Phase Transformation Of TiO2 Research Articles

Effect of calcination temperature on the activity and structure of MnOx/TiO2 adsorbent for Hg0 removal

The influence of calcination temperature (200–800°C) on the activity and structure of MnOx/TiO2 adsorbent prepared by a deposition–precipitation method is investigated by using an elemental mercury (Hg0) removal setup and a variety of techniques such as N2 adsorption/desorption, SEM, XRD, H2-TPR, FTIR, TG-DSC, and XPS. The results exhibit that the Hg0 removal activity of MnOx/TiO2 adsorbent is closely related to the calcination temperature. The Hg0 removal activity firstly increases below 400°C and then decreases with the increase of calcination temperature. Calcination at various temperatures may cause several successive structural changes such as the evaporation of water, decomposition of manganese compounds, enhancement of MnOx crystallization, and the crystal phase transformation of MnOx and TiO2. Some agglomerations of MnOx/TiO2 occur at higher calcination temperature, resulting in the drastic decreases of BET surface area and pore volume. Meanwhile, the particle sizes greatly increase. With an increase in calcination temperature, the oxidation state of manganese would convert from Mn4+ to Mn3+, and the surface chemisorbed oxygen decreases due to the removal of surface chemisorbed oxygen. Excessively higher calcination temperature would lead to the deactivation of MnOx/TiO2.

Achieving phase transformation and structure control of crystalline anatase TiO2@C hybrids from titanium glycolate precursor and glucose molecules

Considerable efforts have focused on functional TiO2@carbonaceous hybrid nanostructured materials (TiO2@C) to satisfy the future requirements of environmental photocatalysis and energy storage using these advanced materials. In this study, we developed a two-step solution-phase reaction to prepare hybrid TiO2@C with tuneable structure and composition from the hydrothermal carbonization (HTC) of glucose. X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) were used to determine the crystallite size, composition, and phase purity. The results of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution TEM (HRTEM) showed that the morphology of the as-synthesized TiO2@C hybrids could be controlled by varying the amount of glucose, also acting as the carbon source. Based on the observations made with different glucose concentrations, a formation mechanism of nanoparticulate and nanoporous TiO2@C hybrids was proposed. In addition, the as-synthesized TiO2@C hybrids with different compositions and structures showed enhanced adsorption of visible light and improved dye-adsorption capacity, which supported their potential use as photocatalysts with good activity. This new synthetic approach, using a nanoprecursor, provides a simple and versatile way to prepare TiO2@C hybrids with tuneable composition, structures, and properties, and is expected to lead to a family of composites with designed properties.

Effect of oxygen and WO3 additive on anatase-to-rutile phase transformation in TiO2 nanoparticles

Phase transformation of TiO2 powder (P25) and pure anatase (PA) was investigated under pure oxygen as well as vacuum from 500 to 1,000 °C. The rutile percentage calculated based on the XRD data was used to estimate the phase transformation process. It was found that the vacuum suppressed the phase transformation of P25 relative to pure oxygen atmosphere. A model was proposed to explain the effect of oxygen on the phase transformation of TiO2. Furthermore, P25 samples showed lower phase transformation temperature (between 600 and 800 °C) compared with PA (over 1,000 °C). The existed rutile phase in P25 was regarded as a transformation inducer due to an interface between anatase and rutile phases since the nucleation activation energy on the interface is lower than that on the surface. And this interface effect is also adopted to explain the role of additive WO3, which retarded the phase transformation of P25 but promoted the phase transformation of PA.

Preparation and characterization of Zr-N-codoped TiO2 nano-photocatalyst and its activity enhanced-mechanism.

Zr-N-codoped TiO2 nano-photocatalyst was prepared through sol-gel method using ammonia water and zirconium nitrate as the source of N and Zr, respectively. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS). XRD results showed that codoping with Zr and N elements could greatly inhibit the phase transformation of TiO2 from anatase to rutile. XPS analysis indicated that Zr4+ was incorporated into the lattice of TiO2 through substituting titanium atoms. Meanwhile, N was also incorporated into the lattice of TiO2 through substituting oxygen atoms and existed in the form of N-Ti-O. DRS revealed that the light absorption edge of Zr-N-TiO2 was significantly red-shifted to visible region, leading to a narrower band gap and higher visible photocatalytic activity. The enhanced visible activity was attributed to the well anatase crystallite, intense light absorbance in visible region and narrow band gap.

