Purification of dye-contaminated water using Si-doped mesoporous Fe3O4 prepared with rice husk SBA-15 as a template: behavior and mechanism

It is still challenging to remove methylene blue (MB) from complex wastewater via one-step adsorption. Herein, an ingenious method was designed to prepare Si-doped mesoporous Fe3O4 (SiMFe3O4) using mesoporous silica derived from rice husk (RHSBA-15) as a template. In this method, enough NaOH was added not only to prepare SiMFe3O4 by facile one-step method but also to remove the template concurrently. SiMFe3O4 was systematically characterized and used as a versatile adsorbent to remove MB from complex wastewater. Results indicated that SiMFe3O4 had prominent MB adsorption capacity in the single dye solution with maximum adsorption capacity of 1022.59 mg/g at Sips model. After 4 reuses (washed with 0.5-M NaOH), MB adsorption capacity of recycled SiMFe3O4 in simulated wastewater was still satisfactory. Furthermore, MB could be removed by SiMFe3O4 from the mixed systems (Acid Fuchsin (AF)/MB, Rhodamine B (RB)/MB, and Xylenol Orange (XO)/MB). Interestingly, the removal capacity of SiMFe3O4 to MB and methyl orange (MO) were significantly enhanced in MO/MB mixed system, while no obvious MO adsorption was detected in its individual solution. It was emphatically elucidated that the adsorption of MO and MB by SiMFe3O4 were due to the synergy between complexation, electrostatic attraction, and hydrogen bonding.