Preparation and characterization of titania powders obtained via hydrolysis of titanium tetraisopropoxide

TiO₂ powders were prepared through the hydrolysis of titanium isopropoxide followed by calcination at temperatures of 200 °C to 600 °C. The obtained powders were characterized by N₂ adsorption-desorption and X-ray powder diffraction. The results confirmed strong dependence between specific surface area of the TiO₂ powders and both the conditions of the hydrolysis process and the calcination temperature. While calcination temperature strongly affected crystallinity of the product, no significant influence of the hydrolysis conditions on this parameter was observed. TiO₂ powders prepared at various conditions were examined as catalysts for photodegradation of Acid Red 18 in water. Photoactivities of the prepared powders were influenced by both the amount of water used to hydrolyze the TiO₂ precursor and the temperature of calcination process. TiO₂ samples calcined at 500 °C appeared to be the most active and the photocatalytic activities of the prepared materials increased along with the amount of water used for the hydrolysis process.     

Phase formation and dielectric properties of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> by slow injection sol–gel technique

A simple sol–gel process incorporating slow precursor injection technique was employed to synthesize homogeneous Ba_0.5Sr_0.5TiO₃ nano powders. The Ba_0.5Sr_0.5TiO₃ samples were subjected to calcination temperatures from 600 to 1,100 °C and sintering temperatures from 1,250 to 1,350 °C for the study of phase formation, crystallite size, particle distribution, and dielectric properties. Single phase Ba_0.5Sr_0.5TiO₃ with a cubic perovskite structure was successfully synthesized after calcination at 800 °C. The average size of the nano particles is 42 nm with a narrow size distribution, and a standard deviation of 10%. The highest values recorded within the investigated range for dielectric constant, and dielectric loss measured at 1 kHz are 1,164 and 0.063, respectively, for Ba_0.5Sr_0.5TiO₃ pellets calcined at 800 °C and sintered at 1,350 °C. Leakage current density measured at 5 V for the Ba_0.5Sr_0.5TiO₃ pellet was found to be 49.4 pA/cm².     

Nanocrystalline TiO<Subscript>2</Subscript> preparation by microwave route and nature of anatase–rutile phase transition in nano TiO<Subscript>2</Subscript>

Nanopowders of TiO₂ has been prepared using a microwave irradiation-assisted route, starting from a metalorganic precursor, bis(ethyl-3-oxo-butanoato)oxotitanium (IV), [TiO(etob)₂]₂. Polyvinylpyrrolidone (PVP) was used as a capping agent. The as-prepared amorphous powders crystallize into anatase phase, when calcined. At higher calcination temperature, the rutile phase is observed to form in increasing quantities as the calcination temperature is raised. The structural and physicochemical properties were measured using XRD, FT–IR, SEM, TEM and thermal analyses. The mechanisms of formation of nano-TiO₂ from the metal–organic precursor and the irreversible phase transformation of nano TiO₂ from anatase to rutile structure at higher temperatures have been discussed. It is suggested that a unique step of initiation of transformation takes place in Ti_1/2O layers in anatase which propagates. This mechanism rationalizes several key observations associated with the anatase–rutile transformation.     

Preparation of rutile (TiO<Subscript>2</Subscript>) nanostructured materials at low temperature from TiCl<Subscript>4</Subscript> aqueous solution

The synthesis of rutile (TiO₂) nanostructured materials at low temperature from TiCl₄ aqueous solution was described. TiO₂ coatings on polystyrene (PS) particles were prepared by layer-by-layer assembly technique. The samples were characterized by DTA-TG, SEM, XPS, TEM and XRD techniques. The experimental results showed that pure rutile-TiO₂ coatings with nanocrystal structure were synthesized at 100 °C. On the surface of PS particles, sphere-type TiO₂ coatings exhibited uniform shape and a narrow size distribution. The amount of TO₂ (wt%) and shell thickness of particles increased with the adding of coating layers. Hollow TiO₂ spheres were obtained by calcination at 450 °C. TiO₂/PS with 2 coating layers showed higher degradation rate. The photocatalytic activity of hollow TiO₂ spheres was higher than that of TiO₂/PS.     