Hierarchical N‐Doped TiO 2 Microspheres with Exposed (001) Facets for Enhanced Visible Light Catalysis

Hierarchical N-doped TiO2 microspheres with exposed (001) facets [N-TiO2-(001)] were synthesized through a simple, fluorine-free solvothermal reaction with subsequent thermal treatment. The results show that the hierarchical N-TiO2-(001) microspheres are made up of numerous TiO2 nanosheets, and that isopropylamine (IPAN) acts as both the nitrogen source and the capping and shape-controlling agent that generates the high-energy (001) facets. In addition, IPAN is also effective in increasing the onset temperature of the phase transformation of TiO2 from anatase to rutile. Compared with the commercially available P25 TiO2, the as-prepared TiO2 microspheres exhibit good photocatalytic activity and high stability under visible-light irradiation. The high photocatalytic performance is derived from the synergy effect of N-doping and the separation of photogenerated electrons and holes among different facets, as evidenced by surface photovoltage spectroscopy.

Structural characterization and optical property of TiO2 powders prepared by the sol–gel method

The structural characteristics and optical property of TiO2 powders with different phases are studied by various techniques in this paper. Butyl titanate and oxalic acid were used as Ti source and catalyst, respectively, for sol–gel synthesis of TiO2 powders. The synthesized products were characterized by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis and photoluminescence techniques. X-ray diffraction patterns confirm TiO2 phase transformation from amorphous to anatase and rutile with the increase in calcination temperatures from 200°C to 700°C. Two exothermic peaks at 275°C and 485°C on the differential scanning calorimetry curve are responsible for the decomposition of the oxalate groups, which can enhance TiO2 phase transformation from amorphous to anatase and rutile. The crystalline sizes of the synthesized TiO2 powders are in the range of 20–65nm. The coherent phase boundary between (200) crystal plane of anatase and (11−2) crystal plane of rutile is determined first time, based on the Fourier transform analysis. The near band edge emission peaks of anatase at 396nm and rutile at 419nm, and four peaks of the different defects in TiO2 crystals can be identified on the photoluminescence spectra of the synthesized TiO2 powders. The activation energies for the grain growths of anatase and rutile were calculated, indicating that the surface chemistry may be a critical parameter to control grain growth. Based on the experimental results, the mechanism for the formation of anatase and rutile TiO2 is discussed.

Preparation and Application of Mesoporous Nanotitania Photocatalysts Using Different Templates and pH Media

Mesoporous nanotitania photocatalysts were prepared by sol-gel method in acidic or basic media. Three types of surfactants, namely, cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, and nonylphenol ethoxylate, were used as templating agents. The effects of surfactant type and pH on the morphology, particle size, surface area, pore-size distribution, UV-Vis absorbance, and TiO2phase transformation were traced by SEM, TEM, BET, and XRD. In absence of surfactants, XRD revealed 54.5% anatase at pH 3-4 and 97.0% at pH 7–9. In presence of surfactant, phase transformation of anatase has been significantly inhibited such that anatase amounts to 82–100% in acidic media. In basic media, the brookite phase appeared in low concentrations (8–15%) while rutile totally disappeared. The photocatalytic performance of the synthesized catalysts was tested via naphthalene degradation, which exhibited high activity in visible irradiation (>400 nm). The data obtained indicate that the surface area and pore volume of the current catalysts are the most effective factors for photocatalytic performance. Nevertheless, at the low pH (acidic) range, the CTAB templated catalyst gave the highest surface area (86.7 cm3/g), which is mainly assigned to acquiring the highest photocatalytic degradation of naphthalene (97% after 4 h irradiation time).

Porous titania microspheres with uniform wall thickness and high photoactivity

Highly porous titania particles were prepared by depositing thin films of titania, using alternating reactions of TiCl4 and hydrogen peroxide, on poly(styrene-divinylbenzene) (PS-DVB) template particles via atomic layer deposition (ALD) at 77°C. The composition of the titania films was verified by XPS analysis and the titania films were directly observed by TEM. TGA/DSC was used to study the thermal decomposition of the polymer template. Porous titania particles with uniform wall thicknesses were successfully obtained after the template PS-DVB was removed by oxidation in air at 400°C for 24h. Verification of the resulting porous structure of the titania particles was done by cross-sectional SEM and nitrogen adsorption–desorption analysis. Porous titania particles were treated at different temperatures. XRD analysis was used to determine the microstructure and phase transformation of titania at elevated temperatures. The photocatalytic activity of these porous titania particles was studied by methylene blue decomposition under UV light at room temperature and was found to be comparable to that of commercial anatase titania nanoparticles (~20nm). Depositing Na2SO4 on TiO2 retarded the TiO2 phase transformation from anatase to rutile during calcination and, thus, greatly increased the photoactivity of the porous titania particles.

