One-pot synthesis of bifunctionalized TiO<Subscript>2</Subscript> mesoporous photocatalyst with visible light response

A series of Fe-doped SH/TiO₂ mesoporous photocatalysts have been firstly prepared by one-pot method using P123 as structure-directing agent. This bifunctionalized mesoporous TiO₂ possesses perfect anatase crystal structure and high surface area. The surface area of Fe-doped SH/TiO₂ mesoporous material is 4 times higher than that of P25. Based on the EPR results, it was found that trivalent Fe ions exist at low spin state and substitutes a part of Ti⁴⁺ ions into TiO₂ lattice. Fe-dropping in TiO₂ extends the adsorption band side of the resulting material to about 600 nm. Much high photocatalytic activity in the degradation of phenanthrene was obtained on the bifunctionalized mesoporous TiO₂ under visible light irradiation (λ > 420 nm), which is 6 times higher than that of pristine mesoporous TiO₂. The enhancement in the photocatalytic activity of bifunctionalized TiO₂ is ascribed to the extended absorption to visible light and strong interaction between SH-groups and PHE molecules.     

Sulfidation/regeneration multicycle testing of nickel-modified ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> desulphurization sorbent

A commercial metal oxide sorbent for the desulphurization of coal-derived gas requires high desulphurization reactivity, mechanical strength, ability to regenerate, and stability to endure many sulfidation-regeneration cycles. In this paper, the sulfur capacity and multiple cycles of a nickel-modified ZnFe₂O₄ sorbent prepared by the sol-gel auto-combustion method were measured in a fixed-bed reactor at middle temperature of 300°C (sulfidation temperature) and 500°C (regeneration temperature). Also, the BET surface area, pore volume, average pore diameter and X-ray diffraction (XRD) patterns of the sorbent through multicycles were studied. Multicycle runs indicate that the sulfidation reactivity decreases slightly during the second cycle and keeps steady in the following cycles. The results indicate that the nickel-modified ZnFe₂O₄ keeps high reactivity and structural stability in the multicycle testing of sulfidation/regeneration.     

A photocatalytic performance of TiO<Subscript>2</Subscript> photocatalyst prepared by the hydrothermal method

Anatase phase nanocrystalline TiO₂ powders were prepared by hydrothermal method with the TTIP (titanium tetra isopropoxide) at 200 oC in a stirred autoclave system. The effects of synthesis conditions on the physical properties of catalyst were investigated by using XRD, SEM, DLS, DSC and BET. The TiO₂ powders obtained from the optimum condition showed uniform spherical shape, crystalline structure, submicron size with a sharp size distribution and few agglomerates. The optimum synthesis conditions were obtained within the covered experimental ranges. The photocatalytic activity of TiO₂ powders prepared by the hydrothermal method was tested for photooxidation of methyl orange.     

Facile synthesis of nano-Li<Subscript>4</Subscript> Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> for high-rate Li-ion battery anodes

One of the most promising anode materials for Li-ion batteries, Li₄Ti₅O₁₂, has attracted attention because it is a zero-strain Li insertion host having a stable insertion potential. In this study, we suggest two different synthetic processes to prepare Li₄Ti₅O₁₂ using anatase TiO₂ nanoprecursors. TiO₂ powders, which have extraordinarily large surface areas of more than 250 m² g^-1, were initially prepared through the urea-forced hydrolysis/precipitation route below 100°C. For the synthesis of Li₄Ti₅O₁₂, LiOH and Li₂CO₃ were added to TiO₂ solutions prepared in water and ethanol media, respectively. The powders were subsequently dried and calcined at various temperatures. The phase and morphological transitions from TiO₂ to Li₄Ti₅O₁₂ were characterized using X-ray powder diffraction and transmission electron microscopy. The electrochemical performance of nanosized Li₄Ti₅O₁₂ was evaluated in detail by cyclic voltammetry and galvanostatic cycling. Furthermore, the high-rate performance and long-term cycle stability of Li₄Ti₅O₁₂ anodes for use in Li-ion batteries were discussed.     

