A functionalized metal-organic framework decorated with O- groups showing excellent performance for lead(ii) removal from aqueous solution

Porous functionalized MOF self-evolution promoting molecule encapsulation and Hg2+ removal

Porous functionalized MOF self-evolution has successfully improved the Hg²⁺ removal performance and implemented dye molecule encapsulation.

Highly efficient removal of Pb2+ by a sandwich structure of metal–organic framework/GO composite with enhanced stability

Sandwich-structured MIL-101(Fe)/GO was successfully synthesized by a one-step hydrothermal method, and exhibited a high adsorption capacity and fast adsorption kinetics.

Water-stable metal-organic frameworks for aqueous removal of heavy metals and radionuclides: A review

Heavy metals and radionuclides in water are a global environmental issue, which has been receiving considerable attention worldwide. Water-stable MOFs are green and recyclable materials to eliminate the environmental impacts caused by the hazardous heavy metal ions and radionuclides in water. This paper presents a systematical review on the current status of water-stable MOFs that capture and convert a wide range of heavy metal ions (e.g., As(III)/As(V), Pb(II), Hg(II), Cd(II), and Cr(III)/Cr(VI)) and radionuclides (e.g., U(VI), Se(IV)/Se(VI) and Cs(I)) in aqueous solution. Water-stable MOFs and MOF-based composites exhibit the superior adsorption capability for these metal species in water. Significantly, MOFs show high selectivity in capturing target metal ions even in the presence of multiple water constituents. Mechanisms involved in capturing metal ions are described. MOFs also have excellent catalytic performance (photocatalysis and catalytic reduction by formic acid) for Cr(VI) conversion to Cr(III). Future research is suggested to provide insightful guidance to enhance the performance of the MOFs in capturing target pollutants in aquatic environment.

Solvent-Triggered Reversible Phase Changes in Two Manganese-Based Metal-Organic Frameworks and Associated Sensing Events

A flexible Mn-based MOF, Mn-sdc-1, has been successfully synthesized by using the ligand 4,4'-stilbenedicarboxylic acid (H₂ sdc). Attributed to the flexibility of the framework, Mn-sdc-1 can transform into a new phase (Mn-sdc-2) with completely different structural geometry; this is induced by trace levels of H₂ O at room temperature. Reversibly, the transformation from Mn-sdc-2 to Mn-sdc-1 can be triggered by DMF upon heating beyond 100 °C. These results inspired a study of the influences of temperature and H₂ O volume in the solid-state transformation of two MOF phases and, for the first time, a phase diagram of MOFs has been depicted. This phase diagram reflects the gradual H₂ O-/temperature-dependent changes between Mn-sdc-1 and Mn-sdc-2, which is very meaningful in achieving the controllable synthesis of these two MOFs and lead to targeting the desired water-stable structure. As a result, the obtained water-stable Mn-sdc-2 can be developed as an excellent Pb²⁺ sensor in aqueous solution through the luminescence quenching effect with a limit of detection of 31.4 nm.

Trapping [PMo12O40]3- clusters into pre-synthesized ZIF-67 toward Mo x Co x C particles confined in uniform carbon polyhedrons for efficient overall water splitting

Bi-transition metal carbides (BTMCs) are promising in catalytic fields, but the synthesis of small-sized BTMCs remains a challenge. Here, Mo x Co x C (mainly below 20 nm in size) confined in uniform carbon polyhedrons (Mo x Co x C@C) was synthesized based on trapping [PMo12O40]3- (PMo12) clusters into pre-synthesized, uniform ZIF-67 (PMo/ZIF-67). The opening of the windows (0.34 nm) of ZIF-67 cages through heating is essential to allow the trapping of PMo12 into the cages. This trapping route provides a new method to successfully combine POMs and MOFs that can not be effectively combined via traditional POMOF-based (simultaneous assembly) routes. It also has advantages in controlling the uniformity and components of the materials. The size matching of PMo12 (1 nm) and the cages (1.16 nm) of ZIF-67 enables effective contact of the Co and Mo sources, thus giving small-sized Mo x Co x C protected by carbon via calcination. The optimized catalysts showed good performance for water splitting with a low η10 of 83 mV (295 mV) for the hydrogen (oxygen) evolution reaction, which is superior to those derived from ZIF-67 and precursors from POMOF-based routes. Our results also indicated that the HER activity is determined by the kind of BTMC, and the activity for the OER is relative to the oxygen-containing species formed during the initial OER test.

