C. Heath Turner

University of Alabama, Tuscaloosa, Alabama, United States

Are you C. Heath Turner?

Claim your profile

Publications (68)195.59 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Recent experimental investigations have found that the rate and conversion of the photopolymerization of 1-vinylimidazole (VIm) can be significantly accelerated with the addition of lithium bistriflimide (LiTf2N). However, the underlying molecular-level interactions responsible for this phenomenon are unclear. The two components, VIm and LiTf2N, are miscible over a wide range of concentrations and form liquid phases at ambient temperature, and if the fundamental behavior of this mixture can be clearly quantified, there are significant opportunities for tuning the polymerization dynamics, polymer structure, and properties. In this work, molecular dynamics (MD) simulations are used to model the underlying pre-polymerization structure of VIm+LiTf2N mixtures at several different concentrations. It is found that the Li+ enhances the site-site interactions of key functional groups involved in the polymerization, and this is suggested to play a major role in the experimentally-observed enhancement of the polymerization behavior.
    No preview · Article · Sep 2015 · Chemical Engineering Science
  • [Show abstract] [Hide abstract]
    ABSTRACT: The emergence of 3D printing has dramatically advanced the availability of tangible molecular and extended solid models. Interestingly, there are few nanostructure models available both commercially and through other do-it-yourself approaches such as 3D printing. This is unfortunate given the importance of nanotechnology in science today. In this work, we have filled part of this gap by designing and 3D printing several block copolymer (BCP) nanostructure morphologies. We used a variety of methods including manually drawing the files within 3D computer design software, using equations with mathematical graphing software, and developing a programming script to convert self-consistent field theory (SCFT) structure data into a 3D printable file. Conversion of SCF data into 3D printable structures may find broader applicability beyond creating BCP nanostructures as SCF calculations are used in a variety of geometric computations. All methods reported herein produced tangible 3D prints of approximately equal quality. These tangible models will be useful for educators, students, and researchers in polymer science and nanotechnology. © 2015 The American Chemical Society and Division of Chemical Education, Inc.
    No preview · Article · Aug 2015 · Journal of chemical education
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Molecular dynamics (MD) simulations are vital tools in modern research as they can provide molecular and atomic level insights into macroscopic behaviors of organic, inorganic, biological and hybrid materials. The analytical process of translating structural coordinates into a complex 3-D structure can be a challenging and engaging computational exercise for students. Here, we describe a detailed methodology for transforming the outputs of MD simulations into tangible forms through the use of dual-extrusion 3-D printing on a commercially available 3-D printer that we operate in our laboratory. Additionally, the printed 3-D structures can provide unique educational opportunities outside of traditional lecture halls and away from computer workstations environments as they provide a tangible representation of data when a digital copy is unavailable or inconvenient to share. We believe that 3-D printing can become a valuable complementary technique with MD and other forms of simulations in the chemical sciences. 3-D printers truly can be used to make just about anything, and this manuscript provides just one example of how this emerging technology can be applied within chemical engineering. As more chemical engineering educators become familiar with 3-D printing, we foresee a number of educational and applied uses including printing of highly complex patterned/porous surfaces, custom laboratory parts/equipment and even functional unit operations.
    Full-text · Article · Jul 2015 · Education for Chemical Engineers
  • C. Heath Turner · Zhongtao Zhang · Lev D. Gelb · Brett I. Dunlap

