Laminar membranes of two-dimensional materials are excellent candidates for applications in water filtration due to the formation of nanocapillaries between individual crystals that can exhibit a molecular and ionic sieving effect, while allowing high water flux. This approach has been exemplified previously with graphene oxide, however these membranes suffer from swelling when exposed to liquid water, leading to low salt rejection and reducing their applicability for desalination applications. Here, we demonstrate that by producing thin (∼5 μm) laminar membranes of exfoliated molybdenum disulfide (MoS) in a straightforward and scalable process, followed by a simple chemical functionalization step, we can efficiently reject ∼99% of the ions commonly found in seawater, while maintaining water fluxes significantly higher (∼5 times) than those reported for graphene oxide membranes. These functionalized MoS membranes exhibit excellent long-term stability with no swelling and consequent decrease in ion rejection, when immersed in water for periods exceeding 6 months. Similar stability is observed when exposed to organic solvents, indicating that they are ideal for a variety of technologically important filtration applications.
Carbon materials
are ubiquitous in energy storage; however, many
of the fundamental electrochemical properties of carbons are still
not fully understood. In this work, we studied the capacitance of
highly ordered pyrolytic graphite (HOPG), with the aim of investigating
specific ion effects seen in the capacitance of the basal plane and
edge-oriented planes of the material. A series of alkali metal cations,
from Li+, Na+, K+, Rb+, and Cs+ with chloride as the counterion, were used at
a fixed electrolyte concentration. The basal plane capacitance at
a fixed potential relative to the potential of zero charge was found
to increase from 4.72 to 9.39 μF cm–2 proceeding
down Group 1. In contrast, the edge-orientated samples display capacitance
ca. 100 times higher than those of the basal plane, attributed to
pseudocapacitance processes associated with the presence of oxygen
groups and largely independent of cation identity. This work improves
understanding of capacitive properties of carbonaceous materials,
leading to their continued development for use in energy storage.
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