Hydrothermal synthesis and enhanced photocatalytic activity of mixed-phase TiO2 powders with controllable anatase/rutile ratio

In this study, mixed-phase TiO₂ powders were novelly synthesized via a facile and mild hydrothermal method without any post-heat treatment. TiOSO₄ and peroxide titanic acid (PTA) were used as inorganic titanium sources, while no special solvent or additive were introduced. The XRD and TEM results showed the mixed-phase TiO₂ powders were composed of anatase and rutile phases, and the PTA sol played an important role on forming the rutile nucleus. The proportion of rutile in the mixed-phase TiO₂ could be easily controlled in the range of 0%–70.5% by changing the amount of PTA sol used in the synthesis process. The UV-Visible absorption spectra indicated the prepared mixed-phase TiO₂ showed enhanced visible light absorption with the increase of rutile ratio. The photodegradation experiments revealed the mixed-phase TiO₂ exhibited the best photocatalytic activity at the rutile ratio of 41.5%, while a higher or lower rutile ratio both resulted in the decrease of photocatalytic activity.     

Selective dissolution of TiO2 crystalline phases: Physicochemical characterization and photocatalytic activity

In this study, different commercially available TiO₂ powders (Degussa P25, pure anatase, and rutile) were submitted to selective dissolution treatments, with H₂O₂/NH₄OH and 10% HF, known to remove rutile and anatase from physical mixtures. The aim was to check whether a particular separation method designed to remove a specific crystalline phase influences the properties of the other phase from the mixture or not. More precisely, we have studied how the HF dissolution method designed to selectively remove the anatase affected the physicochemical and photocatalytic properties of rutile. In a similar way, the changes in the anatase properties were studied, after the H₂O₂/NH₄OH treatment, initially used to remove rutile from the mixture. All the samples were characterized by X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy, diffuse reflectance (DR) ultraviolet–visible, and Raman spectroscopy. The photocatalytic activity of these powders was tested in the oxidation of p-chlorophenol from water. The selective treatment methods not only dissolved the target phase but also changed some physicochemical and the photocatalytic performances of the other TiO₂ crystalline phase in a considerable manner. These aspects should be taken into account in the studies regarding the synergistic effects of anatase and rutile, especially in reconstructed TiO₂ photocatalysts.     

Synthesis of mesoporous TiO2/BMMs via hydrothermal method and its potential application toward adsorption and photocatalytic degradation of crystal violet from aqueous solution

The novel mesoporous TiO₂/BMMs nanocomposites using bimodal mesoporous silica (BMMs) as support and rutile-anatase mixed phase as active species were successfully synthesized via hydrothermal and subsequent calcination method. Their structural and physiochemical properties were characterized by X-ray diffraction, scanning/transmission electron microscopy, BET-isotherms, inductive coupled plasma optical emission spectroscopy, zeta potential, Fourier transform infrared and UV–visible spectroscopy. The results demonstrated that the photocatalytic degradation activity of the synthesized catalysts were extensively enhanced as compare to bare TiO₂, due to the highly uniform dispersion of mixed phases (Anatase and Rutile) TiO₂ on the bimodal mesoporous surfaces. Particularly, the catalytic efficiency became increased as increasing the calcination temperature, showing the highest (98%) overall removal of CV dye using TBH5d as catalyst calcinated at 800 °C. Its most interesting finding is that the % adsorption of TBH5d was 46 %, more than that (26%) of TBH5c calcinated at 600 ℃, however, its % degradation was 21 %, lower than that (39 %) of TBH5c for dye concentration of 20 ppm in 50 min. Meanwhile, the kinetic adsorption and degradation performances were followed the pseudo second and first order models, respectively, further proving the high degradation efficiency of TBH5c with high rate constant than that of TBH5d. Thermodynamic parameters (ΔG_ads, ΔH_ads, and ΔS_ads) were calculated, suggesting the spontaneous and exothermic procedure with high entropy, while the adsorption equilibrium data was fitted to Dubinin-Radushkevich model. Both TBH5c and TBH5d showed an excellent stability and reactivity 71.2 and 61 %, respectively, even after 5th cycles. Thus, these results suggested that that TBH5c may be one of the suitable candidates in wastewater treatments.     