    No preview · Chapter · May 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Bismuth telluride (Bi2Te3) is a well-known thermoelectric material that has a layered crystal structure. Exfoliating Bi2Te3 to produce two-dimensional (2D) nanosheets is extremely important because the exfoliated nanosheets possess unique properties, which can potentially revolutionize several material technologies, such as thermoelectrics, heterogeneous catalysts, and infrared detectors. In this work, the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) is used to exfoliate Bi2Te3 nanoplatelets. In both experiments and in molecular dynamics (MD) simulations, the Bi2Te3 nanoplatelets yield a stable dispersion of 2D nanosheets in the IL solvent, and our MD simulations provide molecular-level insight into the kinetics and thermodynamics of the exfoliation process. An analysis of the dynamics of the Bi2Te3 during exfoliation indicates that the relative translation (sliding apart) of adjacent layers caused by IL-induced forces plays an important role in the process. Moreover, an evaluation of the MD trajectories and electrostatic interactions indicates that the [C4mim]+ cation is primarily responsible for initiating the Bi2Te3 layer sliding and separation, while the Cl- anion is less active. Overall, our combined experimental and computational investigation highlights the effectiveness of IL-assisted exfoliation, and the underlying molecular-level insights should accelerate the development of future exfoliation techniques for producing 2D chalcogenide materials.
    Full-text · Article · Mar 2015 · Langmuir
  • [Show abstract] [Hide abstract]
    ABSTRACT: Sulfur dioxide (SO2) removal is a key component of many industrial processes, especially coal-fired power generation. Controlling SO2 emissions is vital to maintaining environmental quality, as SO2 is a contributor to acid rain, but has value as a chemical feedstock. Although a number of novel solvents/materials including ionic liquids (ILs) have recently been proposed for alternatives to limestone scrubbing for SO2 capture/removal from point sources, the imidazole architecture presents a convenient, inexpensive and efficient class of low volatility and low viscosity solvents to accomplish this goal. On the basis of our prior work with imidazoles for CO2 capture, we have extended our interests toward understanding the relationship between imidazole structure and SO2 absorption. Using a series of imidazole compounds with various substituents at the 1, 2 and/or 4(5) positions of the five-membered ring, SO2 absorption via both chemical and physical mechanisms was observed. The chemical absorption product is a relatively stable 1:1 SO2–imidazole complex, while physical absorption of SO2 is dependent on pressure and temperature. Because imidazoles are relatively small molecules, they are an efficient absorption medium for SO2 and can form adducts wherein the mass fraction of bound SO2 is >40 wt %. The SO2–imidazole complexes were also observed to produce distinct color and/or phase changes that are associated with the nature of the substituents present. The chemically bound SO2 can be released under vacuum at moderate temperature (∼100 °C) and vacuum, yielding the original neat solvent, while the physically dissolved SO2 can be readily removed at ambient temperature under vacuum. This behavior corresponds to a much smaller enthalpy of absorption for physical dissolution (−4 to −13 kJ/mol) as determined via thermodynamic relationships compared to the binding energies of chemical complexation (−35 to −42 kJ/mol) as determined via density functional theory calculations. Increasing chemical complexation energies are correlated with increased substitution on the imidazole ring. Simulations were also employed to gain insight into the structures of the SO2–imidazole complexes, illustrating changes in partial charge distribution before and after complexation as well as confirming a charge transfer complex is formed based on the N–S bond length.
    No preview · Article · Jan 2015 · Industrial & Engineering Chemistry Research
  • [Show abstract] [Hide abstract]
    ABSTRACT: Imidazole-based polymers, such as poly(vinylimidazole), may provide useful properties for membrane-based CO2 capture applications, so it is becoming increasingly important to understand the formation mechanisms and underlying molecular structure of these materials. One of the challenges in the photopolymerization of 1-vinylimidazole (VIm) are slow rates and incomplete monomer conversion. We recently discovered that polymerization rate and overall conversion could be dramatically improved when VIm is in the presence of a bulky salt, lithium bis(trifluoromethylsulfonyl)imide [Li+][Tf2N-]. In this work, molecular dynamics simulations are used to model the intermolecular conformational behavior and thermophysical properties of the VIm-[Li+][Tf2N-] complexes. Molecular conformations of different ratios of [VIm] to salt were characterized in order to identify the structural ordering induced by [Li+][Tf2N-] on the polymerization of [VIm]. The same structural analyses were also performed on systems containing poly(vinylimidazole) [PVIm] in order to explore the conformations and thermophysical properties at different stages of the polymerization reaction. The calculated properties from the molecular dynamics simulations are compared against experimentally-derived structural features and found to be in agreement. Radial distribution functions indicate that [Li+] chelates with the “pyridine-like” nitrogen of the imidazole ring in both [VIm] and [PVIm], while the fluorine atoms of [Tf2N-] have strong interactions with the vinyl groups. Also, as the relative concentration of the salt increases, the probability of vinyl groups aggregating in favorable conformations to polymerization tends to increase (at all temperatures studied). Furthermore, electronic structure calculations have also been performed to identify electrostatic interactions in the systems, such as partial charge assignments and potential dipole interactions with [VIm] and [PVIm].
