Facile synthesis of melamine-based porous polymer networks and their application for removal of aqueous mercury ions

Based on a facile catalyst-free process using Schiff base chemistry, here, highly cross-linked porous aminal networks in high yields (up to 90%) were rapidly prepared via microwave irradiation. The polymer networks contained as high as 50 wt% of nitrogen (N), in situ doped with sulfur (S), with specific surface areas of up to 301 m2 g−1, and were also found to exhibit a solvent-based luminescence property. Adsorption kinetics and isotherm studies demonstrated that the Hg2+ removal by these polymers was extremely rapid (90% being attained within 5 min for a 400 mg L−1 Hg2+ solution) and highly efficient (up to 1172 mg g−1). Particularly these materials also exhibited an excellent selectivity towards Hg2+ over other interfering ions (Cd2+, Ni2+, Zn2+, Cu2+, Co2+, Ca2+, Mn2+ and Mg2+). Studies by FT-IR, Raman and XPS spectra showed that all the N-containing groups (triazine ring, primary amine, and secondary amine) as well as S-containing groups on the polymer matrix could be responsible for the Hg adsorption, through the mechanism of surface complexation.