A Quasi-Metal-Organic Framework Based on Cobalt for Improved Catalytic Conversion of Aquatic Pollutant 4-Nitrophenol

To generate purposely defects that can increase the catalytic activity, cobalt-based metal-organic framework (MOF) TMU-10 has been subjected to thermal treatment under an air atmosphere at temperatures between 100 and 700 degrees C. This process causes partial ligand removal, generating structural defects and additional hierarchical porosity in a convenient way. The resulting materials, denoted as quasi-MOFs, were subsequently employed as catalysts for the room-temperature borohydride reduction of 4-nitrophenol (4-NP). The quasi TMU-10 framework obtained at 300 degrees C (QT-300) exhibits excellent catalytic performance with an apparent rate constant, activity factor, and half-life time of 2.8 X 10(-2) s(-1), 282 g(-1), and 24.8 s, respectively, much better values than those of parent TMU-10. Coexistence of micro and mesopores, coordinatively unsaturated cobalt nodes, tetrahedral Co(II) ions, and Co(III) in QT-300 are responsible for this enhanced activity. Kinetic studies in the range of 25-40 degrees C varying the 4-NP and BH4- concentrations agree with the Langmuir-Hinshelwood model in which both reactants are adsorbed on the catalyst surface. Reduction of 4-NP by the surface-hydrogen species is the rate-determining step.