Nitrogen-Based conjugated microporous polymers for efficient Hg(II) removal from Water: Performance and mechanism

The development of efficient adsorbents for the removal of toxic Hg(II) is crucial in environmental engineering. In this study, we have modified three nitrogen-based conjugated microporous polymers (TAA, PDA, DDA) with nitrogen functional groups and microporosity, resulting in ideal adsorbents for this purpose. Of these, PDA exhibited a record-breaking maximum adsorption capacity to Hg(II) of 1582.6 mg center dot g(-1), and fast adsorption kinetics. Additionally, DDA effectively reduced the Hg(II) concentration from 11.2 ppb to less than 0.01 ppb. They demonstrated robust reusability, retaining over 90% adsorption capacity for at least 25 cycles. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analyses revealed that tertiary nitrogen approached Hg in Hg(OH)(2), forming chelate adsorption with Hg2+, while imine and amino nitrogen formed hydrogen bonds with -OH in Hg(OH)(2) before forming chelate with Hg2+. The strength of binding ability of nitrogen functional groups to mercury followed the order of cyclic N in the oxidized unit (-5.01 eV) > cyclic N in the reduced unit (-5.00 eV) > =N- (-4.85 eV) > -NH- (-2.17 eV). A higher adsorption capacity and faster adsorption equilibrium time resulted from a larger specific surface area and a distribution of micropores closer in size to the mercury ion.

Automated summary

The development of efficient adsorbents for the removal of toxic Hg(II) is crucial in environmental engineering. In this study, nitrogen-based conjugated microporous polymers (TAA, PDA, DDA) were modified with nitrogen functional groups and microporosity, resulting in ideal adsorbents for Hg(II) removal. PDA exhibited a record-breaking adsorption capacity of 1582.6 mg·g(-1), while DDA effectively reduced Hg(II) concentration to less than 0.01 ppb. The binding ability of nitrogen functional groups to mercury was found to be influenced by the specific surface area and pore size distribution of the polymers.