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Wang C.,Shanxi Institute of Coal CAS Chemistry | Wang C.,University of Chinese Academy of Sciences | Shi J.,Shanxi Institute of Coal CAS Chemistry | Cui X.,Shanxi Institute of Coal CAS Chemistry | And 10 more authors.
Journal of Materials Chemistry A | Year: 2016

Despite the significant progress in making hollow structures, it is still a challenge to synthesize some specialized hollow structures. In the present work, we obtained a new hollow hematite structure, tube-in-dodecahedron, by using the stepwise influences of fluoride and phosphate anions. Based on condition-dependent experiments, we proposed a "nucleation-aggregation-recrystallition and etching" mechanism, which also directed us to synthesize a series of hematite hollow structures, including hollow dodecahedron and hollow ellipsoid. The concentration of phosphate was found to play a decisive role in the control of these hollow structures. 0.08 mM is the critical point for keeping the top facets of dodecahedral hematite particles while 0.2 mM is the upper limit for keeping the lateral facets. The magnetic properties of these synthesized hollow hematite structures were found to be closely associated with the structures. The synthesized tube-in-dodecahedral hematite particles exhibited excellent photocatalytic reactivity toward organic dyes. © 2016 The Royal Society of Chemistry. Source

Chen X.,CAS Institute of Mechanics | Xue C.,CAS Institute of Mechanics | Zhang L.,Synfuels China Technology Co. | Hu G.,CAS Institute of Mechanics | And 2 more authors.
Physics of Fluids | Year: 2014

The microfluidic inertial effect is an effective way of focusing and sorting droplets suspended in a carrier fluid in microchannels. To understand the flow dynamics of microscale droplet migration, we conduct numerical simulations on the droplet motion and deformation in a straight microchannel. The results are compared with preliminary experiments and theoretical analysis. In contrast to most existing literature, the present simulations are three-dimensional and full length in the streamwise direction and consider the confinement effects for a rectangular cross section. To thoroughly examine the effect of the velocity distribution, the release positions of single droplets are varied in a quarter of the channel cross section based on the geometrical symmetries. The migration dynamics and equilibrium positions of the droplets are obtained for different fluid velocities and droplet sizes. Droplets with diameters larger than half of the channel height migrate to the centerline in the height direction and two equilibrium positions are observed between the centerline and the wall in the width direction. In addition to the well-known Segré-Silberberg equilibrium positions, new equilibrium positions closer to the centerline are observed. This finding is validated by preliminary experiments that are designed to introduce droplets at different initial lateral positions. Small droplets also migrate to two equilibrium positions in the quarter of the channel cross section, but the coordinates in the width direction are between the centerline and the wall. The equilibrium positions move toward the centerlines with increasing Reynolds number due to increasing deformations of the droplets. The distributions of the lift forces, angular velocities, and the deformation parameters of droplets along the two confinement direction are investigated in detail. Comparisons are made with theoretical predictions to determine the fundamentals of droplet migration in microchannels. In addition, existence of the inner equilibrium position is linked to the quartic velocity distribution in the width direction through a simple model for the slip angular velocities of droplets. © 2014 AIP Publishing LLC. Source

Wang J.,CAS Institute of Mechanics | Ma J.,Nanjing Southeast University | Ni Z.,Nanjing Southeast University | Zhang L.,Synfuels China Technology Co. | Hu G.,CAS Institute of Mechanics
RSC Advances | Year: 2014

Recent experimental studies showed that the access resistance (AR) of a nanopore with a low thickness-to-diameter aspect ratio plays an important role in particle translocation. The existing theories usually only consider the AR without the presence of particles in the pore systems. Based on the continuum model, we systematically investigate the current change caused by nanoparticle translocation in different nanopore configurations. From numerical results, an analytical model is proposed to estimate the influence of the AR on the resistive-pulse amplitude, i.e., the ratio of the AR to the pore resistance. The current change is first predicted by our model for nanoparticles and nanopores with a wide range of sizes at the neutral surface charge. Subsequently, the effect of surface charges is studied. The results show that resistive-pulse amplitude decreases with the increasing surface charge of the nanoparticle or the nanopore. We also find that the shape of the position-dependent resistive-pulse might be distorted significantly at low bulk concentration due to concentration polarization. This study provides a deep insight into the AR in particle-pore systems and could be useful in designing nanopore-based detection devices. © 2014 The Royal Society of Chemistry. Source

Bu Y.,TU Eindhoven | Niemantsverdriet J.W.H.,Syngaschem BV | Niemantsverdriet J.W.H.,Synfuels China Technology Co. | Fredriksson H.O.A.,TU Eindhoven | Fredriksson H.O.A.,Syngaschem BV
ACS Catalysis | Year: 2016

The oxidation state of Cu nanoparticles during CO oxidation in CO + O2 gas mixtures was sensitively monitored via localized surface plasmon resonances. A microreactor, equipped with in situ UV-vis and mass spectrometry, was developed and used for the measurements. Cu nanoparticles of ∼30 nm average diameter were supported on optically transparent, planar quartz wafers. The aim of the study is 2-fold: (i) to demonstrate the performance and usefulness of the setup and (ii) to use the combined strength of model catalysts and in situ measurements to investigate the correlation between the catalyst oxidation state and its reactivity. Metallic Cu is significantly more active than both Cu(I) and Cu(II) oxides. The metallic Cu phase is only maintained under conditions where close to full oxygen conversion is achieved. This implies that kinetic measurements, aimed at determining the apparent activation energy for metallic Cu under realistic steady-state conditions, are difficult or impossible to perform. © 2016 American Chemical Society. Source

The present invention discloses a transition metal nano-catalyst, a method for preparing the same, and a process for Fischer-Tropsch synthesis using the catalyst. The transition metal nano-catalyst comprises transition metal nanoparticles and polymer stabilizers, and the transition metal nanoparticles are dispersed in liquid media to form stable colloids. The transition metal nano-catalyst can be prepared by mixing and dispersing transition metal salts and polymer stabilizers in liquid media, and then reducing the transition metal salts with hydrogen at 100-200 C. The process for F-T synthesis using the nano-catalyst comprises contacting a reactant gas mixture comprising carbon monoxide and hydrogen with the catalyst and reacting. In addition, the transition metal nanoparticles have smaller diameter and narrower diameter distribution, which is beneficial to control product distribution. Meanwhile, the catalyst can be easily separated from hydrocarbon products and reused.

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