Preparation and structure characteristics of nano-Bi_2O_3 powders with mixed crystal structure

The nano-Bi2O3 powders were prepared by a chemical precipitation method with Bi（NO3）3, HNO3 and NaOH as reactants. The structural characteristics and morphology of nano-Bi2O3 powders were investigated by X-ray diffraction and transmission electron microscopy, respectively. The results show that under the optimum condition that 300g/L Bi（NO3）3 reacts at 90℃ for 2h, the Bi2O3 powders with 60nm on the average and 99.5% in purity are obtained. The prepared nano-Bi2O3 powders contain a mixed crystal structure of monoclinic and triclinic instead of traditional structure of monoclinic α-Bi2O3. And the mixed crystal structure is stable in air. The reason for the appearance of the mixed crystal structure may be that the ionic radius ratio of Bi 3+ to O 2- changes easily during the formation of nano-Bi2O3 particles by a chemical precipitation method.

Synthesis and Crystal Structure of a Three-dimensional Mn(Ⅱ) Coordination Polymer with 3-(Pyrazin-2-yloxy)-pyridine and Azide Anion as Mixed Bridge Ligand

A three-dimensional coordination polymer [Mn2（μ1.3-N3）4（μ-PP）2]n （PP = 3-（pyrazin-2-yloxy）-pyridine） has been synthesized with 3-（pyrazin-2-yloxy）-pyridine and azide anion as mixed bridge ligand, and its crystal structure was determined by X-ray crystallography. The crystal data： triclinic system, space group P1, with a = 6.794（4）, b = 9.885（6）, c = 9.947（6） A, α = 64.170（6）, β= 84.190（8）, γ= 85.319（8）°, V = 597.7（6）A^3, Z = 1, C18H14Mn2N18O2, Mr = 624.35, Dc = 1.735 g/cm^3, F（000） = 314 and μ = 1.117 mm^-1. In the crystal, the azide anion acts as a bridge ligand and makes adjacent Mn（Ⅱ） ions connect into a two-dimensional sheet on the ab plane, then 3-（pyrazin-2-yloxy）-pyridine serves as a bidentate bridge ligand to connect neighboring sheets along

Properties of TiO_2-SiO_2 Mixed Oxides and Photocatalytic Oxidation of Heptane and Sulfur Dioxide

A series of TiO 2-XSiO 2[X denotes the molar fraction(%) of silica in the mixed oxides] with different \{n(Ti)\}/n(Si) ratios was prepared with ammonia water as a hydrolysis catalyst. The photocatalysts prepared were characterized by XRD, thermal analysis, FTIR, UV-Vis and SPS. The characterization results of FTIR and UV-Vis spectra show that Ti atoms were gradually changed from octahedral coordination to tetrahedral coordination with the addition of silica, which is not beneficial for obtaining strong Brnsted acidity and higher photocatalytic activity. The photocatalytic activity experiments, which were conducted by using heptane(or SO 2) as the model reactant, showed that TiO 2-SiO 2 containing a suitable amount of silica can exhibit much higher photocatalytic activity than pure TiO 2. The enhanced photocatalytic activity can be attributed to three following factors: (1) smaller crystalline size; (2) higher thermal stability; (3) the new strong Brnsted acidity.

Electrical Conductivity of Sintered Chromia Mixed with TiO_2,CuO and Mn-Oxides

The electrical conductivity of sintered Cr2O3 mixed with 2% and 5% （in molar fraction） TiO2 or CuO was investigated in the temperature range 500-900℃ in air and in At/4 vol. pct H2 atmospheres. The effect of different Mn-oxides on the electrical conductivity of Cr2O3 was also studied under the same conditions. From the conductivity measurements it is established that additions of TiO2 change the defect structure of Cr2O3 and the effect of TiO2 on the electrical conductivity is controlled by TiO2 concentration as well as temperature and O2 partial pressure of the surrounding atmosphere. The conductivity of Cr2O3 increased in air and decreased in the At/H2 atmosphere by CuO additions. The effect of CuO was discussed with possible changes in the defect concentration in Cr2O3. Mixing of Cr2O3 with different Mn-oxides at the same Mn to metal atom fraction decreased the conductivity in air and in Ar/H2 atmospheres. No clear correlation between the spinel fraction and the changes in conductivity could be found.

