Hollow α-Fe2O3 Nanoboxes Derived from Metal Organic Frameworks and Their Superior Ability for Fast Extraction and Magnetic Separation of Trace Pb2+

Hierarchical metals oxide nanostructure derived from annealing of metal-organic frameworks (MOFs) usually have large particle size and low specific surface area and, as a result their activities, become limited. In this work, we incorporated KMnO4 into Prussian blue (PB) microcubes and obtained Mn-doped alpha-Fe2O3 nanoboxes by annealing the complex. We found that KMnO4 stayed inside the pores of the PB framework and restricted the crystal growth of alpha-Fe2O3 during annealing. Consequently, the Mn-doped Fe2O3 nanoboxes have small particle size, large specific area (452 m(2)/g), and a significant amount of adsorbed oxygen in the form of OH- on the surface as determined by X-ray photoelectron spectroscopy. It could serve as an adsorbent to quickly remove the trace-level (40 mg/L) Pb2+ from water. Within 1 min, this nanoadsorbent (0.2 g/L) extracted >70% Pb2+ in the solution, and >91.6% in 15 min. Besides, it also selectively captures Pb2+ (40 mg/L) from a synthetic Pb/Zn mining wastewater containing Zn2+ (40 mg/L) and various kinds of interfering ions (Na+, K+, Mg2+, Ca2+, SO42, NO3-, Cl-). The maximizing capacity of Pb2+ reaches to 900 mg/g when treating concentrated Pb2+ solution (1g/L). The spent adsorbent could be easily retrieved from the solution by magnetic separation. We anticipate the findings here will help to inspire the design of other novel MOFs-derived nanomaterials.