Porous polyimide framework: A novel versatile adsorbent for highly efficient removals of azo dye and antibiotic

Porous organic frameworks (POFs) have aroused considerable interest owe to its high surface areas, superior chemical and thermal stabilities, good mechanical and abundant porosity. In this study, a porous polyimide (PI) with abundant amine groups was synthesized by the reaction of melamine and pyromellitic dianhydride. And its versatile adsorption performance towards organic pollutants, including azo dye (methyl orange (MO)) and antibiotic (tetracycline (TC)) was investigated. The PI was characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), thermogravimetric analysis (TGA), and N-2 adsorption-desorption techniques. The obtained product possessed high thermal stability and exhibited a high surface area (635.5 m(2).g(-1)) and a large pore volume (0.98 cm(3). g(-1)). The pH effect study showed that MO adsorption was highly pH-dependent with an optimal pH 3, while the TC adsorption was effective in the pH range of 6-8. Batch adsorption experiments were carried out to study adsorption kinetics and adsorption thermodynamics. The result showed that the kinetics experimental data were fitted to pseudo-second-order kinetics model better, and adsorption isotherm could be described by the Langmuir isotherm model perfectly. The maximum adsorption capacities calculated from the Langmuir isotherm model are 609.8 and 155.8 mg/g at 318 K. for MO and TC, respectively. The thermodynamic study showed that the adsorptions of TC and MO on PI were spontaneous (Delta G < 0) and endothermic (Delta H > 0). Findings in this study demonstrated that the porous PI should be a powerful adsorbent in organic pollutants removal. (C) 2016 Elsevier B.V. All rights reserved.