Sheng Dai

Oak Ridge National Laboratory, Oak Ridge, Florida, United States

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Publications (616)2882.6 Total impact

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    ABSTRACT: Higher alcohol synthesis from syngas is studied over K/MoS2 domains supported on mesoporous carbon (C), mixed MgAl oxide (MMO), or mixtures thereof. While the carbon support offers high ethanol productivity, the MMO support yields enhanced C3+OH selectivity. MoKMMO-C, whereby Mo is initially contained on MMO then ground with carbon, behaves similar to the parent MoKMMO catalyst, as Mo on MMO has limited mobility during reaction. In contrast, on MoKC-MMO, significant Mo migrates from C to MMO during reaction, giving reactivity associated with Mo species on both supports (high C3+OH selectivity and productivity). MoS2 domain structures are correlated with the selectivity of the catalysts (C3+OH selectivity ∼ double MoS2 layers, total hydrocarbon selectivity ∼ single MoS2 layers). This study advances the understanding of the support’s effect on structure–reactivity relationships for this family of catalysts and introduces a new catalyst composition with desirable reactivity.
    Journal of Catalysis 04/2015; 324. DOI:10.1016/j.jcat.2015.01.015 · 6.07 Impact Factor
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    ABSTRACT: By means of molecular dynamics (MD) simulations, we demonstrate that porous graphene can efficiently separate gases according to their molecular sizes. The flux sequence from the classical MD simulation is H2>CO2≫N2>Ar>CH4, which generally follows the trend in the kinetic diameters. This trend is also confirmed from the fluxes based on the computed free energy barriers for gas permeation using the umbrella sampling method and kinetic theory of gases. Both brute-force MD simulations and free-energy calcualtions lead to the flux trend consistent with experiments. Case studies of two compositions of CO2/N2 mixtures further demonstrate the separation capability of nanoporous graphene.
    Journal of Solid State Chemistry 04/2015; 224:2-6. DOI:10.1016/j.jssc.2014.01.030 · 2.20 Impact Factor
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    ABSTRACT: By creating nanoscale pores in a layer of graphene, it could be used as an effective separation membrane due to its chemical and mechanical stability, its flexibility and, most importantly, its one-atom thickness. Theoretical studies have indicated that the performance of such membranes should be superior to state-of-the-art polymer-based filtration membranes, and experimental studies have recently begun to explore their potential. Here, we show that single-layer porous graphene can be used as a desalination membrane. Nanometre-sized pores are created in a graphene monolayer using an oxygen plasma etching process, which allows the size of the pores to be tuned. The resulting membranes exhibit a salt rejection rate of nearly 100% and rapid water transport. In particular, water fluxes of up to 10(6) g m(-2) s(-1) at 40 °C were measured using pressure difference as a driving force, while water fluxes measured using osmotic pressure as a driving force did not exceed 70 g m(-2) s(-1) atm(-1).
    Nature Nanotechnology 03/2015; DOI:10.1038/nnano.2015.37 · 31.17 Impact Factor
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    ABSTRACT: Room temperature sodium-ion batteries with much lower cost relative to lithium-ion batteries have attracted particular interest for large-scale electrical energy storage in the fields of renewable energies and smart grid. However, most reported cathode materials were synthesized through a conventional high-temperature solid-state method. In order to further save energy and reduce cost, here we show that a series of high-performance cathode materials, sodium vanadium polyanionic compounds, Na3(VO1-xPO4)2F1+2x (x = 0, 0.5 and 1), can been synthesized by a phase-transfer assisted solvo-thermal strategy at a rather low temperature (80 - 140 oC) in one simple step, where an acid-base-coupled extractant was used to attain the phase-transfer of phosphoric acid. More importantly, the used extractant in this route can be recycled. The as-synthesized materials (Na3(VPO4)2F3 and Na3(VOPO4)2F) exhibit a high Na storage capacity of ca. 120 mAh/g which is close to the theoretical capacity and excellent cycling performance. This study makes a significant step to extend this strategy in the synthesis of functional materials from simple binary to complex multicomponent compounds.
    Chemical Communications 03/2015; DOI:10.1039/C5CC01504A · 6.38 Impact Factor
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    ABSTRACT: In this work, a novel IL-based synergistic extraction system utilizing the ionic liquid tricaprylmethylammonium nitrate ([A336][NO3]) and the commercial extractant Di(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP) was developed for the extraction of rare earth (RE) nitrates. Pr(III) was used as a model RE and the effects of key factors, i.e. the ratio of [A336][NO3] to DEHEHP, the acidity of feed solutions, and the concentration of a salting-out reagent, were systematically studied. Our results demonstrate that the mixture of [A336][NO3] and DEHEHP had an obviously synergistic extraction effect for the extraction of Pr(III). The maximum synergistic enhancement coefficient of 3.44 was attained at XA = 0.4 (v%). Alternatively, mixture of [A336][Cl] and DEHEHP hardly extracted Pr(III) from chloride media. Moreover, we investigated the Pr(III) extraction mechanism and demonstrated that Pr(III) can be extracted as the