Facile synthesis of hydroxyl- and amine-riched porous polymer for indium recovery in water

This manuscript presents the first report on employing porous polymers as adsorbents for indium recovery. Specifically, hydroxyl- and amine-riched poly (melamine-formic acid) network (PAN-FA) is successfully synthesized from melamine and formic acid via a facile “one-step” catalyst-free polymerization process, which exhibits hierarchical pores ranging from 0.52 nm to 5.95 nm and large BET specific surface area of 705 m 2  g −1 . The resultant PAN-FA contains large amount of secondary amine and hydroxyl groups capable of chelating with In 3+ ions. Moreover, the highly hydrophilic polymer skeleton and the existence of suitably large mesopores are favorable for the transport of In 3+ ions through the pore channels in water medium. As a result, PAN-FA shows the adsorption capacity of In 3+ ions (206.3 mg g −1 ) in water, surpassing previously reported indium-adsorbents. More importantly, after five cycling experiments, the porous structure of PAN-FA remains stable and the adsorption capacity is nearly unchanged. The combination of cheap raw materials, simple synthesis process, high adsorption capacity for In 3+ ions and pronounced recycling reusability endows PAN-FA with a promising candidate adsorbent for practical indium-recovery application.