Effect of pyrolysis temperature on characteristics of tunable magnetic biochar synthesized from watermelon rind and its tetracycline adsorption performance

Background: Tetracycline is an emerging contaminant in water reservoirs, causing undesirable influences on human society. The promising usage of magnetic biochar (MBC) derived from watermelon rind has been explored in the adsorption of various contaminants owing to its high specific surface area and separability; however, the temperature-dependent changes of MBC and its sorption ability toward antibiotics have not been widely examined. Method: Tunable MBCs could be synthesized via simple pyrolysis of watermelon rind impregnated with FeCl3 at different temperatures (700-900 degrees C). The as-synthesized MBCs were characterized using scanning electron microscopy (SEM), an elemental analyzer, N-2 adsorption/desorption, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffractometry (XRD), and vibrating sample magnetometry (VSM). Then Tetracycline, an emerging contaminant in water reservoirs, was employed as the target contaminant, while adsorption kinetics, isotherm, the effect of pH, and reusability were investigated. Significant findings: The tunability of as-synthesized MBCs could be observed by their distinct changes in structural characteristics when varying pyrolysis temperature. MBC synthesized at 900 degrees C (MBC900) possessed a high-specific surface area (401 m(2).g(-1)) and saturation magnetization (55.29 emu.g(-1)), resulting in a greater amount of sorption sites. Tetracycline adsorption by MBCs followed a pseudo-second-order kinetic model and fitted well with the Freundlich model. MBC900 is an excellent adsorbent with a maximum adsorption capacity of 77.6 mg.g(-1) and could be used for at least five cycles with an insignificant decrease in the adsorption capacity.