Showing papers by "Beijing University of Technology published in 2013"

Porous materials with pre-designed single-molecule traps for CO 2 selective adsorption

Abstract: Despite tremendous efforts, precise control in the synthesis of porous materials with pre-designed pore properties for desired applications remains challenging. Newly emerged porous metal-organic materials, such as metal-organic polyhedra and metal-organic frameworks, are amenable to design and property tuning, enabling precise control of functionality by accurate design of structures at the molecular level. Here we propose and validate, both experimentally and computationally, a precisely designed cavity, termed a 'single-molecule trap', with the desired size and properties suitable for trapping target CO(2) molecules. Such a single-molecule trap can strengthen CO(2)-host interactions without evoking chemical bonding, thus showing potential for CO(2) capture. Molecular single-molecule traps in the form of metal-organic polyhedra are designed, synthesised and tested for selective adsorption of CO(2) over N(2) and CH(4), demonstrating the trapping effect. Building these pre-designed single-molecule traps into extended frameworks yields metal-organic frameworks with efficient mass transfer, whereas the CO(2) selective adsorption nature of single-molecule traps is preserved.

Homogeneous CoO on Graphene for Binder‐Free and Ultralong‐Life Lithium Ion Batteries

Abstract: Ultralong cycle life, high energy, and power density rechargeable lithium-ion batteries are crucial to the ever-increasing large-scale electric energy storage for renewable energy and sustainable road transport. However, the commercial graphite anode cannot perform this challenging task due to its low theoretical capacity and poor rate-capability performance. Metal oxides hold much higher capacity but still are plagued by low rate capability and serious capacity degradation. Here, a novel strategy is developed to prepare binder-free and mechanically robust CoO/graphene electrodes, wherein homogenous and full coating of -Co(OH)(2) nanosheets on graphene, through a novel electrostatic induced spread growth method, plays a key role. The combined advantages of large 2D surface and moderate inflexibility of the as-obtained -Co(OH)(2)/graphene hybrid enables its easy coating on Cu foil by a simple layer-by-layer stacking process. Devices made with these electrodes exhibit high rate capability over a temperature range from 0 to 55 degrees C and, most importantly, maintain excellent cycle stability up to 5000 cycles even at a high current density.

Preparation and characterization of hydrophobic PVDF membranes by vapor-induced phase separation and application in vacuum membrane distillation

Abstract: Hydrophobic symmetric flat-sheet membranes of polyvinylidene fluoride (PVDF) for use in vacuum membrane distillation (VMD) were successfully fabricated by the vapor-induced phase separation (VIPS) method using the double-layer casting process. To avoid the delamination that often occurs in double-layered membranes, the same PVDF polymer was employed in both the upper layer and support layer casting solutions. Solutions with low and high PVDF contents were co-cast as the upper layer and support layer of the membrane that was formed. In the VIPS process, the low PVDF content solution favored the formation of a layer with a porous and hydrophobic surface, whereas the solution with a high PVDF concentration favored the formation of a layer with high mechanical strength. The effect of the vapor-induced time on the morphological properties of the membranes was studied. As the vapor-induced time was increased, the cross-section of the membrane changed from an asymmetrical finger-like structure to a symmetrical sponge-like structure, and the surface of the membrane became rough and porous. The membrane subjected to the longer vapor-induced time also exhibited a higher permeating flux during the VMD process. The best PVDF membrane fabricated in this study had a mean radial pore size of 0.49 μm, and the rough upper surface produced a static contact angle of 145° with water. During the VMD process with a 3.5 wt.% sodium chloride (NaCl) aqueous solution, the best membrane that was fabricated produced a permeating flux of 22.4 kg m−2 h−1 and an NaCl rejection rate of 99.9 % at a feed temperature of 73 °C and a downstream pressure of 31.5 kPa. This performance is comparable to or superior to the performances of most of the flat-sheet PVDF membranes reported in the literature and a polytetrafluoroethylene membrane used in this study.

