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  • 1
    Language: English
    In: Langmuir : the ACS journal of surfaces and colloids, 12 May 2015, Vol.31(18), pp.5164-73
    Description: Double-shelled C/SiO2 hollow microspheres with an outer nanosheet-like silica shell and an inner carbon shell were reported. C/SiO2 aerosol particles were synthesized first by a one-step rapid aerosol process. Then the solid silica layer of the aerosol particles was dissolved and regrown on the carbon surface to obtain novel C/SiO2 double-shelled hollow microspheres. The new microspheres prepared by the facile approach possess high surface area and pore volume (226.3 m(2) g(-1), 0.51 cm(3) g(-1)) compared with the original aerosol particles (64.3 m(2) g(-1), 0.176 cm(3) g(-1)), providing its enhanced enzyme loading capacity. The nanosheet-like silica shell of the hollow microspheres favors the fixation of Au NPs (C/SiO2/Au) and prevents them from growing and migrating at 500 °C. Novel C/C and C/Au/C (C/Pt/C) hollow microspheres were also prepared based on the hollow nanostructure. C/C microspheres (482.0 m(2) g(-1), 0.92 cm(3) g(-1)) were ideal electrode materials. In particular, the Au NPs embedded into the two carbon layers (C/Au/C, 431.2 m(2) g(-1), 0.774 cm(3) g(-1)) show a high catalytic activity and extremely chemical stability even at 850 °C. Moreover, C/SiO2/Au, C/Au/C microspheres can be easily recycled and reused by an external magnetic field because of the presence of Fe3O4 species in the inner carbon shell. The synthetic route reported here is expected to simplify the fabrication process of double-shelled or yolk-shell microspheres, which usually entails multiple steps and a previously synthesized hard template. Such a capability can facilitate the preparation of various functional hollow microspheres by interfacial design.
    Keywords: Microspheres ; Nanostructures -- Chemistry ; Silicon Dioxide -- Chemistry
    ISSN: 07437463
    E-ISSN: 1520-5827
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  • 2
    Language: English
    In: Journal of Power Sources, Nov 15, 2012, Vol.218, p.424(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jpowsour.2012.07.002 Byline: Xuemei Wu (a), Jay Benziger (b), Gaohong He (a) Abstract: Hydrogen recovery from CO.sub.2/H.sub.2 reformate mixtures by selective electrochemical pumping was compared from carbon supported Pt and Pd catalysts. Catalyst coated membranes were prepared by air-brushing a suspension of commercially available 20 wt% Pt/C or 20 wt% Pd/C catalysts and solubilized Nafion in methanol onto Nafion 115 membranes. Electrochemical activity and separation efficiency for the different catalyst layer formulations were evaluated by cyclic voltammetry, polarization and potentiostatic hydrogen pumping. The effective membrane-electrode-assembly (MEA) resistance increased due to dilution of H.sub.2 by CO.sub.2; the effective MEA resistance was greater for Pd/C catalysts than for Pt/C catalysts. CO.sub.2 adsorbed more strongly to Pd catalysts than Pt catalysts reducing the electrochemical active surface area available for hydrogen oxidation/reduction. Pd/C catalysts had an energy efficiency for hydrogen recovery from reformate mixtures approximately 80% that of Pt catalysts. Because Pd is ten times less costly than Pt the results presented here suggest that Pd/C catalysts would be a promising candidate for hydrogen pumps to recover H.sub.2 from reformate mixtures. Author Affiliation: (a) State Key Laboratory of Fine Chemicals, Research and Development Center of Membrane Science and Technology, Dalian University of Technology, Dalian 116024, PR China (b) Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08540, USA Article History: Received 4 May 2012; Revised 28 June 2012; Accepted 1 July 2012
    Keywords: Palladium Catalysts -- Comparative Analysis ; Energy Efficiency -- Comparative Analysis ; Fluorine Compounds -- Comparative Analysis ; Fine Chemicals -- Comparative Analysis ; Palladium -- Comparative Analysis ; Hydrogen -- Comparative Analysis
    ISSN: 0378-7753
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Chemical Engineering Science, Dec 24, 2012, Vol.84, p.120(14)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ces.2012.08.026 Byline: Xiaobin Jiang (a)(b), Baohong Hou (a), Gaohong He (b), Jingkang Wang (a) Keywords: Crystal Layer Growth; Diffusion; Melt Crystallization; Parameter identification; Separations; Simulation Abstract: This paper was concerned with the model development and experimental validation of the detailed crystal layer growth and multi-ions impurity distribution process in the falling film melt crystallization (FFMC) model. The phosphoric acid (PA) was separated and purified by FFMC to obtain a hyperpure phosphoric acid (HPA), which was a vital electronic chemical in IT industry. To establish a valid model, which offered an easy and convenient path of the simulation, dynamic heat and mass balance, approaches were adopted to describe the variation of crystal layer growth rate along the crystallizer. An impurity balance approach was adopted to describe the change of distribution coefficient for multi-ion impurity. A criterion was proposed to determine the formation of branched-porous (B-P) structure. The model was validated by experimental results with various equipments and operational conditions and a good agreement was obtained. The effective distribution coefficient K.sub.eff for multi-ion impurities were less than 0.2 (Na.sup.