Active Sites for Adsorption and Reaction of Molecules on Rutile TiO2(110) and Anatase TiO2(001) Surfaces (cited: 1)

The reactivity of specific sites on rutile TiO₂(110)-(1×1) surface and anatase TiO₂(001)-(1×4) surface has been comparably studied by means of high resolution scanning tunneling microscopy. At the rutile TiO₂(110)-(1×1) surface, we find the defects of oxygen vacancy provide distinct reactivity for O₂ and CO₂ adsorption, while the terminal fivefold-coordinated Ti sites dominate the photocatalytic reactivity for H₂O and CH₃OH dissociation. At the anatase TiO₂(001)-(1×4) surface, the sixfold-coordinated terminal Ti sites at the oxidized surface seem to be inert in both O₂ and H₂O reactions, but the Ti-rich defects which introduce the Ti³⁺ state into the reduced surface are found to provide high reactivity for the reactions of O₂ and H₂O. By comparing the reactions on both rutile and anatase surfaces under similar experimental conditions, we find the reactivity of anatase TiO₂(001) is actually lower than rutile TiO₂(110), which challenges the conventional knowledge that the anatase (001) is the most reactive TiO₂ surface. Our findings could provide atomic level insights into the mechanisms of TiO₂ based catalytic and photocatalytic chemical reactions.     

Determination of equilibrium humidities using temperature and humidity controlled X-ray diffraction (RH-XRD)

Confined growth of crystals in porous building materials is generally considered to be a major cause of damage. We report on the use of X-ray diffraction under controlled conditions of temperature and relative humidity (RH-XRD) for the investigation of potentially deleterious phase transition reactions. An improved procedure based on rate measurements is used for the accurate and reproducible determination of equilibrium humidities of deliquescence and hydration reactions. The deliquescence humidities of NaCl (75.4 ± 0.5% RH) and Ca(NO₃)₂·4H₂O (50.8 ± 0.7% RH) at 25 °C determined with this improved RH-XRD technique are in excellent agreement with available literature data. Measurement of the hydration of anhydrous Ca(NO₃)₂ to form Ca(NO₃)₂·2H₂O revealed an equilibrium humidity of 10.2 ± 0.3%, which is also in reasonable agreement with available data. In conclusion, dynamic X-ray diffraction measurements are an appropriate method for the accurate and precise determination of equilibrium humidities with a number of interesting future applications.     

Preparation of highly (111)-oriented (Pb,La)(Zr,Sn,Ti)O<Subscript>3</Subscript> (PLZST) antiferroelectric thin films by modified sol-gel process using a novel tin source,dibutyloxide of tin

Highly (111)-oriented Pb_0.97La_0.02Zr_0.85Sn_0.13 Ti_0.02O₃(PLZST) antiferroelectric thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates through a modified sol-gel process technique. The electric field-induced antiferroelectric-to-ferroelectric (AFE‐FE) phase transformation behaviour was examined by C-V measurement. The results indicated that antiferroelectric (AFE) to ferrroelectric (FE) switching field , FE to AFE switching field were 315 kV/cm and 240 kV/cm respectively. The temperature dependence of the dielectric constant showed that the Curie temperature (T _c) of the PLZST antiferroelectric thin films was 171°C. The voltage dependent current density of the highly (111)-oriented PLZST film was less than 1.3 × 10⁻⁶ A/cm² over electric field range from 0 to ± 427 kV/cm.     

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.     

