Electrochemical redox induced rapid uptake/release of Pb(II) ions with high selectivity using a novel porous electroactive HZSM-5@PANI/PSS composite film

Abstract

A porous electroactive composite based film made of core@shell nanospheres is uniformly fabricated on the conductive substrate by artfully applying the alternative assembly of the polyaniline/polystyrene (PANI/PSS) and the high-crystalline protonated Zeolite Socony Mobil-5 (HZSM-5) nanospheres via a potential pulse method. The isolated HZSM-5 nanospheres are interconnected and linked up by the chains of PANI/PSS that act as bridges for electron transportation. In this composite film, the HZSM-5 nanospheres provide the protons to further improve the electroactivity of PANI based on the unique proton “round-trip” transfer effect during the electrochemical redox process. The obtained HZSM-5@PANI/PSS composite based film shows fast electrochemical uptake/release ability for the removal of Pb2+ ions from the aqueous solution because of the strong driving force resulting from the electric field, and the adsorption equilibrium time is less than 60 min. When the initial concentration of Pb2+ ions is 100 mg L−1, the ion adsorption quantity reaches 240.6 mg g−1 and retains 97.1% of its initial value after 5 uptake/release cycles. Especially, the selectivity factors of the HZSM-5@PANI/PSS film for Pb2+/Ni2+, Pb2+/Co2+, Pb2+/Cd2+, and Pb2+/Zn2+ reach up to 21.97, 26.19, 24.61, and 39.29, respectively. Such high selectivities for Pb2+ ions are realized by artfully using the significantly lower Gibbs energy of dehydration of Pb2+ ions than that of other listed metal ions, which makes the Pb2+ ions easily adsorbed into the composite film based on the confinement effect of the HZSM-5. Furthermore, the consumed energy for dehydration is supplied by the electric field, resulting in the decrease of the ions transport resistance and the increase of the adsorption capacity of the composite film.