Extending aromatic acids on TiO2 for cooperative photocatalysis with triethylamine: Violet light-induced selective aerobic oxidation of sulfides

Designing visible light photocatalysts with a metal oxide semiconductor as the starting material could expand a new horizon for the conversion and storage of solar energy. Here, the benchmark photocatalyst TiO₂ was used to pursue this goal by anchoring aromatic acids. Extending the aromatic acid was strategically deployed to design TiO₂ complexes with violet light-induced selective aerobic oxidation of sulfide as the probe reaction. With benzoic acid (BA) as the initial molecule, horizontally extending one or two benzene rings furnishes 2-naphthoic acid (2-NA) and 2-anthracene acid (2-AA). Moreover, triethylamine (TEA), an electron transfer mediator, was introduced to maintain the integrity of the anchored aromatic acids. Notably, there was a direct correlation between the π-conjugation of aromatic acid ligand and the selective aerobic oxidation of sulfides. Among the three aromatic acids, 2-AA delivered the best result over TiO₂ due to the most extensive π-conjugated system. Ultimately, violet light-induced selective aerobic oxidation of sulfides into corresponding sulfoxides was conveniently realized by cooperative photocatalysis of 2-AA-TiO₂ with 10 mol% of TEA. This work affords an extending strategy for designing the next-generation ligands for semiconductors to expand visible light-induced selective reactions.     

Influence of titanium oxide on the surface interactions of MO (M=Cu and Ni)/γ-Al2O3 catalysts

The influence of titanium oxide on the surface interactions of MO (M=Cu and Ni)/γ-Al₂O₃ catalysts has been studied by using XRD, LRS and XPS. For the catalysts with titania loadings lower than 0.56 mmol Ti⁴⁺/100 m² Al₂O₃ (i.e., the dispersion capacity), the dispersion of MO oxides on the surface of γ-Al₂O₃ support is significantly suppressed by the dispersed Ti⁴⁺ ions. The inhibiting effect is dependent on the properties of MO oxides. When titania loadings are considerably higher than the dispersion capacity, MO oxides exhibit a rather stronger interaction with the formed TiO₂ particles than the γ-Al₂O₃ support, and some of the dispersed M²⁺ ions might be accommodated by the vacant sites on TiO₂. Therefore, the catalysts can be considered as the compositions of MO/TiO₂ and MO/TiO₂/γ-Al₂O₃ (dispersed titania). TPR results show that either dispersed titania or formed TiO₂ particles can promote the reduction of copper oxide species, but the latter to a greater extent. Based on the consideration of the incorporation model, it is proposed that the surface structure of the support plays an important role in surface interactions.     

An electron microscope study of perovskite-related oxides in the SrTiO system

In order to investigate the relationship between nonstoichiometry and the static dielectric constant, phases in the SrOTiO₂ pseudo-binary system have been studied by X-ray diffraction and electron microscopy. Three ternary oxides were found in the temperature interval 1373–1673°K, Sr₂TiO₄, Sr₃Ti₂O₇, and SrTiO₃. In all of these oxides, nonstoichiometry seems to be taken up by coherent intergrowth of lamellae of various homologous oxides Sr_n+1Ti_nO_3n+1 The results are discussed in terms of the crystal chemistry of the perovskite oxides and factors which influence the magnitude of the static dielectric constant of solids.     

Freeze-drying synthesis and characterisation of Na composites of ZnO,TiO<Subscript>2</Subscript> and ZnTiO<Subscript>3</Subscript> semiconductor oxides

The freeze-drying method of metal oxides synthesis has a number of advantages such as high homogeneity, varying porous structures, morphologies and uniform particle size distribution, etc. Because of these advantages, the binary metal oxides ZnO, TiO₂ and ternary metal oxide ZnTiO₃ were synthesised by the freeze-drying method. The synthesised materials were characterised by X-ray diffraction (XRD), Fourier transform-infra red spectroscopy (FT-IR), UV-VIS spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX). The as-synthesised metal oxides were calcined at different temperatures to study the phase evolution and morphological changes. The crystalline cubic-phase ZnTiO₃ (a = 8.3948 Å) was obtained on calcination of the precursor at 600°C, and decomposed to the cubic phase Zn₂TiO₄ (a = 8.4580 Å) and rutile TiO₂ (a = 4.5955 Å and c = 2.9593 Å) at 1000°C. The band gap of ZnO (3.28?3.10 eV), TiO₂ (3.37?2.97 eV) and ZnTiO₃ (3.92?3.80 eV) calculated using Tauc’s relation was found to vary inversely with calcination temperature and phase transition.     

