Reduction Of Titanium Dioxide Research Articles

A Review: Synthesis and Applications of Titanium Sub-Oxides.

Magnéli phase titanium oxides, also called titanium sub-oxides (TinO2n-1, 4 < n < 9), are a series of electrically conducting ceramic materials. The synthesis and applications of these materials have recently attracted tremendous attention because of their applications in a number of existing and emerging areas. Titanium sub-oxides are generally synthesized through the reduction of titanium dioxide using hydrogen, carbon, metals or metal hydrides as reduction agents. More recently, the synthesis of nanostructured titanium sub-oxides has been making progress through optimizing thermal reduction processes or using new titanium-containing precursors. Titanium sub-oxides have attractive properties such as electrical conductivity, corrosion resistance and optical properties. Titanium sub-oxides have played important roles in a number of areas such as conducting materials, fuel cells and organic degradation. Titanium sub-oxides also show promising applications in batteries, solar energy, coatings and electronic and optoelectronic devices. Titanium sub-oxides are expected to become more important materials in the future. In this review, the recent progress in the synthesis methods and applications of titanium sub-oxides in the existing and emerging areas are reviewed.

Unfolding the Impact of H2-Reduction Treatment in Enhancing the Photocatalytic Activity of Rutile TiO2 Based on Photocarriers Dynamics

In the pursuit of efficient titania photocatalysts for water splitting, several strategies have been employed. One of these is reduction of titania (TiO2) via treatment under hydrogen atmosphere, a promising technique to improve the photocatalytic performance. It has been proposed that electron injection induced by reduction on TiO2 demonstrated an improved photocatalytic activity. However, the dynamical processes involving the photogenerated charge carriers in reduced TiO2 have not been fully explored and understood yet. In this work, we employ time-resolved absorption spectroscopy (TAS) and photoluminescence (PL) measurements to unravel the impact of H2 reduction treatment on the photocarriers in rutile TiO2 (R-TiO2). TAS results revealed that the photoexcited electrons are preferentially filling the shallower trap states of reduced R-TiO2, with the lowest energy limit of ∼0.25 eV below the conduction band minimum, much shallower than that of nonreduced R-TiO2 (∼0.62 eV). Furthermore, these favorable effects of H2-reduction resulted in notable increase of long-lived shallow-trapped electrons, substantially extending the lifetimes of electrons and holes. PL measurements strongly support the positive impact of H2 reduction treatment: the NIR emission (∼850 nm) is largely quenched, indicating that the radiative recombination of deep trapped electrons and holes is significantly reduced. The combined PL and TAS results shed light on the impact of H2 reduction on R-TiO2, and this strategy can be potentially useful for further development of other photocatalytic materials.

Effects of MnO on the smelting process of vanadium titanomagnetite pre-reduced pellets in an electric furnace

MnO is proven as an effective fluxing additive for high-temperature pyrometallurgy processes. The effects of MnO on the electric furnace smelting of vanadium titanomagnetite pre-reduced pellets were systematically studied in this study. The results indicated that MnO addition could reduce the titanium slag viscosity. The activities of titania and silica in the slag decreased with the increasing MnO content. The external views of slag-iron separation showed that the addition of MnO was beneficial for the separation of iron from the slag. The EPMA results indicated that the reduction degree of vanadium oxides was improved with the MnO additions of 1 wt% and 2 wt%, but mitigated with the further increase of MnO. Moreover, the reduction of titanium oxides was suppressed with the increasing MnO content. Finally, it was concluded that the suitable addition of MnO was 2 wt% under the present smelting conditions.