A Transforming Metal Nanocomposite with Large Elastic Strain, Low Modulus, and High Strength

Abstract: Freestanding nanowires have ultrahigh elastic strain limits (4 to 7%) and yield strengths, but exploiting their intrinsic mechanical properties in bulk composites has proven to be difficult. We exploited the intrinsic mechanical properties of nanowires in a phase-transforming matrix based on the concept of elastic and transformation strain matching. By engineering the microstructure and residual stress to couple the true elasticity of Nb nanowires with the pseudoelasticity of a NiTi shape-memory alloy, we developed an in situ composite that possesses a large quasi-linear elastic strain of over 6%, a low Young's modulus of ~28 gigapascals, and a high yield strength of ~1.65 gigapascals. Our elastic strain-matching approach allows the exceptional mechanical properties of nanowires to be exploited in bulk materials.

Microporous metal–organic frameworks with open metal sites as sorbents for selective gas adsorption and fluorescence sensors for metal ions

Abstract: Two cluster-based microporous MOFs containing coordination unsaturated metal(II) sites (or open metal(II) sites) have been constructed from boxlike or cagelike {M3}x SBUs. They both exhibit highly selective uptake for CO2 over CH4 and N2 under ambient conditions. More importantly, MOF-1 also provides an ideal luminescence sensor for selective probing Ba2+ and Cu2+ ions based on significant luminescence enhancement or quenching.

Advances in chitosan-based drug delivery vehicles

Abstract: Within the past few years, chitosan-based drug delivery vehicles have become some of the most attractive to be studied. In contrast to all other polysaccharides, chitosan has demonstrated its unique characteristics for drug delivery platforms, including its active primary amino groups for chemical modification, simple and mild preparation methods for the encapsulation of biomolecules or drugs, mucoadhesion to facilitate transport across mucosal barriers and so on. In this review, an overview of the various types of chitosan-based drug delivery systems is provided, with special focus on polymeric drug conjugates and drug nanocarriers. The first part of the review is concerned with the development and applications of polymeric chitosan–drug conjugates. Then the chitosan-based nanocarrier systems as well as their preparation methods and applications are further discussed.

Porous Co3O4 nanowires and nanorods: Highly active catalysts for the combustion of toluene

Abstract: Porous Co 3 O 4 nanowires and nanorods (Co 3 O 4 -HT, Co 3 O 4 -HT-PEG, Co 3 O 4 -HT-CTAB, and Co 3 O 4 -ME-CTAB, respectively) have been fabricated via the hydrothermal or microemulsion route in the absence and presence of polyethylene glycol (PEG) or cetyltrimethylammonium bromide (CTAB), respectively. Physicochemical properties of the materials were characterized by means of numerous techniques, and their catalytic activities for toluene combustion were evaluated. It is shown that Co 3 O 4 -HT-PEG and Co 3 O 4 -HT-CTAB displayed a porous nanowire-like morphology, whereas Co 3 O 4 -ME-CTAB exhibited a porous nanorod-like shape. The porous Co 3 O 4 samples (surface area = 47–52 m 2 /g) possessed much higher surface oxygen adspecies concentrations and much better low-temperature reducibility than the nonporous counterpart. The Co 3 O 4 -HT-CTAB sample showed the highest catalytic performance ( T 50% = 195 and T 90% = 215 °C at a space velocity of 20,000 mL/(g h)). It is concluded that the excellent catalytic performance of Co 3 O 4 -HT-CTAB was associated with its higher surface area and surface oxygen species concentration, and better low-temperature reducibility.

High responsivity, fast ultraviolet photodetector fabricated from ZnO nanoparticle–graphene core–shell structures

Abstract: We report a simple, efficient and versatile method for assembling metal oxide nanomaterial–graphene core–shell structures. An ultraviolet photodetector fabricated from the ZnO nanoparticle–graphene core–shell structures showed high responsivity and fast transient response, which are attributed to the improved carrier transport efficiency arising from graphene encapsulation.

In situ atomic-scale observation of continuous and reversible lattice deformation beyond the elastic limit

Abstract: The elastic strain sustainable in crystal lattices is usually limited by the onset of inelastic yielding mediated by discrete dislocation activity, displacive deformation twinning and stress-induced phase transformations, or fracture associated with flaws. Here we report a continuous and gradual lattice deformation in bending nickel nanowires to a reversible shear strain as high as 34.6%, which is approximately four times that of the theoretical elastic strain limit for unconstrained loading. The functioning deformation mechanism was revealed on the atomic scale by an in situ nanowire bending experiments inside a transmission electron microscope. The complete continuous lattice straining process of crystals has been witnessed in its entirety for the straining path, which starts from the face-centred cubic lattice, transitions through the orthogonal path to reach a body-centred tetragonal structure and finally to a re-oriented face-centred cubic structure.