Une nouvelle famille structurale: Les titanoniobates et titanotantalates A2Nb6TiO18 et A2Ta6TiO18

New ternary oxides A₂M₆TiO₁₈ (A = Rb, Cs; M = Ta, Nb) have been synthesized by reaction between M₂O₅ and TiO₂ oxides and A₂CO₃ carbonates. They crystallize in the hexagonal system in a cell of dimensions a and c near 7.5 and 8.2 Å, respectively. There is one formula unit in the cell, in good agreement with the observed densities 4.38 and 4.78 for A₂Nb₆TiO₁₈, 6.62 and 6.93 for A₂Ta₆TiO₁₈. The structure has been determined from powder diffraction patterns, from the 64 first reflections (i.e., 190 hkl), and refined to R₁ values ranging from 0.06 and 0.08. It can be described from a basic unit of composition (M₆O₂₄) formed of 3 × 2 octahedra of oxygen atoms, sharing edges and corners, with MO distances ranging from 1.8 and 2.2 Å. Relations with the hexagonal tungsten bronze and pyrochlore-type structures are discussed.     

Photocatalytic activity of TiO2-MO x composites in the reaction of hydrogen generation from aqueous isopropanol solution

The photocatalytic activity of the composites TiO₂-MO _x (M = Ni, Cu, Zn, Fe, Cr) was studied in the reaction of hydrogen generation from aqueous alcoholic suspensions under UV light. The samples modified by the oxides of the metals capable of being reduced from oxides under photocatalytic conditions showed a high catalytic activity. The studied modifiers were divided in three groups in terms of their effect of the photocatalytic activity of TiO₂: activating (NiO, CuO), inhibiting (Fe₂O₃), and indifferent (ZnO, Cr₂O₃).     

Initial corrosion behavior of composite coatings obtained by co-electrodeposition of zinc with nanoparticles of Ti and Ce oxides

The present work reports the results obtained for the electrodeposition of composite Zn coatings on steel by using Ti and Ce oxides nanopowders, separately or in mixture, and a TiO₂·CeO₂ binary oxide. In an attempt to correlate the effects of nanoparticles on corrosion behavior of the composite deposits, the properties of Zn–TiO₂·CeO₂ layers were compared with those referring to similar coatings prepared by using a simple mixture of the two oxides or individual oxides. Corrosion measurements were performed in 0.2 g?L^?1 Na₂SO₄ solution (pH?=?5). The results of electrochemical measurements (open circuit potential measurements, polarization curves, and electrochemical impedance spectroscopy) were corroborated with those obtained by using X-ray diffraction, atomic force microscopy, scanning electron microscopy, and salt spray tests. The results indicate that the composite Zn–(TiO₂?+?CeO₂) coatings exhibit the highest corrosion resistance from all investigated Zn coatings.     

In-situ UV-Raman study on soot combustion over TiO2 or ZrO2-supported vanadium oxide catalysts

UV-Raman spectroscopy was used to study the molecular structures of TiO₂ or ZrO₂-supported vanadium oxide catalysts. The real time reaction status of soot combustion over these catalysts was detected by in-situ UV-Raman spectroscopy. The results indicate that TiO₂ undergoes a crystalline phase transformation from anatase to rutile phase with the increasing of reaction temperature. However, no obvious phase transformation process is observed for ZrO₂ support. The structures of supported vanadium oxides also depend on the V loading. The vanadium oxide species supported on TiO₂ or ZrO₂ attain monolayer saturation when V loading is equal to 4 (4 is the number of V atoms per 100 support metal ions). Interestingly, this loading ratio (V₄/TiO₂ and V₄/ZrO₂) gave the best catalytic activities for soot combustion reaction on both supports (TiO₂ and ZrO₂). The formation of surface oxygen complexes (SOC) is verified by in-situ UV Raman spectroscopy and the SOC mainly exist as carboxyl groups during soot combustion. The presence of NO in the reaction gas stream can promote the production of SOC.     

