Novel zirconium-based MOF@rGO composite aerogel: Towards remediation of Hg(II) polluted water bodies to reach safe drinking limits

Schematic representation of the synthesized NU-1000-SMe@rGO composite aerogel capturing Hg(II). • A novel composite aerogel (NU-1000-SMe@rGO) has been synthesized for Hg(II) removal. • Thiomethyl-functionalized MOF sites exhibit a strong affinity for Hg(II). • NU-1000-SMe@rGO effectively adsorbs Hg(II) from water, even at trace levels. • The treated water meets safe Hg(II) limits for drinking. • The composite is doped with SPIONs to facilitate recovery and cyclic operation. Conventional Hg(II) sorbents, such as activated carbons, have demonstrated high efficiency in removing Hg(II) from water streams with elevated pollutant concentration (ppm levels), typically generated in industrial processes. However, their performance significantly declines when targeting Hg(II) sorption at trace levels (ppb), commonly found in natural watercourses, due to insufficient driving force for sorption at such low concentrations. Even at few ppb, Hg(II) is highly toxic and must be eliminated from drinking water to concentrations lower than 1 ppb. This challenge requires the development of specialized sorbents with high affinity for Hg(II) species. Herein, a new composite aerogel (NU-1000-SMe@rGO), consisting of discontinuous MOF particles embedded in a continuous rGO matrix, was synthesized following a bottom-up approach to address this need. Specific sorption sites for Hg(II) were introduced into the MOF framework through the pre-synthetic incorporation of thiomethyl functionalities (−SMe) in a novel pyrene-based ligand (H 4 TBAPy-SMe), resulting in a new NU-1000-derived structure (NU-1000-SMe). The exceptional potential of the NU-1000-SMe@rGO material for advanced water treatment was demonstrated at diluted concentrations of Hg(II) with low amounts of sorbent. Remarkably, the synthesized NU-1000-SMe@rGO aerogel effectively removes Hg(II) from solutions containing trace levels (15 ppb), lowering the concentration below 1 ppb. Furthermore, by doping the aerogel matrix with superparamagnetic iron oxide nanoparticles (SPIONs) a magnetically responsive system (NU-1000-SMe/SPIONs@rGO) was generated, which enables the easy recovery of the exhausted material after use, allowing for consecutive cycles of sorption–desorption without losing efficiency.