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.

No abstract

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.

No abstract

The hydrogen evolution reaction (HER) plays a crucial role in clean energy production in hydrogen fuel cells. In order to utilise this process effectively, new catalysts are required that are cheap, non-toxic and efficient. In this context, 2D materials such as transition metal dichalcogenides (e.g. MoS 2 ) should offer the desired properties but have so far proven difficult to manufacture into useful devices. In this work, liquid|liquid interfaces are used for the assembly and testing of the catalytic efficiency of a number of 2D materials and their composites, exploiting the ability of the materials to self-assemble at these interfaces and be tested electrochemically in situ. MoS 2 , WS 2 , and graphene were developed for hydrogen evolution at the water|1,2-dichlorobenzene (DCB) interface. The exfoliation process was carried out in DCB and resulted in multi-layer MoS 2 , few layer WS 2 and graphene: when assembled at the water|DCB interface, these materials acted as efficient HER catalysts. HER was investigated using voltammetry, with bulk reaction kinetics monitored by in-situ UVvisible spectroscopy at a constant potential. MoS 2 exhibited the highest performance of the catalysts examined, with an average rate constant of 0.0132 ± 0.063 min -1 at an applied Galvani potential of +0.5 V. This is ascribed to the sulphur edge sites of MoS 2 , which are known to be active for hydrogen evolution predominantly.

Top-down synthesized B-and B,N-doped carbons (e.g., graphenes) have been previously reported as catalysts for the oxygen reduction reaction (ORR), with activity superior to Pt electrocatalysts also previously reported in some cases. Such doped carbon materials are, however, chemically complex and contain multiple sites, which complicate the development of structure−activity relationships and subsequent catalyst optimization. Herein, a number of well-defined B-and B,N-doped polycyclic aromatic hydrocarbons (PAHs), prepared by a "bottom-up" approach, are shown to be active catalysts for the ORR in alkaline solution when deposited on carbon electrodes in contrast to the all carbon-based PAH perylene. Six dissimilar B-doped PAHs have been tested on three working electrodes, and the merits of each electrode for assessing ORR catalytic activity have been determined. A boron-doped diamond electrode was found to have the lowest background activity (relative to glassy carbon and highly ordered pyrolytic graphite ) and thus proved optimal for determining the ORR catalytic activity of the PAHs. Of the six B-doped PAHs studied, two PAHs with the highest lowest unoccupied molecular orbital (LUMO) energy were found to be inactive, whereas the other PAHs with lower LUMO energies were found to be active catalysts for the ORR. Doping of two heteroatoms, doubly B-doped and a B,N-codoped PAH containing separate (nonbonded) B and N atoms, was found to lead to the most active ORR catalysts from this set. This suggests that two proximal (separated only by one or two carbons) electrophilic sites improve the ORR activity of doped PAHs. This is the first study, to the best of our knowledge, which uses well-defined doped PAHs as models to identify potential ORR electrocatalytic moieties present in doped carbons; this approach thus enables definitive structure−activity relationships to be developed in this important area.

Laminar MoS 2 membranes show outstanding potential for practical applications in energy conversion/storage, sensing, and as nanofluidic devices. For water purification technologies, MoS 2 membranes can form abundant nanocapillaries from layered stacks of exfoliated MoS 2 nanosheets. These MoS 2 membranes have previously demonstrated excellent ionic rejection with high water permeation rates, as well as long-term stability with no significant swelling when exposed to aqueous or organic solvents. Chemical modification of these MoS 2 membranes has been shown to improve their ionic rejection properties, however the mechanism behind this improvement is not well understood. To elucidate this mechanism we report the potential dependant ion transport through functionalized MoS 2 membranes. The ionic permeability of the MoS 2 membrane was transformed by chemical functionalization with a simple naphthalene sulfonate dye (sunset yellow) and found to decrease by over a factor of ~10 compared to the pristine MoS 2 membranes and those reported for graphene oxide and Ti 3 C 2 T x (MXene) membranes. The effect of pH, solute concentration, and ionic size/charge on the ionic selectivity of the functionalized MoS 2 membranes is also reported.The potential dependant study of these dye functionalized MoS 2 membranes for ionic sieving with charge selectivity should enable future applications in electro-dialysis and ion exchange for water treatment technologies.

Black phosphorus is a two-dimensional material that has potential applications in energy storage, high frequency electronics and sensing, yet it suffers from instability in oxygenated and/or aqueous systems. Here we present the use of a polymeric stabilizer which prevents the degradation of nearly 68% of the material in aqueous media over the course of ca. 1 month.