Etude thermodynamique des oxydes TiO2−x a 1050°C

g_O2^M (O/Ti) and h z (O/Ti) have been directly measured at 1050°C within the whole homogeneity range of the rutile phase TiO_2?x, respectively, using the method of equilibration between oxides and buffer gaseous mixtures and by means of a high temperature microcalorimeter. These results are discussed in terms of point defects.     

DFT Study of Methylene Blue Adsorption on ZnTiO3 and TiO2 Surfaces (101)

The search for alternative materials with high dye adsorption capacity, such as methylene blue (MB), remains the focus of current studies. This computational study focuses on oxides ZnTiO₃ and TiO₂ (anatase phase) and on their adsorptive properties. Computational calculations based on DFT methods were performed using the Viena Ab initio Simulation Package (VASP) code to study the electronic properties of these oxides. The bandgap energy values calculated by the Hubbard U (GGA + U) method for ZnTiO₃ and TiO₂ were 3.17 and 3.21 eV, respectively, which are consistent with the experimental data. The most favorable orientation of the MB adsorbed on the surface (101) of both oxides is semi-perpendicular. Stronger adsorption was observed on the ZnTiO₃ surface (−282.05 kJ/mol) than on TiO₂ (–10.95 kJ/mol). Anchoring of the MB molecule on both surfaces was carried out by means of two protons in a bidentate chelating (BC) adsorption model. The high adsorption energy of the MB dye on the ZnTiO₃ surface shows the potential value of using this mixed oxide as a dye adsorbent for several technological and environmental applications.     

Rapid Synthesis of Nanocrystalline TiO2/SnO2 Binary Oxides and Their Photoinduced Decomposition of Methyl Orange

A rapid and simple method, the so-called stearic acid method (SAM) was developed to prepare nanostructured TiO₂/SnO₂ binary oxides by combustion of stearic acid precursors. The preparative process was studied by Fourier transform infrared spectroscopy (FT-IR). During the preparative process, metal precursors were dispersed in stearic acid at molecular level. Microstructure of the samples was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), BET specific surface area measurement and the results were compared with those obtained by conventional sol-gel method. The photocatalytic decomposition of methyl orange was used as a model system to determine the relative influences of the preparation method and the concentration of SnO₂ on the photocatalytic activities. It was found that preparative methods affected the crystalline structure of TiO₂/SnO₂ powders and the anatase phase of TiO₂ was stabilized by the addition of SnO₂ in SAM. The samples prepared by SAM showed better dispersity, larger specific surface area and the TiO₂/SnO₂ (r=0.15, SAM) catalyst showed higher photocatalytic activity than Degussa P25.     

Nano-titanium oxide doped with gold,silver, and palladium — synthesis and structural characterization

Nano-titania doped with noble metals (Au/TiO₂, Ag/TiO₂, Pd/TiO₂) has been synthesized by mild hydrolysis of the mixture of metal salts or complexes and titanium isopropoxide ((iPr-O)₄Ti). After thermal decomposition of the obtained precursors, nanomaterials were formed. Morphological characterization of the nanomaterials was provided by scanning electron microscopy (SEM) and stereological analysis, determining the BET specific surface area, and BJH nanoporosity (pore volume, pore size). It has been found that the structure of nanomaterials (size of nanoparticles and agglomerates) depended strongly on the method of the (iPr-O)₄Ti hydrolysis. A minor dependence on the kind of solvents and precursors of noble metals was observed. The presence of doping metal nanoparticles was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Nanomaterial phases were identified by X-ray diffraction (XRD). According to the XRD patterns, Ag/TiO₂ and Pd/TiO₂ products with doping metals in their oxidized form contain Ag-Ti and Pd-Ti phases. Peaks of the metal oxides Ag₂O and PdO are absent in the XRD patterns. The average size of TiO₂ nanoparticles is situated in the region of 20–60 nm, whereas metals are present as about 10–15 nm sized particles and fine nanoparticles.     