Synthesis and photocatalytic activity of nanocrystalline TiO2-SrO composite powders under visible light irradiation

Nano-sized homogeneously distributed TiO₂-20, -40, -60 wt.% SrO composite powders were successfully synthesized by a sol-gel method. The as-received amorphous TiO₂—20 wt.% SrO composite powders were crystallized with anatase TiO₂ at around 750 °C. As calcination temperatures increased, the anatase TiO₂ crystalline phase was transformed to rutile TiO₂ at about 900 °C, whereas nano-sized, squarish SrTiO₃ phase was detected. The peaks obtained after calcining at 1050 °C mainly exhibited the rutile TiO₂ and SrTiO₃ phases. However, a small number of SrO₂ peaks were also detected. For the comparison of photocatalytic activity depending on light sources, TiO₂-SrO composite powders were tested in phenol degradation. TiO₂-60 wt.% SrO composite powder showed good visible light photoactivity for the photo-oxidation of phenol.     

Synthesis of cobalt-orthotitanate inverse spinel nano particles via a novel low temperature solvothermal method: structural,opto-electronical,morphological, surface characterization and photo-catalytical application in mineralization of Remazol Red RB 133

Synthesis of single phase cobalt-orthotitanate inverse spinel nano particles is reported for the first time via a novel solvothermal method at low calcination temperature at 400?°C. The pure phase cobalt-orthotitanate spinel nano particles were prepared using cobalt nitrate and titanium tetraisopropoxide (1:1 molar ratio) as cobalt and titanium sources. The synthesised Co₂TiO₄ nanoparticles were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, surface area analyses (Brauner–Emmett–Teller) (BET) and UV–Vis diffuse reflectance spectroscopy. The XRD results proved the formation of a single phase cobalt-orthotitanate (Co₂TiO₄) nanoparticles by calcination temperature of 400?°C. The FE-SEM results showed that nano particles possess a uniform spherical morphology with an average size of 51 nm. Porosity and specific surface area of cobalt-orthotitanate nano particles was measured by nitrogen adsorption using BET and the results showed surface area of 44.47 m²/g. DRS results showed an optical band gap value of 1.802 eV for cobalt-orthotitanate nano powder. An excellent performance as a nano photo-catalyst toward the degradation of Remazol Red RB 133 (RR133) as a single azo textile dye with excellent efficiency. Mineralization of RR133 by highly active cobalt-orthotitanate nano-catalyst coated on glass surface was applied and 97% TOC removal was observed. This is due to high electron–hole charge separation and high surface area of nano-catalyst.     

Study on crystallinity and morphology controlling of titania using acrylamide gel method and their photocatalytic properties

In this study, polyacrylamide gel method was used for preparation of pure and mixed phase TiO₂ nanoparticles. The influence of synthesis conditions on the physicochemical properties of products was investigated. It was found that the type of acid, which was used for acidifying the precursor solution together with calcination temperature can affect the phase structure, crystalline size, morphology and thereby photocatalytic activity of obtained TiO₂ nanoparticles. Different trends were observed during the phase transformation, particle growth, shift in energy of band gap with the change in tensile strain to compressive strain of the prepared TiO₂ nanomaterial. X-ray diffraction (XRD) showed that prepared nanocrystals, which were calcined at 450 °C have pure anatase and anatase–rutile mixed structures. The prepared samples having crystallite size between 5 nm and 60 nm were observed at different calcination temperatures. In addition, the photocatalytic activities of the prepared samples were evaluated by monitoring the degradation of Cresol Red (CR). The results show that the photocatalyst (TEC_I), exhibits the highest photocatalytic efficiency where 94.7% of CR can be decomposed after UV exposure for 75 min.     

Fabrication of solar light induced Fe-TiO2 immobilized on glass-fiber and application for phenol photocatalytic degradation

Iron-doped anatase titanium dioxide catalysts coated on glass-fiber were successfully synthesized by a dip-coating sol–gel method. The prepared catalysts were characterized by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy to understand the synthesis mechanism, and their photocatalytic activities were evaluated by photodegradation of phenol under simulated solar irradiation. EDX analysis confirmed the existence of iron in the immobilized catalysts. XRD suggested that the phase transition of the catalysts from anatase to rutile were restrained, and almost pure anatase TiO₂ could retain even the calcination temperature reached 800 °C. The UV-Vis diffuse reflectance spectroscopy of the catalysts showed a red shift and increased photoabsorbance in the visible range for all the doped samples. Iron loading and calcination temperature have obvious influences on photocatalytic activity. In this study, the optimal doping dose and calcination temperature were around 0.005 wt% and 600 °C, respectively.     

