New insight into removal of tetracycline by a two-dimensional graphene-like carbon adsorbent prepared using one-step pyrolysis of spent bleaching earth: Adsorption behaviors, mechanisms and cost analysis

Two-dimensional (2-D) graphene materials have high adsorption capacity for tetracycline because of great specific surface areas and abundant oxygen containing functional groups. Yet their application remains limited because of high costs and complex production processes. Here, a simple strategy for preparing 2-D graphene-like materials is proposed; spent bleaching earth (SBE), a by-product of bleaching edible oil, was initially used to prepare the 2-D material. Residual oils and minerals in SBE comprised the carbon sources and templates required for the 2-D material. The properties of SBE were utilized to synthesize mineral carbon material (SBE@C). This 2-D material (0.34-nm thickness) was investigated by checking the distribution of carbon in the SBE@C interlayer, using electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope. The SBE@C’s resulting 2-D graphene-like structure had an extraordinary uptake capacity for both tetracycline (96.48 mg/g) and sulfamethoxazole (94.24 mg/g). Further, the adsorbent featured excellent stability vis-à-vis the competitive cationic coexistence, an extensive range of pH conditions, and multiple recycled uses (3 times), and its high-performance tetracycline adsorption from a real aquatic environment was also evidenced. Spectroscopic and microscopic studies showed that multiple adsorption mechanisms are involved, namely surface complexation, ion exchange, H-bond interaction, and Π-Π stacking.