Powder

Sol-gel with sonochemical process and sol-gel method were used for the fabrication of photocatalytic TiO2 powder and the properties of the TiO2 powder thus prepared were examined and compared. For the synthesis of TiO2 powder, the starting material was Ti-butoxide and H2O and the reaction was carried out at 80 °C in a sol-gel method. On the other hand, Ti-butoxide was reacted with H2O in an ultrasonic frequency of 23 kHz with ultrasonic powers of 800 W for two hours. After evaporation, 24 hours aging time was kept at 400 °C in both cases, the final product appeared was the anatase phase. Ultrasonic chemical method was found to be excellent for flocculation and crushing effects where as in sol-gel method, the product obtained was of high purity and high homogeneity. Sol-gel with sonochemical process has found to be excellent for flocculation and crushing effects. From Sol-gel method, the size of TiO2 particles produced were found to be about 20 nm, spherical, homogeneous while severe agglomeration. In contrast, by sonochemistry method, the size of TiO2 particles produced were about 10 ~ 22 nm size and it has shown more photocatalytic activity than sol-gel sample which is about 28.7 % greater efficiency

Adsorption and photocatalysis of nanocrystalline TiO2 particles prepared by sol–gel method for methylene blue degradation

Titanium dioxide (TiO2) powders were synthesized by using TiO2 colloidal sol prepared from titanium-tetraisopropoxide (TTIP) and used as a starting material by applying the sol–gel method. The effect of aging times and temperatures on physical and chemical properties of TiO2 sol particles was systematically investigated. The results showed that the crystallinity and average particle size of TiO2 can be successfully controlled by adjusting the aging time and temperature. The samples after calcination of TiO2 powders were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and nitrogen adsorption measurements. In addition, the photocatalytic activity of synthesized TiO2 powders was evaluated by studying the degradation of 10ppm aqueous methylene blue dye under 32W high pressure mercury vapor lamp with 100mg of TiO2 powders. The highest photocatalytic activity was observed in TiO2 powder synthesized at 90°C for 0h attributed to the presence of anatase and rutile phases in an 80:20 ratio.

Antibacterial Activity of TiO<sub>2</sub> and Fe<sup>3+</sup> Doped TiO<sub>2</sub> Nanoparticles Synthesized at Low Temperature

Nanocrystalline TiO2 powder with and without Fe3+ doping were successfully synthesized at low temperature by a microwave-assisted sol–gel method. The synthesized TiO2 powders were characterized by XRD, BET, FT-IR and SEM. It was found that anatase phase was formed after refluxed at 80°C using a domestic microwave oven. Antibacterial behavior towards E. coli was then studied under UV and fluorescent irradiation. The synthesized pure TiO2 powder exhibited superior antibacterial activity under fluorescent irradiation compared to the commercial TiO2 (Degussa P25). It can efficiently destroy E. coli bacteria after 20 min with UV irradiation and 3 h with fluorescent light; this good activity is mainly related to the high OH radicals on its surface. It was also observed that the synthesized powders have smaller crystallite size and larger specific surface area than those of Degussa P25 due to the absence of high temperature calcination requirement.

SYNTHESIS OF MESOPOROUS TITANIA BY POTATO STARCH TEMPLATED SOL-GEL REACTIONS AND ITS CHARACTERIZATION

Mesoporous titania powders with high-order crystalline building blocks had been synthesized through the sol-gel process using potato starch gel template. Internal spongelike pore structure of starch gel template was generated by heating the starch granules at 95 °C in water solution and freezing the starch gel at -15 °C. The synthesis routes were performed by immersing the starch gel template for 4 days into the white colloidal solution of TiO2 nanoparticles, which were prepared by hydrolyzing titanium (IV) tetraisopropoxide (TTIP) in ethanol at pH 1. Mesoporous TiO2 powders were obtained by two different ways of template removal, performed by calcination of the TiO2-starch composites at 600 °C for 4 h or combination of extraction with ethanol-HCl (2:1) at 80 °C and calcination at 500 °C for 4 h. Fourier Transform Infra Red (FT-IR) spectra shows both of template removal methods result in decreasing of characteristic vibrational band of the starch hydrocarbon on the resulted TiO2 powders. The X-Ray Diffraction (XRD) pattern imply that the concentrations of starch gel template influence the anatase crystallite peaks intensity of the synthesized TiO2 powders. TiO2 templated by 20% of starch sponges gel has highest intensity of anatase crystallite. Scherrer calculation inidicated that anatase particle size has nanoscale dimmension up to 12.96 nm. The nano-architecture feature of mesoporous TiO2 scaffolds was also evaluated by the Scanning Electron Microscope (SEM). It is shown that mesoporous TiO2 framework consist of nanocrystalline TiO2 particles as buiding blocks. The N2 adsorption-desorption isotherm curves assign that TiO2 powder resulted from extraction-calcination route has higher mesoporosity than that of only calcinated. The synthesized mesoporous TiO2 powder exhibits high Brunauer-Emmet-Teller (BET) specific surface area up to 65.65 m2/g. Keywords: mesoporous TiO2, potato starch, template

Photocatalytic Activity of Microwave Plasma-Synthesized TiO2 Nanopowder

Nanocrystalline TiO2 was synthesized using the microwave plasma technique and characterized using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, laser particle size analyzer, UV-vis spectroscopy and BET surface area analyzer. The synthesized TiO2 powder crystallized in anatase phase and the crystallite sizes were in nanometers. The photocatalytic activity of the compound was determined and compared against the activity of the commercial Degussa P-25 TiO2 catalyst. The degradation rates of the dyes were found to be higher over the synthesized TiO2 as compared to that over commercial Degussa P-25 TiO2.

