Magnetic nanocomposites prepared from red mud and durian husk as an effective bio-adsorbent for methylene blue adsorption

An increasing interest in nanocomposites prepared from agricultural/industrial byproducts has been paid for environmental remediation, especially in water treatment. This study reports the facile preparation of a low-cost magnetic biocomposite of magnetic Fe3O4 nanoparticles (NPs) incorporated with biopolymers extracted from durian husk, called bp-Fe3O4 and examined in the removal of methylene blue (MB) dye. Here, Fe2O3 NPs were first recovered from red mud waste and then converted to magnetic nanostructured Fe3O4 using a one-pot process via carbon combustion. The bp-Fe3O4 inherited the characteristics of each constituent component, while showing slightly higher saturation magnetization than the bare Fe3O4 NPs (19.84 and 18.66 emu/g, respectively), allowing for easy separation from the aqueous solution using a suitable magnet. The MB adsorption on bp-Fe3O4 reached an equilibrium state within 60 min reaction and achieved >90% of removal (at 50 mg/L MB) at an optimal pH range of 6–8. The effective adsorption of MB dye was attributed to both the hydroxylated-Fe3O4 NPs and biopolymers. The material showed excellent reusability tested up to the seventh MB adsorption cycle (decreased by <2% of adsorption efficiency). Overall, the outstanding magnetic properties and low-cost bp-Fe3O4 rendered them easily manipulated and separated, and reusable for water/wastewater treatment of MB dye.