Hydration energies of C60 and C70 fullerenes – A novel Monte Carlo simulation study (original) (raw)
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Hydration behaviour of polyhydroxylated fullerenes
Journal of Physics B-atomic Molecular and Optical Physics, 2011
We have performed semi-empirical as well as density functional theory calculations in order to analyse the hydration properties of both bare C60 and highly hydroxylated C60(OH)26 fullerenes. In all of our calculations, a total of 42 and 98 water molecules are always surrounding our here-considered carbon nanostructures. We found different wetting properties as a function of the chemical composition and structure of the OH-molecular over-layer covering the fullerene surface. In the case of bare C60, water adsorption reveals that the H2O species are not uniformly arranged around the carbon network but rather forms water droplets of different sizes, clearly revealing the hydrophobic nature of the C60 structure. In contrast, in the polyhydroxylated C60(OH)26 fullerenes, the degree of wetting is strongly influenced by the precise location of the hydroxyl groups. We found that different adsorbed configurations for the OH-molecular coating can lead to the formation of partially hydrated or completely covered C60(OH)26 compounds, a result that could be used to synthesize fullerene materials with different degrees of wettability. By comparing the relative stability of our hydroxylated structures in both bare and hydrated conditions we obtain that the energy ordering of the C60(OH)26 isomers can change in the presence of water. The radial distribution function of our hydrated fullerenes reveals that water near these kinds of surfaces is densely packed. In fact, by counting the number of H2O molecules which are adsorbed, by means of hydrogen bonds, to the surface of our more stable C60(OH)26 isomer, we found that it varies in the range of 5-10, in good agreement with experiments. Finally, by comparing the calculated optical absorption spectra of various C60(OH)26 structures in the presence and absence of water molecules, we note that only slight variations in the position and intensity of the electronic excitations are found, indicating that their vacuum optical properties are more or less preserved in aqueous environments.
Theoretical calculations of the structure and UV–vis absorption spectra of hydrated C 60 fullerene
Carbon, 2006
A combined Monte Carlo simulation with semiempirical quantum mechanics calculations has been performed to investigate the structure of hydrated fullerene (C 60 HyFn) and the influence of hydration on its UV-vis spectra. The statistical information of the C 60 fullerene aqueous solution (C 60 FAS) is obtained from NPT ensemble including one C 60 fullerene immerses in 898 water molecules. To obtain an efficient ensemble average, the auto-correlation function of the energy has been calculated. The analyzed center-of-mass pair-wise radial distribution function indicates that, on average, there are 65 and 151 water molecules around the first and second hydration shells, respectively, of a single C 60 molecule. To calculate the average UV-vis transition energies of C 60 HyFn, only the statistically uncorrelated configurations are used in the quantum mechanical calculations (INDO/CIS). These involve hundreds of supramolecular structures containing one C 60 fullerene surrounded by the first hydration shell. The calculated average transitions at 268 and 350 nm are in very good agreement with the experimental prediction.
Structure and Thermophysical Properties of Fullerene C60 Aqueous Solutions
2001
The structure and thermophysical properties of fullerene C 60 aqueous solutions were investigated both experimentally and theoretically. The aggregation kinetics results indicated that the structure of fullerene C 60 aggregates in water could be described as a fractal system. The IR and electronic absorption spectra obtained confirm the presence of the crystalline phase in aqueous solution. The numerical values of thermodynamic coefficients : P , ; T , ; S , c P , and c V , and sound velocity were determined from the measured (P V T ) data. The vibrational spectrum of the crystalline structure (T h symmetry group) formed from the hydrated single fullerene C 60 molecules in aqueous solutions was calculated using the molecular dynamics approach.
Phase diagrams of model C[sub 60] and C[sub 70] fullerenes from short-range attractive potentials
The Journal of Chemical Physics, 2009
We report a computer-simulation study of six model fluids interacting through short-range attractive potentials in order to calculate the vapor-liquid ͑VL͒ diagrams using canonical Monte Carlo simulation. It is found that the binodal curves of these systems correctly reproduce those reported in the literature for C 60 and C 70 Girifalco potentials. Besides, we found that all coexistence curves collapse into a master curve when we rescale with their respective critical points.