Ni<Superscript>2+</Superscript> reduction under solar irradiation over CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> catalysts

The photo-electrochemical characterization of the hetero-system CoFe₂O₄/TiO₂ was undertaken for the Ni²⁺ reduction under solar light. The spinel CoFe₂O₄ was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 V_SCE) is more cathodic than the potential of Ni²⁺/Ni couple (-0.6 V_SCE), thus leading to a feasible nickel photoreduction. TiO₂ with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni²⁺ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni²⁺ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10^-2 min^-1 according to the Langmuir-Hinshelwood model.     

Uniform color coating of multilayered TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films by atomic layer deposition

Thin film optics, based on light interference characteristics, are attracting increasing interest because of their ability to enable a functional color coating for various applications in optical, electronic, and solar industries. Here, we report on the dependence of coloring characteristics on single-layer TiO₂ thicknesses and alternating TiO₂/Al₂O₃ multilayer structures prepared by atomic layer deposition (ALD) at a low growth temperature. The ALD TiO₂ and Al₂O₃ thin films were studied at a low growth temperature of 80°C. Then, the coloring features in the single-layer TiO₂ and alternating TiO₂/Al₂O₃ multilayers using both the ALD processes were experimentally examined on a TiN/cut stainless steel sheet. The Essential Macleod software was used to estimate and compare the color coating results. The simulation results revealed that five different colors of the single TiO₂ layers were shown experimentally, depending on the film thickness. For the purpose of highly uniform pink color coating, the film structures of TiO₂/Al₂O₃ multilayers were designed in advance. It was experimentally demonstrated that the evaluated colors corresponded well with the simulated color spectrum results, exhibiting a uniform pink color with wide incident angles ranging from 0° to 75°. This article advances practical applications requiring highly uniform color coatings of surfaces in a variety of optical coating areas with complex topographical structures.     

Facile synthesis of ZnBi<Subscript>2</Subscript>O<Subscript>4</Subscript>-graphite composites as highly active visible-light photocatalyst for the mineralization of rhodamine B

Novel highly active visible-light photocatalysts in the form of zinc bismuth oxide (ZnBi₂O₄) and graphite hybrid composites were prepared by coupling via a co-precipitation method followed by calcination at 450 °C. The as-prepared ZnBi₂O₄-graphite hybrid composites were tested for the degradation of rhodamine B (RhB) solutions under visible-light irradiation. The existence of strong electronic coupling between the two components within the ZnBi₂O₄-graphite heterostructure suppressed the photogenerated recombination of electrons and holes to a remarkable extent. The prepared composite exhibited excellent photocatalytic activity, leading to more than 93% of RhB degradation at an initial concentration of 50mg·L^-1 with 1.0 g catalyst per liter in 150min. The excellent visible-light photocatalytic mineralization of ZnBi₂O₄-1.0graphite in comparison with pristine ZnBi₂O₄ could be attributed to synergetic effects, charge transfer between ZnBi₂O₄ and graphite, and the separation efficiency of the photogenerated electrons and holes. The photo-induced h+ and the superoxide anion were the major active species responsible for the photodegradation process. The results demonstrate the feasibility of ZnBi₂O₄-1.0graphite as a potential heterogeneous photocatalyst for environmental remediation.     

Solar photocatalytic detoxification of cyanide by different forms of TiO<Subscript>2</Subscript>

The photocatalytic efficiencies of TiO₂ nanocrystals of different modifications (anatase, rutile, P25 Degussa, Hombikat), to oxidize cyanide ion and subsequently the cyanate also, under natural sunlight at 950±25W m⁻² in alkaline solution have been compared. The oxides have been characterized by powder XRD, UV-visible diffuse reflectance and impedance spectroscopies. Under identical solar irradiance, the reaction follows Langmuir-Hinshelwood kinetics on cyanide, and depends on the apparent area of the catalyst bed and dissolved oxygen. However, the adsorption of cyanide on TiO₂ in dark is too small to be measured analytically. The photocatalytic activity of TiO₂ is not solely governed by the band gap or charge-transfer resistance or capacitance or phase composition but is in accordance with the specific surface area or the average crystallite size; rutile is an exception.     

