Facile Fabrication of 3D Graphene–Silica Hydrogel Composite for Enhanced Removal of Mercury Ions

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Abstract
Adsorption is a highly promising and widely used approach to remove Hg(II) ions from contaminated water. The key to this technology is exploring the effective adsorbent. The three-dimensional (3D) graphene as reduced graphene oxide hydrogel (rGH)-encapsulated silica gel (SG-PEI/rGH) was prepared by a moderate chemical reduction strategy using ascorbic acid. This composite structure was characterized by FTIR, XRD, and SEM analysis and used as adsorbents for Hg(II) ions. Its adsorption capacity toward Hg(II) ions was 266 mg/g and increased about 32% compared with the silica gel because of reduced graphene oxide hydrogel (rGH). Mechanism study showed that the high adsorption ability was due to the formation of an N–Hg complex with multi-amino groups on the surface of polyethyleneimine-modified silica gel (SG-PEI) and the rapid diffusion of adsorbed ions attributed to the rGH network structure. This composite SG-PEI/rGH would be a promising material for the removal of Hg(II) ions.

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