Reduced graphene oxide foams modified with caffeic acid for water decontamination: Capture and safe storage of Hg2+

Graphene-based materials are attractive adsorbents for water decontamination. In this work, we have produced eco-friendly reduced graphene oxide (rGO)-based sorbents by the hydrothermal reduction of graphene oxide (GO) in presence of caffeic acid (CA) and further modification with chitosan (CA_CS). Scanning electron microscopy observations show porous macrostructures that turn more compact after CA or CA_CS modification. The specific surface area achieves a maximum value of 293 m 2 g −1 for the pristine rGO foam. The macropores are mainly distributed in a range between 1–170 µm. The Hg 2+ removal efficiency of the rGO-based foams was investigated across several different parameters. The foam modified with caffeic acid exhibited the most promising performance, demonstrating the highest removal efficiency at pH 4–6, with a maximum sorption capacity of 2.79 mg/g as determined by the Sips equation. Kinetic analysis indicates that intraparticle diffusion and the sorption itself are the rate-limiting steps. The notable sorption efficiency, the low desorption rate, and the applicability in real complex water matrices, including tap water, position rGO_CA as a viable material for efficiently capturing Hg(II) from large volumes of water and securely storing it in a small solid volume. • Graphene-based adsorbents are attractive for water decontamination. • Reduced graphene oxide (rGO)-based sorbents are synthesized hydrothermally using caffeic acid. • The specific surface area achieves a maximum value of 293 m 2 g −1 for the pristine rGO foam. • 25 mg/L of rGO_CA foam reduces the Hg 2+ to a residual concentration of less than 10 µg/L in 24 h. • The foam revealed an optimum pH for Hg 2+ removal between 4–6.