Phase relations in the pseudobinary system TiO2Ga2O3

Phase relations and microstructures in the TiO₂-rich part of the TiO₂Ga₂O₃ pseudobinary system have been determined at temperatures between 1373 and 1623°K using X-ray diffraction and electron and optical microscopy. The phases occurring in the system are TiO₂ (rutile), β-Ga₂O₃, a series of oxides Ga₄Ti_m?4O_2m?2 (m odd) which exist above 1463°K, and Ga₂TiO₅, which exists above 1598°K. The width of the phase region occupied by the Ga₄Ti_m?4O_2m?2 phases varies with temperature. At 1473°K it is narrow, and has limits of Ga₄Ti₂₅O₅₆ to Ga₄Ti₂₁O₄₈ while at higher temperatures it broadens to limits of from Ga₄Ti₂₇O₆₀ to Ga₄Ti₁₁O₂₈ at 1623°K. These phases are often disordered and crystals frequently contain partially ordered intergrowths of oxides with various values of m. On the TiO₂-rich side of the phase region there is a continuous change in texture from rutile to the end members of the Ga₄Ti_m?4O_2m?2 structures. The findings are summarized on a phase diagram.     

The photocatalytic properties of amorphous TiO2 composite films deposited by magnetron sputtering

The preparation of amorphous TiO₂ film coupled with various metal-oxide semiconductors and their photocatalytic activities evaluated by photo-degradation of methylene blue and rhodamine B aqueous solution are briefly reviewed. The proposed photoreaction mechanism of the amorphous composite semiconductor and the differences between amorphous TiO₂-based films and crystalline TiO₂ photocatalytic materials in terms of preparation and usage are addressed. The inactive intrinsic amorphous TiO₂ film coupled with various metal oxides were found to gain high photocatalytic activity. These dopants induce forming new energy levels in the band gap of TiO₂ to enhance the charge separation of the photoinduced electrons and holes and extend the light absorption of TiO₂-based photocatalytic films into the visible region. In addition, two different effects of coupling metal oxides have been proved: the introduction of oxides of W, Cr, V, Ag, and Mo can significantly increase the photo-reactivity of amorphous TiO₂ film, while the combination of oxides of Zr, Sn, Sb, Cu, Ta, Fe, and Ni cannot affect the inactivity of pure amorphous TiO₂ film.     

锐钛矿(001)与(101)晶面在光催化反应中的作用

采用水热法制备了(001)和(101)晶面暴露的单晶锐钛矿TiO₂颗粒. 利用光还原沉积贵金属(Au, Ag, Pt)和光氧化沉积金属氧化物(PbO₂, MnO_x)的方法研究了暴露的锐钛矿(001)和(101)晶面在光催化中的作用. 通过透射电子显微镜(TEM)、扫描电子显微镜(STM)、能量色散X射线光谱仪(EDX)和X射线光电子能谱(XPS)的表征, 发现发生光还原反应生成的贵金属粒子主要沉积在暴露的锐钛矿(101)晶面上, 而发生光氧化反应产生的金属氧化物颗粒主要沉积在暴露的锐钛矿(001)晶面上. 此结果表明光激发产生的电子与空穴主要并分别分布在单晶锐钛矿TiO₂的(101)与(001)晶面上, 并在其上参与光催化还原反应和氧化反应. 同时也表明暴露的不同晶面对光生电荷具有分离效应. 基于本研究可以认为同时暴露分别进行氧化和还原反应的晶面可以有效促进光催化反应.     

Significant effect of lanthanide doping on the texture and properties of nanocrystalline mesoporous TiO2

A systematic study of microstructure and photocatalytic properties of lanthanide doping of nanocrystalline mesoporous titanium dioxide is performed. The anatase-to-rutile (A-R) phase transformation of nanosized TiO₂ was significantly inhibited by lanthanide doping and the inhibitory effect was enhanced with the increase of the rare earth radius, i.e., La³⁺>Gd³⁺>Yb³⁺ for different lanthanide dopants. At high calcination temperatures, different texture lanthanide titanium oxides of Ln₄Ti₉O₂₄ (La³⁺, Pr³⁺, Nd³⁺), Ln₂Ti₂O₇ (Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Er³⁺), and Yb₂TiO₅ were developed, respectively, revealing that the structures of lanthanide titanium oxide developed in Ln/TiO₂ depend on the lanthanide radius. Larger radius lanthanides prefer to form higher coordination number lanthanide titanium oxide. In addition, the thermal stability of mesoporous structures of TiO₂ was remarkable improved by lanthanide doping. The photocatalytic properties were studied by employing the photodegradation of Rhodamine B (RB) as a probe reaction. The results indicate that the lanthanide doping could bring about significant improvement to the photoreactivity of TiO₂, and the improvement was sensitive to the atomic electronic configuration.     