The effect of hydrogen bonding interactions between 2-[4-(dimethylamino)phenyl]-3-hydroxy-4H-chromene-4-one in the ground and excited states and dimethylsulfoxide or methanol on electronic absorption and emission transitions

The surface state of optically pure polydisperse TiO₂ (anatase and rutile) was determined by infra-red (IR) spectroscopy analysis in the temperature range of 100–453 K. Anatase A300 spectrum, contrary to rutile R300 one, has a broad three-component absorption band with peaks at 1048, 1137 and 1222 cm⁻¹ in the spectral range of δ(Ti–O–H) deformation vibrations. For rutile R300 we observed a very weak band at 1047 cm⁻¹, and for the thermal treated rutile R900 these bands were not appeared at all. The analysis of temperature dependencies for the mentioned absorption bands revealed the spectral shift of 1222 cm⁻¹ band towards the high frequencies, when the temperature increased, but the spectral parameters of 1137 and 1048 cm⁻¹ bands remained the same. The temperature of 1222 cm⁻¹ band maximum shift was 373–393 K and correlated with DSC data. Obtained results allowed to assign 1222 cm⁻¹ band to the deformation vibrations of OH-groups, bounded to the surface adsorbed water molecules by weak hydrogen bonds (5 kcal/mol). During the temperature growth these molecules desorbed, which also resulted in the intensity decreasing of stretching OH-groups vibration IR-bands at 3420 cm⁻¹. The destruction and desorption of surface water complexes led to Ti–O–H bond strengthening. IR bands at 1137 and 1048 cm⁻¹ were attributed to the stronger bounded adsorbed water molecules, which are also characterized with stretching OH-groups vibration bands at 3200 cm⁻¹. These surface structure were additionally stabilized by hydrogen bonds with the neighbouring TiO₂ lattice anions and other OH-groups, and desorbed at higher temperatures.     

Phase Transition of a Dicyanamide with Rutile‐like Structure: Syntheses and Crystal Structures of α‐ and β‐Cd[N(CN)2]2

Cadmium dicyanamide Cd[N(CN)₂]₂ was synthesized through aqueous ion exchange at room temperature. A reversible phase transition was detected by in situ X‐ray powder diffractometry above 55 °C. The crystal structures of both phases were determined by X‐ray powder diffraction (β‐Cd[N(CN)₂]₂: T = 22 °C, a = 621.60(3), b = 748.76(4), c = 770.21(5) pm, β = 91.784(3)°, P2₁/n (no. 14), Z = 2, wR_p = 0.063, R_p = 0.050, R_F = 0.059; α‐Cd[N(CN)₂]₂: T = 150 °C, a = 624.62(5), b = 752.92(6), c = 768.30(7) pm, Pnnm (no. 58), Z = 2, wR_p = 0.083, R_p = 0.064, R_F = 0.087). Both polymorphs consist of Cd²⁺ and bent planar [N(CN)₂]^— ions. α‐Cd[N(CN)₂]₂ crystallizes analogously to rutile and is isotypic with M^II[N(CN)₂]₂(M = Mg, Cr, Mn, Co, Ni, Cu). The monoclinic low‐temperature polymorph β‐Cd[N(CN)₂]₂ is closely related to that of the orthorhombic high‐temperature polymorph α‐Cd[N(CN)₂]₂ by a translationengleiche transition of index 2.     

Interaction of CO and 02 with Supported Pt Single-Atoms on TiO2(110)

