Energy and mass balances related to climate change and remediation.

The goal of this paper is to provide a forum for a broad interdisciplinary group of scientists and engineers to see how concepts of climate change, energy, and carbon remediation strategies are related to quite basic scientific principles. A secondary goal is to show relationships between general concepts in traditional science and engineering fields and to show how they are relevant to broader environmental concepts. This paper revisits Fourier's early mathematical derivation of the average temperature of the Earth from first principles, i.

Adsorption-induced shape transitions in bistable nanopores with atomically thin walls.

Atomically thin cylindrical nanopores can change shape in response to physically adsorbed gas inside. Coupled to a gas reservoir, an initially collapsed pore can expand to allow the adsorbed gas to form concentric shells on the inner part of the pore, driven by adsorption energetics, not gas pressure. A lattice gas model describes the evolution of the nanotube pore shape and absorbed gas as a function of gas chemical potential at zero temperature.

Corresponding states interpretation of adsorption in gate-opening metal-organic framework Cu(dhbc)₂(4,4'-bpy).

The "universal adsorption theory" (UAT) extends the principle of corresponding states for gas compressibility to describe the excess density of an adsorbed phase at comparable reduced conditions. The UAT helps to describe experimental trends and provide predictive capacity for extrapolation from one adsorption isotherm to that of a different adsorbate. Here, we extend the UAT to a flexible metal-organic framework (MOF) as a function of adsorbate, temperature, and pressure.

Theory of electrocaloric effect in a shape-changing container: gas in a nanotube.

Driven by applied voltage or Ohmic heating, bistable nanotubes filled with gas can transform between expanded and collapsed configurations and by doing so convert energy between mechanical, electrical, and thermal forms. The electrocaloric response, a reversible change of temperature in response to applied voltage, combines the advantages of a working fluid with the lack of internal interfaces characteristic of robust solid-state thermoelectric devices. Such devices could be constructed from any conductive two-dimensional atomically thin material wrapped into an appropriate geometry.

Wetting transitions of water on graphite and graphene.

Water has been predicted theoretically and observed experimentally to exhibit a wetting transition on graphite. Previous study of this problem was based on quite uncertain water-graphite interaction potentials. This paper computes the wetting temperature on graphite using recent, more realistic, interactions.

Novel behavior of monolayer quantum gases on graphene, graphane and fluorographene.

This article discusses the behavior of submonolayer quantum films (He and H2) on graphene and newly discovered surfaces that are derived from graphene. Among these substrates are graphane (abbreviated GH), which has an H atom bonded to each C atom, and fluorographene (GF). The subject is introduced by describing the related problem of monolayer films on graphite.

Experimental and theoretical comparison of gas desorption energies on metallic and semiconducting single-walled carbon nanotubes.

Single-walled carbon nanotubes (SWNTs) exhibit high surface areas and precisely defined pores, making them potentially useful materials for gas adsorption and purification. A thorough understanding of the interactions between adsorbates and SWNTs is therefore critical to predicting adsorption isotherms and selectivities. Metallic (M-) and semiconducting (S-) SWNTs have extremely different polarizabilities that might be expected to significantly affect the adsorption energies of molecules.

Is there a difference in van der Waals interactions between rare gas atoms adsorbed on metallic and semiconducting single-walled carbon nanotubes?

The differences in the polarizabilities of metallic (M) and semiconducting (S) single-walled carbon nanotubes (SWNTs) might give rise to differences in adsorption potentials. We show from experiments and van der Waals--corrected density functional theory that the binding energies of Xe adsorbed on M- and S-SWNTs are nearly identical. Temperature programed desorption experiments of Xe on purified M- and S-SWNTs give similar peak temperatures, indicating that desorption kinetics and binding energies are independent of the type of SWNT.

Van der Waals interactions: accuracy of pair potential approximations.

Van der Waals interactions between single atoms and solids are discussed for the regime of large separation. A commonly employed approximation is to evaluate this interaction as a sum of two-body interactions between the adatom and the constituent atoms of the solid. The resulting potentials are here compared with known results in various geometries.

Frictional temperature rise in a sliding physisorbed monolayer of Kr/graphene.

A quartz crystal microbalance (QCM) with a graphene/Ni(111) electrode has been used to probe frictional heating effects in Kr monolayers sliding on the microbalance electrode in response to its oscillatory motion. The temperatures of the sliding Kr monolayers are observed to rise approximately 13 K higher than their static counterparts, but show surprisingly little dependence on oscillation amplitude. Although counterintuitive, the observation can be explained by noting that the Kr surface residence times are limited, which effectively caps how much the temperature can rise.

Phase behavior of Ar and Kr films on carbon nanotubes.

Recent experiments (Wang et al., 2010) have found evidence of phase transitions of gases adsorbed on a single carbon nanotube. In order to understand the observations, we have carried out classical grand canonical Monte Carlo simulations of this system, for the cases of Ar and Kr on zigzag and armchair nanotubes with radius R > 0.

Transitions of gases physisorbed on graphene.