Li2MTiO4 (M=Mn, Fe, Co, Ni): New cation-disordered rocksalt oxides exhibiting oxidative deintercalation of lithium. Synthesis of an ordered Li2NiTiO4

We describe the synthesis and characterization of a new series of oxides, Li₂MTiO₄ (M=Mn, Fe, Co, Ni) that crystallize in the rocksalt structure. For M=Ni, we have also obtained a low-temperature modification that adopts a Li₂SnO₃-type structure. All the phases, excepting M=Ni, undergo oxidative deinsertion of lithium in air/O₂ at elevated temperatures (>150°C), yielding LiMTiO₄ (M=Mn, Fe) spinels and a spinel-like Li_1+xCoTiO₄ as final products.     

Preparation of titania microfiltration membranes supported on porous Ti–Al alloys

A TiO₂ membrane supported on a planar porous Ti–Al alloy was prepared by combination of electrophoretic deposition and dip-coating. In the electrophoretic deposition process, the membrane thickness increased linearly with the square root of the deposition time, while increased with decrease of the suspension viscosity. The perfect TiO₂/Ti–Al composite membrane was obtained by further dip-coating modification. SEM images showed that the surface of the membrane was defect-free. XRD result indicated that rutile TiO₂ still remained in the membrane bulk as the main phase, while a new phase titanium oxides with the form of Ti_xO_y, where y is less than 2x, was also observed. The supported TiO₂/Ti–Al composite membrane had an average pore size of 0.28 μm, a thickness of 40 μm or so and a pure water flux of 3037 L m⁻² h⁻¹ bar⁻¹.     

Cooperative Photocatalysis with 4-Amino-TEMPO for Selective Aerobic Oxidation of Amines over TiO2 Nanotubes

Attaching π-conjugated molecules onto TiO₂ can form surface complexes that could capture visible light. However, to make these TiO₂ surface complexes durable, integrating 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or its analogues as a redox mediator with photocatalysis is the key to constructing selective chemical transformations. Herein, sodium 6,7-dihydroxynaphthalene-2-sulfonate (DHNS) was obtained by extending the π-conjugated system of catechol by adding a benzene ring and a substituent sodium sulfonate (−SO₃⁻Na⁺). The DHNS−TiO₂ showed the best photocatalytic activity towards the blue light-induced selective aerobic oxidation of benzylamine. Compared to TEMPO, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) could rise above 70% in conversion of benzylamine over the DHNS−TiO₂ photocatalyst. Eventually, a wide range of amines could be selectively oxidized into imines with atmospheric O₂ by cooperative photocatalysis of DHNS−TiO₂ with 4-amino-TEMPO. Notably, superoxide (O₂^•−) is crucial in coupling the photocatalytic cycle of DHNS−TiO₂ and the redox cycle of 4-amino-TEMPO. This work underscores the design of surface ligands for semiconductors and the selection of a redox mediator in visible light photocatalysis for selective chemical transformations.     

Crystal chemistry and magnetic properties of layered metal oxides possessing the K2NiF4 or related structures

There is increasing interest in recent years in the structural chemistry and properties of layered metal oxides possessing the K₂NiF₄ or related structures. Many new oxides of this structure exhibiting novel properties are being reported from time to time in the literature. The crystal chemistry of the oxides of the general formula A₂BO₄ with particular reference to the stability of the K₂NiF₄ structure and the relations between the different structures exhibited by this family of oxides is discussed. Non-stoichiometry in these oxides is another aspect of interest discussed in the article. While K₂NiF₄ itself is a well-known two-dimensional antiferromagnet, oxides of this structure with a variety of magnetic properties are examined in some detail. Besides the ternary A₂BO₄ oxides, the structure and magnetic properties of complex oxides, where the A or/and the B ions are partly substituted by other cations, is discussed. Some of the problems related to this family of oxides that are worth investigating are indicated. Much of the discussion in this article would have relevance in understanding the structure and properties of layered materials.