Performance of dye-sensitized solar cell fabricated using titania nanoparticles calcined at different temperatures

Synthesis of titania (TiO₂) nanoparticles by sol-gel method and their calcination at different temperatures, viz 450 °C, 550 °C and 650 °C (defined as T450, T550 and T650) has been done. Structural analysis indicates that the T450 sample possesses anatase phase. The phase transformation to rutile starts occurring at T550, and, on increasing the calcination temperature, the crystallization and percentage of rutile phase increases. As the temperature increases from 450 to 650 °C, the crystallite size increases by about a factor of two from 11.5 to 20.2 nm. From SEM micrographs, T550 electrode has been found to have appropriate aggregation, which led to enhanced dye desorption, as compared to T450 and T650 based electrodes. TEM images of the synthesized nanoparticles reveal that the particle size increases from 7 to 28 nm on increasing the calcination temperature from 450 to 650 °C. From the photoluminescence and Fourier transform infrared studies, it has been concluded that the surface OH^? groups are reduced on calcination, which affects the electron injection efficiency. The dye sensitized solar cell, fabricated using T550 sample, having a ratio of anatase/rutile 89:11, has been found to achieve the highest conversion efficiency.     

Photocatalytic degradation mechanisms of dimethyl phthalate esters by MWCNTs-anatase TiO2 nanocomposites using the UHPLC/Orbitrap/MS technique

Dimethyl phthalate esters (DMPEs) have been identified as endocrine disrupting plastisizers and emerging contaminants which can be released readily upon exposure to the environment. In this study, MWCNTs/TiO₂ nanocomposites, which possess the potential application for the photocatalytic degradation of DMPEs under UV irradiation, were prepared via simple one-pot sol-gel reaction using titanium isopropoxide (TTIP) as titania precursor and multiwalled carbon nanotubes (MWCNTs). The MWCNTs/TiO₂ nanocomposites was calcined in air for 2 h at the temperatures ranging from 350 to 750 °C. As a result, the MWCNTs/TiO₂ nanocomposites synthesized at calcination temperature of 450 °C demonstrated the highest photodegradation efficiency of 97% after 180 min UV irradiation and its degraded products were evaluated using the ultra high performance liquid chromatography (UHPLC) coupled with a high resolution (HR) Orbitrap mass spectrometry (MS). A primary degradation mechanism was proposed and it was noteworthy that some new intermediates were discovered and reported. This work has developed a simple method for qualitative determination of DMPEs based on HPLC with UV detection.     

Effect of heat treatment on structure evolution and properties of nano zinc titanate ceramics

Nano zinc titanate ceramics are prepared using a conventional solid state method. The obtained compacts are sintered at 800, 900, 1000 and 1100 °C for 3 h. The prepared compacts are analyzed using X‐ray diffraction (XRD) and scanning electron microscopy (SEM) for structural and microstructural studies. Based on the X‐ray diffraction (XRD) data, it is observed the coexistence of ZnTiO₃ and α‐Zn₂TiO₄ phases together at low temperature (800 °C) without the presence of TiO₂ (rutile) contradicting the general mechanism stating the transformation of ZnTiO₃ to α‐Zn₂TiO₄ and TiO₂ at higher temperatures. A new mechanism is proposed to explain the formation of nano ZnTiO₃ and α‐Zn₂TiO₄ structures depending on the role of TiO₂ in achieving this mission. According to this mechanism, we propose a partial diffusion of TiO₂ in the ZnO lattice forming the ZnTiO₃ phase. The second part of TiO₂ acts as a catalyst that facilitates the transformation of nano ZnTiO₃ to nano α‐Zn₂TiO₄. The catalytic power of rutile is achieved from its enhanced tensile stress that induces the phase transition from nano ZnTiO₃ to nano α‐Zn₂TiO₄.     