Thermodynamic Prediction and Synthesis of a Titanium Diboride Powder by Reduction of Titanium Dioxide with Boron Carbide in Argon Atmosphere

Thermodynamic Prediction and Synthesis of a Titanium Diboride Powder by Reduction of Titanium Dioxide with Boron Carbide in Argon Atmosphere

Низкоэнергетическая механическая обработка порошка нестехиометрического карбида титана

Introduction. The practical significance of non-stoichiometric titanium carbides TiCх in various fields of technology and in medicine is expanding. In this regard, it is important to investigate both methods of obtaining titanium carbide powder and its properties in a wide range of stoichiometry. One of the effective ways to influence the physical and mechanical properties of powder systems is its mechanical treatment. Under shock-shear action, which is realized during processing in a ball mill, mechanical energy is transferred to the powder system, as a result of which it is ground, centers with increased activity on newly formed surfaces are formed; phase transformations, crystal lattice deformation, amorphization, formation of defects, etc. are possible. The aim of this work is to study the effect of low-energy mechanical treatment in a ball mill on the structure, phase composition and parameters of the fine crystal structure of non-stoichiometric titanium carbide powder obtained by reduction of titanium oxide with carbon and calcium. Materials and methods. Powder of titanium carbide TiC, obtained by calcium carbonization of titanium oxide was investigated. The powder was treated in a drum type ball mill. The structure of the powders before and after treatment was studied using the Philips SEM 515 scanning electron microscope. The specific surface area was determined by the BET method. The phase composition and parameters of the fine crystal structure of powder materials were investigated by X-ray analyzes. Results and discussion. It was established that an increase of the time of mechanical treatment in a ball mill of a non-stoichiometric titanium carbide powder TiC0.7 leads to an increase in the specific surface area of the powder from 0.6 to 3.4 m2 / g, and the average particle size calculated from it decreases from 2 μm to 360 nm. It is shown that in the process of treatment of the non-stoichiometric titanium carbide TiC0.7 powder, its structural phase state changes. Powder particles consist of two structural components with different atomic ratio of carbon to titanium: TiC0.65 and TiC0.48. Mechanical treatment of titanium carbide powder leads to a decrease in the microstresses of the TiCx crystal lattice and the size of coherently diffracting domains (CDD) from 55 to 30 nm for the TiC0.48 phase. For the TiC0.65 phase, with an increase in the duration of mechanical treatment, as well as for TiC0.48, the size of CDD decreases, and the level of microdistortions of the crystal lattice increases. This indicates that in the process of mechanical treatment, not only the grinding of powder particles occurs, but also an increase in its defects.

Light-induced In-situ Ti3+ Formation in TiO2 Nanosheets for Photocatalytic Hydrogen Evolution

TiO2 has been the benchmark semiconductor for the production of photocatalytic H2 from aqueous media (with and without sacrificial agent). On TiO2 surfaces, the photocatalytic H2 evolution reaction in aqueous environments is kinetically severely hampered. To overcome this limitation and reach reasonable H2 generation rates, a well-elucidated approach is the use of noble metal co-catalysts. In contrast to costly noble metal approaches, it recently has been reported that titania reduction treatments can lead to a noble-metal-free photocatalytic H2 generation. So-called “grey” titania due to Ti3+ states shows intrinsically activated photocatalytic H2 evolution [1–3]. The present work demonstrates the feasibility to use in-situ photoinduced reduction to create Ti3+ states that act as intrinsic catalyst and activate hydrothermal synthetized anatase nanosheets for H2 generation to mediate the transfer of photo-induced charge carriers to the electrolyte.

Chemical Reduction of Titania Supported Gold by Glycerol

Gold was loaded on TiO2 by deposition precipitation method (DPU). The as prepared DPU samples were reduced in the liquid phase through chemical reduction with pure glycerol. The advantage of this method is that, the formation of small particles (less than 7 nm) can be prevented. The chemically reduced 0.93% Au/TiO2 sample exhibited an average gold size of 12.6  0.92 nm while, the H2-reduced counterpart showed 4.2  0.25 nm. The efficacy of the size-controlled catalyst was demonstrated in the selective oxidation of HMF. The chemically reduced samples exhibited excellent selective oxidation performance by forming exclusively one product. This study reveals the possibility of controlling the size of metal-oxide supported gold catalysts.

