Mechanism of Pb(ii) and methylene blue adsorption onto magnetic carbonate hydroxyapatite/graphene oxide

Abstract

Magnetic carbonate hydroxyapatite/graphene oxide (M-CHAP/GO) was successfully prepared by loading magnetic carbonate hydroxyapatite (M-CHAP) onto graphene oxide sheets and was found to be an ideal adsorbent for heavy metal (Pb(II)) and dye (methylene blue). The obtained adsorbent was characterized by SEM, FTIR, XRD, BET, TGA, XPS and zeta potential, respectively. M-CHAP/GO nano-particles possessed a favorable and stable morphology. Moreover, the good magnetic properties of M-CHAP/GO made it simple to recover from water with magnetic separation. The equilibrium adsorption capacity was 277.7 mg g⁻¹ for Pb(II) and 546.4 mg g⁻¹ for methylene blue under the optimal conditions. The pseudo-second-order equation and the Langmuir model showed good correlation with the experimental data and explained well the mechanism of adsorption. It was found that the adsorption process was accomplished mainly via chelation and ion exchange. Thermodynamic studies (ΔG < 0, ΔH > 0, ΔS > 0) implied that the adsorption process was endothermic and spontaneous in nature. The other adsorption mechanisms are further researched in this article. All the experimental results show that M-CHAP/GO nano-particles have potential application in the future of environmental management.