Growth of Mixed Rare Earth Tartrate Crystals (Y_(1-x)Sm_x)_2(C_4H_4O_6)_3·zH_2O from Silica Gels

Experiments performed on the grwth of mixed crystals of rare earth tartrates (Y1-xSmx)2 (C4H4O6)3.zH2O (0≤x≤1) from silica gels at 35~40℃ and 25~30℃ employing single-diffusion technique. are discussed. The crystals maintain spherulitic morphology, irrespective of the value of x, concentration of upper and lower reactants, gel pH, gel age and gel temperature. Formation Of Liesegang rings in this system is a temperature dependent phenomenon. It is shown that with the increase of the value of x the system passes from Liesegangring phenomenon to singlezone phenomenon. Operative mechanism of crystallization in the higher (35~40℃) and lower temperature ranges (25~30℃) is explained. Seeded growth experiments indicate the possibility of increasing the size of the spherulites in the gel medium

Complete removal of phenolic contaminants from bismuth-modified TiO2 single-crystal photocatalysts

Exploring low-cost and highly active photocatalysts is very urgent to accomplish complete removal of phenolic contaminants and overcome the limitations of the existing photocatalysts.In this study,we designed and synthesized noble metal-free TiO2 photocatalysts by introducing bismuth nanoparticles as modifiers of a TiO2 single crystal(Bi-SCTiO2).The Bi-SCTiO2 can make full use of the synergistic effect of a small band overlap and low charge carrier density(Bi)with a high conductivity(single crystal),significantly boosting the separation and migration of the photogenerated charge pairs.Therefore,the Bi-SCTiO2 photocatalyst exhibits a significantly enhanced degradation rate(12 times faster)of 4-nitrophenol than a TiO2 single crystal under simulated sunlight irradiation.Notably,the complete removal of phenolic contaminants is achieved in various water matrices,which not only successfully overcomes the incomplete degradation in many reported photocatalytic systems,but also manifests a significant practical potential for sewage disposal.Therefore,this work presents a new insight in designing and constructing noble metal-free decorated semiconductor single-crystal photocatalysts with excellent activity and cyclability.

Preparation, characterization and photocatalytic activity of N-doped TiO_2 nanocrystals

N-doped TiO2 nanocrystals were prepared using titanium alkoxide as precipitant with different proportional materials. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectra. It is confirmed experimentally that the photocatalytic activity of N-doped TiO2 is much higher than that of Degussa P25, when used for the degradation of crystal violet. The degradation kinetics follows an apparent first-order reaction, which is consistent with a generally observed Langmuir-Hinshelwood mechanism. The doping of TiO2 with nitrogen significantly increases the absorption in the region of visible light. The energy of the band gap of N-doped TiO2 is 2.92 eV. The better performance of N-doped TiO2 can be explained by the fact that it is also excited with longer-wavelength light.

Review of Water-Assisted Crystallization for TiO_2 Nanotubes

TiO_2 nanotubes(TNTs) have drawn tremendous attention owing to their unique architectural and physical properties. Anodizing of titanium foil has proven to be the most efficient method to fabricate well-aligned TNTs,which, however, usually produces amorphous TNTs and needs further thermal annealing. Recently, a water-assisted crystallization strategy has been proposed and investigated by both science and engineering communities. This method is very efficient and energy saving, and it circumvents the drawbacks of thermal sintering approach. In this paper, we review the recent research progress in this kind of lowtemperature crystallization approach. Here, various synthetic methods are summarized, and the mechanisms of the amorphous–crystalline transformation are analyzed. The fundamental properties and applications of the low-temperature products are also discussed. Furthermore, it is proved that the water-assisted crystallization approach is not only applicable to TNTs but also to crystallizing other metal oxides.

