Synthesis of Highly Dispersed Zirconium Diboride for Fabrication of Special-Purpose Ceramic

Reduction of zirconium dioxide with boron carbide and nanofibrous carbon in argon yielded a highly dispersed powder of zirconium diboride. Characteristics of zirconium diboride powders were examined by various analytical methods. The material obtained is represented by a single phase, zirconium diboride. Powder particles are for the most part aggregated. The average size of particles and aggregates is 10.9–12.9 μm with a wide size distribution. The specific surface area of the samples is 1.8–3.6 m² g^–1. The oxidation of zirconium diboride begins at a temperature of 640°C The optimal synthesis parameters were determined: ZrO₂: B₄C: C molar ratio of 2: 1: 3 (in accordance with stoichiometry), process temperature 1600–1700°C, synthesis duration 20 min.     

Local Structure of Amorphous and Highly Dispersed Zirconium Hydroxides and Oxides

The local structure of amorphous and highly dispersed hydroxide and oxide zirconium compounds prepared from zirconyl nitrate solutions by precipitation was studied by an X-ray diffraction technique of radial electron distribution. It was found that X-ray amorphous precipitates were formed at 383 K. These precipitates were polynuclear hydroxo complexes, whose short-range ordering was similar to the structure of a cubic ZrO₂ phase. A special feature of these formations, compared with the cubic oxide phase, is that the closest Zr–Zr distance in them is shortened by 0.2 Å, NO₃ and OH groups are the constituents of an anionic sublattice, and the coordination number of Zr–anion distances is increased. Calcination at 653 K followed by cooling to room temperature resulted in the appearance of a monoclinic ZrO₂ phase with a crystallite size of 60 Å along with the cubic phase. The amount of the former phase depended on the pH of precipitation and on the presence of residual NO₃ and OH groups in precipitates.     

Scientific Bases for the Synthesis of Highly Dispersed Framework Zirconium Phosphate Catalysts for Paraffin Isomerization and Selective Oxidation

Results of the systematic study of the synthesis of highly dispersed framework zirconium phosphates stabilized by ammonium, lanthanum, aluminum, manganese, and cobalt cations are summarized. The synthesis involves the mechanochemical activation of a mixture of solid reactants (salts) or the sol–gel process each followed by the hydrothermal treatment (HTT) of obtained precursors in the presence of surfactants. The genesis of dispersed systems under investigation is studied by modern physical methods providing information on the state of the bulk and surface of the systems. It is found that the local structure of sol nanoparticles and zirconium phosphate crystalline nuclei arising from mechanochemical activation products depends on the nature of initial substances. This, in its turn, makes different crystallization mechanisms possible during the HTT process: the dissolution/precipitation mechanism or the mechanism of oriented mating of primary particles. The crystallization mechanism in HTT and the reaction system composition influence the nature of resulting complex zirconium phosphate phases, their thermal stability, dispersity, and porous structure parameters. The relationship between the bulk structure parameters of framework zirconium phosphates, which are controlled by varying the chemical composition and conditions of synthesis, and the surface characteristics of the systems (the strength and concentration of different Lewis and Br@nsted sites) is studied. It is shown that systems based on framework zirconium phosphates are promising catalysts for paraffin (pentane and hexane) isomerization, the selective oxidation of methane by oxygen into synthesis gas at short contact times, and the oxidative dehydrogenation of propane into propylene.     

Synthesis and Use of Highly Dispersed Zinc Oxide

Methods for synthesis of zinc oxide hydrosols by peptization and condensation were developed. The basic colloid-chemical properties of the sols were determined: electrokinetic properties, size and phase composition of particles, and stability of hydrosols against introduction of electrolytes. The possibility of obtaining antibacterial and UV-protecting cosmetic preparations from the hydrosols obtained was demonstrated.     

