Preparation of three-dimensional biochar-based porous aerogels and the highly efficient removal of Cu2+ and methylene blue

Abstract A new type of biochar-based aerogel beads was prepared to overcome the low adsorption efficiency and the difficult recovery of powdered biochar (BC) after removing Cu 2+ and methylene blue (MB) in wastewater. Graphene oxide (GO) and sodium alginate (SA) were initially introduced into BC matrix to obtain BC-GO-SA aerogel beads with chemical cross-linking, followed by freeze-drying technology. Series of analytical technologies, such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Raman, X-ray photoelectron spectroscopy (XPS), were applied to test the properties of the adsorbents. Adsorption performances of BC-GO-SA on Cu 2+ and MB as well as its reusability, thermodynamic, and co-adsorption performances were investigated. The results demonstrated that the introduction of GO and SA into BC increased the potential adsorption sites to Cu 2+ and MB, which possessed 3D network structure, abundant oxygen-containing functional groups, good thermodynamic, and excellent mechanic properties. The Langmuir isotherm models fitted the adsorption process of Cu 2+ and MB onto aerogel beads better and the maximum adsorption capacity of Cu 2+ and MB were 137.86 mg/g and 232.22 mg/g, respectively, which was larger than that of reported adsorbents. The results of thermodynamic adsorption analysis indicated that both adsorption processes of Cu 2+ and MB onto aerogel beads occurred spontaneously. The adsorption processes was exothermic reaction for Cu 2+ , while an endothermic reaction for MB. More importantly, BC-GO-SA could be separated and recycled as an environmentally friendly adsorbent to maintain a small amount of adsorption loss after five adsorption/desorption cycles. In addition, adsorption experiments of the binary mixture system revealed that Cu 2+ and MB exhibited a competitive adsorption effect and the inhibitory effect of MB on Cu 2+ adsorption was stronger than that of Cu 2+ on MB adsorption.