Microstructure and properties evaluation of TiO2 ceramics with multi-oxides glass additions

A unique glass composition based on GeO2, MoO3 and V2O5 (GMV) was designed to act as a sintering aid to enhance the densification and to adjust the dielectric constant of TiO2. This allows the low temperature co-fired ceramic processing (LTCC) of approximately 750°C to be feasible with a desirable dielectric property. The effect of GMV glass concentration on the densification behavior and dielectrics properties of TiO2 was investigated by dilatometer, x-ray diffractometer, scanning electron microscopy and transmission electron microscopy. The addition of glass not only was found to accelerate the TiO2 phase transformation from anatase to rutile, but also to increase the densification rate and the grain size of TiO2. The glass additive formed a thin continuous liquid phase and rearranged TiO2 particles into a dense microstructure at much lower temperature. The dielectric constants of TiO2 were ranged from 28 to 45 depending on the concentration of glass additive, while the dielectric loss was decreased with the glass concentration as a result of denser TiO2 microstructure.

Influence of Ti film thickness and oxidation temperature on TiO2 thin film formation via thermal oxidation of sputtered Ti film

Single-phase rutile TiO2 films with good crystallinity were obtained by thermal oxidation of sputtered Ti films on Si and quartz substrates. The influence of the Ti film thickness on oxidation was systematically investigated. A temperature of 823K was sufficient to fully oxidize Ti films of <0.2μm in thickness, but 923K was required for complete oxidation of thicker films. The crystal structure, phase, composition, and optical properties of the TiO2 films were investigated using X-ray diffraction (XRD), Raman spectroscopy, energy-dispersive X-ray analysis (EDAX), and UV-vis-NIR spectroscopy. XRD and Raman analyses showed that the TiO2 films are rutile phase. The bandgap of the TiO2 films decreased with increasing thickness. A growth mechanism for TiO2 thin films due to thermal oxidation of sputtered Ti films is proposed. Oxidation commences from the surface and proceeds inside the bulk and Ti→TiO2 phase transformation occurs via different intermediate phases. We found that the oxidation temperature rather than the duration is the dominant factor in the growth of TiO2 thin films.

One-pot solvothermal synthesis of graphene-supported TiO2 (B) nanosheets with enhanced lithium storage properties

A facile process was developed for the synthesis of graphene-supported TiO2 (B) nanosheets (GTBN) composite based on the hydrothermal treatment titanium (III) chloride and graphene oxide in an ethylene glycol. The morphology and microstructure of the composites were examined by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectroscopy. The obtained GTBN show a high thermal stability and the phase transformation of TiO2 (B) to anatase can be prevented by graphene after pyrolysis of GTBN at 350°C for 2h. Furthermore, GTBN exhibited high rate performance and stability of lithium ion batteries, due to the enhanced conductivity of the electrode and accommodation to volume/strain changes during lithium insertion–extraction.

Effects of adding Al2O3 on the crystal structure of TiO2 and the performance of Pd-based catalysts supported on the composite for the total oxidation of ethanol

TiO2, Al2O3–TiO2 composites, and Pd-based catalysts have been prepared by sol–gel and wet-impregnation methods. N2 absorption, XRD, Pd dispersion, DRIFTS, XPS, 27Al MAS NMR, and ethanol oxidation experiments have been performed to assess the properties of the TiO2 oxides and catalysts. The results showed that the addition of 5wt.% Al2O3 to TiO2 plays an important role in stabilizing the anatase structure and preventing phase transformation of TiO2. This is ascribed to the formation of Al–O–Ti chemical bonds in Al2O3–TiO2 crystals. Meanwhile, Pd dispersion on the surface of the Al2O3–TiO2 composites is effectively promoted. The activity of Pd/Al2O3–TiO2 for the total oxidation of ethanol is distinctly higher than that of Pd/TiO2.

