High Temperature Stable Anatase Research Articles

Highly transparent, superhydrophilic and high-temperature stable anatase phase TiO2

Stable anatase phase of TiO2 above 700 °C plays a very important role in the fields of photocatalysis, antibacterial, self-cleaning and solar cells etc. However, the stabilization of the anatase phase of TiO2 at higher temperatures has been very challenging so far. Here, we report a glancing angle deposition (GLAD) employing e-beam evaporation to fabricate slanted nanorods, vertical nanorods, and zig-zag nanorods of TiO2, which show the stabilization of the anatase phase up to 1000 °C. The amorphous nature of the substrate and least oxygen vacancy in the TiO2 are found to be the major cause for the thermal stabilization of the anatase phase. All annealed samples were found to be superhydrophilic when measured immediately after annealing, while the dark storage transforms the samples to hydrophilic. Nevertheless, UV exposure for 10 min reverted them to superhydrophilic. FTIR studies were performed on the samples to understand the role of surface hydrocarbons in the transition from hydrophobic to hydrophilic states. The samples show a transmittance ∼90% in the visible spectrum. The simultaneous existence of a highly transparent, superhydorphilic and high temperature stable anatase TiO2 can give a boost to several fields e.g., smart windows/doors, self-cleaning coatings, etc.

Dimensional constraints favour high temperature anatase phase stability in TiO2 nanorods

High temperature stable anatase phase TiO2 nanostructures have the potential to advance the fields such as photocatalysis, solar cells and batteries. However, it is challenging to grow TiO2 nanostructures that can retain the anatase phase at high temperatures. Here, we report slanted TiO2 nanorods grown on Si substrates by glancing angle deposition technique employing electron beam evaporation to showcase the anatase phase stability up to 800 °C. FESEM surface morphology shows that the nanorods started deforming above 600 °C and collapsed at 800 °C. We carried out image processing of the nanorods assembly and quantified the deformation with annealing temperature. The x-ray diffraction and Raman spectroscopy utilized for the phase information showed that the anatase phase is stable even at 800 °C. Further, we have studied the effect of deformation on wettability of the nanorods system and found that annealed samples are superhydrophilic. Remarkably, the annealed TiO2 nanorods have transformed to hydrophobic when kept in the dark storage due to the structural contribution to contact angle rather than surface energy. Notably, the hydrophobicity increases with time, which was studied for 25 months. The stable high temperature anatase phase could find application in the solar cells, photocatalysis, smart windows, self-cleaning coatings, etc.

Solar light assisted photocatalytic degradation of 1,4-dioxane using high temperature stable anatase W-TiO2 nanocomposites

This work outlines a systematic and detailed study of the modification of anatase TiO2 with tungsten (W). The impact this coupling has on the temperature of the anatase to rutile phase transition and the photocatalytic degradation of 1,4-dioxane, a highly toxic compound that is increasingly present in water bodies is also studied. TiO2 composite photocatalysts with 2, 4, 8 and 16 mol. % W, respectively, were produced using a sol-gel process and then calcined between 500−1000 °C. The crystallinity and phase composition of pure and W-TiO2 photocatalysts were examined using X-ray Diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All W-TiO2 composite photocatalysts demonstrated 100 % anatase crystalline phase at calcination temperatures as high as 800 °C. Due to the retention of 26 % anatase after calcination at 950 °C, 8 mol. % W was established as the optimum W loading for the development of high temperature stable anatase W-TiO2 composite photocatalysts. The % anatase content also significantly impacts the photocatalytic activity of the W-TiO2 composite photocatalysts. In the presence of solar light, 100 % of 1,4-dioxane was successfully degraded by 2-W-TiO2, 4-W-TiO2 and 8-W-TiO2 composite photocatalysts, respectively, calcined at 800 °C. However, as the calcination temperature increases and the % anatase content decreases, only 70 % of 1,4-dioxane was degraded when using 4-W-TiO2 and 8-W-TiO2 calcined at 900 °C. The highest % removal of 1,4-dioxane was also achieved using 8-W-TiO2 calcined at both 800 and 900 °C. 8-W-TiO2 is therefore considered the optimum sample for both photocatalysis and phase transition temperature.

