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1.
This review presents an introduction to the synthesis of metallic nanoparticles by radiation-induced method, especially gamma irradiation. This method offers some benefits over the conventional methods because it provides fully reduced and highly pure nanoparticles free from by-products or chemical reducing agents, and is capable of controlling the particle size and structure. The nucleation and growth mechanism of metallic nanoparticles are also discussed. The competition between nucleation and growth process in the formation of nanoparticles can determine the size of nanoparticles which is influenced by certain parameters such as the choice of solvents and stabilizer, the precursor to stabilizer ratio, pH during synthesis, and absorbed dose.  相似文献   

2.
《中国化学工程学报》2024,68(4):263-275
Microreactors are increasingly used for green and safe chemical processes owing to their benefits of superior mass and heat transfer,increased yield,safety,and simplicity of control.However,immobilizing catalysts in microreactors remains challenging.In this investigation,a technique for creating Cu2O/montmorillonite catalyst coating,using electrostatic attraction for layer-by-layer self-assembly,was proposed.The montmorillonite film's morphology and thickness could be efficiently regulated by adjusting the degree of exfoliation and surface charge of montmorillonite,alongside layer-by-layer coating times.The Cu2O nanoparticles were immobilized using the flow deposition approach.The resulting Cu2O@montmorillonite-film-coated capillary microreactor successfully transformed glycerol into dihydroxyacetone.The conversion of glycerol and product selectivity could be controlled by adjusting the molar ratio of reactants,temperature,residence time,and Cu2O loading.The maximum glycerol conversion observed was 47.6%,with a 27%selectivity toward dihydroxyacetone.The study presents a technique for immobilizing montmorillonite-based catalyst coatings in capillary tubing,which can serve as a foundation for the future application of microreactors in glycerol conversion.  相似文献   

3.
Translated from Steklo i Keramika, No. 10, pp. 11–12, October, 1992.  相似文献   

4.
The phase diagram of the MgO-Y2O3-MgF2-YF3 system (Mg,Y//O,F reciprocal system) at 1273–1773 K was investigated for the very first time using a classical equilibrium/quenching and differential thermal analysis (DTA) experiments followed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analyses. No ternary or quaternary crystalline phase was found, and the eutectic reactions in the reciprocal system were identified. The overall phase diagram of the reciprocal system was also calculated based on the thermodynamic modeling using the CALculation of PHAse Diagram (CALPHAD) method.  相似文献   

5.
Initial phase of heterogeneous nucleation of metal electrochemically deposited under conditions of constant overpotential, has been studied by computer simulation using modified version of the kinetic approach to nucleation. Conditions causing “instantaneous” and “progressive” nucleation have been found. It could be shown that both types can occur at any overpotential, the determining factor being the value of the rate-constant of attachment of atoms to clusters, relative to the value of the anodic component of the current. Specific characteristics of the electrochemical system come into play only as much as they determine the attachment constant.  相似文献   

6.
The refinement of Y2BaCuO5 (Y211) particles is a matter of significant importance in fabricating high‐performance YBa2Cu3O7‐δ (Y123) superconductor bulks by top‐seeded melt growth (TSMG). However, coarsening and epitaxial growth naturally occur to the preexisting Y211 grains in the conventional process, causing an unwanted size enlargement. Here, for the first time, we report a novel TSMG approach in which instead of Y211, modified precursor powders (MPP, Y2O3, and Ba2Cu3Ox) were employed. As a result, massive numbers of Y211 nanoparticles were derived from the homogeneous nucleation catastrophe through peritectic solidification of Y2O3+Bax‐Cuy‐O→Y211. Correspondingly, superior property of trapped field was achieved from the MPP‐processed bulk.  相似文献   

7.
Phase diagrams of the system Al2O3 - SiO2 as presented in the domestic and foreign literature are analyzed. The congruent and incongruent states of mullite, liquation in the solid phase, and the structures of mullite and sillimanite are discussed.Translated from Ogneupory, No. 8, pp. 11 – 14, August, 1995.A lecture delivered to metallurgists and silicate producers at the Ural State Engineering University.  相似文献   

