Graphene-coated silica as a highly efficient sorbent for residual organophosphorus pesticides in water

A new form of graphene-coated silica (GCS) has been prepared by mixing exfoliated graphene oxide with acid-treated silica and reducing it with hydrazine hydrate so that it coats the silica particles. This method is simple, convenient, and robust. The GCS composite particles have been characterized using optical photographs, Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) analysis, and elemental analysis. These analyses show that the reaction effectively coats silica particles with graphene. The composite particles achieve higher levels of adsorption and are more widely applicable than five other sorbents (graphite carbons, activated carbon, pure graphene, C18 silica, and silica) for the eleven pesticides assayed. We discuss the adsorption mechanism and consider it to be dependent on the electron-donating abilities of the S, P, and N atoms and the strong π-bonding network of the benzene rings. This research demonstrates that graphene-based composite materials could be used to remove pesticide residues in aqueous environments.