Lignosulfonate-derived sulfur functionalization of bimetallic Ni/Co-MOF for effective removal of Hg(II) from wastewater.

Abstract

The high toxicity and persistence of mercury (Hg(II)) severely threaten the safety of aquatic environments. In this study, a strategy based on sodium lignosulfonate (Na-LS) functionalized Ni/Co-MOF was proposed, successfully constructing a series of sulfur-doped lignin-MOF composite adsorbents (LS-Ni/Co-MOF). The introduction of Na-LS enabled efficient sulfur doping, which significantly enhanced the Hg(II) adsorption performance of the resulting composites. Batch adsorption experiments at 298 K showed that the Langmuir model calculated the maximum Hg(II) adsorption capacity of 0.5-LS-Ni/Co-MOF, 0.75-LS-Ni/Co-MOF, and 1-LS-Ni/Co-MOF to be 781.7, 799.7, and 802.1 mg g^-1, respectively, with equilibrium attained within 60 min at an initial concentration of 100 mg L^-1. Furthermore, LS-Ni/Co-MOF exhibited highly selective adsorption toward Hg(II) over various competing ions, including Ca(II), Al(III), Pb(II), Cd(II), Mg(II), Co(II), Ni(II), Zn(II), and Mn(II). The K_d values for Hg(II) reached 349237.3, 450760.9 and 471704.5 L g^-1 for 0.5-LS-Ni/Co-MOF, 0.75-LS-Ni/Co-MOF, and 1-LS-Ni/Co-MOF, respectively. After five consecutive adsorption-desorption cycles, the Hg(II) removal efficiency remained above 70%. Dynamic column tests showed a 50% breakthrough time of 3120 min, demonstrating great potential for practical application. In real wastewater, the materials achieved a removal efficiency of 90% for Hg(II). Finally, Spectroscopic analysis and DFT calculations revealed that the adsorption mechanism involves a coordination interaction between the surface hydroxyl and sulfonate groups and Hg(II). This work provides a promising materials design pathway for the functional utilization of lignin and the purification of heavy metal-contaminated wastewater.