High-flux water desalination with interfacial salt sieving effect in nanoporous carbon composite membranes

TL;DR

This study introduces nanoporous carbon composite membranes that achieve high-flux desalination with effective salt rejection through an interfacial salt sieving mechanism, outperforming traditional polymeric membranes in multiple processes.

Contribution

The paper presents a novel nanoporous carbon membrane with a unique salt rejection mechanism and significantly higher freshwater flux compared to existing membranes.

Findings

100% salt rejection across processes

3.5 to 20 times higher freshwater flux

Salt-free interfacial atomic layers

Abstract

Nanoporous carbon composite membranes, comprising a layer of porous carbon fiber structures with an average channel width of 30-60 nm grown on a porous ceramic substrate, are found to exhibit robust desalination effect with high freshwater flux. In three different membrane processes of vacuum membrane distillation, reverse osmosis and forward osmosis, the carbon composite membrane showed 100% salt rejection with 3.5 to 20 times higher freshwater flux compared to existing polymeric membranes. Thermal accounting experiments found that at least 80% of the freshwater pass through the carbon composite membrane with no phase change. Molecular dynamics simulations revealed a unique salt rejection mechanism. When seawater is interfaced with either vapor or the surface of carbon, one to three interfacial atomic layers contain no salt ions. Below the liquid entry pressure, the salt solution is stopped at the openings to the porous channels and forms a meniscus, while the surface layer of freshwater can feed the surface diffusion flux that is fast-transported on the surfaces of the carbon fibers, driven by the chemical potential gradient. As the surface-transported water does not involve a phase change, hence that component involves no energy expenditure in the form of latent heat.