Automated Creation of District Metered Area Boundaries in Water Distribution Systems

Abstract: Accounting for water in a distribution system can be improved by dividing systems into smaller, metered zones. This paper proposes an approach that could create boundaries for district metered areas (DMA) automatically on the basis of the community structure of water distribution systems. Community structure—the gathering of vertices into communities such that there is a higher density of edges within communities than between them—is a common property of many complex systems. For verification, the method was tested on a real-world distribution system, and the result was compared with a manually designed DMA layout. Although further improvements are necessary, because the achieved community structure is in excellent agreement with the zoning plan in reality, this approach is a new addition to the number of automated methods aimed at complementing and eventually substituting the empirical trial-and-error approach.

Understanding the fast lithium storage performance of hydrogenated TiO2 nanoparticles

Abstract: Anatase TiO2 is considered as one of the promising anode materials for lithium ion batteries (LIBs) because of its nontoxicity, safety, and excellent capacity retention. However, the poor rate capability of TiO2 electrodes, caused by the low electrical conductivity and lithium diffusion coefficient, strongly hinders its practical application in high power LIBs. Herein, we report on the fast lithium storage performance of hydrogenated anatase TiO2 nanoparticles (H-TiO2) prepared by a H2 plasma treatment. The scan-rate dependence of the cyclic voltammetry (CV) analysis reveals that the improved rate capability of H-TiO2 results from the enhanced contribution of pseudocapacitive lithium storage on the particle surface. Combined with the structural properties of H-TiO2, it is suggested that the disordered surface layers and Ti3+ species of H-TiO2 play an important role in the improvement of pseudocapacitive lithium storage. The results help to understand the fast lithium storage performance of H-TiO2 and might pave the way for further studies of other hydrogenated metal oxide electrodes for high power LIBs.

Fluorous Metal-Organic Frameworks with Enhanced Stability and High H2/CO2 Storage Capacities

Abstract: A new class of metal-organic frameworks (MOFs) has been synthesized by ligand-functionalization strategy. Systematic studies of their adsorption properties were performed at low and high pressure. Importantly, when fluorine was introduced into the framework via the functionalization, both the framework stabilities and adsorption capacities towards H2/CO2 were enhanced significantly. This consequence can be well interpreted by theoretical studies of these MOFs structures. In addition, one of these MOFs TKL-107 was used to fabricate mixed matrix membranes, which exhibit great potential for the application of CO2 separation.

Variability of computational fluid dynamics solutions for pressure and flow in a giant aneurysm: the ASME 2012 Summer Bioengineering Conference CFD Challenge.

Abstract: Stimulated by a recent controversy regarding pressure drops predicted in a giant aneurysm with a proximal stenosis, the present study sought to assess variability in the prediction of pressures and flow by a wide variety of research groups. In phase I, lumen geometry, flow rates, and fluid properties were specified, leaving each research group to choose their solver, discretization, and solution strategies. Variability was assessed by having each group interpolate their results onto a standardized mesh and centerline. For phase II, a physical model of the geometry was constructed, from which pressure and flow rates were measured. Groups repeated their simulations using a geometry reconstructed from a micro-computed tomography (CT) scan of the physical model with the measured flow rates and fluid properties. Phase I results from 25 groups demonstrated remarkable consistency in the pressure patterns, with the majority predicting peak systolic pressure drops within 8% of each other. Aneurysm sac flow patterns were more variable with only a few groups reporting peak systolic flow instabilities owing to their use of high temporal resolutions. Variability for phase II was comparable, and the median predicted pressure drops were within a few millimeters of mercury of the measured values but only after accounting for submillimeter errors in the reconstruction of the life-sized flow model from micro-CT. In summary, pressure can be predicted with consistency by CFD across a wide range of solvers and solution strategies, but this may not hold true for specific flow patterns or derived quantities. Future challenges are needed and should focus on hemodynamic quantities thought to be of clinical interest.