用于费-托合成的高分散型钴基催化剂*

负载型钴基催化剂是天然气基费托合成的一种重要催化剂,其金属分散度和活性位密度是决定费托合成反应活性和产物选择性（CH4%, C5+%）的关键因素。因此,提高金属钴的分散度和催化剂的还原度是提高金属钴的原子利用率、降低催化剂成本的一条有效途径。本文综述了近年来高分散型钴基催化剂的研究进展,重点探讨了催化剂制备方法、载体类型及贵金属助剂对催化剂分散度和还原性的影响,以及影响高分散型钴基催化剂的费托合成反应活性、产物选择性和反应稳定性的因素,并对负载型钴基催化剂今后的研究发展提出了一些建议。     

高分散TiO_2/SBA-15的制备及光催化性能

提出了一种制备高分散TiO2/SBA-15光催化剂的新方法.以钛酸四正丁酯(TB)和羧基改性的SBA-15(COOH/SBA-15)为原料,利用COOH/SBA-15表面上高分散的羧基与TB的配合作用将TB锚定,经过溶剂热及焙烧处理制得TiO2/SBA-15光催化剂.采用粉末X射线衍射(XRD),N2吸脱附,傅里叶变换红外光谱(FT-IR),透射电镜(TEM)等对所得催化剂进行了表征.结果表明:所得TiO2/SBA-15光催化剂为高结晶度的锐钛矿晶型,TiO2均匀地分散在SBA-15表面,TiO2/SBA-15光催化剂保持较好的介孔特征结构,具有较大比表面积.以降解罗丹明B(RhB)为探针反应,考察了所得TiO2/SBA-15光催化剂的光催化性能.与后处理浸渍法制备的光催化剂相比,本文制备的TiO2/SBA-15光催化剂表现出了更加优越的光催化性能.     

Nanostructure of Dispersed and Compact Nonstoichiometric Vanadium Carbide

Structure and properties of dispersed and compact nanocrystalline vanadium carbide VC0.875 were studied. Dispersed vanadium nanocarbide was prepared by prolonged aging of a coarse-grained VC0.875 powder. It has a unique nanostructure: nanocrystallites of dispersed vanadium carbide have a shape of bent lobes up to 600 nm in diameter and 15-20 nm thick. Annealing and quenching of compact samples of coarsegrained VC0.875 carbide result in the formation of a nanodomain structure. The nanostructured carbide VC0.875 corresponds in composition to the higher boundary of a homogeneity area of a cubic phase and mainly contains ordered V8C7 phase, which belongs to the P4₃32 space group. Cold pressing and subsequent vacuum sintering of vanadium carbide nanopowder at 2000 K gave sintered samples approaching diamond in microhardness.     

Highly Dispersed Zirconium-Containing Oxide Systems: Synthesis,Properties, and Applications

The formation of the phase composition, dispersion, pore structure, and surface state of binary zirconium-containing systems was examined depending on the nature and concentration of the second component, preparation conditions and procedures, and thermal treatment conditions. Various types of interactions were found, which are governed by the nature of the second component and the treatment temperature. The effects of surfactants on the physicochemical properties of precipitates depend on the conditions of synthesis: the surfactant amount retained by a precipitate at pH 3–4 is greater than that at pH 9 by an order of magnitude. The thermolysis of samples synthesized at acidic pH, along with dehydration and dehydroxylation, is accompanied by the decomposition and degradation of surfactants. Because of this, certain compounds and their fragments capable of reducing corresponding phases are removed stepwise. Highly dispersed compositions were obtained at 110–400°C with a minimum particle size of 2.5–16 nm; at 700°C, the particle size was no higher than 20 nm. The ratio between the ionic radii of added and main components is a factor determining the dispersion of formed phases. In this case, changes in the nature of surfactants and in the conditions of a particular synthesis make it possible to prepare highly dispersed systems with monomesoporous structures. The total volume and the average diameter of pores can be controlled over wide limits.     

Adsorption of Cationic Surfactants on Highly Dispersed Silica

Comparative study was made of adsorption of cationic surfactants, decamethoxine, ethonium, and cetyltrimethylammonium bromide, on a highly dispersed amorphous silica at different pH values. Contrary to the adsorption of monoquaternary ammonium compound, cetyltrimethylammonium bromide, the adsorption of bis(quaternary ammonium) compounds, ethonium and decamethoxine, was found to be caused mainly by electrostatic interaction. The adsorption of antiseptic decamethoxine is reversible at pH 6; this may be used to design carriers capable of controlled drug release into the surrounding medium.     

