C. Heath Turner

University of Alabama, Tuscaloosa, Alabama, United States

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Publications (49)126.95 Total impact

  • Haining Liu, Jason E Bara, C Heath Turner
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    ABSTRACT: In this work, we report a computational study of the interactions between metal cations and imidazole derivatives in the gas phase. We first performed a systematic assessment of various density functionals and basis sets for predicting the binding energies between metal cations and the imidazoles. We find that the M11L functional in combination with the 6-311++G(d,p) basis set provides the best compromise between accuracy and computational cost with our metal-imidazole complexes. We then evaluated the binding of a series of metal cations, including Li+, Na+, K+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Ba2+, Hg2+ and Pb2+, with several substituted imidazole derivatives. We find that electron-donating groups increase the metal binding energy while electron-withdrawing groups decrease the metal binding energy. Furthermore, the binding energy trends can be rationalized by the hardness of the metal cations and imidazole derivatives, providing a quick way to estimate the metal-imidazole binding strength. This insight can enable efficient screening protocols for identifying effective imidazole-based solvents and membranes for metal adsorption, and provide a framework for understanding metal…imidazole interactions in biological systems.
    The Journal of Physical Chemistry A 05/2014; · 2.77 Impact Factor
  • Haining Liu, C. Heath Turner
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    ABSTRACT: In this work, first-principles density functional theory (DFT) is used to predict oxygen adsorption on two types of hybrid carbon and boron-nitride nanotubes (CBNNTs), zigzag (8,0), and armchair (6,6). Although the chemisorption of O2 on CBNNT(6,6) is calculated to be a thermodynamically unfavorable process, the binding of O2 on CBNNT(8,0) is found to be an exothermic process and can form both chemisorbed and physisorbed complexes. The CBNNT(8,0) has very different O2 adsorption properties compared with pristine carbon nanotubes (CNTs) and boron-nitride nanotube (BNNTs). For example, O2 chemisorption is significantly enhanced on CBNNTs, and O2 physisorption complexes also show stronger binding, as compared to pristine CNTs or BNNTs. Furthermore, it is found that the O2 adsorption is able to increase the conductivity of CBNNTs. Overall, these properties suggest that the CBNNT hybrid nanotubes may be useful as a gas sensor or as a catalyst for the oxygen reduction reaction. © 2014 Wiley Periodicals, Inc.
    Journal of Computational Chemistry 03/2014; · 3.84 Impact Factor
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    ABSTRACT: In this work, a variety of molecular simulation tools are used to help characterize the selective absorption of CO2 and CH4 in imidazole-based solvents. We focus our efforts on a series of 1-n-alkyl-2-methyl-imidazoles and ether-functionalized imidazoles, over a temperature range of 293 K to 353 K, and we perform detailed analysis of the free volume. We find that the electrostatic potential within the solvent free volume cavities provides a useful indication of the selective absorption of CO2 and CH4. The electrostatic potential calculation is significantly faster than the direct calculation of the chemical potential, and tests with the 1-n-alkyl-2-methyl-imidazoles and the ether-functionalized imidazoles indicate that this may be a useful screening tool for other solvents.
    The Journal of Physical Chemistry B 12/2013; · 3.61 Impact Factor
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    ABSTRACT: Despite the utility of imidazoles for a wide variety of chemical and biological applications as well as the growing research in imidazolium-based ionic liquids (ILs), synthetic studies and characterization data for N-functionalized imidazole derivatives with substituents present at the C(2) and/or C(4) and/or C(5) positions are generally unreported. Here, we modify our prior method for synthesizing monofunctionalized imidazoles and apply it to the production of a library of 30 di- and trifunctionalized alkylimidazoles using only commodity chemicals and avoiding anhydrous solvents or air/water-sensitive reagents. For all products, purities of >98% could be readily achieved, although yields were lower than in our prior work with imidazole, which may be due to mass transfer limitations and/or increased nucleophilicity of substituted imidazole products. Interestingly, we also observe that, when 4-methylimidazole or 2-ethyl-4-methylimidazole is used as a starting material, two regioisomers are inevitably formed. We employed electronic structural calculations to aid in identifying the chemical shifts and quantifying the relative presence of the regioisomers. In both series of compounds where regioisomers could be formed, the 4-methyl regioisomer was favored. Although the formation of similar regioisomers has been previously noted in the literature, it has perhaps not been fully considered in works related to imidazolium-based ILs.
