Green synthesis of a microporous, partially fluorinated ZnII paddlewheel metal–organic framework: H2/CO2 adsorption behavior and solid-state conversion to a ZnO–C Nanocomposite

Abstract

A microporous, partially fluorinated metal–organic framework consisting of ZnII dimeric paddlewheel units, formulated as [Zn(hfipbba)(4bpdb)0.5]·H2O (1) [hfipbba = 4,4- (hexaflouroisopropylene)bis(benzoic acid); 4bpdb = 1,4- bis(4-pyridyl)-2,3-diaza-1,3-butadiene], was synthesized by room-temperature self-assembly and characterized structurally by single-crystal XRD. Compound 1 adopts a 3D microporous framework structure constituted by six-connected ZnII dimeric paddlewheel nodes with {44.610.8}-net topology. Further, rapid synthesis of phase-pure 1 by green synthetic approaches such as mechanochemical and sonochemical routes was achieved. The 3D framework of 1 houses 1D helical channels with narrow pore dimensions of about 3.114.17 Å and exhibits interesting gas-uptake (H2/CO2) properties. The isosteric heats of adsorption Qst for H2 and CO2 were estimated to be 8.8 and 36.4 kJmol–1, respectively. Interestingly, solid-state conversion of 1 to phase-pure hexagonal ZnO nanocrystals of 6.1 0.63 nm in size, embedded in carbonaceous layers to form a ZnO–C nanocomposite (NC), occurred on heating of 1 to 600 °C under vacuum for 2 h. The ZnO–C NC was characterized by XRD, UV/Vis, energy-dispersive X-ray, and TEM analyses. The as-synthesized ZnO–C NC exhibits good photocatalytic activity for the degradation of methylene blue.