+), 0.25 (Fe.sup.3+) and 0.35 (Ca.sup.2+) with proper operation conditions. The resulting model was directly exploited to understand crystal layer growth and impurity distribution behaviors in FFMC from laboratory to industrial scale. More significantly, the model proposed a method for the separation effect evaluation and the key operational conditions (feed rate and cooling rate) determination which could readily develop optimal crystal layer growth route during industrial crystallization. In addition, the model was a vital base to describe the subsequent purification step of FFMC: sweating process. Author Affiliation: (a) School of Chemical Engineering and Technology, State Research Center of Industrialization for Crystallization Technology, Tianjin University, No.97 Weijin Road, Nankai Distrct, Tianjin 300072, China (b) State Key Laboratory of Fine Chemicals, The R&D Center of Membrane Science and Technology, Dalian University of Technology, Dalian, China, 116012 Article History: Received 18 June 2012; Revised 1 August 2012; Accepted 12 August 2012
    Keywords: Phosphoric Acid -- Analysis ; Phosphoric Acid -- Models ; Phosphates -- Analysis ; Phosphates -- Models
    ISSN: 0009-2509
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Water Research, 15 May 2012, Vol.46(8), pp.2535-2544
    Description: The use of turbulence promoter can effectively enhance the permeate flux in crossflow microfiltration (CFMF) of particulate suspensions. Flux enhancement which is generally attributed to the reduction in cake thickness, however, has still not been clearly understood. In this study, the effects of turbulence promoter on cake properties (thickness, porosity and particle size) were investigated during CFMF of calcium carbonate suspension. It indicates that turbulence promoter has important effects on cake properties that directly affect the cake resistance. The significant reduction in thickness and slight increase in porosity are positive to reduce the cake resistance. The remarkable decrease in particle size is the negative effect due to the increased specific resistance of a cake. As a whole, the overall cake resistance is still diminished by turbulence promoter and therefore permeate flux is improved. The theoretical calculation of cake resistance shows a good consistence with the experimental result. The cake properties in both cases (using a turbulence promoter or not) almost exhibit the similar trends under various operating conditions. Differently, the use of turbulence promoter can greatly alleviate the effects of transmembrane pressure or feed concentration on growth of cake layer and intensify the effects of inlet velocity on diminishing the particle deposition. ► Turbulent promoter (TP) has important effects on the cake properties. ► Cake thickness is greatly diminished and porosity is slightly increased. ► Cake particle size is undesirably decreased, increasing the specific resistance. ► Overall cake resistance is reduced by TP and thus permeate flux is enhanced. ► Cake properties are greatly influenced by operating conditions in both cases.
    Keywords: Membrane Fouling ; Flux Enhancement ; Turbulence Promoter ; Cake Properties ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 5
    Language: English
    In: Journal of Colloid And Interface Science, 01 December 2012, Vol.387(1), pp.39-46
    Description: ► A novel core–shell sphere with unique structures and compositions was prepared. ► Fe O and TiO in FTS particles have synergetic interaction with PPy coatings. ► The spheres show good electrocatalytic activity toward the reduction of H O . ► We provide a concept for preparation of new structural function materials. A novel core–shell sphere with controlled shell thickness was synthesized by in situ chemical oxidative polymerization of pyrrole on FTS (Fe O /TiO /SiO composite) surface. The dual porosity of 2–3 nm and 40–50 nm in FTS core particle provides the hybrids with a high surface area to volume ratio, which enormously facilitates the molecule diffusion process. Furthermore, the porous FTS particle encapsulate Fe O and TiO leading to its synergetic interaction with the PPy coating based on FTIR analysis. The unique structure and composition of the hybrid spheres result in new sensing property that is not available from their single counterparts. Cyclic voltammetry results demonstrate that the spheres with appropriate concentration of PPy exhibit enhanced electrocatalytic activity toward the reduction of H O in 0.1 M phosphate buffer solution. The sensing performance tests show that the hybrids possess good linear response in wide H O concentration range (10–4000 μM) and high sensitivity to H O (0.653 A M cm ) at room temperature. The formation mechanism of the spheres was proposed based on the fact that the FTS core was coated firstly by a smooth PPy layer and then PPy nanoparticles. The work reported here provides an alternative concept for preparation of functional materials with new nanostructures and properties.
