Fe–Mn–Ce oxide-modified biochar composites as efficient adsorbents for removing As(III) from water: adsorption performance and mechanisms

In this study, a novel Fe–Mn–Ce oxide-modified biochar composite (FMCBC) was synthesized via pyrolysis to enhance the adsorption capacity of biochar (BC). Scanning electron microscopy-energy-dispersive X-ray spectroscopy confirmed that Fe, Mn, and Ce were successfully loaded onto the surface of the BC. A series of adsorption experiments showed that the FMCBC exhibited improved adsorption of As(III) in an aqueous environment. The adsorption process was well expressed by the pseudo-second-order kinetic model. The adsorption capacity of FMCBC reached 8.74 mg L−1, which was 3.27 times greater than that of BC. The pH of the solution significantly influenced the adsorption of As(III), where the amount of As(III) adsorbed by FMCBC was maximized at pH 3. A high phosphate concentration inhibited adsorption, whereas nitrate and sulfate ions promoted As(III) adsorption and increased the FMCBC adsorption capacity. Similarly, with increasing humic acid concentration, the adsorption capacity of FMCBC for As(III) decreased; however, a low concentration of humic acid promoted adsorption. X-ray photoelectron spectroscopy analysis revealed that the adsorption of As(III) by FMCBC occurred through redox and surface complexation reactions. Therefore, FMCBC has excellent potential for purifying arsenic-contaminated water.