Synthesis and characterization of zinc-organic frameworks with 1,4-benzenedicarboxylic acid and azobenzene-4,4'-dicarboxylic acid

The solvothermal reactions of 1,4-bezenedicarboxylic acid (H2BDC) or azobenzene-4,4'-dicarboxylic acid (H2ABD) with zinc ions/clusters lead to the formation of four crystalline materials. All of these compounds were characterized by x-ray diffraction, optical microscopy, thermo-gravimetric analysis and nitrogen adsorption. Block-shaped crystals (BZ1) with various shapes and sizes were obtained at H2BDC:Zn mole ratio of 1:1 and H2BDC concentration of 0.1 M. At more dilute H2BDC concentration of 0.01 M and H2BDC:Zn mole ratio of 1 : 4, the reaction product was cubic crystals (BZ2) with a size of 250 μm. In the H2ABD system, flat-plate-like crystals (AZ1) were obtained at H2ABD:Zn mole ratio of 1 : 1 and H2ABD concentration of 0.01 M. Meanwhile, thick-block-like crystals (AZ2) were formed at the same H2ABD:Zn mole ratio but at 0.004 M H2ABD. The Langmuir surface area (SLang) of the materials was remarkable, enhanced by diluting the reaction solution. For the compounds synthesized in N,N'-dimethylformamide (DMF), SLang increased from 304.6 m2 g−1 for BZ1 to 2631 m2 g−1 for BZ2 and from 475.8 m2 g−1 for AZ1 to 3428 m2 g−1 for AZ2. Meanwhile, BZ2 synthesized in N,N'-diethylformamide (BZ2/DEF) got the highest SLang of 4330 m2 g−1. Both AZ2 and BZ2 materials were stable up to 400 °C.