Preparation and characterization of a novel Fe3O4-graphene-biochar composite for crystal violet adsorption

Abstract

A novel Fe3O4-graphene-biochar composite (GBC-Fe3O4) was prepared to enhance the adsorption capacity and recollection efficiency of graphene-biochar composites (GBCs). The adsorption characteristics were tested to remove crystal violet (CV), which is a refractory compound in industrial wastewater. Structural and morphological analysis exhibited that a larger surface area, greater thermal stability, and more functional groups were present after Fe3O4 nanoparticles coated the GBC surface. This improved the CV adsorption versus uncoated GBC. The introduction of G and Fe3O4 nanoparticles collectively reduced the zeta potentials of GBC-Fe3O4 to −38.1 ± 1.1 mV versus −24.3 ± 2.2 mV for GBC and −20.7 ± 1.2 mV for BC. The maximum Qmax values were obtained 436.68 mg/g at 40 °C. Fourier transform infrared analysis suggested that the interactions of functional groups, such as aromatic C = C and C = O, –OH, C–C, and π-π played an important role in CV adsorption. The thermodynamic analysis of Langmuir and Freundlich isotherms indicated that the adsorption improved as a spontaneous endothermic process. The saturation magnetization of GBC-Fe3O4 reached 61.48 emu/g, allowing efficient recollection of the material with a magnet. The CV adsorbability of the re-collected GBC-Fe3O4 was 157.31 mg/g, which was slightly lower than freshly prepared GBC-Fe3O4 (199 mg/g). These findings demonstrated that GBC-Fe3O4 was an efficient and reusable multifunctional biochar.