Spherical silica particles decorated with graphene oxide nanosheets as a new sorbent in inorganic trace analysis

• Graphene oxide (GO) covalently bonded to the spherical silica.
• Very stable sorbent for SPE of metal ions.
• Excellent contact with solution due to the softness and flexibility of GO nanosheets.
• Several adsorption–elution cycles without any loss of adsorptive properties.
• High adsorption capacity due to the wrinkled structure of GO nanosheets.

Graphene oxide (GO) is a novel material with excellent adsorptive properties. However, the very small particles of GO can cause serious problems is solid-phase extraction (SPE) such as the high pressure in SPE system and the adsorbent loss through pores of frit. These problems can be overcome by covalently binding GO nanosheets to a support. In this paper, GO was covalently bonded to spherical silica by coupling the amino groups of spherical aminosilica and the carboxyl groups of GO (GO@SiO2). The successful immobilization of GO nanosheets on the aminosilica was confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. The spherical particle covered by GO with crumpled silk wave-like carbon sheets are an ideal sorbent for SPE of metal ions. The wrinkled structure of the coating results in large surface area and a high extractive capacity. The adsorption bath experiment shows that Cu(II) and Pb(II) can be quantitatively adsorbed at pH 5.5 with maximum adsorption capacity of 6.0 and 13.6 mg g−1, respectively. Such features of GO nanosheets as softness and flexibility allow achieving excellent contact with analyzed solution in flow-rate conditions. In consequence, the metal ions can be quantitatively preconcentrated from high volume of aqueous samples with excellent flow-rate. SPE column is very stable and several adsorption–elution cycles can be performed without any loss of adsorptive properties. The GO@SiO2 was used for analysis of various water samples by flame atomic absorption spectrometry with excellent enrichment factors (200–250) and detection limits (0.084 and 0.27 ng mL−1 for Cu(II) and Pb(II), respectively).

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