Au/3DOM Co3O4: highly active nanocatalysts for the oxidation of carbon monoxide and toluene

Abstract: Three-dimensionally ordered macroporous Co3O4 (3DOM Co3O4) and its supported gold (xAu/3DOM Co3O4, x = 1.1–8.4 wt%) nanocatalysts were prepared using the polymethyl methacrylate-templating and bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. The 3DOM Co3O4 and xAu/3DOM Co3O4 samples exhibited a surface area of 22–27 m2 g−1. The Au nanoparticles with a size of 2.4–3.7 nm were uniformly deposited on the macropore walls of 3DOM Co3O4. There were good correlations of oxygen adspecies concentration and low-temperature reducibility with catalytic activity of the sample for CO and toluene oxidation. Among 3DOM Co3O4 and xAu/3DOM Co3O4, the 6.5Au/3DOM Co3O4 sample performed the best, giving a T90% (the temperature required for achieving a conversion of 90%) of −35 °C at a space velocity of 20 000 mL g−1 h−1 for CO oxidation and 256 °C at a space velocity of 40 000 mL g−1 h−1 for toluene oxidation. The effect of water vapor was more significant in toluene oxidation than in CO oxidation. The apparent activation energies (26 and 74 kJ mol−1) over 6.5Au/3DOM Co3O4 were lower than those (34 and 113 kJ mol−1) over 3DOM Co3O4 for CO and toluene oxidation, respectively. It is concluded that the higher oxygen adspecies concentration, better low-temperature reducibility, and strong interaction between Au and 3DOM Co3O4 were responsible for the excellent catalytic performance of 6.5Au/3DOM Co3O4.

Research challenges and perspectives on Wisdom Web of Things (W2T)

Abstract: The rapid development of the Internet and the Internet of Things accelerates the emergence of the hyper world. It has become a pressing research issue to realize the organic amalgamation and harmonious symbiosis among humans, computers, and things in the hyper world, which consists of the social world, the physical world, and the information world (cyber world). In this paper, the notion of Wisdom Web of Things (W2T) is proposed in order to address this issue. As inspired by the material cycle in the physical world, the W2T focuses on the data cycle, namely "from things to data, information, knowledge, wisdom, services, humans, and then back to things." A W2T data cycle system is designed to implement such a cycle, which is, technologically speaking, a practical way to realize the harmonious symbiosis of humans, computers, and things in the emerging hyper world.

Comment on quantum private comparison protocols with a semi-honest third party

Abstract: As an important branch of quantum cryptography, quantum private comparison (QPC) has recently received a lot of attention. In this paper we study the security of previous QPC protocols with a semi-honest third party (TP) from the viewpoint of secure multi-party computation and show that the assumption of a semi-honest TP is unreasonable. Without the unreasonable assumption of a semi-honest TP, one can easily find that the QPC protocol (Tseng et al. in Quantum Inf Process, 2011, doi: 10.1007/s11128-011-0251-0 ) has an obvious security flaw. Some suggestions about the design of QPC protocols are also given.

Controlled generation of uniform spherical LaMnO3, LaCoO3, Mn2O3, and Co3O4 nanoparticles and their high catalytic performance for carbon monoxide and toluene oxidation.

Abstract: Uniform hollow spherical rhombohedral LaMO3 and solid spherical cubic MOx (M = Mn and Co) NPs were fabricated using the PMMA-templating strategy. Hollow spherical LaMO3 and solid spherical MOx NPs possessed surface areas of 21–33 and 21–24 m2/g, respectively. There were larger amounts of surface-adsorbed oxygen species and better low-temperature reducibility on/of the hollow spherical LaMO3 samples than on/of the solid spherical MOx samples. Hollow spherical LaMO3 and solid spherical MOx samples outperformed their nanosized counterparts for oxidation of CO and toluene, with the best catalytic activity being achieved over the solid spherical Co3O4 sample for CO oxidation (T50% = 81 °C and T90% = 109 °C) at space velocity = 10 000 mL/(g h) and the hollow spherical LaCoO3 sample for toluene oxidation (T50% = 220 °C and T90% = 237 °C) at space velocity = 20 000 mL/(g h). It is concluded that the higher surface areas and oxygen adspecies concentrations and better low-temperature reducibility are responsible fo...