改性沸石/TiO2的制备及光催化降解亚甲基蓝

使用碱液侵蚀加煅烧的方法对天然沸石改性,获得改性沸石.以改性沸石为载体,钛酸丁酯为前驱体,使用溶胶-凝胶法制备了改性沸石/TiO2催化剂.使用亚甲基蓝作为目标污染物,测试改性沸石/TiO2催化剂的降解性能.结果表明,采用改性沸石负载TiO2的方法有助于提高光催化剂的利用效率,当TiO2的负载率为6.08;时,对亚甲基蓝的降解效率高达0.935.XRD、SEM-EDS、BET、FTIR测试结果表明,TiO2以纳米尺度在改性沸石表面均匀分布,并且与改性沸石建立了较强的化学键连接,有利于改性沸石/TiO2催化剂的长期性能.     

多孔碳负载纳米TiO2光催化性能研究

采用溶胶-凝胶法在多孔碳表面负载纳米TiO2光催化剂.探讨了不同浸泡时间、热处理温度和热处理时间对样品光催化性能的影响.采用XRD、SEM和紫外-可见光分光光度测试手段对所制备的材料进行表征,并分析各因素对光催化性能的影响.SEM的分析结果表明TiO2是以颗粒或者层的形式覆盖到多孔碳的孔道结构上的,且负载情况良好;光催化正交优化实验得到了各因素对多孔碳负载TiO2光催化性能影响的主次顺序:浸泡时间＞热处理温度＞热处理时间;优化后的实验工艺方案为:浸泡时间60 min、热处理温度700℃、热处理时间60 min.     

PAN/TiO2复合微粒在可见光下的光催化性能研究

采用水相沉淀法合成聚丙烯腈(PAN),并通过化学吸附法将聚丙烯腈附着在纳米TiO2上,制备得到PAN/TiO2复合微粒.通过在可见光下降解罗丹明B,考察了制备过程中复合比例、热处理时间与温度、分子量对光催化活性的影响.光催化活性较高的制备条件是:AN/TiO2摩尔比为1∶120,热处理时间为30 min,热处理温度为270℃.通过在可见光下降解甲基橙、孔雀石绿等,表明PAN/TiO2复合微粒降解污染物具有普适性.     

高比表面纳米二氧化钛胶体、多孔电极及DSC电池的制备

以钛酸四丁酯为前驱物,冰醋酸为水解抑制剂,浓硝酸为胶溶剂,结合溶胶-凝胶与水热处理法成功制备了具有高比表面积的纳米二氧化钛胶体.除水、酸后,浓缩并添加有机粘结剂制成了纳米TiO2浆料.刷制多孔电极并组成电池后测试了其光电特性.调整胶溶剂-浓硝酸的添加量,制备了具有不同颗粒大小、晶型、比表面积的TiO2纳米颗粒.为了提高多孔薄膜的光散射效应,在浆料中添加了400 nm TiO2粉体,研究了其掺入量对电池特性的影响.结果表明,当硝酸加入量为 1 mL、掺入20;大颗粒TiO2时,制备的电池效率达到4.19;(Jsc=8.32 mA/cm2, Voc=0.76 V, FF=66.31;).     

TiO2-Pt-CoPi三元复合物的制备、表征和光催化性能研究

以钛酸正丁酯TBT为原料,采用水热法制备了TiO2纳米片,并用光沉积法将Pt纳米颗粒和CoPi催化剂分步沉积在TiO2纳米片上,制备TiO2-Pt-CoPi三元复合物.利用X射线衍射(XRD)、扫描电镜(SEM)等对样品进行了表征,测试了三元复合物的光催化活性.实验结果表明,通过控制光沉积时间、顺序等因素对复合光催化剂的光催化性能进行优化,大大提升了其完全光解水的光催化活性.     

不同晶型TiO2的制备与光催化性能研究

采用溶胶凝胶法,利用不同温度热处理制备了不同晶体结构的TiO2纳米晶.利用XRD、SEM、EDS、XPS等分析方法对样品的晶体结构、形貌、化学元素组成以及价态进行了表征.结果表明400 ℃、500 ℃热处理TiO2为锐钛矿晶型,600 ℃ 热处理为锐钛矿金红石混合晶型,700 ℃热处理为金红石晶型,单颗粒子呈现类似球形形貌.以罗丹明B为目标污染物,测试了样品的光催化性能,结果表明400 ℃热处理TiO2具有最高的光催化活性,3 h后对罗丹明B的降解率达到94.6;,其反应速率常数达到0.969 h-1.     