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 10 ppm aqueous methylene blue dye under 32 W high pressure mercury vapor lamp with 100 mg of TiO₂ powders. The highest photocatalytic activity was observed in TiO₂ powder synthesized at 90 °C for 0 h attributed to the presence of anatase and rutile phases in an 80:20 ratio.     

Solar photocatalytic degradation of rhodamine B by heat-treated nanometer anatase TiO<Subscript>2</Subscript> powder

The partial phase transformation of nanometer TiO₂ powder from anatase to rutile was realized by heat-treatment, and then a novel photocatalyst which could utilize solarlight was obtained. The heat-treated nanometer TiO₂ powders at different transition stage were characterized by XRD, TEM and UV-vis spectra. In addition, the photocatalytic activity of heat-treated nanometer TiO₂ powder was tested out through the degradation of Rhodamine B dye in aqueous solution under solarlight irradiation. The results reveal that the nanometer anatase TiO₂ powder heat-treated at 500°C for 80 min exhibites the highest photocatalytic activity. That is, Rhodamine B dye can effectively degraded under solarlight irradiation in the presence of heat-treated nanometer TiO₂ powder.     

Processing and photocatalytic properties of Cu-grafted TiO2 powder from acid treated BaTiO3

The respective influences of calcination, drying methods, and washing conditions on the morphologies, surface properties, and photocatalytic activities of TiO₂ powders prepared from acid treatments of BaTiO₃ were investigated. Rutile powder was obtained using the treatment under strong acid conditions. It possesses a bundle-like shape and comprises rutile nanorods. After calcination, characteristic voids were observed in the particles. Anatase powder was obtained by adjusting pH values of a BaTiO₃ suspension to 2.5-3. Drying at 110 °C engendered the formation of spheroidal anatase, although freeze-dried anatase particles assembled into a flake-like shape. The freeze-dried samples show lower crystallinity. With grafting Cu ions, rutile exhibited better photocatalytic performance for the decomposition of gaseous 2-propanol (IPA) under visible light, although it did not work effectively for anatase.     

Synthesis and characterization of anatase photocatalyst powder from sodium titanate compounds

The synthesis of anatase photocatalyst powder from sodium titanate compounds prepared from rutile and sodium carbonate powder was studied. The sodium titanate compounds were derived from the solid-state reactions of three different (1:4, 1:1.58 and 1:0.73) (m/m) ratios of TiO₂:Na₂CO₃ at 850 °C. Then, the powder was dissolved in 5 M H₂SO₄ solution, filtered, washed, dried and calcined at 400, 500 or 600 °C for 2 h. The effects of processing parameters on the resultant phase structure, crystallite size, morphology and the surface area of the synthesized powders were investigated. It was found that the anatase powder with a crystallite size of about 102 nm and a specific surface area of 16.7 m²/g synthesized from sodium titanate compounds with a 1:1.58 (m/m) ratio of TiO₂:Na₂CO₃ and calcined at 600 °C showed the best photocatalytic activity to degrade of methylene blue in aqueous solution under UV irradiation.     

Microstructure of sol–gel synthesized Al2O3–ZrO2(Y2O3) nano-composites studied by transmission electron microscopy

The Al₂O₃–ZrO₂(Y₂O₃) composite powder was synthesized through a sol–gel process using aluminum sec-butoxide and zirconium butoxide as precursors. The as-received powders in an amorphous phase were crystallized with c-ZrO₂ at around 980 °C. As the calcination temperature increased, the c-ZrO₂ crystalline phase was transformed to t-ZrO₂ at about 1200 °C. However, the Al₂O₃ phase in the Al₂O₃–ZrO₂(Y₂O₃) composite powders still existed in an amorphous phase up to 1050 °C. In the sintered body using the calcined powders at 400 °C, the Al₂O₃ phase was crystallized in an α-phase at 1200 °C during the sintering for 2 h. Using the sol–gel Al₂O₃–ZrO₂(Y₂O₃) powder, a typical nano-composite having a nano-crystalline phase (less than 20 nm) can be successfully obtained by a pressureless-sintering process even at 1200 °C for 2 h.Using the sol–gel Al₂O₃–ZrO₂(Y₂O₃) powder, a typical nano-composite having a nano-crystalline phase (less than 20 nm) can be successfully obtained by a pressureless-sintering process even at 1200 °C for 2 h. The values of relative density and Vickers hardness were comparatively high value with about 96.2% and 1100 Hv, respectively, even though it was made at low temperature. In the composite sintered at 1400 °C, the hardness value was saturated with 1570 Hv and the values of fracture toughness were almost same with about 6 MPa m^1/2.     