Kinetic evaluation of photocatalytic degradation of food colorant E 131 VF by copper doped TiO2 nanophotocatalysts prepared at different calcination temperatures

Abstract Pure TiO2 and copper doped TiO2 nanoparticles (Cu-TiO2, Cu/TiO2 molar ratio:​ 0.2-1.2%) were synthesized by a sol–gel method in the presence of various volumes of acetic acid (10–50 mL) in order to optimize the preparation conditions. The prepared samples were calcined at different temperatures (120–750 °C) to investigate the structural properties of TiO2 nanoparticles after calcination. Different techniques such as XRD, FTIR, Raman, UV–Vis DRS, nitrogen physisorption and SEM/EDX were used to characterize the structural and morphological properties of the prepared samples. XR diffraction results showed that TiO2 samples were synthesized in the presence of 40 mL and 50 mL acetic acid including pure anatase phase at calcination temperatures up to 600 °C; however, rutile phase was observed when they were annealed at 750 °C. In the XR diffraction patterns of Cu-TiO2 samples, no copper diffraction was found, while the EDX and DRS analyses proved the presence of copper in Cu-TiO2 samples. The average crystal size of TiO2 increased as the calcination temperature increased, but it was independent of the used acetic acid volume in the preparation process. The Raman spectra confirmed XR diffraction analysis results concerning the formation of pure anatase phase at calcination temperatures up to the 600 °C. The results of nitrogen physisorption, according to the BET model, confirmed that the higher calcination temperature was obviously favored for growth of particles and the agglomerate is related to the decline of specific surface area. The photocatalytic activity of the prepared samples was examined by photocatalytic removal of E 131 VF dye. The kinetics of dye removal fitted zero order and pseudo first order well in the presence of Cu-TiO2 and pure TiO2 respectively. TiO2 nanoparticles prepared in the presence of 10 ml and 50 mL acetic acid and calcined at 500 °C revealed the best catalytic activity. The rate constant of Cu-TiO2 samples decreased from 0.083 (a.u.) for 0 % Cu to 0.0044 (a.u.) for 1.2 % Cu due to the thickness of space charger layer. The obtained results confirmed the synthesis of high temperature stable anatase TiO2 photocatalysts that are promising candida for use in industrial wastewater treatment.

High Temperature Stable Anatase Phase Titanium Dioxide Films Synthesized by Mist Chemical Vapor Deposition

Pure anatase-phase titanium dioxide films stable up to high temperatures were successfully fabricated by the mist chemical vapor deposition method. A post-annealing treatment of the synthesized films was carried out in oxygen atmosphere in the temperature range from 600 to 1100 °C and no anatase to rutile transformation was observed up to 1000 °C. Based on the grazing incidence X-ray diffraction data, the average crystallite size of the titanium dioxide films increased gradually with increasing annealing temperature. The structural analysis revealed that the high thermal stability of the anatase phase can be attributed to the small crystallite size and a sheet-like grain structure. An incomplete anatase to rutile transformation was observed after annealing at 1100 °C.

Green Synthesis of High Temperature Stable Anatase Titanium Dioxide Nanoparticles Using Gum Kondagogu: Characterization and Solar Driven Photocatalytic Degradation of Organic Dye.

The present study reports a green and sustainable method for the synthesis of titanium dioxide (TiO2) nanoparticles (NPs) from titanium oxysulfate solution using Kondagogu gum (Cochlospermum gossypium), a carbohydrate polymer, as the NPs formation agent. The synthesized TiO2 NPs were categorized by techniques such as X-Ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy analysis, Raman spectroscopy, scanning electron microscope- Energy-dispersive X-ray spectroscopy (SEM-EDX), Transmission electron microscopy (TEM), High-resolution transmission electron microscopy (HR-TEM), UV-visible spectroscopy, Brunauer-Emmett-Teller (BET) surface area and particle size analysis. Additionally, the photocatalytic actions of TiO2 NPs were assessed with regard to their ability to degrade an organic dye (methylene blue) from aqueous solution in the presence of solar light. Various parameters affecting the photocatalytic activity of the TiO2 NPs were examined, including catalyst loading, reaction time, pH value and calcination temperature of the aforementioned particles. This green synthesis method involving TiO2 NPs explores the advantages of inexpensive and non-toxic precursors, the TiO2 NPs themselves exhibiting excellent photocatalytic activity against dye molecules.

