Synthesis and performance evaluation of a novel nitrogen-rich cross-linked polyamine for improved mercury uptake from water

In this study, a simple novel nitrogen-rich polyamine adsorbent was synthesized by Mannich polymerisation with 1,8-diaminooctane monomer and p-formaldehyde as a cross-linker polymer. The newly derived polymer was characterised by FT-IR, 13C-NMR, TGA, SEM-EDX and XRD analyses and employed as potential adsorbent for removal of mercury from water. Adsorption kinetics for mercury uptake by the polymer was described by Elovich, and intraparticle diffusion, while the equilibrium data best fitted Redlich-Peterson and Sip models, implying that the Hg uptake mechanism was heterogeneous adsorption driven by combined physisorption, stronger chemisorption and slower intra-particle diffusion. The mercury ions were minimally attracted to the polymer surface at lower pH, yet as the pH increases, the mercury attraction improved, yielding optimal adsorption capacity for mercury at pH 4.5. The monomer chosen, characterised by a high concentration of amine groups and lone pairs, increases amine functionality, which resulted in excellent mercury uptake, mercury ions with a maximum monolayer adsorption capacity of 211.9 mg/g, competitively higher than other polymer-based adsorbents. While circumventing some of the challenges faced with sulphur-bearing polymer adsorbent, the high Hg uptake potential and thermal stability of the new polymer render it a promising adsorbent for remediation of Hg laden water.