Multivariate approach to hydrogenated TiO2 photocatalytic activity under visible light.

The photocatalytic activity of hydrogenated TiO2 was evaluated in the photooxidation of methyl orange (MO). The hydrogenation of TiO2 was carried out by calcination of a mixture of TiO2 P-25 and NaBH4 , at 300 and 350°C for blue TiO2 and black TiO2 , respectively. An experimental design was made for the determination of the best reaction conditions for the oxidation of MO. The influence of catalyst dosage and pH on photocatalytic efficiency was optimized, and the degradation percentage of MO was the response factor. The photocatalytic reaction was performed using a Xenon lamp that simulates the solar light spectrum for the activation of the catalyst. It was determined that both blue and black TiO2 show the greatest activity at pH=2 and 0.8g/L of catalyst. Additionally, the positive influence of hydrogen peroxide in the photocatalytic activity of both hydrogenated catalysts was determined. In parallel, COD and TOC were also studied. PRACTITIONER POINTS: The extent of titania reduction by hydrogenation is dependent on the reaction time with sodium borohydride. The extent of titania reduction affects the photocatalytic activity in the oxidation of methyl orange. An excess of catalyst reduction inhibits the oxidation of the dye because of the increase of recombination points. The best reaction conditions were determined by multivariate optimization as pH 2 and 0.8 g L-1 of hydrogenated catalyst. The addition of hydrogen peroxide into the reaction system improves the oxidation yield attributed to their electron accepting capacity.

Effect of Wettability between Molten Salt with Graphite Anode on the Electro-Reduction of Titanium Dioxide

The wettability between different molten salts and a graphite anode was studied using the sessile drop method, and the effect of the wettability of the anode on the reduction of titanium dioxide was also investigated. The results indicate that KCl exhibits superior wetting of the graphite anode, and that the addition of KCl improves the wettability of graphite by CaCl2-based mixed molten salts. The amount of KCl added should be controlled due to its poor oxygen solubility. The results of the electro-reduction of TiO2 in different molten salts demonstrates that the wettability of the anode by the molten salts greatly affects the deoxidation efficiency. Better wettability of the graphite anode by molten salt could accelerate the deoxidation rate of TiO2.

Pressure-induced thermoelectric properties of strongly reduced titanium oxides

This is the first systematic investigations about thermoelectric properties of strongly reduced titanium oxides, accomplished by high-pressure and high-temperature method.

Study on Carbothermal Reduction of Titania in Molten Iron

Abstract In order to improve the reduction rate of titania in molten iron, various iron powders containing C, Si, Mn and S were melted. The experiments were carried out on the reduction of titania through a high-temperature tube furnace at 1,723–1,823 K. The quantitative effects of C, Si, Mn, S and temperature on the reduction of titania were investigated in the current study. The results demonstrated that when the carbon content, the manganese content and the temperature increased by 1 %, 0.1 % and 100 K, the reduction rate increased by 0.008 %/h, 0.001125 %/h and 0.0235 %/h, respectively; when the sulfur content increased by 0.01 %, the reduction rate decreased by 0.004875 %/h; the reduction rate was irregular with the change of silicon content in molten iron. The phase at the reaction interface after the experiment was confirmed to be the Fe2Ti3O9 which was considered to be the combination product between iron oxide and titania; the lower titanium oxides were unstable and hard to be observed. The reduction was affected by the concentration of various elements in molten iron and the activity interaction coefficients between various elements. The rate constants for reduction were calculated at 1,723 K, 1,773 K and 1,823 K; the apparent activation energy was calculated as 209 kJ/mol through the rate constants and temperatures according to the Arrhenius equation.