Facile synthesis of single-crystalline rutile TiO_2 nano-rods by solution method

A convenient and scalable technique for the synthesis of rutile titanium dioxide(TiO2) nano-rods was presented by using bulk TiO2 powder, sodium hydroxide(NaOH) and distilled water as raw materials. X-ray diffraction(XRD) and field emission scanning electron microscopy(FESEM) studies indicate that the prepared sample is crystalline and free from any impurities, however, it has no distinct shape and possesses a huge degree of agglomeration, and the average crystal size is around 40 nm. After annealing the sample at 600 °C for 2 h, it is observed through FESEM that nano-rods are formed. And XRD analysis shows that the nano-rods are single crystalline with distinct and smooth surfaces in different sizes with average length of about 1 μm and diameter of about 80 nm. Further UV-visible spectroscopy and Raman studies were conducted for the prepared sample and the band gap of the final product is found to be 3.40 eV.

Photo Degradation of Dyes from Their Aqueous Solutions of Their Binary Mixture, Using TiO2 as the Oxidant with Different Sources of Energy

The photodegradation has been widely used in water and waste water treatment of all the methods like froth flotation coagulation etc., photodegradation appears to offer the best prospects for overall treatment of dyestuff effulent. Photodegradation of aniline blue and crystal violet dyes from aqueous solutions of their binary mixture was carried out using TiO2 as photocatalyst. By carrying out photodegradation, varying the experimental parameters, the optimum conditions required for maximum degradation was found out. The photodegradation of dye was carried out using different sources of energy like solar radiation and microwave radiation. The degradation studies were carried out at temperatures 25 ℃, 35 ℃ and 45 ℃ so as to calculate the rate constant and activation parameters. Both energy sources are equivalent in causing degradation in all respects except time and dose of photo catalyst. Time required is less for microwave than solar radiation, but dose of photo catalyst needed was high for microwave radiation. These results will be helpful in designing effluent treatment plants in industries.

溶胶凝胶法制备三维规则排列大孔TiO_2材料

以聚苯乙烯微球 (LatexSphere)离心后形成的三维规则排列的胶晶 (colloidcrystal)作模板 ,用钛酸丁酯、水、乙醇等配制的溶胶填充微球之间的间隙 ,然后原位形成凝胶 ,最后通过焙烧除去微球得到三维规则排列大孔TiO2 材料 (3DOM)。溶胶的浓度一般控制在 0 5～ 1 0md/L之间。焙烧过程的升温速度应控制在 5℃ /min以下。得到的样品表面可观察到五颜六色的彩光。从SEM照片可观察到 ,球形孔大小均匀 ,排列整齐 ,孔壁填充完全。孔径在 5 30nm左右 ,孔的排列呈面心立方结构 ,孔与孔之间由小孔窗相互交连。XRD表明孔壁含有锐钛矿和金红石两种晶型 ,2种晶型质量分数大约各占 5 0 %。

退火温度对纳米TiO_2薄膜结构和亲水性的影响

采用射频磁控溅射方法制备出纳米二氧化钛 (TiO2 )薄膜 ,研究了不同退火温度对薄膜微观结构和超亲水性的影响。结果表明 :退火温度升高 ,晶粒长大 ,孔隙率减小 ;常温制备 30 0℃以下退火的TiO2 薄膜为无定形结构 ,亲水性差 ;4 0 0℃～ 6 5 0℃退火的薄膜为锐钛矿结构 ,表现出超亲水性 ;80 0℃退火薄膜为金红石结构 。

TiO_2纳米粒子包覆聚苯乙烯球的结晶性能与表面光电压特性

Hybrid microballs with polystyrene cores coated by titania nanoparticles were prepared by miniemulsion polymerization. The crystallization morphology and photovoltage properties of the hybrid particles after calcination were characterized by Scanning Electron Microscope(SEM), X-ray diffraction and surface photovoltage spectra(SPS). The crystal morphology has a critical effect on the threshold. It is found that the materials become prous, the thresholds of TiO 2 particles blue-shift with their particle sizes decreasing and crystal phase changing from anatase TiO 2 to rutile TiO 2. The SPS results showed that the peak height was three times the height of common TiO 2 nanoparticles.

