Now showing 1 - 10 of 27
  • Publication
    Hydrogen bond dynamical properties of adsorbed liquid water monolayers with various TiO2 interfaces
    Equilibrium classical molecular dynamics (MD) simulations have been performed to investigate the hydrogen bonding kinetics of water in contact with rutile-(110), rutile-(101), rutile-(100), and anatase-(101) surfaces at room temperature (300 K). It was observed that anatase-(101) exhibits the longest-lived hydrogen bonds in terms of overall persistence, followed closely by rutile-(110). The relaxation times, defined as the integral of the autocorrelation of the hydrogen bond persistence function, were also larger for these two cases, while decay of autocorrelation function was slower. The increased number and overall persistence of hydrogen bonds in the adsorbed water monolayers at these surfaces, particularly for anatase-(101), may serve to promote possible water photolysis activity thereon.
      576Scopus© Citations 24
  • Publication
    Mechanisms for thermal conduction in hydrogen hydrate
    (American Institute of Physics, 2012-01-23) ; ;
    Extensive equilibrium molecular dynamics (MD) simulations have been performed to investigate thermal conduction mechanisms via the Green-Kubo approach for (type II) hydrogen hydrate, at 0.05 kbar and between 30 and 250 K, for both lightly-filled H2 hydrates (1s4l) and for more densely-filled H2 systems (2s4l), in which four H2 molecules are present in the large cavities, with respective single- and double-occupation of the small cages. The TIP4P water model was used in conjunction with a fully atomistic hydrogen potential along with long-range Ewald electrostatics. It was found that substantially less damping in guest-host energy transfer is present in hydrogen hydrate as is observed in common type I clathrates (e.g., methane hydrate), but more akin in to previous results for type II and H methane hydrate polymorphs. This gives rise to larger thermal conductivities relative to common type I hydrates, and also larger than type II and H methane hydrate polymorphs, and a more crystal-like temperature dependence of the thermal conductivity.
      650Scopus© Citations 23
  • Publication
    Routes to visible light active C-doped TiO2 photocatalysts using carbon atoms from the Ti precursors
    In this work, different thermal treatments of titanium isopropoxide-derived photo-catalyst precursors, designed with the purpose of generating C-doped TiO2 photo-catalysts using carbon atoms present in the TiOx gel precursors as dopants, are presented. Specifically, these look at varying the standard calcination techniques using heat treatments in He (rather than calcination in air) and lower temperature calcinations (200 °C rather than 500 °C). The formed materials are characterised using N2 physisorption, XRD, UV Visible spectroscopy and XPS and their activities in promoting the oxidation of 4-chlorophenol under visible-light-only conditions were analysed. The nature of carbon remaining on the (or in the) material is discussed found to be both surface graphitic carbon and carbon present in anionic dopant positions. The different contributions of each type of carbon to the catalytic photo-activity under visible light are discussed.
      444Scopus© Citations 25
  • Publication
    Towards the design of novel boron- and nitrogen-substituted ammonia-borane and bifunctional arene ruthenium catalysts for hydrogen storage
    Electronic-structure density functional theory calculations have been performed to construct the potential energy surface for H2 release from ammonia-borane, with a novel bifunctional cationic ruthenium catalyst based on the sterically bulky β-diketiminato ligand (Schreiber et al., ACS Catal. 2012, 2, 2505). The focus is on identifying both a suitable substitution pattern for ammonia-borane optimized for chemical hydrogen storage and allowing for low-energy dehydrogenation. The interaction of ammonia-borane, and related substituted ammonia-boranes, with a bifunctional η6-arene ruthenium catalyst and associated variants is investigated for dehydrogenation. Interestingly, in a number of cases, hydride-proton transfer from the substituted ammonia-borane to the catalyst undergoes a barrier-less process in the gas phase, with rapid formation of hydrogenated catalyst in the gas phase. Amongst the catalysts considered, N,N-difluoro ammonia-borane and N-phenyl ammonia-borane systems resulted in negative activation energy barriers. However, these types of ammonia-boranes are inherently thermodynamically unstable and undergo barrierless decay in the gas phase. Apart from N,N-difluoro ammonia-borane, the interaction between different types of catalyst and ammonia borane was modeled in the solvent phase, revealing free-energy barriers slightly higher than those in the gas phase. Amongst the various potential candidate Ru-complexes screened, few are found to differ in terms of efficiency for the dehydrogenation (rate-limiting) step. To model dehydrogenation more accurately, a selection of explicit protic solvent molecules was considered, with the goal of lowering energy barriers for H-H recombination. It was found that primary (1°), 2°, and 3° alcohols are the most suitable to enhance reaction rate. © 2014 Wiley Periodicals, Inc.