8.
9.
《Ceramics International》2023,49(6):9632-9641
Hydrogen peroxide (H2O2) is frequently used in various chemical reactions, the food industry, environmental protection, and the medical and biological fields. Cost-effective, simple, and quick detection technologies with great sensitivity are highly desired. The emerging two-dimensional MXene is favorable in the sensing field due to its outstanding conductivity, stability, and large surface area. Moreover, the in-situ generated TiO2-X on Ti3C2 MXene has been proven an excellent biosensor material due to its biocompatibility. Herein, we decorated Cu/Cu2O nanoparticles onto Ti3C2 MXene with in-situ generated TiO2-X nanoparticles, forming heterojunction through a simple one-step hydrothermal process. The Cu/Cu2O/TiO2-X/Ti3C2 (Cu/Cu2O/TT) exhibits good electrochemical sensing capability toward H2O2, with a linear range up to 28.328 mM, a sensitivity of 312 μA mM?1 cm?2, and a detection limit (LOD) of 0.42 μΜ. The synergistic interactions between Cu/Cu2O nanoparticles and TiO2-X/Ti3C2 heterojunction not only improved electron transfer and electrocatalytic activity, but also facilitated the mobility of targeting molecules on the catalyst due to the abundance of exposed catalytic sites. Therefore, compared to TiO2-X/Ti3C2, Cu/Cu2O/TT has a lower LOD, faster reaction, and five times the sensitivity. Additionally, the outstanding photoelectrochemical (PEC) sensing performance is demonstrated of Cu/Cu2O/TT for H2O2 detection, displaying a low LOD, long-term stability, repeatability, and selectivity. This report may expand the application of MXene-based materials as electrochemical sensors.  相似文献   

10.
11.
Particle size distributions from a series of experiments involving the photo-oxidation of iron pentacarbonyl [Fe(CO)5] in ozone at atmospheric pressure and 295 K are reported for a range of initial reactant concentrations, varying photolysis rates and particle growth times. These data sets were used to test a model which describes the formation of FeO3 in the gas phase, followed by clustering to produce primary Fe2O3 particles. These subsequently coagulate to form fractal-like structures as a result of magnetic dipole coupling of the primary particles.For the smallest size, spherical particles, Smoluchowski theory was used to determine a coagulation constant (kS) of 7.0×10?10 cm3 s?1, indicating a primary particle diameter of 6.6 nm, in very good agreement with the optimised value used in the particle growth model for this system.Finally, these findings are used in discussion of the formation and growth of Fe2O3 ‘meteoric smoke’ particles in the upper atmosphere.  相似文献   

12.
The computer simulation of the processes of the nucleation and growth of nanoparticles in heterogeneous media (for example, in polymer solution or porous polymer matrix) in the presence of surfactant has been carried out. Heterogeneous medium has been modeled by a system of pores that limit the region of the nanoparticle formation. It is assumed that surfactant molecules, which were present in the system initially, adsorb on the surface of the nanoparticles and slow down their growth in the oversaturated solution. The complete blocking of the nanoparticles occurs when their surface is covered by the surfactant molecules to a certain degree and their growth stops. It is shown that the degree of heterogeneity and the value of surfactant concentration significantly affect both the mean size of the nanoparticles and the character of their size distribution.  相似文献   

13.
Cu K-absorption edge and EXAFS measurements on binary Cu/ZnO and ternary Cu/ ZnO-Al2O3 catalysts of varying compositions on reduction with hydrogen at 523 K, show the presence of Cu microclusters and a species of Cu1+ dissolved in ZnO apart from metallic Cu and Cu2O. The proportions of different phases critically depend on the heating rate especially for catalysts of higher Cu content. Accordingly, hydrogen reduction with a heating rate of 10 K/min predominantly yields the metal species (>50%), while a slower heating rate of 0.8 K/min enhances the proportion of the Cu1+ species ( 60%). Reduced Cu/ZnO-Al2O3 catalysts show the presence of metallic Cu (upto 20%) mostly in the form of microclusters and Cu1+ in ZnO as the major phase ( 60%). The addition of alumina to the Cu/ZnO catalyst seems to favour the formation of Cu1+/ZnO species.  相似文献   