氮镧共掺杂的二氧化钛光催化剂制备及其工艺优化

采用溶胶凝胶法,以三乙胺为氮源,制备氮和镧共掺杂的TiO2光催化剂.通过X射线衍射(XRD)、扫描电镜(SEM)、紫外-可见漫反射光谱(UV-Vis DRS)对样品进行表征.以亚甲基蓝为目标降解物,在可见光下考察光催化剂的催化活性,结果表明0.8N/La/TiO2具有较好的催化活性,采用正交法对0.8N/La/TiO2催化亚甲基蓝进行工艺优化,影响亚甲基蓝降解的主次顺序为:时间>亚甲基蓝初始浓度>催化剂用量>反应温度,该反应的最佳工艺组合为时间(180 min)、催化剂用量(30 mg)、亚甲基蓝初始浓度(10 mg/L)、反应温度(30 ℃),在该条件下,亚甲基蓝的降解率达到79.3;,催化反应过程近似符合一级反应动力学方程.     

溶胶-凝胶法制备S掺杂TiO2纳米粉体的光催化性能

本研究采用溶胶-凝胶法制备了S掺杂TiO2纳米粉体.采用X射线衍射(XRD)、热重差热(TG-DTA)、傅里叶变换红外光谱(FT-IR)、透射电子显微镜(TEM)、能量弥散X射线能谱(EDS)及X射线光电子能谱(XPS)等测试手段对其进行了表征,以亚甲基蓝为模拟污染物,评价了不同热处理条件下的粉体在可见光下的光催化活性.结果表明:S掺杂对TiO2由锐钛矿型向金红石型的转变有抑制作用,但对其微观形貌没有影响;部分S进入TiO2晶格间隙形成Ti-O-S键,部分S以SO2-4的形式吸附于TiO2表面,S含量约为0.3at;;S掺杂TiO2纳米粉体具有较高的可见光催化活性,当硫酸钠加入量为10;,550 ℃煅烧1 h的S/TiO2样品的光催化活性最佳,在可见光下对亚甲基蓝的2 h降解率由未掺杂的74.12;提高至86.15;.     

低铂Pt/SiC制备及对氧还原反应的催化性能表征

采用乙二醇回流法成功制备了理论含铂量为14;的Pt/SiC阴极催化剂.利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、X射线光电子能谱(XPS)对催化剂晶型结构、表面形貌和表面电子结构进行了表征.应用循环伏安法和旋转圆盘电极进行电化学测试,研究了Pt/SiC催化剂对氧还原反应催化活性.结果表明,在180℃条件下合成的Pt/SiC催化剂的平均粒径为3.4 nm,Pt是面心立方结构.Pt在SiC表面以0价为主,有利于O2在其表面的吸附和解离.Pt/SiC-180催化剂具有与商业Pt/C(20;)催化剂相近的氧还原催化性能.Pt/SiC-180催化剂的起始还原电位为0.95 V,氧还原过程以4-电子路径为主,且稳定性和抗甲醇中毒性能明显优于商业Pt/C催化剂.优良的催化性能和较低的含铂量使其有望成为低铂燃料电池阴极催化潜在材料.     

生物质改性纳米TiO2的制备及其结构表征

采用溶胶-凝胶法制备了系列生物质改性复合纳米TiO2.以亚甲基蓝溶液为模拟污染物,考察了其可见光催化活性,并确定了最佳制备工艺.通过X射线光电子能谱(XPS)、X射线衍射(XRD)、场发射扫描电镜(FESEM)、紫外-可见漫反射光谱(UV-Vis-DRS)、荧光光谱(PL)等手段对催化剂样品进行了表征.实验结果表明,催化剂对亚甲基蓝的光催化降解适应一级反应动力学,复合TiO2和纯TiO2的反应速率常数分别为0.4990 h-1和0.0305 h-1,且复合催化剂实现了C、N、S、P、K等多元素的共掺杂.相比纯TiO2,复合TiO2的比表面积增大,结晶度升高,光生载流子复合率降低,吸收边带红移,禁带宽度窄化了0.09 eV.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Study of the possibility of interactive control of the surface profile of X-ray optical elements

We investigate the possibility of controlling the curvature parameters of parabolic mirrors that are modular elements of two types consisting of a base and thin inserts placed at the opposite side of the work surface. In the first type of modular elements, bending is controlled by the difference in the coefficients of the thermal expansion of the base and inserts. In the second type of elements, the profile is changed by the piezoelectric straining of the inserts under an electric field. A correlation is established between the parameters of modular elements and their surface curvature profile.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.