On the effects of induced polarizability at the water-graphene interface via classical charge-on-spring models

Modeling Water Interactions with Graphene and Graphite via Force Fields Consistent with Experimental Contact Angles

Accurate simulation models for water interactions with graphene and graphite are important for nanofluidic applications, but existing force fields produce widely varying contact angles. Our extensive review of the experimental literature reveals extreme variation among reported values of graphene-water contact angles and a clustering of graphite-water contact angles into groups of freshly exfoliated (60° ± 13°) and not-freshly exfoliated graphite surfaces. The carbon-oxygen dispersion energy for a classical force field is optimized with respect to this 60° graphite-water contact angle in the infinite-force-cutoff limit, which in turn yields a contact angle for unsupported graphene of 80°, in agreement with the mean of the experimental results. Interaction force fields for finite cutoffs are also derived. A method for calculating contact angles from pressure tensors of planar equilibrium simulations that is ideally suited to graphite and graphene surfaces is introduced. Our methodology is widely applicable to any liquid-surface combination.

Multiscale computational simulation of pollutant behavior at water interfaces

The investigation of pollutant behavior at water interfaces is critical to understand pollution in aquatic systems. Computational methods allow us to overcome the limitations of experimental analysis, delivering valuable insights into the chemical mechanisms and structural characteristics of pollutant behavior at interfaces across a range of scales, from microscopic to mesoscopic. Quantum mechanics, all-atom molecular dynamics simulations, coarse-grained molecular dynamics simulations, and dissipative particle dynamics simulations represent diverse molecular interaction calculation methods that can effectively model pollutant behavior at environmental interfaces from atomic to mesoscopic scales. These methods provide a rich variety of information on pollutant interactions with water surfaces. This review synthesizes the advancements in applying typical computational methods to the formation, adsorption, binding, and catalytic conversion of pollutants at water interfaces. By drawing on recent advancements, we critically examine the current challenges and offer our perspective on future directions. This review seeks to advance our understanding of computational techniques for elucidating pollutant behavior at water interfaces, a critical aspect of water research.

Size Matters: Free-Energy Calculations of Amino Acid Adsorption over Pristine Graphene

There is still growing interest in graphene interactions with proteins, both for its possible biological applications and due to concerns over detrimental effects at the cellular level. As with any process involving proteins, an understanding of amino acid composition is desirable. In this work, we systematically studied the adsorption process of amino acids onto pristine graphene via rigorous free-energy calculations. We characterized the free energy, potential energy, and entropy of the adsorption of all proteinogenic amino acids. The energetic components were further separated into pair interaction contributions. A linear correlation was found between the free energy and the solvent accessible surface area change during adsorption (ΔSASAads) over pristine graphene and uncharged amino acids. Free energies over pristine graphene were compared with adsorption onto graphene oxide, finding an almost complete loss of the favorability of amino acid adsorption onto graphene. Finally, the correlation with ΔSASAads was used to successfully predict the free energy of adsorption of several penta-l-peptides in different structural states and sequences. Due to the relative ease of calculating the ΔSASAads compared to free-energy calculations, it could prove to be a cost-effective predictor of the free energy of adsorption for proteins onto nonpolar surfaces.

Molecular modeling study on the water-electrode surface interaction in hydrovoltaic energy

The global energy problem caused by the decrease in fossil fuel sources, which have negative effects on human health and the environment, has made it necessary to research alternative energy sources. Renewable energy sources are more advantageous than fossil fuels because they are unlimited in quantity, do not cause great harm to the environment, are safe, and create economic value by reducing foreign dependency because they are obtained from natural resources. With nanotechnology, which enables the development of different technologies to meet energy needs, low-cost and environmentally friendly systems with high energy conversion efficiency are developed. Renewable energy production studies have focused on the development of hydrovoltaic technologies, in which electrical energy is produced by making use of the evaporation of natural water, which is the most abundant in the world. By using nanomaterials such as graphene, carbon nanoparticles, carbon nanotubes, and conductive polymers, hydrovoltaic technology provides systems with high energy conversion performance and low cost, which can directly convert the thermal energy resulting from the evaporation of water into electrical energy. The effect of the presence of water on the generation of energy via the interactions between the ion(s) and the liquid-solid surface can be enlightened by the mechanism of the hydovoltaic effect. Here, we simply try to get some tricky information underlying the hydrovoltaic effect by using DFT/B3LYP/6-311G(d, p) computations. Namely, the physicochemical and electronic properties of the graphene surface with a water molecule were investigated, and how/how much these quantities (or parameters) changed in case of the water molecule contained an equal number of charges were analyzed. In these computations, an excess of both positive charge and negative charge, and also a neutral environment was considered by using the Na+, Cl-, and NaCl salt, respectively.

Spin-lattice relaxation time in water/graphene-oxide dispersion

We present the results of the calculations of the spin-lattice relaxation time of water in contact with graphene oxide by means of all-atom molecular dynamics simulations. We fully characterized the water-graphene oxide interaction through the calculation of the relaxation properties of bulk water and of the contact angle as a function of graphene oxide oxidation state and comparing them with the available experimental data. We then extended the calculation to investigate how graphene oxide alters the dynamical and relaxation properties of water in different conditions and concentrations. We show that, despite the diamagnetic nature of the graphene oxide, the confining effects of the bilayers strongly affect the longitudinal relaxation properties of interfacial water, which presents a reduced dynamics due to hydrogen bonds with oxygen groups on graphene oxide. This property makes graphene oxide an interesting platform to investigate water dynamics in confined geometries and an alternative contrast-agent for magnetic resonance imaging applications, especially in view of the possibility to functionalize graphene oxide from theranostic perspectives.