      461Scopus© Citations 6
  • Publication
    Molecular dynamics study of water in contact with TiO2 rutile-110, 100, 101, 001 and anatase-101, 001 surface
    We have carried out classical molecular dynamics of various surfaces of TiO2 with its interface with water. We report the geometrical features of the first and second monolayers of water using a Matsui Akaogi (MA) force field for the TiO2 surface and a flexible single point charge model for the water molecules. We show that the MA force field can be applied to surfaces other than Rutile-(110). It was found that water OH bond lengths, H-O-H bond angles and dipole moments do not vary due to the nature of the surface. However, their orientation within the first and second monolayers suggest that planar Rutile-(001) and Anatase-(001) surfaces may play an important role in not hindering removal of the products formed on these surfaces. Also, we discuss the effect of surface termination in order to explain the layering of water molecules throughout the simulation box.
      1166Scopus© Citations 80
  • Publication
    Implicit and explicit solvent models for modelling a bifunctional arene ruthenium hydrogen-storage catalyst: a classical and ab initio molecular simulation study
    Classical and ab initio, density functional theory- and semiempirical-based molecular simulation, including molecular dynamics, have been carried out to compare and contrast the effect of explicit and implicit solvation representation of tetrahydrofuran (THF) solvent on the structural, energetic, and dynamical properties of a novel bifunctional arene ruthenium catalyst embedded therein. Particular scrutiny was afforded to hydrogen-bonding and energetic interactions with the THF liquid. It was found that the presence of explicit THF solvent molecules is required to capture an accurate picture of the catalyst's structural properties, particularly in view of the importance of hydrogen bonding with the surrounding THF molecules. This has implications for accurate modeling of the reactivity of the catalyst.
      329Scopus© Citations 5
  • Publication
    Visible light active C-doped titanate nanotubes prepared via alkaline hydrothermal treatment of C-doped nanoparticulate TiO2: Photo-electrochemical and photocatalytic properties
    Carbon-doped titanate nanotubes (C-TNT) were formed via alkaline hydrothermal treatment of a TiO2 nanoparticulate material pre-doped with carbon. Attempts to form C and W co-doped titanate nanotubes using analogous C and W co-doped nanoparticulate materials were unsuccessful. Physical characterisations, such as X-ray diffraction, N2 physisorption and Transmission Electron Microscopy, confirmed the formation of titanate nanotubes ~7 nm in diameter and hundreds of nm in length with increased surface areas relative to the nanoparticulate precursors. X-ray Photoelectron Spectroscopy confirmed the retention of substitutional carbon dopant and the exclusion of tungsten dopant from the doped TNT materials. Converting doped (or undoped TiO2) into C-TNT (or TNT) slightly increases the material’s bandgap but the C-TNT material (in contrast to TNT and undoped TiO2) absorbs into the visible region of the spectrum. C-doped and un-doped titanate nanotube materials were more active in promoting the photo degradation of 4-chlorophenol under visible light than their analogous nanoparticulate precursors. C-TNT was the most photocatalytically active material tested. However, photocurrent response measurements showed C-TNT to be less effective at generating current following irradiation than both its nanoparticulate analogue and nanoparticulate P25 when screen printed onto electrode surfaces. We ascribe this to non-optimal alignment of the TNTs on the electrode surface.