In view of the high activity of Pt single atoms in the low-temperature oxidation of CO, we investigate the adsorption behavior of Pt single atoms on reduced rutile TiO\begin{document}$ _2 $\end{document}(110) surface and their interaction with CO and O\begin{document}$ _2 $\end{document} molecules using scanning tunneling microscopy and density function theory calculations. Pt single atoms were prepared on the TiO\begin{document}$ _2 $\end{document}(110) surface at 80 K, showing their preferred adsorption sites at the oxygen vacancies. We characterized the adsorption configurations of CO and O\begin{document}$ _2 $\end{document} molecules separately to the TiO\begin{document}$ _2 $\end{document}-supported Pt single atom samples at 80 K. It is found that the Pt single atoms tend to capture one CO to form Pt-CO complexes, with the CO molecule bonding to the fivefold coordinated Ti (Ti\begin{document}$ _{5 \rm{c}} $\end{document}) atom at the next nearest neighbor site. After annealing the sample from 80 K to 100 K, CO molecules may diffuse, forming another type of complexes, Pt-(CO)\begin{document}$ _2 $\end{document}. For O\begin{document}$ _2 $\end{document} adsorption, each Pt single atom may also capture one O\begin{document}$ _2 $\end{document} molecule, forming Pt-O\begin{document}$ _2 $\end{document} complexes with O\begin{document}$ _2 $\end{document} molecule bonding to either the nearest or the next nearest neighboring Ti\begin{document}$ _{5 \rm{c}} $\end{document} sites. Our study provides the single-molecule-level knowledge of the interaction of CO and O\begin{document}$ _2 $\end{document} with Pt single atoms, which represent the important initial states of the reaction between CO and O\begin{document}$ _2 $\end{document}.     

Cr掺杂金红石相TiO2(110)单晶薄膜的制备、表征及光催化活性

采用脉冲激光沉积术(PLD)同质外延生长了表面原子级平整的6%(原子比)Cr 掺杂的金红石相TiO₂(110)单晶薄膜, 采用扫描隧道显微镜(STM)、扫描隧道谱(STS)、X 射线光电子能谱(XPS)和紫外光电子能谱(UPS)对其进行了表征. 结果表明: Cr 掺杂对TiO₂(110)-(1×1)表面的形貌没有明显影响, 但是提高了掺杂薄膜在负偏压的导电性; Cr与晶格O键合而呈现+3价态, 由此在TiO₂的价带顶上方~0.4 eV处引入杂质能级. 紫外-可见光吸收谱显示薄膜的光吸收能力被扩展到~650 nm, 处于可见光范围. 借助STM以单个甲醇分子的光解反应检测了薄膜的光催化活性. 仅观察到紫外光照射下甲醇分子的脱氢反应, 在可见光照射下(λ>430 nm)甲醇分子没有发生反应, 表明单独的Cr掺杂可能不足以提高TiO₂在可见光下的催化活性.     

(C5H14N2)[Zn3(HPO4)4], a New 3D Open‐framework Zincophosphate Synthesized by Hydrothermal Reversible Transformation of (C5H14N2)[Zn2(HPO4)3]·H2O

In the system ZnO/H₃PO₄/H₂O/1,4‐diazacycloheptane (C₅H₁₂N₂), a new zincophosphate (ZnPO), (C₅H₁₄N₂)[Zn₃(HPO₄)₄] ( I ), was prepared by hydrothermal transformation (180 °C) of the known ZnPO hydrate (C₅H₁₄N₂)[Zn₂(HPO₄)₃]·H₂O ( II ). The thermally‐induced transformation is reversible; upon keeping the heterogeneous mixture of I and mother liquor at 80 °C recrystallization of II was observed. Single‐crystal X‐ray crystallography revealed that I possesses a unique three‐dimensional (3D) open‐framework structure built from corner‐linked ZnO₄ and HPO₄ tetrahedra. The (3,4)‐connected framework of I differs considerably from the 3D open‐framework ZnPO structure of II . Crystal data for I : Monoclinic system, space group Cc (No. 9) , Z = 4, a = 9.1389(6), b = 23.627(2), c = 9.3073(6) Å, β = 109.463(7)°, T = 298 K.     

Phase transformation behavior of (Pb,La)(Zr,Sn,Ti)O<Subscript>3</Subscript> and Pb (Nb,Zr,Sn,Ti)O<Subscript>3</Subscript> antiferroelectric thin films deposited on LaNiO<Subscript>3</Subscript>-buffered silicon substrates by sol-gel processing

Antiferroelectric (Pb,La)(Zr,Sn,Ti)O₃ (PLZST) and Pb(Nb,Zr,Sn,Ti)O₃ (PNZST) thin films have been fabricated on LaNiO₃/Pt/Ti/SiO₂/Si substrates by a sol-gel processing. These films showed highly preferred (100) orientation due to the grain-on-grain local epitaxial growth. The PLZST films close to the AFE-FE phase boundary showed the electric-field-induced ferroelectric (FE) state, which could return back to its original AFE state only when the thermal activation was high enough. The AFE to FE phase transformation in PNZST films can be adjusted by the dc bias field in temperature. Phase transformation behavior of PNZST and PLZST antiferroelectric thin films were investigated as a function of temperature and dc bias field.     