Effect of hydrogen peroxide on the structure and photocatalytic activity of titania

Great attention has been paid to the fabrication of TiO2 hollow microspheres (TiO2-HMS) with enhanced photocatalytic activity due to the low density, high surface area, good surface permeability, and greater light-harvesting capacity. In this paper, TiO2-HMS were fabricated by a simple hydrothermal route in a Ti(SO4)2–H2O2 mixed solution at 180 °C for 10 h. The prepared photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and nitrogen adsorption–desorption isotherms. The photocatalytic activity of the photocatalysts were evaluated by degradation of Brilliant Red X3B (X3B), an anionic dye, and the formation of the photo-induced hydroxyl radicals (·OH) under UV irradiation. The presence of hydrogen peroxide not only results in the formation of TiO2-HMS but also stimulates the phase transformation of TiO2 from anatase to rutile. The photocatalytic activity of the photocatalyst was found to first increase and then to decrease with the increase in the amount of H2O2. H2O2 can enhance the crystallization of anatase TiO2. However, too much H2O2 results in the formation of the rutile phase, which has a negative role on the photocatalytic activity of TiO2-HMS.

Polymorphic phase transformation of Degussa P25 TiO2 by the chelation of diaminopyridine on TiO62− octahedron: Correlation of anatase to rutile phase ratio on the photocatalytic activity

A series of nitrogen-doped Degussa P25 photocatalysts were synthesized successfully by grinding and calcination method using 2,6-diaminopyridine (DAP) as a nitrogen precursor. The prepared samples were characterized by various analytical methods. The phase contents of anatase and rutile in the Degussa P25 powders have been altered by simply changing the proportion of DAP. A mechanism involving chelated DAP molecule on TiO62− octahedron is discussed. The enhanced activity is attributed to synergistic effect in the two phase solid material. Due to the low activation barrier, the effective inter particle electron transfer between the two polymorphs is quite efficient only when they are in close proximity with similar crystallite sizes. The transfer of electrons from the rutile phase to lattice/electron trapping sites of anatase and also to the Ti3+-Vo defect level created by the dopant favors effective charge separation and enhance the photocatalytic activity under solar illumination.

Reaction mechanism and kinetics analysis of the phase transformation of TiO2 from the anatase phase to the rutile phase

The kinetic mechanism of the phase transformation of TiO2 from the anatase phase to the rutile phase was investigated. TiO2 powders were prepared with different pH value of the starting solution via the thermal hydrolysis method in this study. The pH values of the starting solutions have significant effects on the phase transformation temperatures of the thermal hydrolysis reaction. As the reaction temperatures were raised, the conversion from the anatase phase to the rutile phase was increased. A core–shell morphology of the prepared TiO2 samples was suggested via the signals of the anatase phase and the rutile phase in UV–vis spectrum analysis. Through the isothermal heating process of the reaction kinetics, the controlling reaction in the phase transformation process from the anatase phase to the rutile phase was determined to be the three-dimensional phase boundary controlled process. The activation energy of the phase transformation was increased with an increase in the pH value of the starting solution.

Synthesis and characterization of C–N–S-tridoped TiO2 nano-crystalline photocatalyst and its photocatalytic activity for degradation of rhodamine B

C–N–S-tridoped TiO2 nano-photocatalysts were synthesized through simple one-step sol–gel reactions in the presence of biomolecule cystine. The resulting materials were characterized by X-ray diffraction (XRD), N2 physical adsorption, X-ray photoelectron spectroscopy (XPS), Fourier transition infrared spectra (FT-IR), and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). XRD results showed that tridoping with C, N and S could effectively restrain the phase transformation of TiO2 from anatase to rutile and growth of the crystallite sizes. DRS results revealed the light absorption of C–N–S-tridoped TiO2 was red-shifted to visible region. XPS and FT-IR analysis demonstrated that S was incorporated into the lattice of TiO2 through substituting titanium atoms, N might coexist in the forms of N–O–Ti and O–Ti–N in tridoped TiO2, and C could form a mixed layer of carbonate on the surface of TiO2. Further, the activities of the as-synthesized catalysts were evaluated for the photodegradation of rhodamine B (RhB) in aqueous suspension under visible and UV light irradiation. It was found that C–N–S-tridoped TiO2 presented higher photocatalytic activity than that of pure TiO2 and P25 TiO2. The excellent photocatalytic activity of C–N–S-tridoped TiO2 could be attributed to the small crystal size, high surface area, large surface hydroxyl groups, strong light absorption in visible region and narrow band gap.

