We report a class of pK a -directed, precise incorporation of phosphonate ligands into a zirconium-based metal−organic framework (Zr-MOF), MOF-808, via ligand exchange. By replacing of formate ligands with methylphosphonic acid (MPA), ethanephosphonic acid (EPA), and vinylphosphonic acid (VPA), whose pK a values are slightly higher than that of the benzenetricarboxylic acid (BTC) linker in MOF-808, daughter MOFs can be synthesized without controlling the stoichiometric amounts of added MPA. The methylphosphonate MOFs (808-MPAs) demonstrate high porosities, with only small changes in the pore diameter and specific surface area when compared with the parent MOF-808. PXRD patterns and structure refinements indicate the expansion of the lattice for all MOFs after decorating with methylphosphonate ligands. The XPS spectra reveal a charge redistribution of the Zr 6 node after ligand exchange. FTIR and 31 P MAS NMR spectra, combined with DFT calculation, suggest that the methylphosphonate ligand is connected to the Zr 6 node as CH 3 P(O)(OZr)(OH) species with an accessible acidic P−OH group. Besides, 808-MPAs demonstrate excellent chemical stability in concentrated HCl, concentrated HNO 3 , hot water, and 0.2 mol/L trifluoroacetic acid solutions. Impressively, 808-MPAs show ultrafast adsorption performance for uranyl ions using the ion-exchange property of P−OH sites in their cavity environment, with an equilibrium time of 10 min, much quicker than the previous adsorbents. The present study demonstrates a series of important proof-of-concept examples of the pK a -directed Zr-MOFs with tunable phosphonate-terminated ligands, which can extend to other phosphonate-functionalized Zr-based framework platforms in the near future.

The photochemistry and sodium storage process have been generally considered as two separated approaches without strong connection. Here, ultraviolet (UV) irradiation was applied to sodium-ion batteries to improve the electrochemical performance of MoS2-based composites. C@MoS2@CN nanospheres consist of double protective structures, including inner hollow carbon spheres with a thin wall (C) and outer N-doping carbon nanosheets (CNs) derived from polydopamine. The special nanostructure possesses the virtues such as wide-interlayer spacing, flexible feature with great structure integrity, and rich active sites, which endow the fast electron transfer and shorten the ion diffusion pathways. Under the excitation of UV-light, intense electrons and holes are accumulated within MoS2-based composites. The excited electrons can promote the preinsertion of Na+. More importantly, dense electrons promote the electrolyte to decompose and hence form a stable solid electrolyte interphase in advance. After UV-light irradiation treatment in the electrolyte, the initial Coulombic efficiency of C@MoS2@CN electrodes increased from 48.2 to 79.6%, and benefiting from the fine nanostructure, the C@MoS2@CN electrode with UV irradiation treatment delivered a great rate performance 116  mAh g–1 in 20 s and  super cycling stability that 87.6% capacity was retained after 500 cycles at 500 mA g–1. When employed as anode for sodium-ion hybrid capacitors, it delivered a maximum power density of 6.84 kW kg–1 (with 114.07  Wh kg−1 energy density) and a maximum energy density of 244.15 Wh g–1 (with 152.59 W kg–1 power density). This work sheds new viewpoints into the applications of photochemistry in the development of energy storage devices.

No abstract