    Industrial & Engineering Chemistry Research. 08/2013; 52(34):11880–11887.
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    ABSTRACT: Branched gold nanoparticles are synthesized via a soft-template-directed process using a biological buffer, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). These branched Au nanoparticles are mainly tetrapods and show distinct absorption in the range of 700–1000 nm. A combined experimental and computational study suggests that at high concentration, the HEPES molecules self-assemble into structures with long-range order serving as soft templates to direct the formation of the anisotropic gold nanoparticles. Detailed analyses of surface chemistry and structure indicate the formation of a molecular bilayer structure for the stabilization of the branched Au nanostructures. Our density-functional theory (DFT) calculations predict that the sulfonate group of the HEPES molecules prefers to bind to the Au surfaces, while the free hydroxyl groups facilitate the self-assembly and bilayer formation through the formation of hydrogen bonds. By comparing three different buffer molecules, our study demonstrates the critical importance of ligand chemistry in the directed formation of anisotropic metallic nanoparticles.
    The Journal of Physical Chemistry C. 08/2013; 117(33):17143–17150.
  • Zhongtao Zhang, C. Heath Turner
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    ABSTRACT: In order to explore possible ways of using metallocene compounds in heterogeneous catalysis and in sensor applications, we present a theoretical characterization of cyclopentadienyl (Cp) + transition metal (TM) complexes adsorbed on boron-doped carbon nanotubes (B-CNTs) and boron-doped graphenes. Using spin-polarized density functional theory calculations, we present a systematic study of the geometries, energetics, and electronic properties of CpTM (where TM = Fe, Ni, Co, Cr, Cu) adsorbed on both pristine and boron-doped carbon supports. Our work reveals significant increases of the binding energies between CpTM and boron-doped CNTs and graphenes (versus pristine carbon supports), surpassing even the adsorption strength of the isolated metals atoms (by about 2 eV). According to our electronic structure analysis, both the delocalization of the TM-d state by the presence of the Cp ring and the interactions between the Cp ring and the carbon substrate are responsible for the enhancement of the binding energies. This stabilization may play an important role in immobilizing ferrocene-based catalysts. Moreover, tunable metallicities of CpTMs adsorbed on pristine and on B-CNTs are observed, indicating potential applications of CpTM/B-CNT complexes in nanoelectronics and as sensors. Using these complexes, we also probed the adsorption of O2 molecules, as an initial indicator of catalytic performance. Both chemisorption (with an elongated O–O bond) and dissociative chemisorption were found on CpFe/B-CNT (8,0) complexes.
    The Journal of Physical Chemistry C. 04/2013; 117(17):8758–8766.
  • Haining Liu, Jason E. Bara, C. Heath Turner
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    ABSTRACT: A deeper understanding of the acid/base properties of imidazole derivatives will aid the development of solvents, polymer membranes and other materials that can be used for CO2 capture and acid gas removal. In this study, we employ density functional theory calculations to investigate the effect of various electron-donating and electron-withdrawing groups on the proton affinity of 1-methylimidazole. We find that electron-donating groups are able to increase the proton affinity relative to 1-methylimidazole, i.e., making the molecule more basic. In contrast, electron-withdrawing groups cause a decrease of the proton affinity. When multiple substituents are present, their effects on the proton affinity were found to be additive. This finding offers a quick approach for predicting and targeting the proton affinities of this series of molecules, and we show the strong correlation between the calculated proton affinities and experimental pKa values.
    Chemical Physics 04/2013; 416:21–25. · 1.96 Impact Factor
  • Wei An, C. Heath Turner
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    ABSTRACT: Using density functional theory methods, we investigate the relative stability of three types of 1D Ni nanostructures. The first two are conceived from the growth of either Ih or Oh symmetry 0D nanoparticles of Ni, and the third, a Ni (6,3) nanorod (NR), is a hexagonal close-packed structure (both on the surface and along the axis direction). Our calculations show that 1D Ni NRs as well as Ni double-walled and triple-walled nanotubes, are more stable than comparable-sized Ni 0D nanoparticles. We explore the potential of NRs as a prototype catalyst by calculating the alloying effect of M (M = Mo, Fe, Co, and Cu) on the adsorption of C and S under full coverage of atomic O. The calculated results suggest that Ni-based 1D NRs are highly reactive toward O-binding, an indication that anode oxidation may be achieved at much lower temperatures. By forming a NiM surface alloy, the binding strength of C and S can be reduced. In particular, Fe and Cu seem to be the most promising metal dopants in Ni-based 1D NR systems for suppressing the formation of C and S (whereas Co promotes the binding of C). Also, it is found that the Ni0.75Mo0.25 (6,3) NR model collapses its tubular structure due to strong binding with O.
