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

Abstract

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 KMnO 4 into Prussian blue (PB) microcubes and obtained Mn-doped α-Fe 2 O 3 nanoboxes by annealing the complex. We found that KMnO 4 stayed inside the pores of the PB framework and restricted the crystal growth of α-Fe 2 O 3 during annealing. Consequently, the Mn-doped Fe 2 O 3 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) Pb 2+ from water. Within 1 min, this nanoadsorbent (0.2 g/L) extracted >70% Pb 2+ in the solution, and >91.6% in 15 min. Besides, it also selectively captures Pb 2+ (40 mg/L) from a synthetic Pb/Zn mining wastewater containing Zn 2+ (40 mg/L) and various kinds of interfering ions (Na + , K + , Mg 2+ , Ca 2+ , SO 4 2− , NO 3 − , Cl − ). The maximizing capacity of Pb 2+ reaches to 900 mg/g when treating concentrated Pb 2+ 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.

Well‐Defined Cu2O/Cu3(BTC)2 Sponge Architecture as Efficient Phenolics Scavenger: Synchronous Etching and Reduction of MOFs in confined‐pH NH3⋅H2O

“…Taking Cu 3 (BTC) 2 as a proof of concept, only by adjusting the pH of NH 3 ⋅H 2 O within a much small range (10-11), the bulk Cu 3 (BTC) 2 can readily be shaped into nanoscale Cu 3 (BTC) 2 of distinguishable sizes and shapes, highly dependent on the pH values. Particularly at pH = 11, NH 3 ⋅H 2 O exhibited weak reducibility that triggers a reduction of part of Cu 3 (BTC) 2 sponge-like architecture. The Cu 2 O/Cu 3 (BTC) 2 derivative, i.e., sponge-like CuO x , was efficient in catalyzing the phenol removal, outperforming its counterparts and many other Cubased catalysts reported in literatures.…”

“…of inorganic materials like metal oxides, [2] chalcogenides, [3] and noble metals. [4] As compared, rare reports were on the surfactant principles to prepare MOFs, an emerging class of novel advanced materials composed of metal-containing nodes and organic linkers, [5] probably since the impurity surfactants could break or change the backbone (metal-ligands coordination bonds) of MOFs.…”

“…Herein, we demonstrated that NH 3 ⋅H 2 O solution can readily shape the bulk Cu 3 (BTC) 2 into low-dimensional counterparts with tunable sizes and shapes dependent on its pH values within a confined region. Particularly at pH = 11, NH 3 ⋅H 2 O exhibited a weak reducibility that triggers a reduction of part of Cu 3 (BTC) 2 into Cu 2 O, while shaping the other into Cu 3…”

“…[18] It means besides the Cu 2 O, a significant amount of Cu 3 (BTC) 2 was retained in CuBTC-NH 3 -11. Considering that the mass fraction of Cu in pristine Cu 3 (BTC) 2 and Cu 2 O was ≈27% and ≈89% respectively, the mass fraction of Cu 2 O in hybrid can roughly be ≈50%. By the way, this hybrid seems relatively stable in built NH 3 ⋅H 2 O system, as the copper ions will not be leached anymore as time prolonged ( Figure S3, Supporting Information) and the sponge structure was well preserved ( Figure S4 (Figure 4b,c), which should be the residual Cu 3 (BTC) 2 particles.…”

“…Currently, one of burgeoning directions of MOFs is to be converted into functional oxides with inherited morphologies and porosities. [22] As such, the derivative of Cu 3 (BTC) 2 , CuO x is an excellent catalyst for the organics degradation, [23] yet its catalytic performance is highly dependent on the crystalline size and dispersion state of nanounits. [24] To describe the structural benefit of products (Figure 5a), all the Cu 3 (BTC) 2 were annealed in air at 350 °C and converted into CuO (JCPDS no.…”