Adsorption of mercury(ii) with an Fe3O4 magnetic polypyrrole–graphene oxide nanocomposite

Abstract

To enhance the ability to remove mercury(II) from aqueous media, an Fe₃O₄ magnetic nanocomposite (PPy–GO) composed of polypyrrole (PPy) and graphene oxide (GO) was synthesized in situ and characterized via scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), zeta potential analysis, vibrating sample magnetometer (VSM) and the Brunauer–Emmett–Teller (BET) method. The performance of the magnetic PPy–GO for adsorbing mercury(II) from water along with the effects of solution pH, adsorbent dosage, coexisting ions, reaction time and temperature were studied in detail. The adsorption kinetics, isotherms and thermodynamics were investigated in detail to gain insights into the adsorption process. The results show that the BET surface area of the magnetic PPy–GO reached 1737.6 m² g⁻¹. The Langmuir capacity of the magnetic PPy–GO for mercury(II) adsorption was 400.0 mg g⁻¹ at 300 K and pH 7 ± 0.1. After adsorption, the magnetic PPy–GO nanocomposite could be efficiently separated from water via a magnetic field. The adsorption process was endothermic and spontaneous and occurred in accord with the Langmuir and pseudo-second-order models. The overall adsorption of mercury(II) not only involved chemisorption, but was also partially governed by intra-particle diffusion. Data from the preliminary application of magnetic PPy–GO to remove heavy metals from real electroplating effluent indicated a high removal efficiency of over 99% for mercury(II). Finally, a possible adsorption mechanism was discussed. All data showed that the magnetic PPy–GO material is a promising adsorbent to remove mercury(II) from aqueous media.