Molecularly imprinted TiO(2) thin film using stable ground-state complex as template as applied to selective electrochemical determination of mercury

Molecular recognition sites for mercury ions were imprinted in TiO₂ film using stable ground-state complex of 1-amino-8-naphtol-3,6-disodium sulfonate (ANDS) and mercury ions as template. The complex ratio between mercury ions and ANDS was estimated to be 2:1. Compared with the controlled and pure TiO₂ electrodes, the imprinted electrode revealed selectivity towards the imprinted ions. Linear calibration plots for mercury ions were obtained and the regression equation was I_p (μA) = 4.29 × 10⁻⁷ + 19.40 [Hg²⁺] with a detection limit of 3.06 × 10⁻⁹ mol/l. The imprinted electrode could be used for more than 1 month. Recoveries were calculated at both high and low concentrations, with a mean recovery of 99.6%.     

Outermost and inner-shell electronic properties of ClC(O)SCH2CH3 studied using HeI photoelectron spectroscopy and synchrotron radiation

A study of valence electronic properties of S-ethyl chlorothioformate (S-ethyl chloromethanethioate), ClC(O)SCH(2)CH(3), using HeI photoelectron spectra (PES) and synchrotron radiation is presented. Moreover, the photon impact excitation and dissociation dynamics of ClC(O)SCH(2)CH(3) excited at the S 2p and Cl 2p levels are elucidated by analyzing the total ion yield (TIY) spectra and time-of-flight mass spectra acquired in multicoincidence mode [photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO)]. The HeI photoelectron spectrum is dominated by features associated with lone-pair electrons from the ClC(O)S- group, the HOMO at 9.84 eV being assigned to the n(π)(S) sulfur lone-pair orbital. Whereas the formation of C(2)H(5)(+) ion dominates the fragmentation in the valence energy region, the most abundant ion formed in both the S and Cl 2p energy ranges is C(2)H(3)(+). Comparison with related XC(O)SR (X = H, F, Cl and R = -CH(3), -C(2)H(5)) species reveals the impact of the alkyl chain on the photodissociation behavior of S-alkyl (halo)thioformates.     

Synthesis and characterization of (hydroxypropyl)cellulose/TiO2 nanocomposite films

A new method of synthesis of TiO₂ nanoparticles as well as preparation of the organic–inorganic hybrid nanocomposite films of (hydroxypropyl)cellulose (HPC)/TiO₂ is presented. At the first stage, the oxotitanium hydrogel phase was obtained by the mineralization of (tetra‐isopropyl)orthotitanate (TIPT) modified by the methacrylic acid (MAA) in 15 wt% solution of H₂O₂ at room temperature and subsequent annealing at the temperature of 85°C. The crystallization of the nanoparticles of TiO₂ was conducted at the oxotitanium hydrogel phase at temperatures around 120°C in the closed vessel. Nanocomposite hybrid films were prepared by the casting method from a solution of HPC and TiO₂ nanoparticles in the water. The films of nanocomposite with 10 µm thickness are transparent to visible light and have a lower glass transition temperature compared with HPC in the bulk. This shift of the glass transition is interpreted in terms of packing density of HPC in the interface of HPC nanocomposite with TiO₂. The X‐ray diffraction pattern of the nanocomposite film suggests a lower amount of mesomorphic phase of HPC in the composite compared with HPC in the bulk. Copyright © 2007 John Wiley & Sons, Ltd.     