Rapid, Selective Heavy Metal Removal from Water by a Metal-Organic Framework/Polydopamine Composite

Drinking water contamination with heavy metals, particularly lead, is a persistent problem worldwide with grave public health consequences. Existing purification methods often cannot address this problem quickly and economically. Here we report a cheap, water stable metal-organic framework/polymer composite, Fe-BTC/PDA, that exhibits rapid, selective removal of large quantities of heavy metals, such as Pb²⁺ and Hg²⁺, from real world water samples. In this work, Fe-BTC is treated with dopamine, which undergoes a spontaneous polymerization to polydopamine (PDA) within its pores via the Fe³⁺ open metal sites. The PDA, pinned on the internal MOF surface, gains extrinsic porosity, resulting in a composite that binds up to 1634 mg of Hg²⁺ and 394 mg of Pb²⁺ per gram of composite and removes more than 99.8% of these ions from a 1 ppm solution, yielding drinkable levels in seconds. Further, the composite properties are well-maintained in river and seawater samples spiked with only trace amounts of lead, illustrating unprecedented selectivity. Remarkably, no significant uptake of competing metal ions is observed even when interferents, such as Na⁺, are present at concentrations up to 14 000 times that of Pb²⁺. The material is further shown to be resistant to fouling when tested in high concentrations of common organic interferents, like humic acid, and is fully regenerable over many cycles.

Efficient heavy metal removal from industrial melting effluent using fixed-bed process based on porous hydrogel adsorbents

High adsorption capacity, fast adsorption kinetics, good reusability and low cost are highly demanded for adsorbents used in practical adsorption process. In this study, a porous double network Jute/Polyacrylic acid (Jute/PAA) gel was prepared using simple free-radical polymerization of acrylic acid in Jute aqueous solution. The high permeability of Jute/PAA hydrogel with about 80 wt% water made internal adsorption sites fully expose to metal ions. The Jute/PAA gel adsorbent could efficiently adsorb heavy metals in melting wastewater, especially Cd²⁺ and Pb²⁺. The adsorbent showed very high adsorption capacities of 401.7 mg/g for Cd²⁺ and 542.9 mg/g for Pb²⁺. Moreover, the adsorption equilibrium reached within only 10 min for 40 mg/L of Cd²⁺ and Pb²⁺ using 1 g/L adsorbent. Meanwhile, the removal efficiencies reached 81.0% for Pb (C₀ = 3.825 mg/L), 79.3% for Cd (C₀ = 6.075 mg/L), 83.4% for Cu (C₀ = 9.325 mg/L), 29.8% for Zn (C₀ = 188.6 mg/L), 22.3% for Mn (C₀ = 17.05 mg/L), 96.2% for Cr (C₀ = 0.25 mg/L) and 99.8% for Fe (C₀ = 9.75 mg/L) in melting wastewater using 1 g/L adsorbent in 2 h. In particular, the concentrations of Pb, Cd and Cr decreased below 0.001 mg/L using 4 g/L adsorbent. In the fixed-bed column experiments, the treatment volume of melting wastewater reached 2900 BV (32.8 L) only producing 50 BV (565 mL) eluent. This work develops a highly practical adsorption process based on hydrogel adsorbents for the removal of heavy metals in actual wastewater.

Four new metal–organic frameworks based on diverse secondary building units: sensing and magnetic properties

Four new metal–organic frameworks based on diverse secondary building units were assembled and 1 showed high selectivity in the detection of CrO₄²⁻, Cr₂O₇²⁻, MnO₄⁻ and Fe³⁺.

Structural diversity and magnetic properties of Co(ii)/Mn(ii)/Ni(ii) coordination polymers constructed from an unsymmetrical tetracarboxylic acid and varying N-donor ligands

Seven coordination polymers with diverse structures based on an unsymmetrical tetracarboxylate and varying N-donor ligands were prepared. Complex 7 exhibits strong ferromagnetism.

Enhanced glucose sensing based on a novel composite CoII-MOF/Acb modified electrode

A novel electrochemical sensor composed of a composite of Co^II-MOF/acetylene black exhibits enhanced sensing behavior for glucose detection.

A robust Zn(ii)/Na(i)-MOF decorated with [(OAc)2(H2O)2]n2n− anions for the luminescence sensing of copper ions based on the inner filter effect

A robust Zn(ii)/Na(i)-based MOF decorated with [(OAc)₂(H₂O)₂]_n²ⁿ⁻ anions was synthesized and employed as the probe for Cu²⁺ detection.