      704Scopus© Citations 34
  • Publication
    Dynamical and energetic properties of hydrogen and hydrogen–tetrahydrofuran clathrate hydrates
    Classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the dynamical and energetic properties in hydrogen and mixed hydrogen-tetrahydrofuran sII hydrates at 30 and 200K and 0.05 kbar, and also at intermediate temperatures, using SPC/E and TIP4P-2005 water models. The potential model is found to have a large impact on overall density, with the TIP4P-2005 systems being on average 1 % more dense than their SPC/E counterparts, due to the greater guest-host interaction energy. For the lightly-filled mixed H2-THF system, in which there is single H2 occupation of the small cage (1s1l), we find that the largest contribution to the interaction energy of both types of guest is the van der Waals component with the surrounding water molecules in the constituent cavities. For the more densely-filled mixed H2-THF system, in which there is double H2 occupation in the small cage (2s1l), we find that there is no dominant component (i.e., van der Waals or Coulombic) in the H2 interaction energy with the rest of the system, but for the THF molecules, the dominant contribution is again the van der Waals interaction with the surrounding cage-water molecules; again, the Coulombic component increases in importance with increasing temperature. The lightly-filled pure H2 hydrate (1s4l) system exhibits a similar pattern vis-à-vis the H2 interaction energy as for the lightly-filled mixed H2-THF system, and for the more densely-filled pure H2 system (2s4l), there is no dominant component of interaction energy, due to the multiple occupancy of the cavities. By consideration of Kubic harmonics, there is some evidence of preferential alignment of the THF molecules, particularly at 200 K; this was found to arise at higher temperatures due to transient hydrogen bonding of the oxygen atom in THF molecules with the surrounding cage-water molecules.
      460Scopus© Citations 21
  • Publication
    Electrophoretic deposition of poly(3-decylthiophene) onto gold-mounted cadmium selenide nanorods
    Molecular mechanisms of electrophoretic deposition (EPD) of poly(3-decylthiophene) (P3DT) molecules onto vertically aligned cadmium selenide arrays have been studied using large-scale, nonequilibrium molecular dynamics (MD), in the absence and presence of static external electric fields. The field application and larger polymer charges accelerated EPD. Placement of multiple polymers at the same lateral displacement from the surface reduced average deposition times due to “crowding”, giving monolayer coverage. These findings were used to develop and validate Brownian dynamics simulations of multilayer polymer EPD in scaled-up systems with larger inter-rod spacings, presenting a generalized picture in qualitative agreement with random sequential adsorption.
      616Scopus© Citations 6
  • Publication
    Application of a novel microwave plasma treatment for the sintering of nickel oxide coatings for use in dye-sensitized solar cells
    In this study the use of microwave plasma sintering of nickel oxide (NiOx) particles for use as p-type photoelectrode coatings in dye-sensitized solar cells (DSSCs) is investigated. NiOx was chosen as the photocathode for this application due to its stability, wide band gap and p-type nature. For high light conversion efficiency DSSCs require a mesoporous structure exhibiting a high surface area. This can be achieved by sintering particles of NiOx onto a conductive substrate. In this study the use of both 2.45 GHz microwave plasma and conventional furnace sintering were compared for the sintering of the NiOx particles. Coatings 1 to 2.5 μm thick were obtained from the sintered particles (mean particle size of 50 nm) on 3 mm thick fluorine-doped tin oxide (FTO) coated glass substrates. Both the furnace and microwave plasma sintering treatments were carried out at ~ 450 °C over a 5 minute period. Dye sensitization was carried out using Erythrosin B and the UV-vis absorption spectra of the NiOx coatings were compared. A 44% increase in the level of dye adsorption was obtained for the microwave plasma sintered samples as compared to that obtained through furnace treatments. While the photovoltaic performance of the DSSC fabricated using the microwave plasma treated NiOx coatings exhibited a tenfold increase in the conversion efficiency in comparison to the furnace treated samples. This enhanced performance was associated with the difference in the mesoporous structure of the sintered NiOx coatings.
      2445Scopus© Citations 44