Three-dimensional hybrid nitrogen/oxygen-containing components modified graphene oxide as a recyclable adsorbent for rapid adsorption of REEs

Abstract

Due to the well dispersibility of graphene oxide (GO) in aqueous solution, it is very difficult to separate GO after adsorption. Therefore, various organic/inorganic molecules have been composited with GO to produce novel adsorbents with relatively lower dispersibility and better adsorption performance. The rational selection of these organic/inorganic molecules seems very important. In this work, three-dimensional (3D) (graphene oxide-N-benzyloxycarbonylglycine) GO-ZG composites were synthesized by an easy-to-operate, one-step hydrothermal method. The 3D GO-ZG composites were illustrated by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM), powder x-ray diffraction (PXRD), Raman spectroscopy and specific surface area (SSA) analysis. The effects of GO-to-ZG mass ratio (x: y), hydrothermal reaction time, and hydrothermal reaction temperature were investigated. The adsorption properties of 3D GO-ZGx:y composites toward rare earth elements (REEs) were studied. The results showed that the composite with a GO-to-ZG mass ratio of 2:1, reaction time of 6 h, and reaction temperature of 120 ºC possessed the best adsorption performances. Further investigation of the adsorption conditions on 3D GO-ZG2:1/6 h/120 ℃ composites toward REEs including initial solution pH value, contact time, initial REE3+ concentration, and contact temperature was carried out. The adsorption of REEs could reach equilibrium in 60 min at room temperature. The adsorption capacities of 3D GO-ZG2:1/6 h/120 ℃ composite for La3+, Yb3+, Nd3+, Er3+ and Y3+ were 44.56, 53.64, 45.96, 50.48 and 30.63 mg·g-1, respectively. Ten adsorption/desorption cycles revealed that GO-ZG2:1/6 h/120 ℃ composite possessed good stability and recoverability. The adsorption mechanism of REEs by GO-ZG2:1/6 h/120 ℃ composite can be summarized as ion exchange, surface complexation, and electrostatic attraction. The as-prepared GO-ZG2:1/6 h/120 ℃ composite might be used as a renewable and structurally stable adsorbent in the adsorption.