Band gap and density of states of the hydrated C60 fullerene system at finite temperature

Open-[60]fullerenols with water adsorbed both inside and outside

The water affinity on [60]fullerenols was found to be governed by surface electrostatic potential while water aggregation is initiated by the hydroxy groups attached on the carbon surface. The molecular water adsorption at the internal sphere caused a significnat inhibition of water adsorption at the external carbon surface.

Boosting Photocatalytic Activity Using Reduced Graphene Oxide (RGO)/Semiconductor Nanocomposites: Issues and Future Scope

Semiconductor nanoparticles are promising materials for light-driven processes such as solar-fuel generation, photocatalytic pollutant remediation, and solar-to-electricity conversion. Effective application of these materials alongside light can assist in reducing the dependence on fossil-fuel driven processes and aid in resolving critical environmental issues. However, severe recombination of the photogenerated charge-carriers is a persistent bottleneck in several semiconductors, particularly those that contain multiple cations. This issue typically manifests in the form of reduced lifetime of the photoexcited electrons-holes leading to a decrease in the quantum efficiency of various light-driven applications. On the other hand, semiconducting oxides or sulfides, coupled with reduced graphene oxide (RGO), have drawn a considerable interest recently, partly because of the RGO enhancing charge separation and transportation through its honeycomb sp² network structure. High electron mobility, conductivity, surface area, and cost-effectiveness are the hallmark of the RGO. This Mini-Review focuses on (1) examining the approach to the integration of RGO with semiconductors to produce binary nanocomposites; (2) insights into the microstructure interface, which plays a critical role in leveraging charge transport; (3) key examples of RGO composites with oxide and sulfide semiconductors with photocatalysis as application; and (4) strategies that have to be pursued to fully leverage the benefit of RGO in RGO/semiconductors to attain high photocatalytic activity for a sustainable future. This Mini-Review focuses on areas requiring additional exploration to fully understand the interfacial science of RGO and semiconductor, for clarity regarding the interfacial stability between RGO and the semiconductor, electronic coupling at the heterojunction, and morphological properties of the nanocomposites. We believe that this Mini-Review will assist with streamlining new directions toward the fabrication of RGO/semiconductor nanocomposites with higher photocatalytic activity for solar-driven multifunctional applications.

Thermodynamics of hydration of fullerols [C60(OH)n] and hydrogen bond dynamics in their hydration shells

Molecular dynamics simulations of fullerene and fullerols [C₆₀(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 C₆₀ in water is positive (52.8 kJ/mol), whereas its value for C₆₀(OH)₃₀ is highly negative (-427.1 kJ/mol). The effects of surface hydroxylation become more dominant once the fullerols become soluble.

Insights into enhanced visible-light photocatalytic activity of C60 modified g-C3N4 hybrids: the role of nitrogen

Unsaturated N₂ atoms in the interfaces play a major role in promoting the photocatalytic performance of C₆₀ modified g-C₃N₄ hybrids.

Two-dimensional van der Waals C60 molecular crystal

Two-dimensional (2D) atomic crystals, such as graphene and transition metal dichalcogenides et al. have drawn extraordinary attention recently. For these 2D materials, atoms within their monolayer are covalently bonded. An interesting question arises: Can molecules form a 2D monolayer crystal via van der Waals interactions? Here, we first study the structural stability of a free-standing infinite C60 molecular monolayer using molecular dynamic simulations, and find that the monolayer is stable up to 600 K. We further study the mechanical properties of the monolayer, and find that the elastic modulus, ultimate tensile stress and failure strain are 55-100 GPa, 90-155 MPa, and 1.5-2.3%, respectively, depending on the stretching orientation. The monolayer fails due to shearing and cavitation under uniaxial tensile loading. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the monolayer are found to be delocalized and as a result, the band gap is reduced to only 60% of the isolated C60 molecule. Interestingly, this band gap can be tuned up to ±30% using strain engineering. Owing to its thermal stability, low density, strain-tunable semi-conducting characteristics and large bending flexibility, this van der Waals molecular monolayer crystal presents aplenty opportunities for developing novel applications in nanoelectronics.

Adsorption of Polar and Nonpolar Molecules on Isolated Cationic C60 , C70 , and Their Aggregates

Physisorption on graphite, graphene, nanotubes, and other graphitic structures has been the subject of numerous studies, partly driven by interest in the nature of order in two-dimensional systems, their phase transitions, and the use of graphitic scaffolds for reversible storage of hydrogen at high volumetric density and low mass. In contrast, physisorption on individual fullerenes or small aggregates of fullerenes has remained largely unexplored, last but not least, because of technical challenges. A summary of recent progress in identifying specific adsorption sites on positively charged C₆₀ , C₇₀ , and their aggregates is given in this Minireview. Adsorption energies and storage capacities for helium, hydrogen, methane, oxygen, nitrogen, water, and ammonia are determined. Mass spectrometric data reveal the formation of a commensurate phase in which all hollow sites of C₆₀ or C₇₀ are occupied. This phase is identified for all nonpolar molecules, including oxygen, which does not form a commensurate phase on planar graphite. The polar molecules, on the other hand, do not wet fullerenes and they do not form this commensurate phase. A hierarchy of other distinct adsorption sites are identified for nonpolar molecules, namely, groove sites for fullerene dimers and beyond, and dimple sites for fullerene trimers and beyond. Furthermore, evidence is presented for the preferential adsorption of hydrogen and methane in registered sites on fullerene dimers. The interpretation of experimental data that merely count the number of preferred adsorption sites is aided by molecular dynamics simulations, which utilize interaction potentials derived from ab initio calculations to determine adsorption energies.

Effects of hydroxyl group distribution on the reactivity, stability and optical properties of fullerenols

We investigate the impact of hydroxyl groups on the properties of C(60)(OH)(n) systems, with n = 1, 2, 3, 4, 8, 10, 16, 18, 24, 32 and 36 by means of first-principles density functional theory calculations. A detailed analysis from the local density of states has shown that adsorbed OH groups can induce dangling bonds in specific carbon atoms around the adsorption site. This increases the tendency to form polyhydroxylated fullerenes (fullerenols). The structural stability is analyzed in terms of the calculated formation enthalpy of each species. Also, a careful examination of the electron density of states for different fullerenols shows the possibility of synthesizing single molecules with tunable optical properties.

Structure and UV−Vis Spectrum of C60 Fullerene in Ethanol: A Sequential Molecular Dynamics/Quantum Mechanics Study

A molecular dynamics simulation combined with semiempirical quantum mechanics calculations has been performed to investigate the structure, dynamical, and electronic properties of pure C60 in liquid ethanol. The behavior of the fullerene alcoholic solution was obtained by using the NPT ensemble under ambient conditions, including one C60 fullerene immersed in 1000 ethanol molecules. Our analyzed center-of-mass pairwise radial distribution function indicated that, on average, there are 32, 72, 132, and 187 ethanol molecules around, respectively, the first, second, third, and fourth solvation shells of the C60 molecule. To investigate the UV-vis transition energies of C60 in the presence of ethanol, we have considered constituents of the time uncorrelated supramolecular structures of the first solvation shell, i.e., clusters of C60@{EtOH}32 types. The semiempirical calculations were performed at the intermediate neglect of differential overlap level with configuration interaction singles (INDO/CIS). Our results have pointed out that the characteristic C60 UV-vis absorbance peaks are slightly shifted to longer wavelengths, as compared to the isolated molecule. These findings are in connection with the weak donor-acceptor character of the interactions involving electron lone pairs of oxygen atoms on the solvent and the fullerene surface.