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Among the carbon-based two-dimensional (2D) materials, graphene oxide (GO) has been attracting growing interest because of its ability to be utilized in the field of water remediation. Therefore, an atomistic understanding of the transport properties of water in layered GO is pivotal for the development of novel GO membranes. Surprisingly, the very issue of the 2D self-diffusion of water confined between two GO sheets appears to be controversial, and simulations showing either a slowdown or no effect have been reported. In any case, the formation of hydrogen bonds, i.e., among the confined water and between water and the GO functional groups, was identified to control diffusion. However, the results of molecular dynamics (MD) simulations heavily depend on the forces used. Density functional theory (DFT) and empirical force fields are opposite when it comes to accuracy and numerical costs. As a compromise in the present study, we performed MD simulations using a DFT-based tight-binding method to investigate the diffusion of water confined between GO sheets. Specifically, we considered six GO/water models, differing in the ordering of the epoxide and hydroxyl groups as well as in the thickness of the water layer. For these models having GO interlayer distances between 8 and 12 Å, we find a reduction of the diffusion coefficient by a factor between 2 and 3 compared with bulk water. One possible origin of this effect is the temporary trapping of water within hydrogen-bonded water bridges between the GO sheets. The proposed mechanism should be taken into account in the development of, for instance, GO membranes for water remediation or applications in the field of selective transport in separation membranes.

No abstract

Among the carbon-based two-dimensional materials, graphene oxide (GO) has been attracting a growing interest due to its capability to be utilized in the field of water remediation. Therefore, an atomistic understanding of the transport properties of water in layered GO is pivotal for the development of novel GO membranes. Surprisingly, the very issue of the two-dimensional self-diffusion of water confined between two GO sheets appears to be controversial and simulations showing either a slow-down or no effect have been reported. In any case the formation of Hydrogen bonds, i.e. among the confined water and between water and the GO functional groups, was identified to control diffusion. However, results of molecular dynamics simulations heavily depend on the used forces. Density functional theory and empirical force fields are on opposite when it comes to accuracy and numerical costs. As a compromise in the present study we performed molecular dynamics simulations using a density functional theory-based tight method (xTB) to investigate the diffusion of water confined between GO sheets. Specifically, we considered six GO/water models, differing in the ordering of epoxide and hydroxyl groups as well as in the thickness of the water layer. For these models, having GO inter-layer distances between 8 and 12 \AA{} we find a reduction of the diffusion coefficient by a factor in between two and three as compared with bulk water. One possible origin of this effect is the temporary trapping of water within Hydrogen-bonded water bridges between the GO sheets. The proposed mechanism should be taken into account when developing, for instance, GO membranes for water remediation or applications in the field of selective transport in separation membranes.

Among the serious environmental problems that attracted much attention from the broader public is the high toxicity of dioxins. Considerable efforts have been made to develop techniques and materials that could help in their efficient removal from the environment. Due to its high specific surface area and generous active sites, outstanding structural and electronic properties antimonene is considered for a variety of potential applications in different fields such as energy storage, electrocatalysis, and biomedicine. The present study adds to this portfolio by suggesting antimonene as a promising candidate for dioxin capture. Using density functional theory (DFT) calculations we studied the adsorption of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) on the pristine antimonene and Ca-, Ti-, and Ni-doped antimonene. Three configurations of the adsorption of TCDD on antimonene were analyzed. The results obtained from calculating adsorption energies, charge transfer, charge density differences, and densities of states (DOS) give evidence that antimonene outperforms the other nanomaterials that have been previously suggested for dioxin capture application. Therefore, we propose these substrates (i.e., pristine and doped antimonene) as potential capture agents for removing such toxic organic pollutants.