制备条件对纳米TiO_2晶型及其晶相含量影响的研究

分别用TiCl4 ,Ti(SO4 ) 2 和Ti(OC4 H9) 4为原料制备纳米二氧化钛粉体。用XRD和TEM对纳米二氧化钛粉体的晶型及晶粒形貌进行了分析。研究了在同一条件下制备的 3种纳米二氧化钛粉体对光催化降解亚甲基蓝溶液的影响 ;结果表明 :在相同的制备条件下 ,用TiCl4 为原料制备的纳米二氧化钛晶型较易控制 ,容易得到含有一定金红石相、催化活性较高的混合晶型的纳米二氧化钛 ;因此 ,其降解效果优于其他两种。同时研究了外界条件 (如分散剂、干燥方式、温度及烧结温度等 )对纳米二氧化钛晶相及其含量变化的影响。实验结果为 :用异丙醇做分散剂时 ,当分散剂与水的体积比为 3时 。

SiO_2-TiO_2复合微粒的研究

通过溶胶法制备了 18nm和 40 nm两种粒径均匀、单分散的 Si O2 - Ti O2 复合微粒 ,确定了最佳合成条件。电镜照片显示 ,水和 Ti O2 粒子接枝于 Si O2 粒子表面 ,成针状向外生长。对包覆过程、复合纳米粉末煅烧行为、表面改性的研究表明 ,110 0℃～ 12 0 0℃ Ti O2 由锐钛型向金红石型转变 ,Si O2 的鳞石英晶型也开始形成。甲醇改性的 TS纳米粉末能较好的再分散于乙醇中。

纳米TiO_2对PET结晶行为、流变和力学性能的影响

通过二阶熔融共混法制备了聚对苯二甲酸乙二醇酯 (PET) /纳米二氧化钛 (TiO2 )复合材料 ,并使用TEM对纳米TiO2 在基体中的分散状态进行了观察。研究了纳米TiO2 对PET的结晶行为、流变与力学性能的影响。发现纳米TiO2 粒子在PET基体树脂中起到了成核剂的作用 ,明显提高了基体树脂结晶温度、结晶速率 ,并使材料的DSC曲线形状发生显著变化 ,出现熔融双峰。纳米TiO2 的加入明显降低了PET的熔体粘度。并且发现在较低和较高剪切速率区 ,PET/纳米TiO2 体系粘度随剪切速率的变化趋于平缓 ;而在中等剪切速率区 ,其流动行为表现出假塑性流体特性。纳米TiO2 对PET有明显的增强增韧作用 ,加入 3 %可使材料的拉伸和断裂强度提高 2 5 % ;加入 1%可使材料缺口冲击强度提高 10 %。

Sol-gel法制备纳米TiO2锐钛矿相的晶化动力学

采用Sol gel技术制备了纳米级锐钛矿TiO2 ,并在 30 0～ 4 5 0℃之间发生了非晶向纳米晶的转变 ,运用非等温结晶过程的计算原理经过数学变换 ,计算了Avrami指数n、晶化激活能E、晶粒长大维数m和晶粒长大激活能Q等动力学参数。结果表明 ,在非晶向纳米晶的转变过程中 ,纳米晶体的特殊结构m对应着独特的动力学性质。

纳米TiO_2的晶型、粒径与光催化活性

分析了纳米 Ti O2 的晶型、粒径与光催化活性的关系 ,指出了高催化活性下的晶型和控制晶型的条件以及高催化活性下的粒径范围和保持粒子分散的方法。

焙烧温度对TiO_2薄膜的光催化氧化性能的影响

采用溶胶—凝胶法制备TiO2 薄膜 (玻片为载体 ) ,比较在不同的焙烧温度下制备的TiO2 薄膜对有机物的光催化氧化性能 ,用D XAX - 12 0 0全自动X射线衍射仪检测在不同的焙烧温度下制备的TiO2 薄膜的晶型结构 ,计算其锐钛型和晶红石晶型所占比例 ,从而确定通过控制焙烧温度来控制各种不同比例的晶型结构 ,提出温度对TiO2 薄膜对有机物的光催化氧化性能的影响机制。