Modification of nano-sized zinc zeolitic 2-methylimidazolate frameworks (zif-8) by solvent assisted ligand exchange and post-sythetic modification to enhance functionality towards catalysis, gas storage and drug delivery

[摘要] English: Zeolitic Imidazolate Framework-8 nanoparticles (nZIF-8) were successfully synthesized duringisothermal benchtop reactions, with different reagent concentrations in methanol. At an optimalconcentration, an average particle size of 22 nm was achieved for nZIF-81500 with an externalsurface area of 320 m2 g-1. Addition of triethylamine (TEA) in different molar ratios duringsynthesis, increased the yield of nZIF-8 from 40 to 85 %. Particle sizes decreased to 16 nm athigh TEA concentrations.Time resolved Solvent Assisted Ligand Exchange (SALE) of nZIF-8 with2-mercaptobenzimidazole, 2-aminobenzimidazole, 2-phenylimidazole and presynthetic modifiedbenzimidazole-thioesters, resulted in a ~13% exchange of the 2-methylimidazolate linkers ofnZIF-8. Following an identical SALE procedure, the exchange with imidazole and2-nitroimidazole, both without any attached benzene rings, reached a maximum exchange of 86and 66 %, resulting in new zni and frl topologies respectively. All the SALE processes gaveparticle sizes below 100 nm, except when 2-mercaptobenzimidazole and 2-nitroimidazole wereused. All nZIF-8 materials with SOD topologies remained microporous throughout the SALEprocess. Four different post synthetic modification (PSM) techniques were developed for aminoandester functionalised nZIF-8 particles. PSM of lithiated SALEM-2 with (PPh3)2PdCl2, gave a1.2 wt % Pd content, with an improved BET surface area (100 m2 g-1 larger). An iron content of8.3 wt % was achieved via amidation of amino functionalised nZIF-8 with ferrocenecarboxylicacid. Sebacoyl chloride and polyacrylic acid were successfully anchored to the surface of aminofunctionalised nZIF-8.The SALE products of nZIF-8 were screened for catalysis of the Knoevenagel condensationbetween ferrocenecarboxaldehyde and malononitrile. Amine-containing nZIF-8 gave a lower TOFthan nZIF-81500, suggesting a different catalytic pathway via an imine route. CO2 adsorption ofnZIF-8 was doubled to 77 cm3g-1, after SALE with imidazole derivatives containing NO2 andSH electron withdrawing groups. H2 uptake of all nZIF-8 derivatives was on par with theChahine rule, with SALEM-216h-Pd adsorbing 3.07 wt % of H2 at 77 K.

[发布机构] University of the Free State