High-throughput screening of transition metal-doped TiO<Subscript>2</Subscript> in photodecomposition of phenol under visible light

A catalyst library consisting of 20 catalysts with different metal and weight fraction-doped TiO₂ was prepared at one time for discovering the novel metal-doped TiO₂ photocatalyst, which is active under visible light irradiation. Combinatorial microbeam XRD and UV-vis spectrometer were used for analysis of crystal structure and photoactivity of 20 catalysts in the library, respectively. Photodecomposition of phenol was chosen as a probe reaction. The library preparation, XRD characterization and reaction test for 20 catalysts were completed within 48 hours. Among the catalysts in the library, 1.5 wt% Co/TiO₂ showed the best activity for phenol degradation. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Highly ordered mesoporous CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> with crystalline walls

The highly ordered mesoporous CoFe₂O₄ and CuFe₂O₄ with crystalline walls can be synthesized by hard template with using mesoporous silica SBA-15 as hard template and using ferric nitrate, cobalt nitrate, and copper nitrate as metal precursors. These new mesoporous materials above have high surface areas, narrow pore size distribution, and large pore volumes, which are believed to be valuable for the potential application in the field of sensors, catalysis, message recording, magnetics, and biology. This work provides a method to fabricate the highly ordered mesoporous materials composed of multi-metal oxides with crystalline walls. The development of such versatile approach is of great significance in practical application. It can be envisaged that this established method is significantly expandable to the controlled synthesis of the mesoporous functional materials with diverse compositions.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

Phase equilibria in the Ho<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

The phase formation is investigated and the phase diagram of the Ho₂O₃-SrAl₂O₄ system is constructed. A ternary compound, namely, Ho₂SrAl₂O₇, is revealed. It is established that this compound undergoes incongruent melting.     

Phase Equilibria in the Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> System

The phase equilibria are investigated and the phase diagram is constructed for the Gd₂O₃-SrAl₂O₄ pseudobinary join of the Gd₂O₃-SrO-Al₂O₃ ternary oxide system. One ternary compound, namely, Gd₂SrAl₂O₇, is revealed in the Gd₂O₃-SrAl₂O₄ join. It is found that this compound undergoes congruent melting.     

Combustion of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Al thermit mixtures in steel tubes

Explored was the combustion of Fe₂O₃/TiO₂/Al thermit mixtures in steel tubes upon variation in green composition and with special emphasis on the dependence of combustion temperature T _c and burning velocity U on reaction heat Q. Special attention was given to incompleteness of combustion for compositions with low Q.     

A study on synthesis and properties of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles by solvothermal method

Magnetic nanoparticles (Fe₃O₄) were synthesized by the solvothermal method using FeCl₃ · 6H₂O and ethylene glycol as a reactant. Powder X-ray diffraction, FT-IR, TEM, SEM, and VSM were used to characterize the magnetic particles. The reacting factors, such as reacting time, the concentration of iron source and surfactant, especially the effect of NaAc · 3H₂O, were studied. The results indicated that NaAc · 3H₂O plays the role not only as a dispersant but also a structure-directing agent. The synthesized Fe₃O₄ particles showed excellent magnetic property, which made them have potential for application in magnetic nanodevices and biomedicine.     

Thermal hydrolysis as a new method of synthesis of the CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel ferrite

A new method has been proposed for synthesizing spinel ferrites, i.e., thermal hydrolysis, which makes it possible to obtain a single-phase product of high purity for a short time. A polycrystalline sample of the CoFe₂O₄ composition has been prepared. The phase composition and morphology of the sample have been investigated and its crystal structure has been refined. The static magnetic characteristics have been measured.     

Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Interaction of O<Subscript>2</Subscript>, O<Subscript>3</Subscript>, and H<Subscript>2</Subscript>O<Subscript>2</Subscript> with an activated carbon

The results of the modification of AG-OV-1 activated carbon under various conditions (by atmospheric oxygen at elevated temperatures and by hydrogen peroxide or ozone) are given. The effect of the used modifier on changes in the porosity, surface state, and adsorption capacity of activated carbon is evaluated.     

Photocatalytic activities and specific surface area of TiO<Subscript>2</Subscript> films prepared by CVD and sol-gel method

The photocatalytic activity of CVD grown films shows significant, non-linear (sigmoid-like) dependency on the film thickness. However, the photocatalytic activity of sol-gel grown film is almost independent of the film thickness. The specific surface area of sol-gel grown films is very small, regardless of the film thickness. Conversely, the specific surface area of CVD grown films indicates significant thickness dependency. The specific area and photocatalytic activity were found to show very similar dependencies on the film thickness.