Chemical functionalization of low-dimensional materials such as nanotubes, nanowires and graphene leads to profound changes in their properties and is essential for solubilizing them in common solvents. Covalent attachment of functional groups is generally achieved at defect sites, which facilitate electron transfer. Here, we describe a simple and general method for covalent functionalization of two-dimensional transition metal dichalcogenide nanosheets (MoS₂, WS₂ and MoSe₂), which does not rely on defect engineering. The functionalization reaction is instead facilitated by electron transfer between the electron-rich metallic 1T phase and an organohalide reactant, resulting in functional groups that are covalently attached to the chalcogen atoms of the transition metal dichalcogenide. The attachment of functional groups leads to dramatic changes in the optoelectronic properties of the material. For example, we show that it renders the metallic 1T phase semiconducting, and gives it strong and tunable photoluminescence and gate modulation in field-effect transistors.

Covalent functionalization of monolayered transition metal dichalcogenides by phase engineering

We created a unique sodium ion battery (NIB, SIB) cathode based on selenium in cellulose-derived carbon nanosheets (CCNs), termed Se-CCN. The elastically compliant two-dimensional CCN host incorporates a high mass loading of amorphous Se (53 wt%), which is primarily impregnated into 1 cm3 g−1 nanopores. The results in facile sodiation kinetics due to short solid-state diffusion distances and a large charge transfer area of the nanosheets were established. The architecture also leads to an intrinsic resistance to polyselenide shuttle and to disintegration/coarsening. As a Na half-cell, the Se-CCN cathode delivers a reversible capacity of 613 mA h g−1 with 88% retention over 500 cycles. The exceptional stability is achieved by using a standard electrolyte (1 M NaClO4 EC-DMC) without secondary additives or high salt concentrations. The rate capability is also superb, achieving 300 mA h g−1 at 10C. Compared to recent state-of-the-art literature, the Se-CCN is the most cyclically stable and offers the highest rate performance. As a Se–Na battery, the system achieves 992 W h kg−1 at 68 W kg−1 and 384 W h kg−1 at 10144 W kg−1 (by active mass in a cathode). We are the first to fabricate and test a Se-based full NIB, which is based on Se-CCN coupled to a Na intercalating pseudographitic carbon (PGC) anode. It is demonstrated that the PGC anode increases its structural order in addition to dilating as a result of Na intercalation at voltages below 0.2 V vs. Na/Na+. The {110} Na reflections are distinctly absent from the XRD patterns of PGC sodiated down to 0.001 V, indicating that the Na metal pore filling is not significant for pseudographitic carbons. The battery delivers highly promising Ragone chart characteristics, for example yielding 203 and 50 W h kg−1 at 70 and 14000 W kg−1 (via total material mass in the anode and cathode).

Exceptional energy and new insight with a sodium–selenium battery based on a carbon nanosheet cathode and a pseudographite anode

Triselenium dicyanide from malononitrile and selenium dioxide. One-pot synthesis of selenocyanates

A synthetic, spectroscopic, and theoretical study of Ex(CN)2 (E = S, Se; x = 1−3) is described. The X-ray structures of Se2(CN)2 and Se3(CN)2 have been determined. Se2(CN)2 crystallizes in a chiral space group with the CN groups approximately gauche.

E2(CN)2 (E = S, Se) and related compounds

13C NMR and FT-IR spectra of thiocyanogen, S2(CN)2, selenocyanogen, Se2(CN)2, and related compounds

138. The oxidation of potassium selenocyanate by iodine pentafluoride

440. Reaction of organomercury compounds with covalent selenocyanates

Triphenyl-lead selenocyanate has been prepared by the reaction of tetraphenyl-lead with selenium diselenocyanate, by the metathesis of triphenyl-lead chloride with potassium selenocyanate, and by cleavage of hexaphenyldiplumbane with selenium diselenocyanate. Tetramethyl- and tetraethyl-lead reacted similarly with selenium diselenocyanate to give trialkyl-lead selenocyanates, and under more forcing conditions tetraphenyl-lead yielded diphenyl-lead diselenocyanate. By contrast, cleavage of hexaphenyldistannane yielded triphenyltin isoselenocyanate which was also prepared by metathesis. The reaction between triphenylthallium and selenium diselenocyanate afforded diphenylthallium selenocyanate. The infrared spectra and structure of these compounds are briefly considered.

M. J. Sprague

Papers

138. The oxidation of potassium selenocyanate by iodine pentafluoride

440. Reaction of organomercury compounds with covalent selenocyanates

Selenocyanation reactions of organometallic compounds of lead, tin, and thallium