Influence of calcination parameters on the TiO2 photocatalytic properties

Nanocrystalline titanium dioxide (TiO₂) powders with different crystal phase composition were obtained by controlled hydrolysis and post-thermal treatments. The physicochemical properties of the powders were investigated by XRD, TEM/EDS, N₂ physic adsorption and DRS. The results obtained show that the particle size and crystalline structure are parameters strongly dependent on the calcination conditions, mainly temperature and heating rate. The influence of the TiO₂ phase composition on its photocatalytic activity, concerning the methylene blue photodegradation was studied. It was found that higher TiO₂ photocatalytic activity is related with the co-existence of the three TiO₂ polymorphs: anatase, brookite and rutile.     

Preparation N-F-codoped TiO2 nanorod array by liquid phase deposition as visible light photocatalyst

An efficient method for the preparation of N-F-codoped visible light active TiO₂ nanorod arrays is reported. In the process, simultaneous nitrogen and fluorine doped TiO₂ nanorod arrays on the glass substrates were achieved by liquid phase deposition method using ZnO nanorod arrays as templates with different calcination temperature. The as-prepared samples were characterized by Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectra measurements. It was found that calcination temperature is an important factor influencing the microstructure and the amount of N and F in TiO₂ nanorod arrays samples. The visible light photocatalytic properties were investigated using methylene blue (MB) dye as a model system. The results showed that N-F-codoped TiO₂ nanorod arrays sample calcined at 450 °C demonstrated the best visible light activity in all samples, much higher than that of TiO₂ nanoparticles and P25 particles films.     

Formation behavior of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> from CaTiO<Subscript>3</Subscript>, CuO and TiO<Subscript>2</Subscript>

The formation behavior of CaCu₃Ti₄O₁₂ (CCTO) had been investigated via solid state reaction from CaTiO₃, CuO and TiO₂ powders. In the temperature range from 750 to 1,200 °C, the reaction sequence was traced by XRD, and the microstructure evolution of calcined powders was also investigated by SEM. CCTO began to form owing to the reaction between CaTiO₃, CuO and TiO₂ at around 850 °C, and became the major phase at 1,000 °C. Finally, the single phase CCTO was obtained at 1,150 °C. However, CCTO was decomposed at CaTiO₃, CuO and TiO₂ when the temperature increased to 1,200 °C. In addition, no other intermediate phases occurred in the synthesized process. The formation behaviors indicated that CaTiO₃ prevented the formation and growth of CCTO.     

Solubility of NiO in Pechini-derived ZrO<Subscript>2</Subscript> examined with SQUID magnetometry

The solubility of NiO in ZrO₂ was studied by X-ray diffraction, TEM, and SQUID magnetometry. Lattice parameter measurements from a similar, established oxide system, NiO−10YSZ, were first used to show that SQUID magnetometry can effectively measure solubility. ZrO₂ specimens with 0, 0.5, 1, 2, 3, and 5 percent by mol NiO were prepared via the Pechini method. The specimens were calcined in air at 500, 600, and 1000 °C. The paramagnetic response of the specimens measured with SQUID magnetometry revealed that up to 5 percent by mol NiO is soluble in ZrO₂ for specimens calcined at 500 and 600 °C. The relatively large solubility compared with NiO−10YSZ occurs due to the very fine grain size (5–10 nm). The fine grain size is also responsible for stabilizing the tetragonal phase of ZrO₂. At the 1000 °C calcination temperature, the ZrO₂ is entirely monoclinic, exhibits larger grains (>45 nm), and only dissolves about 0.5 percent by mol or less NiO. The correlations between grain size, ZrO₂ polytype, and NiO addition are discussed.