Preparation of polypyrrole-incorporated mesoporous carbon-based composites for confinement of Eu(iii) within mesopores

Abstract

Mesoporous polymer-carbon composite (CMPEI/CMK-3) materials were successfully prepared by incorporation of a chelating polymer, carboxymethylated polyethyleneimine (CMPEI), into a mesoporous carbon (CMK-3) and for immobilization of Eu(III) ions, commonly used surrogates for radioactive Am(III) ions. After Eu(III) ions were loaded onto the CMPEI/CMK-3 composite, they were subsequently confined by incorporation of polypyrrole (ppy) into the mesopores of the composites. Ppy was prepared as soluble short-chain polymers using NO⁺ ions as oxidizing agents in a mildly acidic solution. These polymer chains were easily adsorbed on the walls of Eu-CMPEI/CMK-3 composites, efficiently immobilizing the Eu(III) ions. The use of a metal-free oxidizing agent, NO⁺, in mildly acidic conditions (pH 6) ensured the minimal loss of Eu(III) ions from the composites during polymerization. The resulting ppy/Eu-CMPEI/CMK-3 composites were characterized by electron microscopy, X-ray diffraction and N₂ sorption analysis. The results from these characterizations commonly supported the conclusion that ppy was incorporated into the mesopores of the composites, altering the mesoporous features and reducing the pore volumes of the CMK-3 supports. Eu(III)-leaching tests showed that the presence of ppy layers in the composites could significantly improve the retention of Eu(III) ions. This study demonstrated that chelating polymer-based composites can be used for removal and long-term confinement of radioactive actinide species by properly optimizing polymer incorporation processes.