    The Journal of Physical Chemistry C. 01/2013; 117(3):1315–1322.
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    ABSTRACT: Molecular simulations are used to probe the thermophysical properties of a series of N-functionalized alkylimidazoles, ranging from N-methylimidazole to N-heptylimidazole. These compounds have been previously synthesized, and their solvation properties have been shown to be potentially useful for CO(2) capture from industrial sources. In this work, we use first-principles calculations to fit electrostatic charges to the molecular models, which are then used to perform a series of molecular dynamics simulations. Over a range of different temperatures, we benchmark the simulated densities and heat capacities against experimental measurements. Also, we predict the Henry's constants for CO(2) absorption and probe the solvents' structures using molecular simulation techniques, such as fractional free volume analysis and void distributions. We find that our simulations are able to closely reproduce the experimental benchmarks and add additional insight into the molecular structure of these fluids, with respect to their observed solvent properties.
    The Journal of Physical Chemistry B 05/2012; 116(22):6529-35. · 3.61 Impact Factor
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    ABSTRACT: Iron oxide nanowhiskers with dimensions of approximately 2 × 20 nm were successfully synthesized by selectively heating an iron oleate complex. Such nanostructures resulted from the difference in the ligand coordination microenvironments of the Fe(III) oleate complex, according to our electronic structure calculations and thermogravimetric analysis. A ligand-directed growth mechanism was subsequently proposed to rationalize the growth process. The formation of the nanowhiskers provides a unique example of shape-controlled nanostructures, offering additional insights into nanoparticle synthesis.
    Nano Letters 02/2011; 11(3):1141-6. · 13.03 Impact Factor
  • Wei An, Daniel Gatewood, Brett Dunlap, C. Heath Turner
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    ABSTRACT: We present density-functional theory calculations of the chemisorption of atomic species O, S, C, H and reaction intermediates OH, SH, and CHn (n = 1, 2, and 3) on M/Ni alloy model catalysts (M = Bi, Mo, Fe, Co, and Cu). The activity of the Ni alloy catalysts for solid-oxide fuel cell (SOFC) anode oxidation reactions is predicted, based on a simple descriptor, i.e., the binding energy of oxygen. First, we find that the binding of undesirable intermediates, such as C and S, can be inhibited and the catalytic activity of planar Ni-based anodes can be tuned towards oxidation by selectively forming a bimetallic surface alloy. In particular, Cu/Ni, Fe/Ni, and Co/Ni anode catalysts are found to be most active towards anode oxidation. On the other hand, the Mo/Ni alloy surface is predicted to be the most effective catalyst in terms of inhibiting the deposition of C and S (while still preserving relatively high catalytic activity). The formation of a surface alloy, which has the alloy element enriched on the topmost surface, was found to be critical to the activity of the Ni alloy catalysts.Research highlights▶ Density-functional theory is used to model the activity of Ni-alloy catalysts. ▶ Chemisorption of O, S, C, H, OH, SH, and CHn is predicted. ▶ Catalytic activity for SOFC anode oxidation is strongly dependent upon surface alloy. ▶ Ni-alloy compositions include Bi, Mo, Fe, Co, and Cu.
    Journal of Power Sources 01/2011; 196(10):4724-4728. · 5.26 Impact Factor
  • B Fu, W An, C H Turner, G B Thompson
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    ABSTRACT: The in situ growth stress and postgrowth stress relaxation during the L1(0) chemical ordering of Fe0.54Pt0.46 thin films have been characterized. The compressive stress is reduced with an increase in order parameter. The postgrowth stress relaxation rate increased with the order parameter and is rationalized in terms of an increase in the interfacial energy contribution at the grain boundaries because of chemical order. Density functional theory calculations were performed to quantify possible diffusion pathways and binding energies for Fe and Pt that may mitigate surface migration.
