Nano-sized Rutile TiO2 Research Articles

Reversible phase transformation phenomenon in titanium dioxide films: Evidence beyond interface-nucleation and dissolution-precipitation kinetics

The re-crystallization kinetics and rutile to anatase reversible phase transformation (PT) in nano-crystalline titanium dioxide (TiO2) are reported. Initially, an amorphous TiO2 film is used for the present study and in situ isothermal annealing dependent nucleation and growth kinetics of anatase and rutile phase is studied at low temperature (∼523 K) and well explained using Johnson–Mehl–Avrami-Kolmogorov (JMAK) model. The anatase nanocrystallite (NCs) transformation into rutile phase is reported with isothermal annealing for longer time and temperature dependent annealing in lower temperature range 523 K–673 K and explained using interface-nucleation mechanism. Furthermore, the thermodynamic stability of rutile NCs and lattice stress-induced reversible PT in nano-sized rutile TiO2 are confirmed in moderate temperature range (623 K - 973 K) and well explained using x-ray diffraction, micro-Raman spectroscopy and near edge x-ray absorption fine structure spectroscopy studies. However, annealing at higher temperature (1123 K - 1323 K) induces the growth of anatase NCs and their natural transform into rutile phase are explained by well-known dissolution–precipitation mechanism. Activation energy of rutile PT is quantified and found higher for dissolution-precipitation mechanism than that for interface nucleation at earlier stage. Thus, overall PT kinetics at different temperature range is well understood by invoking in three step mechanism: I) early stage anatase-to-rutile transformation is dominated by interface-nucleation, II) then intermediate stage reversible rutile-to-anatase PT and, III) at later stages, anatase-to-rutile PT is controlled by dissolution–precipitation mechanism.

Magnèli phase TinO2n-1 bulks prepared by SPS followed by carbon reduction and their thermoelectric performance

We fabricated Magnèli phase TinO2n-1 compacts from nano-sized rutile TiO2 powder by spark plasma sintering (SPS) followed by carbon reduction at elevated temperatures. These compacts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that the n value in Magnèli phase TinO2n-1 mainly depended on the reduction temperature and holding time. Higher reduction temperature or longer holding time favored to smaller n value through withdrawing more oxygen atoms from the lattice of TiO2. Meanwhile, the thermoelectric properties including electrical resistivity, thermal conductivity, Seebeck coefficient, power factor and ZT value of these compacts were measured or calculated. The electrical conductivity was greatly improved while Seebeck coefficient still kept rather large values, which resulted in an extremely high value of power factor at elevated temperature. The highest power factor reached 6.5 × 10−4 W m−1 K−2 at 973 K and the greatest ZT value ran up to 0.1 at 873 K.

A Kinetic Study of Electrochemical Lithium Insertion into Nanosized V2O5 and Nanosized Rutile TiO2

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Thermo- and Photo-Degradation of LDPE and PP Films Using Metal Oxides as Catalysts

Degradation of LDPE and PP films using the photo sensitive metal oxides or pro-oxidants (e.g. Fe2O3, CuxO, ZnO, and TiO2 at various particle sizes) as the catalysts in both thermo- and photo-oxidation of plastic films with oxygen followed by photolytic process to give free radicals has been studied. Our preliminary study in hexane solution found that the carbonyl index (CI) increased under the shortwave ultraviolet (254nm) significantly greater than under the longer wave (366nm) due to its greater energy and highly absorbed by the pro-oxidants generating more free radical concentration which could then be photolysed into carbonyl compounds. The pro-oxidant blended PE and PP films under ultraviolet (254nm) irradiation showed the carbonyl index elevation at the beginning and then reducing to a constant level similarly in most cases. This probably suggested that the carbonyl primarily formed and degraded into other free radicals. Under shortwave ultraviolet irradiation for 72 hours, the LDPE films containing nano-sized rutile-TiO2 and nano-sized anatase-TiO2 (1%w/w) were able to reduce the film tensile strength by 32% and 55%, respectively. The film containing micron-sized commercial TiO2 lower the film tensile strength only by 7-10%. However, the tensile strength of the TiO2 blended PP films tends to increase possibly because the rate of cross linkage exceeds the rate of scission.

Crystal and electronic structure of lithiated nanosized rutile TiO2 by electron diffraction and electron energy-loss spectroscopy

The crystal and electronic structure of the lithiated nanosized rutile TiO2 were studied using electron diffraction and electron energy-loss spectroscopy (EELS) in a transmission electron microscopy. EELS reveals the Li K-edge at the energy-loss position of ∼61 eV. After lithiation, the t2g-eg crystal-field splitting on both Ti L2,3-edge and O K-edge decreases, the O K-edge shifts toward a higher energy-loss position and the separation between the pre-edge peak and main peak on the O K-edge decreases, suggesting that the lithiation of rutile TiO2 was accompanied by the reduction in Ti ion, indicating a charge transfer from Li to Ti.

Treatment of nano-sized rutile TiO2 powder in hydrogen peroxide under microwave irradiation and investigation on its sonocatalytic activity

In this work, a novel nano-sized mixed-crystal TiO2 catalyst was obtained under microwave irradiation in hydrogen peroxide solution and its sonocatalytic activity was also investigated through degradation of congo red dye. It was found that the sonocatalytic degradation effect of congo red using nano-sized mixed-crystal TiO2 powder was much higher than that using pure nano-sized rutile phase TiO2 powder. At last, the congo red dyes in aqueous solution were degraded completely and became some simple inorganic ions such as NO 3 − , SO 4 2− and so on. The experiments indicated that the degradation method using such treated nano-sized rutile TiO2 powder as sonocatalyst could be used to treat those non- or low-transparent wastewaters effectively.

Genotoxic effects of nanosized and fine TiO2

The in-vitro genotoxicity of nanosized TiO(2) rutile and anatase was assessed in comparison with fine TiO(2) rutile in human bronchial epithelial BEAS 2B cells using the single-cell gel electrophoresis (comet) assay and the cytokinesis-block micronucleus test. BEAS 2B cells were exposed to eight doses (1-100 microg/cm(2)) of titanium(IV) oxide nanosized rutile (>95%, <5% amorphous SiO(2) coating; 10 x 40 nm), nanosized anatase (99.7%; <25 nm), or fine rutile (99.9%; <5 microm) for 24, 48, and 72 h. Fine rutile reduced cell viability at lower doses than nanosized anatase, which was more cytotoxic than nanosized rutile. In the comet assay, nanosized anatase and fine rutile induced DNA damage at several doses with all treatment times. Dose-dependent effects were seen after the 48- and 72-h treatments with nanosized anatase and after the 24-, 48- (in one out of two experiments), and 72-h treatments (one experiment) with fine rutile. The lowest doses inducing DNA damage were 1 microg/cm(2) for fine rutile and 10 microg/cm( 2) for nanosized anatase. Nanosized rutile showed a significant induction in DNA damage only at 80 microg/cm(2) in the 24-h treatment and at 80 and 100 microg/ cm(2) in the 72-h treatment (with a dose-dependent effect). Only nanosized anatase could elevate the frequency of micronucleated BEAS 2B cells, producing a significant increase at 10 and 60 microg/cm( 2) after the 72-h treatment (no dose-dependency). At increasing doses of all the particles, MN analysis became difficult due to the presence of TiO(2) on the microscopic slides. In conclusion, our studies in human bronchial epithelial BEAS 2B cells showed that uncoated nanosized anatase TiO(2) and fine rutile TiO(2) are more efficient than SiO( 2)-coated nanosized rutile TiO(2) in inducing DNA damage, whereas only nanosized anatase is able to slightly induce micronuclei.