neutral complexation species Pr(NO3)3﹒xDEHEHP and the ion-type species [A336]y﹒Pr(NO3)3+y. These extraction processes can effectively hamper the release of organic cation-ligands into the aqueous phase. The synergistic extraction effect is mainly derived from the enhanced solubility of the extracted species in the ionic liquid phase. The extraction behaviors of Pr(III) could be properly described by Langmuir and pseudo-second-order rate equations. Increased temperature was unfavorable for the extraction reaction but greatly improved the extraction rate. Interestingly, the mixed IL extraction system has an obviously synergistic extraction effect for light REs (LREs, La - Eu), but an anti-synergistic effect for heavy REs (HREs, Gd - Lu, Y), thus, indicating that our synergistic extraction system is helpful for the separation of LREs from HREs. In addition, the high selectivity between REs and non-REs suggested that the recovery of REs from a complicated high-salt leachate could be highly possible. It demonstrates that the IL-based synergistic extraction strategy developed in this work is promising and sustainable, and as a result, the development of an IL-based synergistic extraction process for the recovery of REs is straightforwardly envisaged.
    Green Chemistry 03/2015; DOI:10.1039/C5GC00360A · 6.85 Impact Factor
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    ABSTRACT: In this work we have determined the room temperature electrochemical reactions of SnO2 thin films and mesoporous carbons filled with SnO2 anodes with Na, and compare the results with those obtained during the reaction with Li. We show that SnO2 can reversibly deliver up to 6.2 Li/SnO2 whereas the reaction with Na is significantly limited. The initial discharge capacity is equivalent to less than 4 Na/SnO2, which is expected to correspond to the formation of 2 Na2O and Sn. This limited discharge capacity suggests the negative role of the formed Na2O matrix upon the reversible reaction of Sn clusters. Moreover, the reversible cycling of less than 1 Na/SnO2, despite the utilization of 6–7 nm SnO2 particles, is indicative of sluggish reaction kinetics. The origin of this significant capacity reduction is probably due to the formation of a diffusion limiting interface. Furthermore, there is a larger apparent hysteresis compared to Li. These results point to the need to design composite structures of SnO2 nanoparticles with suitable morphological and conductivity components.
    Journal of Power Sources 02/2015; 284(1):1-9. DOI:10.1016/j.jpowsour.2015.02.152 · 5.21 Impact Factor
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    ABSTRACT: We report a direct fluorination method under fluorine gas atmosphere using a fluidized bed reactor for converting nanophase iron oxide (n-Fe2O3) to electrochemically stable and higher energy density iron oxyfluoride/fluoride phase. Interestingly, no noticeable bulk iron oxyfluoride phase (FeOF) phase was observed even at fluorination temperature close to 300oC. Instead, at fluorination temperatures below 250 °C, scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) and x-ray photoelectron spectroscopy (XPS) analysis showed surface fluorination with nominal composition, Fe2O3-xF2x (x < 1). At fluorination temperature of 275 °C, STEM-EELS results showed porous interconnected nano-domains of FeF3 and Fe2O3 coexisting within the same particle with overall the particles become less dense after fluorination. We performed potentiometric intermittent titration (PITT) and electrochemical impedance spectroscopy (EIS) studies to understand the lithium diffusion (or apparent diffusion) in both the oxyfluoride and mixed phase FeF3 + Fe2O3 composition and correlate to their electrochemical performance. Further, we analyze from a thermodynamical perspective, the observed formation of the majority fluoride phase (77 % FeF3) and the absence of the expected oxyfluoride phase based on the relative formation energies of oxide, fluoride, and oxyfluorides.
    ACS Nano 02/2015; DOI:10.1021/acsnano.5b00191 · 12.03 Impact Factor
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    ABSTRACT: Herein, we report a fast (15 min) and solvent-free mechanochemical approach to polymers of intrinsic microporosity(PIMs) with high molecular mass and low polydipersity by solid grinding. The enhanced reaction efficiency results from the instantaneous frictional heating and continuously exposing active sites within those solid reactants.
    02/2015; DOI:10.1039/C4TA07196D
  • Journal of Materials Chemistry A: Materials for Energy and Sustainability 02/2015;
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    ABSTRACT: Lanthanum-transition-metal perovskites with robust mesoprous frameworks (meso-LaMO3) are synthesized through use of ionic liquids. The resultant samples demonstrate a rather high activity for CO oxidation, by taking advantage of unique nanostructure-derived benefits. This synthesis strategy opens up a new opportunity for preparing functional mesoporous complex oxides of various compositions.
    Chemical Communications 02/2015; DOI:10.1039/C5CC00534E · 6.38 Impact Factor
  • Chemical Communications 02/2015; · 6.38 Impact Factor
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    ABSTRACT: A soft chemistry synthetic strategy based on a Friedel–Crafts alkylation reaction is developed for the textural engineering of phenolic resin (PR) with a robust mesoporous framework to avoid serious framework shrinkage and maximize retention of organic functional moieties. By taking advantage of the structural benefits of molecular bridges, the resultant sample maintains a bimodal micro-mesoporous architecture with well-preserved organic functional groups, which is effective for carbon capture. Moreover, this soft chemistry synthetic protocol can be further extended to nanotexture other arene-based polymers with robust frameworks.
