A rich-amine porous organic polymer: an efficient and recyclable adsorbent for removal of azo dye and chlorophenol

Abstract

A novel rich-amine porous organic polymer (RAPOP) was synthesized via the Schiff base reaction with melamine (MA) and terephthalaldehyde (TA) as the monomers. The structures and properties of the as-prepared polymer were then systematically characterized by Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and N₂ adsorption–desorption techniques. The results confirmed that the nanoparticles were constructed first and then assembled to form a porous structure with a high specific surface area of 368.05 m² g⁻¹ and a large pore volume of 0.651 cm³ g⁻¹ arising from highly cross-linked aminal networks. It's fascinating adsorption performances towards azo dyes (methyl orange (MO)) and chlorophenol (2,4-dichlorophenol (2,4-DCP)) have also been investigated. The results show that solution pH 3 was an optimal condition for MO while the adsorption of 2,4-DCP was effective at pH 7, and the RAPOP dosages were decided accurately at 5 mg for MO and 10 mg for 2,4-DCP. The adsorption kinetics indicated that the adsorption equilibrium times were about 40 seconds for 2,4-DCP and 240 minutes for MO, and both followed a pseudo-second-order model. The isotherm data shown that it agreed well with the Langmuir isotherm with maximum adsorption amounts of 454.545 mg g⁻¹ and 188.697 mg g⁻¹ for MO and 2,4-DCP at 298 K, respectively. The adsorptions of MO and 2,4-DCP on RAPOP were both spontaneous and endothermic. In addition, the RAPOP could retain its high efficiency after desorption and regeneration. This study demonstrates that the RAPOP is a promising adsorbent for the removal of pollutants from aqueous solutions.