Hysteretic phase transformation of two-dimensional TiO2

Of the various forms of TiO2 (anatase, rutile, and brookite), anatase is reported to be the best photocatalysts. High-temperature stable anatase TiO2 photocatalyst is required for antibacterial applications in building materials. Hysteretic effect of phase transformation in two-dimensional pure TiO2 is observed. The transformation from anatase to rutile phase varies with a large temperature range (400–1000 °C). The delayed phase transformation of 2D anatase TiO2 results from the synergetic effect of its own anomalous phase evolution and 2D morphologic structure.

Selective Solar Photocatalysis by High Temperature Stable Anatase TiO2

High temperature stable nanocrystalline anatase TiO2 is well known for its aqueous mediated non-selective photocatalysis. Here we first report the selective solar photocatalysis of high temperature stable anatase TiO2, prepared through a modified sol–gel technique using titanium isopropoxide and ammonium fluoride. As synthesised samples calcined at 500 and 700 °C were characterized by various techniques such as XRD, FTIR, TEM, diffuse reflectance spectroscopy, BET surface area analyser and XPS. TiO2 samples calcined at 500 and 700 °C (TNF500 & TNF700) selectively degraded cationic methylene blue (MB) over anionic methyl orange (MO) from an aqueous mixture of MB and MO dye. The selective photocatalysis was well accounted by zeta potential measurements.

High-Temperature Stable Anatase Titanium Oxide Nanofibers for Lithium-Ion Battery Anodes

Control of the crystal structure of electrochemically active materials is an important approach to fabricating high-performance electrodes for lithium-ion batteries (LIBs). Here, we report a methodology for controlling the crystal structure of TiO2 nanofibers by adding aluminum isopropoxide to a common sol-gel precursor solution utilized to create TiO2 nanofibers. The introduction of aluminum cations impedes the phase transformation of electrospun TiO2 nanofibers from the anatase to the rutile phase, which inevitably occurs in the typical annealing process utilized for the formation of TiO2 crystals. As a result, high-temperature stable anatase TiO2 nanofibers were created in which the crystal structure was well-maintained even at high annealing temperatures of up to 700 °C. Finally, the resulting anatase TiO2 nanofibers were utilized to prepare LIB anodes, and their electrochemical performance was compared to pristine TiO2 nanofibers that contain both anatase and rutile phases. Compared to the electrode prepared with pristine TiO2 nanofibers, the electrode prepared with anatase TiO2 nanofibers exhibited excellent electrochemical performances such as an initial Coulombic efficiency of 83.9%, a capacity retention of 89.5% after 100 cycles, and a rate capability of 48.5% at a current density of 10 C (1 C = 200 mA g-1).

WITHDRAWN: High Temperature Stable Anatase Phased Pure TiO2 with Enhanced Visible Light Degradation

WITHDRAWN: High Temperature Stable Anatase Phased Pure TiO2 with Enhanced Visible Light Degradation

A Review on High Temperature Stable Anatase TiO<sub>2</sub> Photocatalysts

This review focuses on the recent developments of high temperature stable anatase TiO2 photocatalyst. Eventhough TiO2 exists in different forms anatase, rutile and brookite, anatase phase stabilization is often the key to obtain the highest photocatalytic performance for TiO2, particularly for the use as an antibacterial and self-cleaning coatings in high temperature processed ceramics. Different methods available for the anatase stabilization in literature are critically reviewed and emphasis is placed on relatively recent developments. Currently available methods of anatase stabilizations are classified in to four categories viz (i) doping with metal ions (ii) doping with non-metal ions (iii) co-doping with metal and non-metal ions and (iv) dopant free stabilization by oxygen richness. Further to this, the application of these high temperature stabilized anatase TiO2 photocatalyst on various ceramics substrates such as tile, glass and sanitary wares as self-cleaning and antibacterial coatings are also been briefly discussed.

