Azo-bridged porphyrin-based conjugated microporouspolymer: synthesis and gases storage properties

A novel conjugated microporous polymer (Azo-1) based on porphyrin block and azo (-NN-) bridge was successfully synthesized by potassium hydroxide assisted nitrogen-nitrogen coupling reaction. The new prepared materials Azo-1 was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA). Besides, the surface area of Azo-1 was measured by N2 sorption/desorption at 77 K. CO2 (273 and 298 K) and H2 (77 K and 87 K) physisorption properties at different temperatures were also studied to further look into the gases storage properties of Azo-1. FT-IR spectroscopy was useful for probing the structure of such kind of insoluble networks. The peak at 1 597 cm-1 in the FT-IR spectrum indicates that there are plenty of azo bonds in this material. The SEM image of Azo-1exhibits a typical amorphous morphology. Simultaneously, the enlarged TEM image of Azo-1 shows obvious porous structure. The thermal stability of Azo-1 was analyzed by TGA under nitrogen flow. This material shows its onset weight loss (about 5% weight loss) at 195, which suggests that this material possesses high thermal stability. The N2 sorption isotherms were measured at 77 K to characterize the porosity of this network. The specific BET surface area of Azo-1 was high up to 571 m2/g. The calculated pore size distribution based on non-local density functional theory (NL-DFT) indicates that Azo-1 has two very narrow pores at 1.6 and 4.0 nm. Besides, the CO2 uptake of Azo-1 under 273 K was up to 94.2 mg/g, and the H2 uptake under 77 K was up to 8.6 mg/g. Based on the CO2 and H2 sorption/desorption isotherms, the isosteric heat for adsorption of CO2 and H2 was calculated as high as 37 and 7 kJ/mol, respectively.