The magnetic biochar was prepared using Ulva fasciata marine algae and used to remove Methylene blue (MB) as model organic molecule. A comprehensive characterization was conducted on pristine Ulva fasciata biochar (UFBC) and UFBC modified by Fe3O4 (UFBC-MIO) by using SEM, EDX, FTIR, TEM, BET, and XRD along with the PZC. The adsorption of MB was noted as 20.83 mg g-1 for UFBC and 50.12 mg g-1 for UFBC-MIO, at pH = 9, 2 g L-1 dosage and T = 298 K with approx. 85 mg L-1 MB concentration. The higher performance of UFBC-MIO was explained by formation of higher surface area and pore volume. The mechanism of adsorption depicted as pore-filling and electrostatic interaction was identified as physisorption. The adsorption model followed the Langmuir isotherm and the kinetic studies disclosed pseudo-second-order for both adsorbents. The thermodynamic study revealed that the process is non-spontaneous, decreased in randomness and was exothermic. The UFBC-MIO was easily recovered and regenerated through its magnetic property and exhibited 89% MB removal after 5 cycles at pH = 9, 2 g L-1 dosage and T = 298 K with 86.37 mg L-1 of MB. The magnetic biochar of algae Ulva fasciata is an excellent adsorbent recommended for the removal of cationic dyes from wastewaters.
