Polyethyleneimine-functionalized pectin fibers as effective adsorbents for the removal of mercury ions from aqueous solution: Characterization, performance, and mechanism

The purification of mercury-contaminated water has garnered significant attention due to the severe biotoxicity of mercury. To efficiently remove mercury ions (Hg(II)) from aqueous solutions, a nitrogen-rich biomass adsorbent material, polyethyleneimine (PEI)-functionalized pectin fibers (PEI-pectin fibers), were synthesized using glutaraldehyde as a cross-linking agent between PEI and pectin. PEI-pectin fibers demonstrated excellent stability and Hg(II) adsorption performance across a broad pH range. The maximum adsorption capacity of PEI-pectin fibers for Hg(II) reached 466.2 ± 23.8 mg/g at pH 5, significantly surpassing the performance of previously reported adsorbents. The synthesis mechanism and adsorption behavior were elucidated using density functional theory, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Adsorption was primarily driven by coordination between Hg(II) and nitrogen-containing functional groups on PEI, along with cation exchange between Hg(II) and Ca(II) ions associated with the carboxyl groups in pectin. Furthermore, Hg(II)-loaded PEI-pectin fibers were easily regenerated using a 0.05 M Na₂EDTA solution. PEI-pectin fibers maintained excellent Hg(II) removal efficiency under various conditions, including ultra-low mercury concentrations, varying adsorbent dosages, and the presence of competing ions. The fibers demonstrated strong selectivity for Hg(II), high resistance to interference from common cations and anions, and retained over 94 % removal efficiency even in high-salinity environments. These findings highlight PEI-pectin fibers as a highly promising and cost-effective biomass adsorbent material for the efficient removal of Hg(II) from wastewater.