Effect of magnetic carrier NiFe2O4 nanoparticles on physicochemical and catalytic properties of magnetically separable photocatalyst TiO2/NiFe2O4

A series of magnetically separable photocatalyst TiO2/NiFe2O4(TN) with different mass ratios of NiFe2O4 to TiO2 was prepared by sol-gel method. The X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM), ultraviolet-visible spectroscopy(UV-Vis), Brunauer-Emmett-Teller(BET) surface analysis and photoluminescence spectroscopy(PL) were used to characterize the photocatalyst TN. The XRD patterns of TN indicate that adulterating a smidgen of NiFe2O4 into TiO2(about 0.1%, mass ratio) can promote the phase transformation of TiO2, however, when the doped amount of NiFe2O4 surpasses 1%, the introduction of NiFe2O4 can inhibit the growth of TiO2 crystal grain and reduce the size of TiO2 crystal grain. The XPS results of TN indicate that some Fe3+ replace Ti4+ of the TiO2 lattice forming Fe-O-Ti bonds. The PL analysis of TN shows that the NiFe2O4 nanoparticles in photocatalyst TN play the role of the effective recombination centre of the photogenerated electrons and holes, leading to the decrease in photocatalytic activity.

Effects of pH Value on Composite Structure of Poly-titanium-ion/Montmorillonite and Its TiO&lt;SUB&gt;2&lt;/SUB&gt; Nano-particle

The montmorillonite composite structure samples were prepared using a hydrolysation-intercalation composite method with TiOSO4·2H2O as a precursor of TiO2 nano-particles and montmorillonite as substrate by controlling the pH value of the montmorillonite suspension. The changes of the structure, phase and crystal size of the samples were characterized by X-ray diffraction method. The results show that the pH value of montmorillonite suspension has a significant influence on the hydrolyzation of TiOSO4·2H2O, so the composite structure of hydratedtitanium-oxide/montmorillonite is affected. When the pH value of montmorillonite suspension is 0.5, the poly-titanium-ions are with the lower electrovalence and extent of polymerization and easily intercalate the interlayer space of montmorillonite, moreover, the structural layers of montmorillonite are separated best. The crystal size of anatase in the TiO2/montmorillonite composite samples calcinated at 700°C is smallest and reaches 13.4 nm. After calcination at 1100°C, the relative content of anatase in the composite structure reaches 35%. Compared with pure TiO2 nano-particle sample, TiO2/Montmorillonite composite sample has a higher phase transition temperature 第 12期 吕 霞, 等: pH值对聚合钛离子/蒙脱石复合结构及其 TiO2纳米粒子属性的影响研究 1295 from anatase phase to rutile phase and smaller crystal size of TiO2. Montmorillonite structure layer has a significant blocking effect on the TiO2 phase transformation and grain growth.

Electrochemical fabrication of lanthanum-doped TiO2 nanotube array electrode and investigation of its photoelectrochemical capability

Highly ordered lanthanum-doped (La-doped) TiO2 nanotube arrays were prepared by electrochemical anodization process on a Ti sheet, followed by cathodic electrochemical process using lanthanum nitrate solution as the La source, and at last were analyzed by SEM, XPS, FTIR, XRD, and DRS characterization techniques. The analytical results demonstrated that the La doping could promoted phase transformation of TiO2 from the anatase to rutile. Red shifted and enhanced absorption intensities of certain peaks in both UV and visible light regions were also observed. Moreover, a new state of Ti3+ was founded after calcinations. The photoelectrochemical results indicated that La doping can significantly enhance the photoconversion efficiency of the TiO2 nanotube array electrode. The maximum photoconversion efficiency was 0.598%, which was obviously more than 2-fold higher than the undoped one (0.257%) under the same supporting electrolyte solution. The photoelectrocatalytic (PEC) degradation result of p-nitrophenol (PNP) was used to investigate the PEC activities of the as-prepared electrode. The La-doped TiO2 nanotube array electrode showed much higher degradation efficiencies (99.33%) than the undoped TiO2 nanotube array electrode (70.16%) under the same condition.

One-step synthesis of Fe–N–S-tri-doped TiO2 catalyst and its enhanced visible light photocatalytic activity

Fe–N–S-tridoped TiO2 was synthesized through simple one step sol–gel reactions in the presence of ammonium ferrous sulfate. The resulting materials were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance spectrum and surface photovoltage spectroscopy. Results revealed that Fe and S were incorporated into the lattice of TiO2 by substituting for some Ti atoms and N for O atoms in the lattice of TiO2. Tri-doping with Fe, N and S could inhibit the phase transformation of TiO2 from anatase to rutile, restrain the growth of crystallite sizes, extended the light absorption into the visible region and separate photoinduced charge carriers. The visible photocatalytic activity of Fe–N–S-tridoped TiO2 was higher than that of N-TiO2 and P25 TiO2. The enhanced photocatalytic activity was attributed to the small crystallite size, high crystallinity, the intense light absorption in visible region, narrow band gap and high separation efficiency of photoinduced charge carriers.