Scalable route to mesoporous iron oxides and their Cr(VI) ions uptake capacity study

Here we demonstrate a simple and scalable synthetic route for preparing porous iron oxides with tunable porosity characteristics by using the high-energy mechanical ball milling technique. Nanocomposites composed of networked hematite encapsulated in silica were produced. Silica was utilized as scaffolds to form nanocomposites and then was etched off hydrothermally in a NaOH solution. The formation mechanism of porous iron oxides, effects of volume ratio of silica to magnetite, milling period, calcination temperature and concentration of NaOH solution were studied systematically. The formation process was monitored by applying a variety of techniques, such as scanning and transition electron microscopes (SEM and TEM), and X-Ray diffractometer (XRD). SEM and TEM studies revealed that a jelly-like solid-state nanocomposite of silica and iron oxide was produced after milling process, and networked iron oxide structures encapsulated in silica displayed a high mass contrast and their grain size decreased with elongating milling period. Barrett–Joyner–Halender (BJH) method analysis indicated that the pore width and Brunauer–Emmett–Teller (BET) specific surface area of iron oxide decreased with the increase of milling period and volume ratio of silica to iron oxide, and porosity increased with increasing volume ratio of silica to iron oxide. Magnetic measurement revealed the superparamagnetic nature of the mesoporous materials at room temperature. Further, absorption capacity of Cr (VI) ions onto mesoporous magnetite was checked to evaluate its toxic ions uptake ability.