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, illustrat...

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

Ion imprinting technology (IIT) aims to recognize ions while retaining the unique virtues of molecular imprinting technology (MIT), namely structure predictability, recognition specificity and application universality. Owing to special coordination or electrostatic interactions, ion imprinted polymers (IIPs) are generally compatible with aqueous media and have advantages over most molecularly imprinted polymers (MIPs). IIPs can achieve effective identification of water-soluble ions, especially heavy metals and radioactive elements that cause increasing concerns. The purpose of this review is to summarize recent advances of ion imprinting, focusing on the current status and challenges in fundamentals and applications that involve almost all types of ions and ion-related molecular imprinting. In addition, various smart strategies are highlighted, such as surface imprinting, stimuli-responsive imprinting, dual/multiple components imprinting, click chemistry, and microwave-assisted heating. In this review, the elemental periodic table is first utilized as a template to introduce ion classification standards for various IIPs, including main groups, transition elements, actinides, rare earths, metalloids, anion imprinting and secondary imprinting. Finally, the challenges and possible solution strategies plus future trends are also proposed (302 references).

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Current status and challenges of ion imprinting

The ever-increasing human demand for safe and clean water is gradually pushing conventional water treatment technologies to their limits. It is now a popular perception that the solutions to the existing and future water challenges will hinge upon further developments in nanomaterial sciences. The concept of rational design emphasizes on 'design-for-purpose' and it necessitates a scientifically clear problem definition to initiate the nanomaterial design. The field of rational design of nanomaterials for water treatment has experienced a significant growth in the past decade and is poised to make its contribution in creating advanced next-generation water treatment technologies in the years to come. Within the water treatment context, this review offers a comprehensive and in-depth overview of the latest progress in rational design, synthesis and applications of nanomaterials in adsorption, chemical oxidation and reduction reactions, membrane-based separation, oil-water separation, and synergistic multifunctional all-in-one nanomaterials/nanodevices. Special attention is paid to the chemical concepts related to nanomaterial design throughout the review.

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Rational design of nanomaterials for water treatment

Developing a smart adsorbent that can efficiently detect and remove toxic organophosphorus pesticides is important but still a great challenge. Here, a novel MOF-based smart adsorbent, Fe3O4@SiO2@UiO-67, was successfully fabricated via a versatile layer by layer assembly strategy and applied to the simultaneous selective recognition, detection and removal of glyphosate. The prepared smart adsorbent contains Zr–OH groups with high affinity for phosphate groups, endowing it with selective recognition and a higher adsorption capacity for glyphosate. Moreover, combining it with glyphosate leads to changes in the fluorescence intensity of the smart adsorbent, and incorporating silica impedes electron transfer between UiO-67 and the magnetic core, which can lead to the identification of the adsorbate and its concentration, and achieve a lower detection limit. Furthermore, using Fe3O4 as the magnetic core of the smart adsorbent facilitates the separation and removal process via an external magnetic field. Under optimized conditions, the obtained smart adsorbent exhibits excellent detection and adsorption performance with a high adsorption capacity (256.54 mg g−1), good reusability, and a low detection limit (0.093 mg L−1) for glyphosate, implying that the smart adsorbent has integrated the advantages of the individual components. All of this indicates that MOF-based smart adsorbents are promising for synchronous adsorption/detection and the removal of OPPs, presenting a viable option for monitoring water quality and treating wastewater.

The simultaneous detection and removal of organophosphorus pesticides by a novel Zr-MOF based smart adsorbent

Heavy metal ions are highly toxic and widely spread as environmental pollutants. New strategies are being developed to efficiently remove these toxic ions. Herein, we use the intrinsic advantages of metal–organic frameworks (MOFs) and develop a porous Zn(II)-based MOF decorated with O− groups for the removal of Pb2+. Benefiting from its multiple porosity, sufficient adsorption sites and strong affinity, the activated MOF material exhibits an ultrahigh Pb2+ uptake capacity (616.64 mg g−1), surpassing all those of reported MOF adsorbents. Moreover, it can selectively capture Pb2+ with high efficiency (>99.27%) against background ions. Even in the presence of a high concentration of competitive ions, such as Ca2+ or Mg2+, effective removal (>99.21%) can also be achieved in a short time. The excellent removal performance demonstrates the strong electrostatic attraction and coordination interaction between the highly accessible O− groups and Pb2+. The possible adsorption mechanism was systematically verified by zeta potential, FT-IR and XPS studies. Our work reveals the enormous potential of functionalized MOFs as an appealing platform to construct sorbent materials.

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

In order to develop a highly efficient method for direct removal of lead from acidic wastewater (pH 2.0), we introduce a novel highly ordered Pb2+ imprinted mesoporous silica (PbIMS) SBA-15 combining co-condensation and functionalized iminodiacetic acid (IDA). Fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray (EDX) analysis provided the components of PbIMS. The solid-state 13C NMR spectra demonstrated the successful embedment of IDA in the mesoporous silica. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis confirmed that Pb2+ was coordinated by the N atom and carboxyl O atom of IDA. The results of transmission electron microscopy (TEM), small angle X-ray diffraction (XRD) and N2 adsorption–desorption measurement confirmed that the PbIMS preserved a highly ordered hexagonal P6mm mesostructure. The Brunauer–Emmett–Teller (BET) surface area was 762 m2 g−1. The saturated adsorption capacity of PbIMS toward lead reached up to 103 mg g−1 at pH 2.0, which was greater even than that of the simply modified SBA-15 by IDA at pH 4.5. The values of selectivity coefficients of PbIMS for six competing metal ions ranged from 67.3 to 12.7. The adsorption of Pb2+ reached equilibrium within 7 min. The adsorption efficiency of PbIMS was above 93% after six extraction–stripping cycles. The investigation conducted with real samples of strongly acidic wastewater demonstrated the ability of PbIMS to efficiently remove lead below the current China regulatory standard.

Efficient removal of lead from highly acidic wastewater by periodic ion imprinted mesoporous SBA-15 organosilica combining metal coordination and co-condensation

We prepared highly ordered metal ion imprinted mesoporous silica (IIMS) through co-condensation using a combination of molecular imprinting technology and traditional mesoporous materials. Copper ion is used as the template. Besides the periodic hexagonal structure, nano-sized wall thickness, and large surface area, it is found that the IIMS has highly specific recognition ability for the template. The imprinting factor of IIMS exhibits a maximum value of 3.7 at pH 2.5. The material shows fast binding kinetics for Cu2+ (complete equilibrium reach only within 5 min) and the saturation adsorption capacity reaches up to 0.39 mmol g−1. Homogeneous binding sites are confirmed by the Langmuir isothermal model and the Langmuir–Freundlich isothermal model. The heterogeneity index is 0.992 with a value similar to those found for molecularly imprinted polymers prepared using covalent imprinting. The recovery of the silica stays above 90% after six extraction–stripping cycles. Furthermore, the silica has significant potential for water treatment applications.

Youwen Tang

Papers

Efficient removal of lead from highly acidic wastewater by periodic ion imprinted mesoporous SBA-15 organosilica combining metal coordination and co-condensation

Highly ordered metal ion imprinted mesoporous silica particles exhibiting specific recognition and fast adsorption kinetics

Methyl parathion imprinted polymer nanoshell coated on the magnetic nanocore for selective recognition and fast adsorption and separation in soils.