    Keywords: Hybrid Spheres ; Sensitivity ; Polypyrrole ; Synergetic Interaction ; Sensor ; Porous Materials ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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  • 6
    Language: English
    In: Chemical Engineering Science, Sept 29, 2015, Vol.134, p.671(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ces.2015.05.030 Byline: Xiaobin Jiang, Xuehua Ruan, Wu Xiao, Dapeng Lu, Gaohong He Abstract: In this paper, a novel metastable zone width (MSZW) analysis technology was proposed. This membrane distillation-response (MDR) technology was established on a response mechanism in which the transmembrane flux sharply decreased when the crystals nucleated on the pores of the microporous membrane interface. The robustness and effectiveness of the proposed technology were established by comparing its performance with the conventional optical technology (laser intensity response, LIR), while, the MDR technology had the advantage of detecting the nucleation in optically opaque solution compared to LIR. Detailed simulations on several typical binary aqueous solution systems were implemented to represent the role of T.sub.f, T.sub.p and A/V.sub.0 on the supersaturation degree modification. The simulative results revealed the other advantages of MDR for controlling accuracy and flexibility during MSZW measurement. This technology could provide meaningful original data for the process design and optimization of typical and novel crystallization processes. Author Affiliation: State Key Laboratory of Fine Chemicals, R&D Center of Membrane Science and Technology, School of Chemical Engineering, Dalian University of Technology, Dalian, Liaoning 116024, People's Republic of China Article History: Received 21 March 2015; Revised 15 May 2015; Accepted 19 May 2015
    ISSN: 0009-2509
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: Chemical Engineering Science, March 22, 2013, Vol.91, p.111(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ces.2012.12.048 Byline: Xiaobin Jiang (a)(b), Baohong Hou (a), Gaohong He (b), Jingkang Wang (a) Keywords: Melt crystallization; Fractals; Porous media; Separations; Simulation; Sweating Abstract: This paper describes the model development of dynamic sweating in falling film melt crystallization (FFMC) using fractal porous media theory. The crystal layer has the characteristics of a fractal porous medium. An overall mass balance is applied to determine the structural and characteristic parameters of the crystal layer. Two ideal hypothetical models are adopted to describe the dynamic change of flow rate in sweating under sweating conditions. The characteristic factor [phi] is introduced to modify the model to describe the real process. The model is validated by experiment, and the simulated result agrees well with the experimental result. The model is then exploited to understand sweating behavior and the structure and permeability variations of the crystal layer in FFMC. More significantly, the sweating model is also an important part of the model system of the overall FFMC process. Author Affiliation: (a) School of Chemical Engineering and Technology, State Research Center of Industrialization for Crystallization Technology, Tianjin University, Tianjin 300072, China (b) State Key Laboratory of Fine Chemicals, R&D Center of Membrane Science and Technology, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China Article History: Received 20 August 2012; Revised 21 December 2012; Accepted 21 December 2012
    Keywords: Permeability -- Analysis ; Permeability -- Models ; Flow (Dynamics) -- Analysis ; Flow (Dynamics) -- Models
    ISSN: 0009-2509
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: Journal of Membrane Science, Feb 15, 2013, Vol.429, p.13(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.memsci.2012.11.026 Byline: Xiaoming Yan (a)(b), Gaohong He (a), Xuemei Wu (a), Jay Benziger (b) Keywords: Ionomer; Ionic conductivity; Water permeation; Polyether-ether ketone Abstract: Water sorption, water transport and ion transport are compared for polyether-ether ketone polymers functionalized with sulfonic acid, quaternary amine hydroxide, and imidazolium hydroxide. Water sorption in all three ionomers increases modestly with increasing water activity up to a.sub.w =0.6 and then increases more rapidly between 0.6〈a.sub.w 〈1.0. Ionic conductivity in all three ionomers is negligible for a.sub.w 〈0.6; ionic conductivity increases exponentially with increasing water activity for a.sub.w 〉0.6. The increase in ion conductivity with increasing water activity is 10 times greater for the proton exchanged polymer compared to the hydroxide exchanged polymers. Water permeation from partially saturated vapor streams is primarily diffusion limited for all three ionomers and the permeation rates were approximately the same. Water pervaporation from liquid water appeared to be interfacial transport limited for membranes〈120[mu]m thick; the pervaporation rates at 40 and 60[degrees]C were independent of membrane thickness. Water sorption and transport show little dependence on the mobile ion while the ion transport appears to depend on both ion size and hydrophilicity of the fixed ion. Author Affiliation: (a) State Key Laboratory of Fine Chemicals, Research and Development Center of Membrane Science and Technology, School of Chemical Engineering, Dalian University of Technology, Dalian, LN 116024, China (b) Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08540, United States Article History: Received 30 August 2012; Revised 6 November 2012; Accepted 7 November 2012
    ISSN: 0376-7388
    Source: Cengage Learning, Inc.
