Molecular dynamics modeling and simulation of water desalination through a double-walled carbon nanotube with moiré pattern

Freshwater scarcity has emerged as a major challenge of our time. Under this context, the importance of an efficient and energy-saving water desalination method is highlighted. In recent years, carbon nanotube (CNT) membrane characterizing with high permeability has attracted much attention in research, and it is regarded as a promising alternative to the conventional reverse osmosis technology. This work aims at numerically investigating the water desalination ability of a novel type of CNT membrane structure, namely the double-walled carbon nanotube (DWCNT) with Moiré pattern. After establishing the physical CNT models and running the molecular dynamics (MD) simulation of the water desalination system, it is found that both the single-walled carbon nanotube (SWCNT) and DWCNT can desalinate the seawater successfully while the water permeability of DWCNT is at least 18.9% higher than that of SWCNT within the same time. As far as the Moiŕe pattern adopted in this study is concerned, the water permeability of DWCNT without Moiŕe pattern is 18.6% higher than that with Moiré pattern.

Se concentration dependent superstructure transformations of CuSe monolayer on Cu(111) substrate

As one of the most distinctive members of the monolayer transition metal monochalcogenides (TMM) family, the CuSe monolayer with a honeycomb structure has drawn much attention in the past few years. Depending on the Se concentration, the CuSe monolayer has two distinct superstructures on a Cu(111) substrate, a one dimensional (1D) moiré pattern, and two dimensional (2D) periodic nanopores. Here, we devise a strategy for simultaneous fabrication of the two superstructures of the CuSe monolayer on a Cu(111) substrate via artificially creating a density gradient of the Se concentration by an off-centered deposition method. At the boundary of the two superstructures, an intermediate state of the CuSe monolayer with a 2D hexagonal moiré pattern connected by six twisted petal-like stripes is observed. High-resolution scanning tunnelling microscopy characterizations of three distinct CuSe monolayer superstructures demonstrate that the Se density can effectively modulate the stress in the CuSe monolayer formed by the lattice mismatch, driving the superstructure transformation from 1D moiré pattern through 2D intermediate states to 2D periodic nanopores. In addition, scanning tunnelling spectroscopy measurements show that the intermediate state features a semiconducting behaviour with a band gap of ~ 2.0 eV. Our findings open up a new route for superstructure transformation control of 2D materials.