The behavior of gases physically adsorbed on graphene might be expected to be similar to that of ones adsorbed on graphite. Here, three kinds of phase transitions are examined for gases adsorbed on suspended, free-standing graphene. In one case, the quasi-two-dimensional condensation of a van der Waals fluid is evaluated, using perturbation theory.

Anomalous effective dimensionality of quantum gas adsorption near nanopores.

Three problems involving quasi-one-dimensional (1D) ideal gases are discussed. The simplest problem involves quantum particles localized within the 'groove', a quasi-1D region created by two adjacent, identical and parallel nanotubes. At low temperature (T), the transverse motion of the adsorbed gas, in the plane perpendicular to the axes of the tubes, is frozen out.

Structural, electronic, optical and vibrational properties of nanoscale carbons and nanowires: a colloquial review.

This review addresses the field of nanoscience as viewed through the lens of the scientific career of Peter Eklund, thus with a special focus on nanocarbons and nanowires. Peter brought to his research an intense focus, imagination, tenacity, breadth and ingenuity rarely seen in modern science. His goal was to capture the essential physics of natural phenomena.

Adsorption of ammonia on graphene.

We report on experimental studies of NH3 adsorption/desorption on graphene surfaces. The study employs bottom-gated graphene field effect transistors supported on Si/SiO2 substrates. Detection of NH3 occurs through the shift of the source-drain resistance maximum ('Dirac peak') with the gate voltage.

Interaction thresholds for adsorption of quantum gases on surfaces and within pores of various shapes.

Adsorption within pores and on surfaces occurs because of the attractive potential provided by the adsorbent. If the attraction is too weak, however, adsorption does not occur to any significant extent. This paper evaluates the criterion for such adsorption, at zero temperature, of the quantum gases 4He and H2.

Van der Waals dispersion forces between dielectric nanoclusters.

Various methods are evaluated for their ability to calculate accurate van der Waals (VDW) dispersion forces between nanoclusters. We compare results for spheres using several methods: the simple Hamaker two-body method, the Lifshitz (DLP) theory with the Derjaguin approximation, the Langbein result for spheres, and our "coupled dipole method" (CDM). The assumptions and shortcomings of each method are discussed.

Fully retarded van der Waals interaction between dielectric nanoclusters.

The van der Waals (dispersion) interaction between an atom and a cluster or between two clusters at large separation is calculated by considering each cluster as a point particle, characterized by a polarizability tensor. For the extreme limit of very large separation, the fully retarded regime, one needs to know just the static polarizability in order to determine the interaction. This polarizability is evaluated by including all many-body (MB) intracluster atomic interactions self-consistently.

van der Waals forces between nanoclusters: importance of many-body effects.

van der Waals interactions between nanoclusters have been calculated with a self-consistent, coupled dipole method. The method accounts for all many-body (MB) effects. Comparison is made between the exact potential energy, V, and the values obtained with two alternative methods: the sum of two-body interactions and the sum of two-body and three-body interactions.

Capillary condensation in cylindrical nanopores.

Using grand canonical Monte Carlo simulations, we have explored the phenomenon of capillary condensation (CC) of Ar at the triple temperature inside infinitely long, cylindrical pores. Pores of radius R = 1 nm, 1.7 nm, and 2.

Evolution of topological order in Xe films on a quasicrystal surface.

We report results of the first computer simulation studies of a physically adsorbed gas on a quasicrystalline surface Xe on decagonal Al-Ni-Co. The grand canonical Monte Carlo method is employed, using a semiempirical gas-surface interaction, based on conventional combining rules, and the usual Lennard-Jones Xe-Xe interaction. The resulting adsorption isotherms and calculated structures are consistent with the results of LEED experimental data.

Designing van der Waals Forces between Nanocolloids.

van der Waals (VDW) dispersion forces are often calculated between colloidal particles by combining the Dzyaloshinskii-Lifshitz-Pitaevskii (DLP) theory with the Derjaguin approximation; however, several limitations prevent using this method for nanocolloids. Here we use the Axilrod-Teller-Muto 3-body formulation to predict VDW forces between spherical, cubic, and core-shell nanoparticles in a vacuum. Results suggest heuristics for "designing" nanocolloids to have improved stability.

Possible one-dimensional 3He quantum fluid formed in nanopores.

Heat capacity measurements have been made down to 5 mK for 3He fluid films adsorbed in one-dimensional (1D) nanometer-scale pores, 28 A in diameter, preplated with 4He of 1.47 atomic layers. At low 3He density, the heat capacity shows a density-dependent, Schottky-like peak near 150 mK asymptoting to the value corresponding to a 2D Boltzmann gas at high temperatures.

Lattice-gas Monte Carlo study of adsorption in pores.

A lattice-gas model of adsorption inside cylindrical pores is evaluated with Monte Carlo simulations. The model incorporates two kinds of sites: (a line of) "axial" sites and surrounding "cylindrical shell" sites, in the ratio 1:7. The adsorption isotherms are calculated in either the grand canonical or canonical ensembles.