Thermal decomposition of monocalcium aluminate decahydrate (CaAl2O4.10H2O) investigated by in-situ synchrotron X-ray powder diffraction, thermal analysis and 27Al, 2H MAS NMR spectroscopy

The stability of monocalcium aluminate decahydrate, with the nominal composition CaAl(2)O(4).10H(2)O (CAH(10)), has a decisive role for the strength development and durability of cementitious materials based on high alumina cements. This has prompted an investigation of the thermal transformation of crystalline monocalcium aluminate decahydrate in air to an amorphous phase by in-situ synchrotron X-ray powder diffraction in the temperature range from 25 to 500 degrees C, by DTA/TGA, and (2)H, (27)Al MAS NMR spectroscopy. The decomposition includes the loss of hydrogen-bonded water molecules in the temperature range up to 175 degrees C, coupled with a reduction of the unit cell volume from 1928 A(3) at 25 degrees C, to 1674 A(3) at 185 degrees C. Furthermore, X-ray diffraction shows that CaAl(2)O(4).10H(2)O starts to transform to an amorphous phase at approximately 65 degrees C. This phase is fully developed at approximately 175 degrees C and it converts to crystalline CaAl(2)O(4) when heated to 1300 degrees C. The thermal decomposition in the temperature range from approximately 65 to approximately 175 degrees C involves both formation of an amorphous phase including AlO(4) tetrahedra and structural changes in the remaining crystalline phase.     

溶胶-凝胶法制备Polyme/MS/SiO2(M=Pb,Cd)复合纳米材料

采用溶胶-凝胶结合水热结晶技术,可成功把高聚物引入MS-SiO2网络结构,合成一种新型的有机-无机硫化物即Polymer/MS/SiO2(M=Pb,Cd)复合纳米材料,其中聚甲基丙烯酸甲酯或聚丙烯酰胺等高聚物的引入将有效地防止无机粒子团聚,控制粒子尺寸,前者还能形成核-壳结构复合粒子.作者还详细讨论了该复合纳米材料的热分析,结果表明,聚合物的存在提高了原有MS-SiO2(M=Pb,Cd)材料的热稳定性.     

Low-temperature and high-pressure structural behaviour of NaBi(MoO4)2—an X-ray diffraction study

NaBi(MoO₄)₂ has been characterized by single-crystal and powder X-ray diffraction in the temperature and pressure ranges 13-297 K and 0-25 GPa, respectively. The domain structure developing below proves that NaBi(MoO₄)₂ undergoes a ferroelastic phase transition associated with tetragonal I4₁/a to monoclinic I2/a symmetry change. The character of the unit cell evolution as a function of temperature indicates a continuous transition with the spontaneous strain as an order parameter. The structural distortion, due to small displacements of Bi³⁺ and Na⁺ ions, develops slowly. Therefore the overall changes, as measured in single-crystal diffraction at 110 and 13 K, appear to be subtle. High-pressure powder X-ray diffraction shows that the elastic behaviour is anisotropic, the linear compressibility along the a- and c-axes of the tetragonal unit cell being β_a=2.75(10)×10^-3 and , respectively. The cell contraction, stronger along the c-axis, causes the distances between the MoO₄ layers to be shortened. Consequently, the cation migration in the channels formed by MoO₄ tetrahedra becomes hindered, and any symmetry lowering phase transition is not observed up to 25 GPa. The zero-pressure bulk modulus is , and its pressure derivative .     

锂电池阴极材料Li(CoxAl1-x)O2的溶胶-凝胶法合成及表征

采用溶胶-凝胶方法合成了锂二次电池阴极材料Li(CoxAl₁-x)O₂,并采用XRD方法分析了材料的相变过程、烧结时间对材料合成的影响及不同Al/Co比掺杂对材料相变的影响,并进行了结构表征.研究表明,材料结构随Al固溶度的增大及温度的升高呈现出a轴缩短,c轴伸长的趋势.材料晶相稳定温度在600～900℃之间,烧结时间在3h以上.