The Journal of Physical Chemistry B, 2003
A comparative study, strictly by computer simulation, of the phase diagrams and sublimation enthalpies of model C nG60 fullerenes is presented. Gibbs ensemble and Gibbs-Duhem integration Monte Carlo simulations were carried out with the effective potentials of Girifalco. The triple-point properties were determined by a direct method recently proposed by us. It is based on the behavior of the Gibbs ensemble simulations at the lowest temperature limit, and it does not involve free-energy calculations or any other theoretical approach. According to the present results, the liquid phases of the studied fullerenes (C 60 , C 70 , C 76 , and C 84 ) extend over ∼450 K. No sign of liquid supercooling was observed. The triple-point temperatures increase from C 60 to C 84 . This and the simultaneous effect of molecular size cause a relative dislocation of the phase diagrams to higher critical temperatures and lower densities. The simulated enthalpies of sublimation increase from C 60 to C 84 , and they are in very good agreement with the available experimental data. It is suggested that at least the predicted triple-point properties should approach those of real fullerenes. There is a strong correlation between the phase properties and the details of the interaction potentials, clearly reflected in the relative location of the phase diagram and enthalpy curves. On the whole, the simulated results are in good accordance with those recently reported by Abramo et al. (Abramo, M. C.; Caccamo, C.; Costa, D.; Pellicane, G. Europhys. Lett. 2001, 54, 468) from a combination of simulation, modified hypernetted chain (MHNC) theory, and a kind of "corresponding states" rule and confirm the consistency of the MHNC theoretical approach. The reduced properties, which also include the critical-and triple-point pressures as well as the sublimation enthalpies, confirm that some kind of corresponding states rule may be established for fullerenes. On the basis of that, the enthalpy of sublimation of C 96 is predicted.
Structure of C60 fullerene in water: spectroscopic data
Carbon, 2004
The structure of C 60 fullerene aqueous solution in dependence on the C 60 fullerene concentration in the water was studied and analyzed in detail using various spectroscopic techniques such as UV-VIS, Raman and IR-spectroscopy and small-angle neutron scattering (SANS). The obtained experimental results were confirmed by theoretical quantum-chemical calculations of the C 60 fullerene structure in water.
The Journal of Physical Chemistry B, 2003
Gibbs ensemble Monte Carlo simulations were carried out to calculate the vapor-liquid and vapor-solid coexistence curves for three fullerenes: C 60 , C 70 , and C 96 . Single-site potentials with parameters proposed by Girifalco and Pacheco/Ramalho were used to describe the interactions of the fullerene molecules. It is observed that the liquid-phase temperature range (as measured by the reduced triple point temperature, T t /T c ) decreases considerably for C 60 compared to 12-6 Lennard-Jonesium and eventually disappears for C 96 as the potential wells become narrower with increasing molecular weight of the fullerenes. This confirms previous theoretical predictions that the width of the potential well has an important influence on the overall shape of a phase diagram. However, calculations of reduced second virial coefficients show that the fullerene phase diagrams can be described by an extended principle of corresponding states. The Gibbs ensemble simulations yield a triple point temperature of 1876 ( 13 K for C 60 and the Girifalco potential, in excellent agreement with recent calculations by Hasegawa and Ohno and Costa et al.
Quasi-equilibrium distribution of pristine fullerenes C60 and C70 in a water–toluene system
Carbon, 2017
An improved technique of the ultrasound-assisted reversible liquideliquid transfer of pristine (unmodified) C 60 and C 70 fullerenes between organic solutions and aqueous fullerene dispersions (AFD; another notation in general use, nC 60 , nC 70) without any additional reagents (media modifiers) was developed. To our knowledge, this is the first report of such a fullerene transfer from an AFD to an organic phase. Based on the observation of this fullerene reversible transfer, their distribution between the aqueous and organic phases was considered. A quasi-equilibrium transfer mechanism was proposed, which makes it possible to estimate distribution constants, K D , as 6 and 2, for C 60 and C 70 respectively, in a wateretoluene system. Under the optimum conditions, AFDs of C 60 and C 70 with the concentrations 180 ± 20 and 70 ± 20 mM, respectively, were obtained from the corresponding solutions in toluene. Based on UV/vis spectroscopy, total organic carbon, headspace GCeMS, and MALDI measurements, a reliable analytical procedure to measure fullerene concentrations and to monitor the concentration of residual toluene in AFDs was proposed. AFDs of a mixture of fullerenes C 60 and C 70 were characterized by the developed technique.
The Journal of Chemical Physics, 2017
Molecular dynamics simulations of fullerene and fullerols [C 60 (OH) n , where n = 2-30] in aqueous solutions have been performed for the purpose of obtaining a detailed understanding of the structural and dynamic properties of these nanoparticles in water. The structures, dynamics and hydration free energies of the solute molecules in water have been analysed. Radial distribution functions, spatial density distribution functions and hydrogen bond analyses are employed to characterize the solvation shells of water around the central solute molecules. We have found that water molecules form two solvation shells around the central solute molecule. Hydrogen bonding in the bulk solvent is unaffected by increasing n. The large decrease in solvation enthalpies of these solute molecules for n > 14 enhances solubilisation. The diffusion constants of solute molecules decrease with increasing n. The solvation free energy of C 60 in water is positive (52.8 kJ/mol), whereas its value for C 60 (OH) 30 is highly negative (427.1 kJ/mol). The effects of surface hydroxylation become more dominant once the fullerols become soluble.