    Angewandte Chemie 02/2015; DOI:10.1002/ange.201500305
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    ABSTRACT: A soft chemistry synthetic strategy based on a Friedel–Crafts alkylation reaction is developed for the textural engineering of phenolic resin (PR) with a robust mesoporous framework to avoid serious framework shrinkage and maximize retention of organic functional moieties. By taking advantage of the structural benefits of molecular bridges, the resultant sample maintains a bimodal micro-mesoporous architecture with well-preserved organic functional groups, which is effective for carbon capture. Moreover, this soft chemistry synthetic protocol can be further extended to nanotexture other arene-based polymers with robust frameworks.
    Angewandte Chemie International Edition 02/2015; DOI:10.1002/anie.201500305 · 11.34 Impact Factor
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    ABSTRACT: A new ionic liquid (IL) based on a “neutral” ligand, 4-propylpyridine, is obtained via complexation with AlCl3. It is found that the asymmetric cleavage of AlCl3 generates AlCl2+ and AlCl4−, and the former is coordinated by 4-Pr-Py to produce the Al-containing cations ([AlCl2(4-Pr-Py)2]+). The AlCl3/4-propylpyridine IL with a molar ratio of 1.3/1 is highly fluidic with a viscosity of 42.8 mPa · s and an ionic conductivity of 5.0 × 10−4 S/cm at room temperature. In contrast to conventional ILs for electroplating aluminum in which the electrochemically active species are Al-containing anions (for example Al2Cl7−), this new IL has an Al-containing cation as the electroactive species, which is beneficial to electrodeposition of aluminum.
    Electrochimica Acta 02/2015; 160. DOI:10.1016/j.electacta.2015.02.020 · 4.09 Impact Factor
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    ABSTRACT: Poly(acrylamidoxime) adsorbents are often invoked in discussions of mining uranium from seawater. While the amidoxime-uranyl chelation mode has been established, a number of essential binding constants remain unclear. This is largely due to the wide range of conflicting pKa values that have been reported for the amidoxime functional group. To resolve this existing controversy we investigated the pKa values of the amidoxime functional group using a combination of experimental and computational methods. Experimentally, we used spectroscopic titrations to measure the pKa values of representative amidoximes, acetamidoxime and benzamidoxime. Computationally, we report on the performance of several protocols for predicting the pKa values of aqueous oxoacids. Calculations carried out at the MP2 or M06-2X levels of theory combined with solvent effects calculated using the SMD model provide the best overall performance, with a root mean square deviation of 0.46 pKa units and 0.45 pKa units, respectively. Finally, we employ our two best methods to predict the pKa values of promising, uncharacterized amidoxime ligands, which provides a convenient means for screening suitable amidoxime monomers for future generations of poly(acrylamidoxime) adsorbents.
    The Journal of Physical Chemistry B 01/2015; DOI:10.1021/jp512778x · 3.38 Impact Factor
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    ABSTRACT: Nanoporous ionic organic networks (PIONs) with a high ionic density (three cation-anion pairs per unit) have been synthesized by a facile SN2 nucleophilic substitution reaction. Owing to the electrostatic and steric effect, those ionic networks with porous channels can stabilize and support gold (Au) nanoparticles (NPs) in 1-2 nm. The Au@PION hybrid materials used as a heterogeneous catalyst were highly active, selective, and stable in the aerobic oxidation of saturated alcohols.
    Nano Letters 01/2015; DOI:10.1021/nl504780j · 13.03 Impact Factor
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    ABSTRACT: Metal-organic frameworks (MOFs) are a diverse family of hybrid inorganic–organic crystalline solids synthesized by assembling secondary building units (SBUs) and organic ligands into a periodic and porous framework. Microporous MOF materials, due to their high permeability and size selectivity, have attracted tremendous interest in gas storage and separation, large molecule adsorption, catalysis, and sensing. Despite the significant fabrication challenges, nanosized MOF particles can be fabricated to display enhanced gas storage and separation abilities in comparison to the parent MOF bulk counterparts under special synthesis conditions. So far, the majority of MOF nanocrystals have been derived from the controlled nucleation and growth of molecular precursors in homogeneous solutions. However, synthesis protocols based on nucleation and growth from dilute solution precursors are difficult to adapt to the synthesis of other nanoscopic materials, such as thin film and mixed-matrix membranes, which limits the practical applications of MOFs. This article discusses the current status of synthetic methods that have been utilized to fabricate MOF-based nanoscopic materials and ultrathin membranes from nanoscopic metal oxide precursors.
    CrystEngComm 01/2015; DOI:10.1039/C4CE02419B · 3.86 Impact Factor
  • Angewandte Chemie 01/2015; 127(3):1055-1055. DOI:10.1002/ange.201411640
  • Angewandte Chemie International Edition 01/2015; 54(3):1041-1041. DOI:10.1002/anie.201411640 · 11.34 Impact Factor

