Methotrexate anti-cancer drug removal using Gd-doped Fe3O4: Adsorption mechanism, thermal desorption and reusability

One of the means of removing anthropogenic contaminants such as anti -cancer drugs from widely understood water environments is through adsorption. However, it is imperative to ensure that adsorbed contaminants do not find their way back into the environment, hence the quest for this study. Gadolinium (Gd)-doped Fe3O4 was synthesized, characterized, and applied for the removal of methotrexate (MEX), an anti -cancer drug. The incorporation of Gd did not alter the crystal structure of magnetite, having crystallite size and the d -spacing of 10 nm and 2.516 angstrom respectively. The magnetic saturation slightly reduced from 71 before doping to 67 emu g -1 after adding 5% atomic weight of Gd. The BET -specific surface area increased from 87 to 102 m2 g-1 when the content of Gd was 15%. The particle size is within the range of 10-20 nm. The dopant shifted the isoelectric point of the adsorbent nanoparticles to a more positive value which favored the adsorption of methotrexate at pH 7. The adsorption capacity increased from 28 mg g-1 (0%_Gd) to 64 mg g-1 (5%_Gd). The addition of CaCl2, due to the hydrophobic effect increased the amount of MEX that was removed. To ensure that the adsorbed MEX did not escape to the environment, Gd-doped Fe3O4 was thermally decomposed from the surface of the doped magnetite and reused for up to 4 cycles. The proposed mechanisms of adsorption were due to electrostatic and hydrogen bond interaction.