The interboundary properties and kinematics of N719 dye with titania photoanode framework and spectral responses with different electrolytes

Titanium oxide is as ancient in age as our planet but its use for photoanode is more recent. It exists naturally as rutile (the second most abundant), anatase and brookite ores. The anatase several metastable states trigger diverse spectral responses with Magnifera Indica Linn. (M.indica L) dye as it is synthesized with an N719 dye grown on its matrix. Facile doctor blade method and high temperature sintering at 723 Kwere used in fabrication. Doping of titanium oxide in effect lowers the band gap of TiO2 for photo-excitation caused by a bathochromic shift and simultaneously decreases the rate of recombination in photogenerated electron–hole pairs. This study explored the visible light induced photocatalytic action of doped M.indica L DSSC towards reduction of titaniumoxide bandgap. The SEMmicrographs reveal themolecular interactions and the interplay as electrolytes percolate the intricate N719 dye/Titania framework. Detailed analysis stem from comparison of M.indica L crude faction and the batch separated faction using FTIR spectroscopy. The absorbance peak, rates of reaction and % transmittance identify the particular chromophores responsible for the reaction. Result shows the batch-separated hexane faction approximately 1000 times more efficient than its crude faction although the ff of the crude was only about twice that of the hexane faction. The optical study showed that doping ions lead to an increase in the absorption edge wavelength, and a decrease in the band gap energy of TiO2 nanoparticles. The doped TiO2 nanoparticles in general showed higher photocatalytic activities than the pure ones.

Evolution of reduced Ti containing phase(s) in MgH2/TiO2 system and its effect on the hydrogen storage behavior of MgH2

The present study aims to consolidate information regarding the catalytic reaction mechanism of MgH2/TiO2 hydrogen storage system. Reduction of titania, resulting to evolution of a monoxide rock salt nanocrystalline phase was identified by in-situ X-ray diffraction (XRD) study of a 3 mol% TiO2 additive mixed MgH2. Existence of homogeneously distributed Ti in a crystalline rock salt matrix was confirmed by combined analysis of X – ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and elemental chemical mapping techniques. Moreover, titanium in Ti3+ and Ti2+ valance states was confirmed by X - ray photoelectron spectroscopy (XPS). Differential scanning calorimetry (DSC) study proves that the reduced Ti oxide phases promote the low temperature dehydrogenation of MgH2. The present observations reiterate that the MgO rock salt layer existing in oxide additives loaded MgH2 is not necessarily a barrier layer that blocks the diffusion of hydrogen.

Reduction Behaviors of Iron, Vanadium and Titanium Oxides in Smelting of Vanadium Titanomagnetite Metallized Pellets

The complicated reduction behaviors of iron, vanadium and titanium oxides must be accurately controlled for the successful smelting of vanadium titanomagnetite. The aim of this study is to investigate the effects of the binary basicity, MgO content, smelting temperature, duration and reductants on the reduction of iron, vanadium and titanium oxides during the electric furnace smelting of vanadium titanomagnetite metallized pellets. The results demonstrate that the recovery ratios of both iron and vanadium increase as the binary basicity increases from 0.9 to 1.2, whereas the reduction of titanium oxides is mitigated when the basicity is maintained at 1.1. Compared to its weak effect on the recovery ratio of iron, increasing MgO content improves the vanadium recovery ratio. A low content of titanium in molten iron is obtained when the MgO content in the slag is lower than 11%, whereas the titanium content in the molten iron increases as the MgO content increases further. Moreover, the iron and vanadium recovery ratios, and the Ti content in the molten iron, increase with increasing smelting temperature, duration and reductant content.

Kinetic modeling of liquefied petroleum gas (LPG) reduction of titania in MATLAB

In the present study, reduction of Titania (TiO2) by liquefied petroleum gas (LPG)-hydrogen-argon gas mixture was investigated by experimental and kinetic modelling in MATLAB. The reduction experiments were carried out in the temperature range of 1100-1200°C with a reduction time from 1-3 hours and 10-20 minutes of LPG flowing time. A shrinking core model (SCM) was employed for the kinetic modelling in order to determine the rate and extent of reduction. The highest experimental extent of reduction of 38% occurred at a temperature of 1200°C with 3 hours reduction time and 20 minutes of LPG flowing time. The SCM gave a predicted extent of reduction of 82.1% due to assumptions made in the model. The deviation between SCM and experimental data was attributed to porosity, thermodynamic properties and minute thermal fluctuations within the sample. In general, the reduction rates increased with increasing reduction temperature and LPG flowing time.