Fast Amperometric Immunoassay Utilizing Highly Dispersed Electrode Material

Abstract

An immunoassay technique based on a high surface area carbon immunoelectrode is described. Dispersed ULTI carbon serves as a carrier for immobilized antibodies and also as an electrode material. ‘Sandwich’ scheme of immunoassay of rabbit IgG (as a model analyte) has been used. Iodine formed as a result of the enzymatic oxidation of iodide by peroxidase-label has been detected amperometrically. Using dispersed carbon material as a solid support for immobilization of immunoagents and as an electrode material improves the efficiency of immuno-interaction and the sensitivity of electrochemical assay due to the high area-to-volume ratio of solid to liquid phases.

The method based on ‘sandwich’ immunoassay is conducted at 21°C. The time of each stage of incubation (with analyte and with peroxidase-antibody conjugate) is 10 min. Electrochemical detection of peroxidase-labeled immuno-complex does not exceed several minutes. The technique allows fast determination of rabbit IgG with a low detection limit, in the nanomolar range. By comparison, the conventional technique based on ELISA, being performed under the same conditions (temperature and incubation time) does not allow any quantitative determination of IgG for concentration lower then 100 nM.     

Unconventional Method for Obtaining Homogeneous Highly Dispersed Suspensions

The possibility of obtaining suspensions with very small particle radius and low polydispersity coefficient in tubular turbulent apparatus though specific hydrodynamics of reagent motion in fast chemical reactions was studied.     

One Step Preparation of Highly Dispersed TiO2 Nanoparticles

A facile approach was developed to prepare highly dispersed TiO₂ nanoparticles with selected phase. The crystallization phase of the nanoparticles can be easily tuned from anatase to rutile by the dosage of hydrochloric acid in the reaction system. The crystallite size of the as-prepared anatase TiO₂ nanoparticles was ca. 3.2 nm with high dispersion. A transparent TiO₂ colloid was obtained by dispersing the as-prepared anatase TiO₂ nanoparticles in deionized water without any organic additives added. The concentration of TiO₂-H₂O colloid can be as high as 1600 g/L. The optical transmittance of TiO₂-H₂O colloid with a low concentration was nearly 100% in the visible region. Furthermore, anatase TiO₂ nanoparticles(TiO₂-NPs) showed superior photocatalytic performance compared to rutile TiO₂-NPs.     

超声辅助浸渍法制备高分散Pt/CMK-3-US加氢脱萘催化剂

以CMK-3介孔碳作为载体,分别采用传统浸渍法、超声辅助浸渍法、载体硝酸处理法和表面活性剂辅助浸渍法备了Pt/CMK-3、Pt/CMK-3-US、Pt/CMK-3-HNO_3和Pt/CMK-3-CTAB催化剂,并通过表征和催化性能评价进行研究。表征方法包括XRD、BET、SEM、TEM和H2-TPR,结果表明Pt/CMK-3中Pt分散性最差,Pt/CMK-3-HNO_3和Pt/CMK-3-CTAB中Pt的分散度较好,但是HNO_3对介孔碳的孔道结构有破坏作用,且Pt/CMK-3-HNO_3和Pt/CMK-3-CTAB中的介孔碳的表面性质具有明显变化,只有超声法可以在很好地保持CMK-3的孔道结构和表面性质的基础上提高铂的分散度,Pt的粒径在3 nm左右。萘加氢催化性能评价结果表明Pt/CMK-3-US的催化加氢活性及产物选择性高于Pt/CMK-3,且明显高于Pt/CMK-3-HNO_3和Pt/CMK-3-CTAB。萘转化率可以达到98%以上,十氢萘选择性可以达到95%以上。     