14.
黄磷炉渣是采用磷矿、硅石、焦炭通过电炉法经1400-1600℃高温还原生产黄磷时得到的固体废弃物,具有很高的反应活性,其主要成分为硅、钙元素的化合物,采用磷酸浸取时可反应生成水合二氧化硅和可溶性钙盐,以实现硅钙分离,制取有价产品.文中通过热力学计算,绘制了298.15 K下Ca-P-H2O系的电位-pH图,并通过分析发...  相似文献   

15.
溶剂热法制备铜与氧化亚铜纳米晶   总被引:2,自引:0,他引:2  
利用溶剂热法,以五水硫酸铜、氢氧化钠、无水乙醇为原料,在无水条件下通过乙醇还原氧化铜制得了形状均一、分散性较好的纳米铜颗粒;在有水条件下通过乙醇还原氧化铜合成出了一维氧化亚铜纳米棒。利用X射线粉末衍射仪(XRD)及高分辨透射电镜(HRTEM)对合成产物进行了物相与形貌分析。在实验中还发现反应温度与溶剂中水的加入量是影响乙醇还原性的主要因素,并由此决定了最终产物的相组成。  相似文献   

16.
Condensation phase transitions from metastable fluids occur by nucleation with accompanying cluster growth and eventual Ostwald ripening. In closed batch systems the supersaturation declines as clusters nucleate and grow, causing an increase in the stable critical nucleus size. During ripening the subcritical clusters are considered to dissolve spontaneously, so that their mass is released to contribute to further growth of remaining clusters. A model based on the dynamics of cluster size distributions (CSDs) represents this sequence of phenomena in terms of four-dimensionless parameters: initial supersaturation, power on the cluster-mass expression for the growth rate coefficient, and parameters for nucleation rate and Gibbs-Thomson effect. A numerical solution of the scaled governing equations for CSD and supersaturation shows the transition from nucleation and growth to ripening, which can occur over a relatively long time period, thus separating the stages. The asymptotic ripening stage shows a power law increase in average cluster mass as the CSD evolves to (minimum) polydispersity index of unity.  相似文献   

17.
The mixed copper–silver oxide, Cu2Ag2O3, has been prepared by co-precipitation and tested for ambient temperature carbon monoxide oxidation. The catalyst demonstrated appreciable low temperature oxidation activity and the catalyst aged for 4 h was the most active. Carbon monoxide conversion increased with time-on-stream, reaching steady state after ca. 1000 min. Acomparison of the catalytic activity has been made with a representative sample of a high activity hopcalite, mixed copper/manganese oxide catalyst. On the basis of CO oxidation rate data corrected for the effect of catalyst surface area the Cu2Ag2O3, aged for 4 h was at least as active as the hopcalite.  相似文献   

18.
19.
以导电玻璃(FTO)为基底,采用连续阴极电沉积方法在多孔结构的ZnO薄膜上合成具有单一(111)择优取向的Cu2O,制备了Cu2O/ZnO复合薄膜.采用X射线衍射和扫描电镜分别对薄膜的结构及形貌进行了表征.光吸收谱显示复合薄膜在可见光范围内具有较好的光吸收性能.可见光催化降解罗丹明B的实验表明,由于在两半导体接触界面上发生了电荷的转移,Cu2O/ZnO复合薄膜比单一的Cu2O薄膜具有更高的光催化活性,在2.5 h内对罗丹明B的降解率可达到70%,而在相同条件下Cu2O薄膜的降解率仅为60%.  相似文献   

20.
The Stochastic Fields transported PDF method for turbulent reacting flows has been used to model the nucleation and growth of dibutyl phthalate particles in a hot, turbulent jet in a colder background for which experimental data is available. The aerosol population is modelled using an assumed log-normal size distribution. It has been found that neglecting the effect of turbulent fluctuations leads to the peak particle concentration being predicted too close to the jet and the concentration downstream underpredicted. However, this effect was small compared to that of adjusting modelled surface tension. Only by adjusting this was it possible to reproduce correctly the downstream evolution of particle number found in experiment. Particle mass mean diameter was significantly underpredicted at the centre of the jet, which may be due to the inability of log-normal size distribution to capture the distribution in detail. Taking account of turbulent fluctuations leads to increased mean particle size at the edge of the plume. The extent of this increase is strongly dependent on the choice of micromixing timescale.  相似文献   

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