Influence of carbon nanocone structure on ultra-efficient water flow

TL;DR

This study tackles the challenge of achieving ultra-efficient, selective water transport through nanoscale channels by examining carbon nanocones (CNCs) as biomimetic, hourglass-inspired membranes. Using nonequilibrium molecular dynamics with the $TIP4P/2005$ water model, the authors quantify how CNC apex angle and opening diameter, hydrogen-bond dynamics, and applied pressure gradients influence flow through a CNC-based membrane. The key finding is that CNCs can dramatically enhance water flux relative to nanotubes of similar size, with flow magnitudes increasing with opening size and apex angle; hydrogen-bond disruption along the cone also modulates transport, linking geometry to performance. The work demonstrates the potential of CNC membranes for desalination and selective filtration, highlighting the interplay between transport speed, selectivity, and structural control as a route to next-generation nanofluidic devices.

Abstract

In this study, using nonequilibrium molecular dynamics simulation, the water flow in carbon nanocones is studied using the TIP4P/2005 rigid water model. The results demonstrate a nonuniform dependence of the flow on the cone apex angle and the diameter of the opening where the flow is established, leading to a significant increase in the flow in some cases. The effects of cone diameter and pressure gradient are investigated to explain flow behavior with different system structures. We observed that some cones can optimize the water flow precisely. Nanocones with a larger opening facilitate the sliding of water, significantly increasing the flow, thus being promising membranes for technological use in water impurity separation processes. Nanocones with narrower opening angles limited water mobility due to excessive confinement. This phenomenon is linked to the ability of water to form a larger hydrogen-bond network in typical systems with diameters of this size, obtaining a single-layer water structure. Nanocones act as selective nanofilters capable of allowing water molecules to pass through while blocking salts and impurities. The conical shape of their structures creates a directed flow that improves separation efficiency. Membranes based on carbon nanocones are becoming promising for clean, smart, and efficient technologies. The combination of transport speed, selectivity, and structural control put them ahead of other nanostructures for various purposes.

Figures (8)

• Figure 1: Snapshot of the carbon nanocones used in the simulations, with the following opening angles (a) 19.2$^{\circ}$, (b) 38.9$^{\circ}$, (c) 60$^{\circ}$, (d) 84.6$^{\circ}$, (e) 112.9$^{\circ}$ e (f) schematic showing of the parameters of the nanocone dimensions of interest.
• Figure 2: The constructed system used in this work. A snapshot of the dual reservoir system shows the graphene pistons and the carbon nanocone membrane in the center. Graphene pistons 1 and 2 apply pressure P$_{1}$ and P$_{2}$ to the fluid. The blue arrows indicate the direction in which the pistons apply force to the water reservoirs, R$_{1}$ and R$_{2}$. The water flow was created by applying a pressure to reservoir R$_{1}$ that is greater than the pressure applied to reservoir R$_{2}$. The water molecules appear as a red oxygen atom connected to two white hydrogen atoms, and the carbon molecules in shades of gray.
• Figure 3: Log of the flow rate as a function of the pressure gradient applied to the carbon nanocone CNC-19.2$^{\circ}$ and carbon nanotube ($7,7$).
• Figure 4: Flow rate as a function of the pressure gradient applied to the carbon nanocones.
• Figure 5: Density maps in the $xy$ direction for the carbon nanocones. Dark blue regions have a low probability of finding water molecules, while red regions have a high probability of finding water molecules.