    No preview · Conference Paper · Nov 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: Previous work has characterized specific physical properties and CO2 solubility of 1-n-alkylimidazole solvents for use in pre- and post-combustion CO2 capture during gas treating. This research project explores the CO2 solubility and physical properties of multiply-branched alkylimidazole solvents to determine the effects of functional group position(s) on various chemical and physical attributes. Using this information, additional correlations between ring substitution and physical properties can be derived to optimize the characteristics. Synthesis and purification of these compounds were followed by tests to determine density, viscosity, and vapor pressure as functions of temperature and ring substitution, and these properties were shown to be comparable to previously-tested 1-n-alkylimidazoles. The solvents in general were found to have low viscosities (<15 cP) and negligible vapor pressures (<0.5 mbar). CO2 solubility experiments also showed that multiply-branched alkylimidazoles have similar if not improved absorption capacities relative to ionic liquids and 1-n-alkylimidazoles. In future work, polymeric membranes can be synthesized from these compounds to determine CO2 permeability and selectivity as a function of ring substitution. The ultimate goal of this research is to find an imidazole-based solvent with low volatility and high CO2 absorption capacity or an imidazole-based membrane structure with high CO2 permeability and selectivity that can be easily manufactured for application in large-scale industry for the reduction of atmospheric CO2 emissions.
    No preview · Conference Paper · Nov 2014
  • Zhongtao Zhang · C. Heath Turner
    [Show abstract] [Hide abstract]
    ABSTRACT: The redox properties of CpTM (Cp = cyclopentadienyl and TM = transition metal) on B-doped, N-doped, and pristine graphene complexes are evaluated using density functional theory in order to determine the possibility of using these complexes as novel redox-active materials for electrochemical applications. The CpFe/B-doped graphene complexes with a series of different side chains are found to have comparable redox potentials to ferrocene molecules and other ferrocene-based electrochemical sensors (in water and in acetonitrile solution), which indicates the potential application of these complexes to substitute for ferrocene-based electrochemical systems. The redox potentials of CpFe on pristine and N-doped graphene indicate that they would function as reducing agents. In addition, the charge transfer mechanism during the redox process is investigated and visualized using deformation charge densities, frontier orbitals, and natural bond orbital (NBO) population analyses. Large charge redistributions are observed during the redox process, which also transforms the bonding between the TM centers and the supports into a more ionic interaction.
    No preview · Article · Oct 2014 · The Journal of Physical Chemistry C
  • Zhongtao Zhang · C. Heath Turner
    [Show abstract] [Hide abstract]
    ABSTRACT: Molecular dynamics (MD) simulations are used to investigate the hydration, the water-induced interactions, and the dispersion behavior of boron-doped single-walled carbon nanotubes (B-CNTs) within aqueous solutions. Models of B-CNTs with various diameters and B-doping patterns are developed, with partial charges calculated from first-principles density functional theory (DFT). Using MD simulations, the potential of mean force (PMF) of one, two, and three solvated B-CNTs are evaluated, and these results are compared to pristine CNTs. The hydration behavior of the B-CNTs is also quantified by evaluating the water density profiles and hydrogen bonds during the solvation. Our MD simulations indicate the presence of water-induced interactions with B-CNTs over prolonged distances, as compared to pristine CNTs. In particular, the B-CNTs are more resistant to reaggregation than pristine CNTs. These simulation results thoroughly characterize the effects of substitutional doping of CNTs on their dispersion behavior in aqueous solution, and our atomistic simulations of B-CNTs are used to parametrize coarse-grained models of the nanotube-nanotube interactions.
    No preview · Article · Aug 2014 · The Journal of Physical Chemistry C
  • Haining Liu · C. Heath Turner
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · May 2014 · Journal of Computational Chemistry
  • Haining Liu · Jason E Bara · C Heath Turner
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · May 2014 · The Journal of Physical Chemistry A
  • Source
    Haining Liu · Zhongtao Zhang · Jason E Bara · C Heath Turner
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Dec 2013 · The Journal of Physical Chemistry B
  • Haining Liu · Jason E. Bara · C. Heath Turner
    [Show abstract] [Hide abstract]
    ABSTRACT: There has been increasing interest in developing new materials for CO2 capture. One of the approaches is to synthesize polymer membrane using imidazole derivatives as the monomer. These imidazole derivatives are able to react with aqueous CO2 to form bicarbonate anions, thus enabling facilitated transport of CO2 through the membrane. In order to better understand the chemical and thermophysical properties of imidazole derivatives, we have employed quantum mechanics and molecular dynamics methods to calculate the proton affinities, 1H NMR chemical shifts, and absorption properties of a variety of imidazole derivatives. From our simulations, a quantitative characterization of the effect of various exocyclic substituents on the proton affinity of imidazole was achieved. In particular, we find that electron-donating groups are able to increase the proton affinity of imidazole. In addition, the calculated 1H NMR chemical shift and thermophysical properties are in excellent with experiment. These results will be helpful for future experimental design of new materials to be used for CO2 capture.
    No preview · Conference Paper · Nov 2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: Branched gold nanoparticles were 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 700-900 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 prefer 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.
    No preview · Conference Paper · Nov 2013
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Aug 2013 · Industrial & Engineering Chemistry Research
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Aug 2013 · The Journal of Physical Chemistry C
  • Zhongtao Zhang · C. Heath Turner
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Apr 2013 · The Journal of Physical Chemistry C
  • Haining Liu · Jason E. Bara · C. Heath Turner
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Apr 2013 · Chemical Physics
  • Source
    Wei An · C. Heath Turner
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Jan 2013 · The Journal of Physical Chemistry C