Synthesis and characterization of a new multifunctional aliphatic poly(amic acid): An efficient polymeric adsorbent for removing the heavy metal ions

Abstract

The heavy-metal ions in wastewater have attracted intense attention due to environmental issues, including their toxicity, bioaccumulation tendency, and persistency in nature. Despite other strategies for heavy metal removal from wastewater, adsorption is one of the most promising methods, owing to its simplicity and efficiency. To conserve the carboxyl and amine functional groups and prevent amidation reaction, a new aliphatic tertiary poly(amic acid) with linear and cyclic spacers was synthesized via the catalyst-free process. The ring opening of ethylenediaminetetraacetic acid dianhydride (EDTADA) by piperazine, a bifunctional cyclic secondary diamine, was conducted in a polar solvent (DMF) in a nitrogen atmosphere for 3 h. The characterization was conducted by FTIR and NMR, and their morphology and elemental composition were investigated by field emission scanning electron microscopy and energy dispersive X-ray (FESEM-EDX). As-synthesized aliphatic tertiary poly(amic acid) could be separated as a white powder with an O/N ratio of 0.93 ± 0.03 and morphology of woven fiber. The white powder showed an average molecular weight (M̅w) of ∼12,000 and a polydispersity index (PDI) of 1.52 ± 0.05. In addition, the poly(amic acid) TGA/DTA analysis showed a high thermal stability with stepwise degradation with the onset of 346 °C. The poly(amic acid) DSC profile displayed a high glass transition at 124 °C. The Brunauer–Emmett–Teller (BET) surface area and pore volume were determined to be 146.05 m2/g and 0.78 cm3/g. The poly(amic acid) contains the mesopores and macropores based on its pore size distribution curve. Regarding an acidic pH and abundance of functional groups, as-prepared tertiary poly(amic acid) was employed as a heterogeneous adsorbent of different types of heavy-metal ions, including Ag (I), Cr (III), and Cu (II). A removal efficiency > 90 % after 10 min for three heavy metal ions demonstrates a strong chelating capacity of as-prepared tertiary poly(amic acid). An adsorption capacity of > 50 mg per gram of poly(amice acid) was recorded for three heavy-metal ions with a pH of 3 or higher than 3. Poly(amic acid) exhibited good recyclability. This work exhibited the applicability of novel poly(amic acid) as an efficient adsorbent for the heavy metal ions removal from wastewater.