An effective method for the preparation of high temperature stable anatase TiO2 photocatalysts

An efficient, rapid and straightforward method for the preparation of nitrogen and fluorine (N, F) codoped high temperature stable anatase using a microwave pre-treatment is reported. Using a single source, ammonium fluoride (NH4F) for both nitrogen and fluorine, effective doping of the precursor titanium isopropoxide (TTIP) was possible. These samples were characterised for their structural and optical properties using X-ray diffraction (XRD), Fourier Transform IR (FTIR), Raman spectroscopy and UV–vis spectroscopy. In terms of the anatase to rutile transition enhancement using a novel microwave assisted technique, the sample prepared in a composition of 1:8 TiO2: NH4F at 1200°C was seen to be most effective, having stable anatase present at 57.1% compared to undoped TiO2 being 100% rutile from 900°C. This method involves the production of ammonium oxofluorotitanates (NH4TiOF3) at low temperatures. The inclusion of these intermediates greatly reduces the particle size growth and delays the anatase to rutile transition. The photocatalytic activity of these materials was studied by analysing the degradation of an organic dye, rhodamine 6G as a model system and the rate constant was calculated by pseudo-first-order kinetics. These results showed that the doped sample (0.0225min−1) was three times more active than the undoped sample (0.0076min−1) and over seven times faster than the commercial TiO2 photocatalyst standard Degussa P-25 calcined at 1200°C (0.0030min−1). The formation of intermediate compounds, oxofluorotitanates, was identified as the major reason for a delay in the anatase to rutile transition.

Improved high temperature stability of anatase TiO2 photocatalysts by N, F, P co-doping

Among the three commonly occurring phases (anatase, rutile, and brookite) of TiO2, the anatase form is reported to be the best photocatalyst due to the improved charge-carrier mobility and the greater number of surface hydroxyl groups. The anatase to rutile transition in titania photocatalysts usually occurs at a temperature between 500°C to 700°C. Development of a high temperature stable (above 1000°C) anatase phase is important for various environmental applications (e.g. self-cleaning ceramic tiles, anti-microbial sanitary wares, etc.). In this study, the use of ammonium hexafluorophosphate as a single source dopant (method A) and urea, trifluoroacetic acid and phosphoric acid as multiple sources (method B) was undertaken to improving its high temperature stability. Method A was seen to produce a more stable anatase phase, with 68% anatase present at 1100°C, compared to method B which showed 100% rutile at 900°C. Kinetic analysis shows a marked increase in the photocatalytic degradation of a model dye using materials calcined at 1100°C for method A (0.042min−1) compared to that for method B (0.005min−1) and the commercial photocatalyst Evonik-Degussa AEROXIDE® (0.031min−1) at 1100°C. XPS results showed that, the only dopant detected at high temperatures is phosphorus in its P5+ form. The incorporation of phosphorus has proved to be an effective method in stabilising the anatase phase at high temperature. The current investigation also showed that a single source precursor is more favourable to obtain high temperature stable anatase phase photocatalysts.

Direct synthesis and characterization of high temperature stable anatase TiO2 nanospheres from peroxo-titanium complex

Phase pure anatase nanospherical TiO2 has been obtained by sol dissolution method using TiCl3 as a precursor. The effect of annealing temperature on the properties of TiO2 has been studied and discussed. The structural, morphological and optical properties of the synthesized powder were determined using XRD, SEM, AFM, TEM, UV-Visible and flourimetry. The anatase phase of synthesized TiO2 using this method has a higher thermal stability up to 800 °C after which it is transformed into rutile phase. The crystallite size increases with the annealing temperature. The shift in absorption towards the visible region is observed for the anatase phase. The material showed fluorescence properties emitting light of 410 nm. The study also evaluated the photodegradation of a congo red as model dye. The TiO2 powder has shown good catalytic properties due to its high surface area. The proposed method is simple, fast, and efficient and reproducible for the synthesis of homogeneous nanospheres of TiO2, which will be applicable in possible optoelectronic devices.

