The reactions were typically conducted by heating a pelletized mixture of Ti 2PTe 2 and M in vacuum at temperatures up to 400 ☌ (see the ‘Methods’ section for a detailed synthesis procedure).
We tested a series of alkali, alkali earth, transition and post-transition metals ( M) for their intercalation properties into Ti 2PTe 2. Metal intercalation and structural characterization The absence of metal species between the double Te layers suggests relatively weak interlayer interactions and thus intercalation chemistry.
It is isostructural with 3R-type Ta 2CS 2 (ref. The individual slabs are stacked such that a rhombohedral structure is formed. The structure of T 2PTe 2 ( T=Ti, Zr) is built up of slabs of hexagonal closed-packed triple Te–P–Te layers with T atom being octahedrally coordinated by three Te and three P atoms (see Fig. Prior intercalation studies are largely confined to binary tellurides such as TiTe 2, ZrTe 2 and IrTe 2, with a primary interest in superconductivity and ferromagnetism 28, 29. In this study, we utilize the smaller electronegativity of tellurium to provide a softer Lewis base, compared with O, S and Se 27, within the layered tellurides, Ti 2PTe 2 and Zr 2PTe 2, which we expect will promote a higher degree of covalency to selectively bind heavy metals. In both systems, the high selectivity is ascribed to the favourable interactions between the soft Lewis base S 2– ions of the host layer and the soft Lewis acid of the metal ions as a guest. 26), via an aqueous solutions with excess lighter alkali metal ions and protons. Recently, Kanatzidis and colleagues have demonstrated that several layered sulfides exhibit highly selective ion-exchange properties for Sr, Hg, Pd and Cd within K 2 xMn xSn 3– xS 6 (0.5< x<0.95 refs 24, 25) and Cs within 2Ga 2Sb 2S 7 Traditional absorbents and ion-exchangers like activated carbon, clays and zeolites also suffer from this problem 21, 22, 23. However, the poor selectivity in these materials hinders the preferential sorption of heavy metals, which is of environmental significance in the remediation of important toxic heavy metals pollutants, such as Cd, Pb and Hg 20. For instance, TaS 2 is capable of intercalating alkali metals, alkali earth metals and nearly all 3 d transition metals as well as organic amines 13, 14, 15, 16, 17, 18, 19. Rather weak interlayer (vdW) interactions and a flexible interlayer spacing allows for incorporation of not only the lowest charged small alkali metal cations, but also many other heavier metals in the periodic table. The rich intercalation chemistry that has been discovered for layered materials with van der Waals (vdW) interactions, which includes V 2O 5, MNCl ( M=Ti, Zr), MX 2 ( M=Ti, Zr, Ta and so on X=S, Se), MP X 3 ( M=Mg, Fe, Ni and so on X=S, Se), MoS 2 and MO X ( M=Ti, V, Fe and so on X=Cl, Br) 8, 9, 10, 11, 12, yields various chemical and physical properties. However, two key areas of particular note are those materials serving as reservoirs to store and release alkali metal ions, for example, Li + for high performance for energy storage devices 4 and the tuning of exotic superconductivity in Na xCoO 2♱.3H 2O, Li x(THF) yHfNCl (THF, tetrahydrofuran) and Cu xBi 2Se 3 upon intercalation 5, 6, 7. The structural diversity of these solids gives rise to a vast array of applications too extensive to summaries. Intercalation compounds allow incorporation or exchange of foreign atoms or molecules into the voids of various topologies in the host lattices such as cages (zeolites and so on) 1, channels (h-WO 3 and so on) 2 and two-dimensional (2D) spaces (graphite and so on) 3 and represent an important frontier in solid state chemistry. The current method of controlling selectivity provides opportunities in the search for new materials for various applications that used to be possible only in a liquid. Interestingly, the intercalation reactions proceed in solid state and at surprisingly low temperatures (for example, 80 ☌ for cadmium in Ti 2PTe 2). Here we show that the layered telluride T 2PTe 2 ( T=Ti, Zr) displays exclusive insertion of transition metals (for example, Cd, Zn) as opposed to alkali cations, with tetrahedral coordination preference to tellurium. An evolving area of materials chemistry, however, is to capture metals selectively, which is of technological and environmental significance but rather unexplored.
Light alkali metals are generally most easily intercalated due to their light mass, high charge/volume ratio and in many cases strong reducing properties.
Layered materials embrace rich intercalation reactions to accommodate high concentrations of foreign species within their structures, and find many applications spanning from energy storage, ion exchange to secondary batteries.