Enhanced sorption of Mn2+ ions from aqueous medium by inserting protoporphyrin as a pendant group in poly(vinylpyridine) network

The main goal of the present work was to evaluate the effect of protoporphyrin (PP) (as pendant group) incorporated into a poly(vinylpyridine) [poly(VPY)] polymer network on the sorption of Mn2+ ions from an aqueous medium. The sorbent materials – poly(PP-co-VPY) and poly(VPY) – were characterized by SEM, FTIR, elemental analysis and nitrogen adsorption–desorption measurements (BET – Barrett–Joyner–Halenda and BJH – Brunauer–Emmett–Teller). It was observed that the pseudo-second-order kinetic model fitted the experimental data very well (R2 = 0.9967), confirming that the Mn2+ sorption onto poly(PP-co-VPY) took place via chemical reactions (chemisorption). To describe the equilibrium between the Mn2+ ions and sorbents and estimate the maximum sorption capacity, different models, including Langmuir, Freundlich, Dubinin–Radushkevich and dual-site non-linear Langmuir–Freundlich equations, were applied to the experimental data. The dual-site Langmuir–Freundlich model provided the best fit for poly(PP-co-VPY) and poly(VPY), yielding the maximum sorption capacity of 5.0 and 1.79 mg g−1, respectively. These findings suggest the presence of homogeneous and heterogeneous binding sites able to sorb Mn2+ ions. Binary solutions of Mn2+/Zn2+, Mn2+/Pb2+ and Mn2+/Fe3+ were submitted to competitive sorption in the polymers. The results obtained for these systems demonstrated 4.75, 18.24 and 388-fold increases in the rate of the Mn2+ sorption onto poly(PP-co-VPY), when compared with poly(VPY). The protoporphyrin incorporation into poly(VPY) network appears to be an interesting approach to polymer synthesis by the homogeneous solution method focused on the preparation of solid-phase extraction columns.

• A new copolymer – poly(protoporphyrin-co-vinylpyridine) was prepared. • The copolymer presents high surface area and pore volume in comparison to poly(vinylpyridine). • The life time of adsorbent was very high. • The pseudo-second-order kinetic model fitted the experimental data very well (R2 = 0.9967). • Maximum sorption capacity was found to be 5.0 mg g−1.