A three-dimensional water-stable cationic metal-organic framework (MOF) pillared by a neutral ligand and with Ni(II) metal nodes has been synthesized employing a rational design approach. Owing to the ordered arrangement of the uncoordinated tetrahedral sulfate (SO4 (2-) ) ions in the channels, the compound has been employed for aqueous-phase ion-exchange applications. The compound exhibits rapid and colorimetric aqueous-phase capture of environmentally toxic oxoanions (with similar geometries) in a selective manner. This system is the first example of a MOF-based system which absorbs both dichromate (Cr2 O7 (2-) ) and permanganate (MnO4 (-) ) ions, with the latter acting as a model for the radioactive contaminant pertechnetate (TcO4 (-) ).
At hree-dimensional water-stable cationic metalorganic framework (MOF) pillared by an eutral ligand and with Ni II metal nodes has been synthesized employing arational design approach. Owing to the ordered arrangement of the uncoordinated tetrahedral sulfate (SO 4 2À )i ons in the channels,the compound has been employed for aqueous-phase ion-exchange applications.T he compound exhibits rapid and colorimetric aqueous-phase capture of environmentally toxic oxoanions (with similar geometries) in aselective manner.This system is the first example of aM OF-based system which absorbs both dichromate (Cr 2 O 7 2À )a nd permanganate (MnO 4 À )i ons,w ith the latter acting as am odel for the radioactive contaminant pertechnetate (TcO 4 À ).Water pollution has become ap ressing global concern and the sequestration of toxic contaminants present in water streams has attracted significant research attention. In particular,t he widespread growth of modern industry has meant that the segregation of heavy-metal contaminants from industrial effluents has become apertinent problem.[1] Several inorganic pollutants,present in the form of oxoanions,feature prominently in the list from the Environment Protection Agency (EPA) of priority pollutants.[2] Attempts have been made to capture and remove these species from water streams through the development of materials and/or methods for selective entrapment. In particular,m uch research has focused on the separation of Cr VI ions,g enerated, for example,f rom chromium plating,p igment synthesis,a nd leather tanning,because of the severe health hazards posed by its predominant ionic form.[3] Similarly,t he presence of pertechnetate (TcO 4 À )i ons in radioactive waste vitrification poses serious disposal issues because of the long half-life and facile mobility of the ions.[4] Although several techniques, such as ion exchange,a dsorption, and photocatalytic reduction, have been trialed for this purpose, [5] in general the preferred routes have applied ion-exchange pathways owing to cost, sensitivity,simplicity,and selectivity considerations. [6] Thel imitations of the currently employed ion exchangers, such as slow process kinetics and poor selectivity,actuates the development of newer materials or optimization of the performance of the currently studied adsorbents.Metal-organic frameworks (MOFs), built from organic linkers and metal ions,have evolved as an important class of porous materials. [7] Thefact that the pore size and surface of MOFs can be easily tuned renders these compounds suitable for selective sorption and separation applications.[8] As asubclass,cationic MOFs have attracted significant attention as anion receptors/separators because of the confinement of substitutable uncoordinated anionic species.[9] Generally,such frameworks are fabricated from neutral N-donor ligands wherein the residual charge-balancing ions reside in the void spaces.[10] Although porous cationic materials,i ncluding MOFs,h ave been explored for several applications as anion-exchange h...
In spite of the interest of a-MoS 3 based nanomaterials, the amorphous nature of the MoS 3 phase makes it challenging to control and understand its chemical reactivity. In particular, the type of the structural building unit such as Mo 3 triangular vs Mo chain is still debated, while the ambivalent interpretation of the nature of sulfur species (S 2− , S 2 2− ) and Mo−Mo bonds leads to ambiguous interpretations of spectroscopic data and reactivity. By density functional theory (DFT), we simulate the energetic, structural, and spectroscopic features of relevant zero-dimensional 0D-, 1D-, and 2D-MoS 3 triangular, chain-like polymorphs, including unprecedented ones (ring, wave, and helix) and revisit the interpretation of EXAFS, IR-RAMAN, and XPS experimental data. We analyze how Mo k S 3k clusters of a few k atoms may grow up to infinite (periodic replica) MoS 3 polymorphs. The evolution of the growth energy and the computed IR spectra within the density functional perturbation theory level suggest the coexistence of various polymorphs in the MoS 3 phase as a function of sizes. Molecular dynamics simulations reveal how the small triangular Mo k S 3k oligomers may transform into condensed MoS 3 patches resembling embryos of the 2D 1T′-MoS 2 phase. Finally, we discuss some plausible transformation pathways from one polymorph to another.
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