超声辅助浸渍法制备高分散Pt/CMK-3-US加氢脱萘催化剂

以CMK-3介孔碳作为载体,分别采用传统浸渍法、超声辅助浸渍法、载体硝酸处理法和表面活性剂辅助浸渍法备了Pt/CMK-3、Pt/CMK-3-US、Pt/CMK-3-HNO₃和Pt/CMK-3-CTAB催化剂,并通过表征和催化性能评价进行研究。表征方法包括XRD、BET、SEM、TEM和H₂-TPR,结果表明Pt/CMK-3中Pt分散性最差,Pt/CMK-3-HNO₃和Pt/CMK-3-CTAB中Pt的分散度较好,但是HNO₃对介孔碳的孔道结构有破坏作用,且Pt/CMK-3-HNO₃和Pt/CMK-3-CTAB中的介孔碳的表面性质具有明显变化,只有超声法可以在很好地保持CMK-3的孔道结构和表面性质的基础上提高铂的分散度,Pt的粒径在3 nm左右。萘加氢催化性能评价结果表明Pt/CMK-3-US的催化加氢活性及产物选择性高于Pt/CMK-3,且明显高于Pt/CMK-3-HNO₃和Pt/CMK-3-CTAB。萘转化率可以达到98%以上,十氢萘选择性可以达到95%以上。     

Formation of Finely Dispersed Structures in Alloys of Aluminum with Cobalt and Zirconium

Russian Journal of Physical Chemistry A - Rapidly quenched alloys of aluminum with cobalt and zirconium are investigated using a combination of means of physicochemical analysis to study the...     

Preparation of Thermostable Highly Dispersed Titanium Dioxide from Stable Hydrosols

A large set of stable nanodispersed TiO₂ hydrosols differing in particle structure and dispersion medium composition was synthesized. For highly dispersed TiO₂ samples obtained by calcination of dried sols at 500°C phase compositions, sizes of primary crystallites, and specific surface areas were found. The factors affecting thermal stability of TiO₂ nanoparticles were analyzed. The sol containing the most thermostable nanoparticles was used to produce a highly efficient catalyst for cyclohexanone ammoximation.     

SiO2-Supported Highly Dispersed Rh Catalysts

A series of Rh/SiO₂ catalysts were prepared by a sol-gel method, characterized by N₂ physical adsorption, H₂ chemisorption and FTIR, and studied in the hydrogenolysis of propane. The results show that rhodium exists in very high, nearly atomic dispersion in the catalysts after reduction; this was not obtained by conventional preparative methods. This revised version was published online in June 2006 with corrections to the Cover Date.     

高分散铂的巯基化聚苯胺复合物用于甲醇电催化氧化

采用电化学氧化还原方法一步合成聚苯胺/电还原氧化石墨烯(PANI/ERGO),通过电化学辅助2,5-二巯基-1,3,4-噻二唑(DMc T)与聚苯胺(PANI)发生巯基点击反应得到巯基化的聚苯胺/电还原氧化石墨烯(DMcT-PANI/ERGO),以此引进了大量S和N官能团,采用电沉积的方法在巯基化聚苯胺复合物上有效分散铂纳米颗粒(PtNPs)。扫描电镜(SEM)表明铂纳米颗粒能均一高效地分散在巯基化聚苯胺复合物上;循环伏安法(CV)表明PtNPs/DMcT-PANI/ERGO和未经巯基化的复合物材料PtNPs/PANI/ERGO比较,具备较高的电化学活性面积,并且能较好的电催化氧化甲醇。     

Biosynthesis of Highly Dispersed Palladium Nanoparticles Using Astraglmanna Aqueous Extract

Biosynthesis of nanoparticles has received increased attention due to a growing need to develop environmentally benign technologies in material synthesis and employment of secondary metabolites from plant extract that has emerged as a novel technology for this purpose. In this study, a rapid and biogenic process for fabrication of palladium nanoparticles (PdNPs) is reported. Highly dispersed palladium nanoparticles were successfully prepared by using aqueous extract of Astraglmanna, a non‐toxic and eco‐friendly material, without extra surfactant, capping agent, and template. The PdNPs were characterized by using UV—Visible spectroscopy, scanning electron microscope ‐ energy dispersive spectra (SEM‐EDX), Fourier transform infra red spectroscopy (FTIR), dynamic light scattering (DLS) and X‐ray diffraction (XRD) analysis. Transmission electron microscopic (TEM) images of the PdNPs were recorded and mean size of the biosynthesized nanoparticles was found to be approximately 15 nm.