    Physical Review Letters 08/2010; 105(9):096101. · 7.73 Impact Factor
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    ABSTRACT: A hydrogen-powered solid oxide fuel cell (SOFC), with a Pt cathode and a Ni anode, is modeled with a kinetic Monte Carlo (KMC) simulation technique. A series of reversible elementary steps are adopted from experiments and theories for simulating the oxygen reduction reaction near the cathode–electrolyte interface and the hydrogen-oxidation mechanism near the anode–electrolyte interface. By studying the change in the ionic current density, the sensitivity of the kinetic parameters is analyzed, and the influence of various operating conditions and different material properties are also explored. The results show that the dominant elementary process is the oxygen incorporation into the yttria-stabilized zirconia (YSZ) electrolyte at the cathode. Increasing the applied bias voltage, operating temperature, and relative permittivity of the YSZ, but reducing the thickness of the YSZ enhance the ionic current density and improve the efficiency of the SOFC.
    Journal of Power Sources. 07/2010;
  • Wei An, C. Heath Turner
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    ABSTRACT: We present density-functional-theory calculations of structural, electronic, and magnetic properties of platinum-alloy strings templated on a boron-doped single-wall carbon nanotube (6,6) model, B-SWCNT(6,6). Our calculations show that the alloy strings demonstrate strong molecular recognition, forming well-defined covalent bonds with the substrate and lead to the self-assembly of stable monatomic chains. The electronic and magnetic features of the Pt-alloy string/B-SWCNT(6,6) composite systems are mainly controlled by the presence of a magnetic alloying element (i.e., Fe, Co, and Ru). By changing the composition of the Pt alloy, the easy magnetization axis of the system can oscillate between the directions parallel and perpendicular to the tube axis. Our studies suggest that pure transition-metal (TM) or TM-alloy strings anchored on a substrate via strong molecular interactions can still possess sizable magnetic anisotropy due to spin-orbital coupling effects.
    Physical review. B, Condensed matter 05/2010; · 3.77 Impact Factor
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    ABSTRACT: Platinum nanoparticles supported on metal oxide surfaces have shown great potential as heterogeneous catalysts to accelerate electrochemical processes, such as the oxygen reduction reaction in fuel cells. Recently, the use of magnetic supports has become a promising research topic for easy separation and recovery of catalysts using magnets, such as Pt nanoparticles supported on iron oxide nanoparticles. The attachment of Pt on iron oxide nanoparticles is limited by the wetting ability of the Pt (metal) on ceramic surfaces. A study of Pt nanoparticle attachment on iron oxide nanoparticle surfaces in an organic solvent is reported, which addresses the factors that promote or inhibit such attachment. It was discovered that the Pt attachment strongly depends on the capping molecules of the iron oxide seeds and the reaction temperature. For example, the attachment of Pt nanoparticles on oleic acid coated iron oxide nanoparticles was very challenging, because of the strong binding between the carboxylic groups and iron oxide surfaces. In contrast, when nanoparticles are coated with oleic acid/tri-n-octylphosphine oxide or oleic acid/oleylamine, a significant increase in Pt attachment was observed. Electronic structure calculations were then applied to estimate the binding energies between the capping molecules and iron ions, and the modeling results strongly support the experimental observations.
    Journal of Applied Physics 01/2010; 107(9):311-1. · 2.21 Impact Factor
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    ABSTRACT: In order to improve the performance, reliability, and efficiency of solid oxide fuel cells, it is important to understand the underlying atomic-level interactions and mechanisms that dictate the global operation dynamics. As a complement to the ongoing experimental progress in this area, a great deal of atomistic-level modeling studies has recently appeared in the literature. This chapter reviews the development of kinetic Monte Carlo simulation approaches for translating atomic-level information into experimentally observable properties. The combination of advanced experimental techniques with atomic-level simulations should provide the insight necessary for the optimal design of next-generation fuel cells.
    Annual Reports in Computational Chemistry 01/2010; 6:201-234.
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    ABSTRACT: A kinetic Monte Carlo model is developed to simulate the oxygen reduction reaction and frequency response at the cathode of a 9 mol % yttria-stabilized zirconia fuel cell, using an asymmetrical cell scheme. To investigate the frequency-response characteristics, ac electrochemical impedance spectra have been studied with respect to variations of different electrolyte thicknesses, temperature, oxygen partial pressure, and relative permittivity of the electrolyte. Within a wide frequency range , our results show that both electrolyte and reaction resistances are strongly temperature-dependent, with the former linearly proportional to the thickness of the electrolyte, as expected. Among the physical parameters that we studied, the temperature and the thickness of the electrolyte have the most profound influence on both the ionic current density and the ac impedance spectra of the fuel cell. The oxygen partial pressure and the relative permittivity of the electrolyte have a smaller influence on the impedance within the frequency range of this study.