Calciothermic reduction of titanium dioxide and molybdenum trioxide under pressure of nitrogen gas

Explored was the phenomenology of calciothermic reduction in model green mixtures containing metal oxides with strong (TiO2) and weak (MoO3) Me–O bonds. In case of high affinity metal (Ti), the process occurs in two stages: (1) combustion reaction of Ca with N2 yielding calcium nitride and (2) calciothermic reduction of TiO2 to give TiN. In case of low affinity metal (Mo), the above reactions proceed in parallel, without noticeable time delay.

Atomic-scale investigation of a new phase transformation process in TiO2 nanofibers.

Crystallography of phase transformation combining transmission electron microscopy (TEM) with in situ heating techniques and X-ray diffraction (XRD) can provide critical information regarding solid-state phase transitions and the transition-induced interfaces in TiO2 nanomaterials theoretically and experimentally. Two types of reduced titanium oxides (Ti3O5, Ti6O11) are found during ex situ and in situ heating of TiO2 (B) nanofibers with a specific morphology of the {100} single form (SF) in air and vacuum. The results indicate that the phase transformation process from TiO2 (B) follows the TiO2 (B) → Ti3O5 → Ti6O11 → anatase sequence for the nanofibers with the {100} SF. The occurrence of such a phase transition is selective to the morphology of TiO2 (B) nanofibers. The corresponding orientation relationships (COR) between the four phases are revealed according to the TEM characterization. Four types of coherent interfaces, following the CORs are also found. They are TiO2 (B)/Ti3O5, TiO2 (B)/Ti6O11, Ti6O11/anatase and TiO2 (B)/anatase respectively. The habit plane for the TiO2 (B) to Ti3O5 transition is calculated as the {100}TB by using the invariant line model. The detailed atomic transformation mechanism is elucidated based on the crystallographic features of the four phases.

Synthesis of fine dispersed titanium diboride from nanofibrous carbon

This paper presents the experimental data on the synthesis of titanium diboride (TiB2) fine dispersed powder carried out in laboratory scale. TiB2 powder was prepared by the reduction of titanium dioxide with boron carbide and nanofibrous carbon in an argon atmosphere. The powders of TiB2 were characterized by X-ray diffraction (XRD), elemental analyses, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), low-temperature nitrogen adsorption, particle size analysis, simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC). The resulting material contains a single phase – titanium diboride. The particles of the powder were predominantly aggregated. The average size of the particles and the aggregates were 7.4–8.0µm with a wide size of distribution. The specific surface values of samples obtained were 2.4–5.8m2/g. The oxidation of titanium diboride began from the temperature of 450°C. In this work, the optimal synthesis conditions were estimated: the molar ratio was TiO2:B4C:C=2:1:3 (according to stoichiometry), the temperature was 1600°C, the process duration was 20–30min.

Reduced Titanium Oxide as Carbon-Free Support of Non-Precious Metal Oxide-Based Cathodes for PEFCs