Photoactivity of mechanochemically prepared nanoparticulate titanium dioxide investigated by EPR spectroscopy

Titanium dioxide nanopowders were prepared by mechanochemical synthesis in a high-energy ball mill using TiOSO4·xH2O and Na2CO3 followed by annealing in the temperature range 200–800°C. The UVA photonic efficiency of radical processes on synthesized TiO2 powders was determined by in situ EPR spectroscopy, using, as indicators, the N-oxide spin trapping agents (5,5-dimethyl-1-pyrroline N-oxide and 5-(diisopropoxy-phosphoryl)-5-methyl-1-pyrroline N-oxide) or the radical cation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate, ABTS+). The results obtained by monitoring the photoinduced generation of hydroxyl radical spin adducts correlated with those found by the investigation of the photoreduction of ABTS+. The presence of iron and chromium ions, which were evidenced in samples milled in steel, decreased the photonic efficiency of radical processes. The presence of a sulfate salt matrix during the annealing process distinctly inhibits the transformation of anatase to rutile. The highest photocatalytic activity was shown by anatase samples which were prepared by milling in corundum and annealed at 700°C. They were composed of crystallites with a mean size of 25–30nm and well developed crystal faces.

Nanosized TiO2 Photocatalyst Powder via Sol‐Gel Method: Effect of Hydrolysis Degree on Powder Properties

Nanosized TiO2 powder was synthesized via sol‐gel method using titanium tetraisopoxide (TPT) as the precursor. Mol ratios of water to TPT were varied from 1 (Powder A), 2 (Powder B), 3 (Powder C), and 4 (Powder D) to evaluate effect of hydrolysis degree. TG/DTA curves showed that amorphous phase turned to anatase crystal structure at ca. 415, 337, 310, and 339∘C for Powders A, B, C, and D, respectively. XRD analysis showed that all the synthesized TiO2 powders were 100% in anatase form with Powders B and C showing considerably higher crystallinities. The powders obtained at lower water to TPT mol ratios were spherical in shape and they became bar‐like shapes higher mol ratios. The lower hydrolysis degree led to higher surface area of the Powder A (24.8 m2/g) compared to Powder B (14.6 m2/g). From phenol photocatalytic measurement, Powder B was the most efficient attributed to its higher crystallinity.

Synthesis of Nanocrystalline TiO2 and Reduced Titanium Oxides via Rapid and Exothermic Metathesis Reactions

Nanocrystalline titanium dioxide is conventionally produced by aqueous precipitation reactions, followed by annealing post-treatment, which can also cause structural conversions from the photocatalytically active anatase to rutile phases. Solvent-free exothermic solid-state metathesis (SSM) reactions have shown wide utility in the synthesis of binary solids. This paper describes the application and chemical flexibility of the SSM method for the synthesis of TiO2 from TiCl3 and Na2O2. The use of an insulating crucible and addition of a NaCl heat sink to this rapid and exothermic SSM led to improved product crystallinity and increases in anatase to rutile TiO2 phase content. Small particle size products were synthesized at high salt dilution levels. The photocatalytic activity of SSM synthesized TiO2 powders containing some anatase TiO2 were comparable to a commercial TiO2 standard, even though the SSM powders had 30−50% lower surface areas. By changing the Na2O2 reagent to a more oxygen deficient one, Na2O, reduced titanium phases, primarily Ti2O3, were synthesized along with Na−Ti−O structures.

Nanostructured alumina doped TiO2 ceramics for gas sensors

ABSTRACTNanostructured TiO2 based ceramics were synthesized using citrate-nitrate auto combustion method with different concentrations of aluminum oxide as dopant. The powder x-ray diffraction data showed that synthesized TiO2 powders, pure as well as alumina doped TiO2 had anatase phase. Dopant concentration was varied between 0 and 15 wt%. Particle size analysis showed that the particle size was in the range of 50 to 80nm for nanosized TiO2 calcined between 600 and 800°C. Average particle size of doped powders was generally less than pure TiO2. BET specific average surface area was between 10 and 25 m2/g. Doping upto 10wt% alumina is not effective in retarding anatase crystallite growth. The resistance of Al doped TiO2 sample is found to be lower than that of pure TiO2. Al2O3 doped TiO2 sensor was found to be selective to CO sensing at an operating temperature of 600 °C.

Preparation of TiO2Powder by Modified Two-Stage Hydrolysis

Nano-sized TiO2 powders were synthesized by modified hydrolysis reaction using two-stage treatments of acid/base catalyst. Using an acidic catalyst, the primary particle size of assynthesized TiO2 was smaller than using basic catalyst, but rutile ratio and the particle size were increased after heat treatment due to the dense packing of particles. However, in the synthesized TiO2 powder using a basic catalyst persist the anatase phase and a loosely aggregation of particle after heat treatment. It was found that the catalyst used in the first stage determines the primary particle size. However the phase, the packing density and degree of dispersion of TiO2 powder were determined by the secondly applied catalyst. Therefore, the addition sequence of catalysts is the most important key to prepare fine powders for photocatalytic use and solar cell. In this study, an acid treatment followed by a base is suggested as best route to obtaining fine size and distribution of particles and high content of anatase phase.