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  • 9
    Language: English
    In: Industrial & Engineering Chemistry Research, 10/24/2018, Vol.57(42), pp.14254-14260
    Description: Methanol vapor as a contaminant presented in industrial streams leads to catalysts deactivation. Therefore, it needs deep removal with adsorption technique. The isotherms and effective diffusion coefficients of methanol vapor are essential to design the purification process. The equilibrium sorption of methanol steam on commercial zeolites NaX, KA, and CaA and activated alumina were tested using an intelligent gravimetric analyzer, respectively. The equilibrium experiments were carried out at 303.2 K and pressures of up to 19.6 kPa, and the results obtained were fitted with the Dubinin-Astakhov (D-A) model. Moreover, the diffusion of methanol vapor in the adsorbents was investigated, and the effective diffusion coefficients were obtained with fitting the Fick diffusion model. The adsorbents are compared on the basis of adsorption capacities for methanol steam, and the descending order of zeolites is NaX 〉 CaA 〉 KA 〉 Al2O3. The sorption equilibrium experimental results of methanol steam on NaX, KA, and CaA agree well with D-A isotherm model, while it is not very well consistent on Al2O3. The equilibrium adsorption capacities of methanol vapor are consistent with the effective diffusion coefficients on the adsorbents.
    Keywords: Methanol ; Adsorbent ; Aluminium-Oxide ; Contamination ; Contaminants ; Diffusion-Coefficient ; Adsorption-Equilibrium ; Catalyst-Deactivation ; Diffusion ; Zeolites ; Diffusion-Model ; Kinetics ; Methanol ; Adsorptionsmittel ; Aluminiumoxid ; Kontamination ; Schmutzstoff ; Diffusionskoeffizient ; Adsorptionsgleichgewicht ; Katalysatordeaktivierung ; Diffusion ; Zeolith ; Diffusionsmodell ; Kinetik ; Engineering;
    ISSN: 0888-5885
    E-ISSN: 1520-5045
    Source: American Chemical Society (via CrossRef)
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  • 10
    Language: English
    In: Journal of Power Sources, 15 November 2012, Vol.218, pp.424-434
    Description: Hydrogen recovery from CO /H reformate mixtures by selective electrochemical pumping was compared from carbon supported Pt and Pd catalysts. Catalyst coated membranes were prepared by air-brushing a suspension of commercially available 20 wt% Pt/C or 20 wt% Pd/C catalysts and solubilized Nafion in methanol onto Nafion 115 membranes. Electrochemical activity and separation efficiency for the different catalyst layer formulations were evaluated by cyclic voltammetry, polarization and potentiostatic hydrogen pumping. The effective membrane-electrode-assembly (MEA) resistance increased due to dilution of H by CO ; the effective MEA resistance was greater for Pd/C catalysts than for Pt/C catalysts. CO adsorbed more strongly to Pd catalysts than Pt catalysts reducing the electrochemical active surface area available for hydrogen oxidation/reduction. Pd/C catalysts had an energy efficiency for hydrogen recovery from reformate mixtures approximately 80% that of Pt catalysts. Because Pd is ten times less costly than Pt the results presented here suggest that Pd/C catalysts would be a promising candidate for hydrogen pumps to recover H from reformate mixtures. ► H was purified with a PEM hydrogen pump with Pd/C catalysts. ► Pd/C catalysts were less efficient than Pt/C catalysts for H purification. ► CO adsorbs on Pd catalysts reducing the electroactive surface area. ► The effective MEA resistance increases with decreases in H partial pressure. ► Gas phase diffusion contributes to the effective MEA resistance.
    Keywords: Hydrogen Purification ; Electrochemical Separations ; Electrocatalyst Coated Membranes ; Engineering
    ISSN: 0378-7753
    E-ISSN: 1873-2755
    Source: ScienceDirect Journals (Elsevier)
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