Publication Stats

14k Citations
2,882.60 Total Impact Points

Institutions

  • 1991–2015
    • Oak Ridge National Laboratory
      • Chemical Sciences Division
      Oak Ridge, Florida, United States
  • 1988–2015
    • The University of Tennessee Medical Center at Knoxville
      Knoxville, Tennessee, United States
  • 2014
    • Huazhong University of Science and Technology
      • State Key Laboratory of Coal Combustion (SKLCC)
      Wu-han-shih, Hubei, China
    • Zhejiang University
      • Department of Chemical and Biochemical Engineering
      Hang-hsien, Zhejiang Sheng, China
    • Vanderbilt University
      • Department of Chemical and Biomolecular Engineering
      Nashville, Michigan, United States
  • 2013
    • East China University of Science and Technology
      Shanghai, Shanghai Shi, China
  • 2012
    • Brookhaven National Laboratory
      New York, New York, United States
  • 2011–2012
    • Fudan University
      • Department of Chemistry
      Shanghai, Shanghai Shi, China
  • 2009–2011
    • New Mexico State University
      • Department of Chemistry and Biochemistry
      Las Cruces, New Mexico, United States
    • Brown University
      • Department of Chemical and Biochemical Engineering
      Providence, Rhode Island, United States
  • 2008
    • Jilin University
      • State Key Laboratory of Inorganic Synthesis and Preparative
      Yung-chi, Jilin Sheng, China
    • Georgia Institute of Technology
      • School of Civil & Environmental Engineering
      Atlanta, Georgia, United States
  • 2007
    • Cornell University
      • Department of Chemistry and Chemical Biology
      Итак, New York, United States
  • 2005
    • University of Vic
      Vic, Catalonia, Spain
    • National Cheng Kung University
      • Department of Chemistry
      臺南市, Taiwan, Taiwan
  • 2003
    • Oregon State University
      • School of Electrical Engineering and Computer Science
      Corvallis, OR, United States
  • 2002
    • Solid State Scientific Corporation
      Hollis, New Hampshire, United States
  • 1997–2002
    • University of Tennessee
      • Department of Chemistry
      Knoxville, Tennessee, United States
  • 2001
    • The Scripps Research Institute
      • Department of Cell and Molecular Biology
      La Jolla, California, United States
    • Nankai University
      • College of Environmental Science and Engineering
      Tianjin, Tianjin Shi, China
    • Donald Danforth Plant Science Center
      San Luis, Missouri, United States