Synthesis of graphene oxide/citric acid/sodium alginate composite aerogel beads for high adsorption of methylene blue

Abstract

The discharge of wastewater containing organic dye pollutants exacerbates contamination in natural water bodies. In this study, a porous three-dimensional (3D) graphene oxide/citric acid/sodium alginate (GO/CA/SA) aerogel microsphere was prepared via a cross-linking and freeze-drying method using graphene oxide (GO), citric acid (CA), and sodium alginate (SA) as raw materials, and applied for the adsorption of methylene blue (MB). The GO/CA/SA aerogel beads were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), Zeta potential, energy dispersive spectroscopy (EDS), and X ray photoelectron spectroscopy (XPS). Adsorption experiments revealed that the adsorption capacity of GO/CA/SA for MB reached a very high capacity of 994 mg/g. The adsorption behavior conformed to the Langmuir isotherm model and the pseudo-second-order kinetic model. Combined with thermodynamic parameters, the adsorption process was identified as a spontaneous exothermic reaction dominated by chemisorption. Further analysis by XPS, FT-IR, and zeta potential confirmed that the adsorption mechanism of MB onto GO/CA/SA consists of hydrogen bonding, π–π interaction, and electrostatic force. Moreover, in the presence of the anionic dye methyl orange (MO), the neutral dye rhodamine B (RhB), and humic acid (HA), GO/CA/SA maintained good adsorption performance and selectivity toward MB. Additionally, with ethanol desorption, GO/CA/SA can be reused for five adsorption–desorption cycles with MB removal over 90%. GO/CA/SA aerogel beads demonstrate high potential as an efficient adsorbent for the removal of MB from wastewater.