Effective and simple removal of Hg from real waters by a robust bio-nanocomposite

Abstract

This work describes a novel method for integrating a graphene oxide/polyethyleneimine (GOPEI) nanocomposite into a natural three-dimensional scaffold of marine spongin (MS). The objective is to exploit GOPEI's superior performance for sorption of Hg from real water matrices at a realistic low initial Hg concentration (50 μg L⁻¹) and to overcome one of the GOPEI nanocomposite's limitations, which is shared by other nanocomposites: its disintegration into fine particulates over time when dispersed in water, requiring a subsequent step of filtration or centrifugation. To facilitate the sorption process in general, we considered encapsulating the GOPEI in MS. Additionally, because MS has a high affinity for Hg, a synergistic effect on Hg removal was anticipated. GOPEI was infused layer by layer into the MS cubes by electrostatic contact between the oppositely charged GO and PEI, up to three successive layers. To prevent the generated layers from detaching, the materials were coated with a layer of GOPEI-infused alginate (Alg) (calcium cross-linked) that enabled the sorbate to diffuse freely without leaching the sorbent. The nanocomposite finally surpassed the original GOPEI and MS materials in terms of Hg sorption in ultrapure (MQ) and bottled water, with removal (R, %) of 97.3% and 96.5%, respectively, confirming the predicted synergistic effect. MS and MSGOPEI3–Alg both have a fairly comparable R% of approximately 90% in seawater. Cyclic mechanical compression testing in water was used to evaluate the novel nanocomposite material's robustness. There was no evidence of disintegration, indicating its simplicity of use.