    Journal of The Electrochemical Society. 12/2009; 157(1):B90-B98.
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    Wei An, X C Zeng, C Heath Turner
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    ABSTRACT: We present density-functional theory calculations of the dehydrogenation of methane and CH(x) (x=1-3) on a Cu/Ni(111) surface, where Cu atoms are substituted on the Ni surface at a coverage of 14 monolayer. As compared to the results on other metal surfaces, including Ni(111), a similar activation mechanism with different energetics is found for the successive dehydrogenation of CH(4) on the Cu/Ni(111) surface. In particular, the activation energy barrier (E(act)) for CH-->C+H is found to be 1.8 times larger than that on Ni(111), while E(act) for CH(4)-->CH(3)+H is 1.3 times larger. Considering the proven beneficial effect of Cu observed in the experimental systems, our findings reveal that the relative E(act) in the successive dehydrogenation of CH(4) plays a key role in impeding carbon formation during the industrial steam reforming of methane. Our calculations also indicate that previous scaling relationships of the adsorption energy (E(ads)) for CH(x) (x=1-3) and carbon on pure metals also hold for several Ni(111)-based alloy systems.
    The Journal of Chemical Physics 11/2009; 131(17):174702. · 3.12 Impact Factor
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    Yuping Bao, Wei An, C Heath Turner, Kannan M Krishnan
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    ABSTRACT: We report a combined experimental and computational study on the critical role of surfactants in the nucleation and growth of Co nanoparticles synthesized by chemical routes. By varying the surfactant species, Co nanoparticles of different morphologies under similar reaction conditions (e.g., temperature and Co-precursor concentration) were produced. Depending on the surfactant species, the growth of Co nanoparticles followed three different growth pathways. For example, with surfactants oleic acid (OA) and trioctylphosphine oxide (TOPO) used in combination, Co nanoparticles followed a diffusional growth pathway, leading to single crystalline nanoparticles. Multiple-grained nanoparticles, through an aggregation process, were formed with the combination of surfactants OA and dioctylamine (DOA). Further, an Ostwald ripening process was observed in the case of TOPO alone. Complementary electronic structure calculations were used to predict the optimized Co-surfactant complex structures and to quantify the binding energy between the surfactants (ligands) and the Co atoms. These calculations were further applied to predict the Co nanoparticle nucleation and growth processes based on the stability of Co-surfactant complexes.
    Langmuir 10/2009; 26(1):478-83. · 4.38 Impact Factor
  • Wei An, C. Heath Turner
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    ABSTRACT: The binding nature, magnetic, and electronic properties of transition-metal (TM) monatomic chains anchored on boron-doped single-walled carbon nanotubes (B-SWCNTs) are studied using density-functional theory. The TM systems studied here include Au, Pt, Ru, Pd, Ag, Co, Ni, Cu, W, and Ti, which are well-known for their technical importance. In conjunction, prototype semiconducting SWCNT(8,0) and metallic SWCNT(6,6) were chosen to model the general features of B-doped SWCNTs. It is found that the TM-strings exhibit well-defined covalent bonds with the boron-doped SWCNTs, in contrast to the pristine SWCNTs. The TM-string/B-SWCNT composites exhibit high stability and unexpected electronic properties, which are relevant to applications in nanoelectronics, spintronics, nanocatalysis, and sensor devices.
    Journal of Physical Chemistry C - J PHYS CHEM C. 08/2009; 113(34).

Publication Stats

224 Citations
126.95 Total Impact Points

Institutions

  • 2005–2014
    • University of Alabama
      • Department of Chemical and Biological Engineering
      Tuscaloosa, Alabama, United States
  • 2008–2010
    • George Washington University
      • Department of Chemistry
      Washington, D. C., DC, United States
  • 2006
    • Tuskegee University
      • Department of Chemical Engineering
      Tuscaloosa, AL, United States
  • 2001–2003
    • North Carolina State University
      • Department of Chemical and Biomolecular Engineering
      Raleigh, NC, United States
    • University of Pittsburgh
      • Chemical and Petroleum Engineering
      Pittsburgh, PA, United States