Visible and UV photocatalytic characterization of Sn–TiO2 electrospun fibers

Nanostructured fiber-mats have large surface area, high reactivity, low weight and low agglomeration tendency. These are advantages if compared with nanoparticles for photocatalytic application. In this work, high temperature stable anatase titanium dioxide fiber-mats doped with tin (0.5–15%) were produced by electrospinning technology. The precursors used were titanium propoxide (TiP) and Tin 2-ethylhexanoate. They were hydrolyzed in acetic acid and mixed with an alcoholic solution of 10wt.% PVP. The effect of heat treatment on the microstructure characteristics and the photocatalytic activity of the fiber-mats in comparison with a commercial TiO2 powder (Degussa P-25) were studied. After the electrospinning process, a thin, porous fiber-mat was obtained. This material was dried in air at room temperature for 24h. These fibers were then heat treated from 450 to 800°C for 3h at a heating rate of 1.4°C/min. The fiber-mats were then, characterized using N2 adsorption – BET surface area, X-ray diffraction for crystalline phase determination, and SEM and TEM analyses for morphological characterization. The photocatalytic properties were studied using as model system the degradation of methyl orange in water (20ppm) under UV-A or visible light. The results show that the photoactivity increases with the increment in heat treatment temperature until 650°C, when the fibers start to become densified and the surface area drops significantly due to sintering. The addition of Sn was beneficial to the photoactivity of TiO2 fibers.

Photocatalytic Activity of Anatase Fiber-Mats

ABSTRACTNanostructured fiber-mats have large surface area, high reactivity, low weight and low agglomeration tendency. These are advantages if compared with nanoparticles for photocatalytic application. Fiber-mats can be used not only as a photocatalytic material on their own, but also incorporated in different surfaces or fabrics and as well as a filtration membrane. In this work, high temperature stable anatase titanium dioxide fiber-mats doped with silica (0.5 to 30 %) or doped with tin (0.5 to 15 %) were produced by electrospinning technology. The precursors used were titanium propoxide (TiP), tetrapropoxysilane (TPS) and tin 2-ethylhexanoate. They were hydrolyzed in acetic acid and mixed with an alcoholic solution of 10 wt% polyvinylpirrolidone. The effect of heat treatment on the microstructure characteristics and the photocatalytic activity of the fiber-mats in comparison with a commercial TiO2 powder (Evonik P-25) were studied. After the electrospinning process, a thin, porous fiber-mat was obtained. This material was dried in air at room temperature for 24h. These fibers were then heat treated from 500 to 800°C for 3 hours at a heating rate of 1.4°C/min. The fiber-mats were then characterized using N2 adsorption (BET method) for surface area measurements, X-ray diffraction for phase determination, SEM and TEM analyses for morphological characterization. The photocatalytic activity was studied using as model system the degradation of methyl orange in water (20ppm) under UV-A light. As-obtained fibers are amorphous but become crystalline after heat treatment. As the heat treatment temperature increases the surface area decreases significantly. Quite the opposite happens with the rutile to anatase ratio and the anatase and rutile crystallite sizes, which increase with higher heat treatment temperatures. The photoactivity increases with the increment in heat treatment temperature until 650°C, when the fibers start to become denser and the surface area drops due to sintering. Fibers produced at higher temperatures and with lower amounts of Si and Sn are predominantly anatase and are generally more photoactive under UV-A radiation.

High temperature stable mesoporous anatase TiO2 photocatalyst achieved by silica addition

Abstract An aqueous sol–gel method was developed to synthesize a high temperature stable anatase titania photocatalyst by doping with silica. Doping was achieved in titania by the addition of silica sol prepared from tetra ethyl orthosilicate (TEOS). 1, 2, 5 and 15 mol% silica–titania mixed oxide were prepared and characterised by X-ray diffraction, Raman spectroscopy, surface area analysis and diffuse reflectance spectra. Fully anatase phase was obtained at 1000 °C by the addition of 15 mol% silica. The 15Si–Ti (15 denotes mol% of silica) had a specific surface area of 187.3 m 2 /g at 500 °C and it retains a value of 93.0 m 2 /g at 800 °C, whereas the undoped one shows 48.7 m 2 /g at 500 °C and zero value at 800 °C. Moreover, the 15Si–Ti composition retains the pore diameter in the mesoporous range (4.6 nm) at this high temperature of 800 °C. The photocatalytic analysis showed that the system with silica added possessed a higher activity than pure titania. The 15Si–Ti sample calcined at 800 °C decolourised the methylene blue dye within 30 min (rate constant 0.084 min −1 ), whereas the undoped sample decolourised the dye after 180 min (rate constant 0.018 min −1 ). The present method of preparation offers the advantages of inexpensive precursor, homogeneous distribution of the dopant over titania at nano-level and enables control over the powder characteristics of titania.