Introduction The development of polymer electrolyte fuel cells (PEFCs) has attracted tremendous interest, because they have many advantages, including high power density, high energy conversion efficiency, and low operating temperatures. Recently, PEFCs has been already commercialized as power supply of fuel cell vehicles and residential use. Generally, platinum-based alloys supported carbon black are used as catalysts in both the anode and cathode of PEFCs. However, Pt is high cost and limited resources. In addition, carbon support is fundamentally unstable under cathode conditions to oxidize at high potential region. The development of alternative catalysts with high stability for oxygen reduction reaction (ORR) is required for wide spread of PEFCs. This catalyst needs two components, precious-metal-free active sites for ORR and carbon-free electro-conductive supports. We have focused on group 4 and 5 metal oxide-based compounds as both precious-metal-free materials with active sites and electro-conductive materials. As an alternative support of carbon , we focused on titanium Magnéli sub-oxides (TinO2n-1; 4≦n≦10), particularly Ti4O7, because of its high chemical stability in acid electrolyte and high conductivity. However, the formation of Ti4O7 needs to reduce at high temperature, 1050 oC, under 4% H2 for 20-60 h1). Such a high temperature caused the drastic particle growth and morphology destruction. In this study, we applied solid-phase reduction at low temperature by using NaBH4 2) to investigate the appropriate condition for the formation of reduced titanium oxides as support. Experimental Rutile type TiO2 powder (ca. 30 nm) was mixed with NaBH4. The mixture was heat-treated under Ar atmosphere at 300 - 400oC for 24 h. After heat-treatment, we washed products with deionized water and 0.1 M hydrochloric acid to obtain the reduced titanium oxide powders. X–ray diffraction spectroscopy (XRD, Rigaku Ultima IV) was performed to determine the crystalline structure of the powder. Results and discussion Figure 1 shows the XRD patterns of the reduced powders heat-treated at various temperatures. The peaks near 27.4o identical to first main peak of TiO2 rutile were gradually decreased from 300 to 360 oC, and the peaks near 23.8 o and 33.0 o identical to Ti2O3 appeared above 350 oC, indicating that the formation of bulk Ti2O3 gradually proceeded above 350 oC. On the other hand, the temperature over 375 oC caused transition to amorphous phase. These results suggested that it was difficult to form the Ti4O7 phase by solid-phase reduction at low temperature. We need to find an appropriate condition to form the Ti4O7 phase. On the other hand, it was reported that the bulk Ti2O3 has much larger conductivity than TiO2 3). However, the all reduced powders showed large resistance measured by two-terminal resistance measurement. The large resistance was caused by the contact resistance due to the passive layer formed on the nano-particles. In order to reduce the contact resistance, we think that the formation of the electro-conductive network structure is effective by control the morphology of the reduced oxides. Acknowledgments The authors thank New Energy and Industrial Technology Development Organization (NEDO) for financial support. The Institute of Advanced Sciences (IAS) in Yokohama National University was supported by the MEXT Program for Promoting Reform of National Universities. References 1) M. Hamazaki, A. Ishihara, Y. Kohno, K. Matsuzawa, S. Mitsusima, and K. Ota, Electrochemistry, 83, 817 (2015). 2) S. Tominaka, Chem. Commun., 48, 7949 (2012). 3) S. Tominaka, Inorg. Chem, 51, 10136 (2012) Figure 1

Effects of Dissolving Agents on Particle Size Reduction of Titanium Dioxide Synthesized by Solution Combustion Technique

High photocatalytic activity of nanoparticulate titanium dioxide has attracted worldwide attention. Synthesis techniques of the nanoparticles, however, often require high energy supply or costly initial reagents. Solution combustion technique is an energy-effective technique capable of synthesizing nanosized titanium powders. This research aimed at utilizing a less expensive initial reagent in synthesis of nanoparticulate titanium dioxide by the solution combustion technique. The research also examined effects of dissolving agents on chemical composition and particle sizes of the synthesized powders. A low-cost initial reagent, titanium dioxide with average particle size of 154 nanometers, was dissolved in sulfuric acid or dispersed in nitric acid prior to the combustion. Experimental results revealed that the pure anatase phase titanium dioxide was successfully obtained in powders prepared from both sulfuric acid and nitric acid. The average particle size of the powder prepared from sulfuric acid was 77 nanometers, while that of the powder prepared from nitric acid was 117 nanometers. The difference in particle sizes was attributed to solubility of the initial reagent in the acid. Complete solution of initial reagent in sulfuric acid was the main factor attributed to finer particle size.