A Pyridyltriazol Functionalized Zirconium Metal-Organic Framework for Selective and Highly Efficient Adsorption of Palladium

Bioinspired Construction of Uranium Ion Trap with Abundant Phosphate Functional Groups

Highly efficient extraction of radioactive uranium from aqueous solution remains a serious task in the nuclear energy field. To address this, we here create an effective uranium ion trap by using a novel and facile strategy that introduces bioinspired moiety phytic acid (PA) into highly robust PCN-222. The resultant metal-organic framework (MOF)-based uranium ion trap (PCN-222-PA) with a high density of accessible phosphate groups exhibits a remarkable U(VI) uptake capacity (401.6 mg·g^-1), surpassing most of the reported phosphorus-modified MOFs and various other MOF adsorbents. Kinetics study reveals that PCN-222-PA can reduce the uranium concentration from 10 mg L^-1 to 21 μg L^-1, below the acceptable limit defined by the US Environmental Protection Agency. In addition, PCN-222-PA also shows good selectivity and high stability as well as excellent recyclability toward uranium capture. Our work demonstrates a new strategy to design functional MOFs with abundant phosphate groups and provides a new perspective for extracting uranium from aqueous solution.

Postsynthetic Modification of Metal-Organic Frameworks by Vapor-Phase Grafting

A vapor-phase grafting strategy is developed for the postsynthetic modification of metal-organic frameworks (MOFs). On the basis of the Schotten-Baumann reaction between acyl chloride (-COCl) and amino (-NH₂) groups and hydrolysis of -COCl, the carboxylated MOFs could be prepared through simple exposure in vaporized acyl chloride molecules and immersion in water. The modified MOFs have well-maintained crystalline structures and porosities and show substantially improved fluoride removal performance.

Origins of Clustering of Metalate-Extractant Complexes in Liquid-Liquid Extraction

Effective and energy-efficient separation of precious and rare metals is very important for a variety of advanced technologies. Liquid-liquid extraction (LLE) is a relatively less energy intensive separation technique, widely used in separation of lanthanides, actinides, and platinum group metals (PGMs). In LLE, the distribution of an ion between an aqueous phase and an organic phase is determined by enthalpic (coordination interactions) and entropic (fluid reorganization) contributions. The molecular scale details of these contributions are not well understood. Preferential extraction of an ion from the aqueous phase is usually correlated with the resulting fluid organization in the organic phase, as the longer-range organization increases with metal loading. However, it is difficult to determine the extent to which organic phase fluid organization causes, or is caused by, metal loading. In this study, we demonstrate that two systems with the same metal loading may impart very different organic phase organizations and investigate the underlying molecular scale mechanism. Small-angle X-ray scattering shows that the structure of a quaternary ammonium extractant solution in toluene is affected differently by the extraction of two metalates (octahedral PtCl₆^2- and square-planar PdCl₄^2-), although both are completely transferred into the organic phase. The aggregates formed by the metalate-extractant complexes (approximated as reverse micelles) exhibit a more long-range order (clustering) with PtCl₆^2- compared to that with PdCl₄^2-. Vibrational sum frequency generation spectroscopy and complementary atomistic molecular dynamics simulations on model Langmuir monolayers indicate that the two metalates affect the interfacial hydration structures differently. Furthermore, the interfacial hydration is correlated with water extraction into the organic phase. These results support a strong relationship between the organic phase organizational structure and the different local hydration present within the aggregates of metalate-extractant complexes, which is independent of metalate concentration.

Advanced applications of Zr-based MOFs in the removal of water pollutants

The global water pollution is caused by the increase of industrial and agricultural activities, which have produced various toxic pollutants. Pollutants in water generally consist of metal ions, pharmaceuticals and personal care products (PPCPs), oil spills, organic dyes, and other organic pollutants. Amongst the adsorbents that have been developed to deal with pollutants in water, Zr-based metal-organic frameworks (MOFs) have drawn scientists' great attention due to their excellent stability and adjustable functionalization. Herein, the present review article introduces the synthetic methods of functionalized Zr-based MOFs and summarizes their applications in water pollution treatment. It also clarifies the interactions and removal mechanisms between pollutants and Zr-based MOFs. The use of these MOFs with eminent adsorption ability and recycling performance have been discussed in detail. Zr-based MOFs also face some challenges such as high cost, lack of real water environment applications, selective removal of pollutants, and low ability to remove composite pollutants. Future research should focus on addressing these issues. Although there is still a blank of the practical utility of Zr-based MOFs on a commercial scale, the research reported to date clearly shows that they are very promising materials for the water treatment.

Ionic Liquid-Functionalized Magnetic Metal-Organic Framework Nanocomposites for Efficient Extraction and Sensitive Detection of Fluoroquinolone Antibiotics in Environmental Water

Herein, the hydrophobic carboxyl-functionalized ionic liquid (IL-COOH) was encapsulated into the prepared Fe₃O₄@Zr-MOFs, and the novel water-stable IL-COOH/Fe₃O₄@Zr-MOF nanocomposites were first synthesized. The polydopamine-functionalized Fe₃O₄ was introduced to construct the core-shell structure via layer-by-layer modification, and the controlled growth of Zr-MOFs was achieved, which realized the adjustment of charged properties of nanocomposites and simplified the adsorption or extraction process. The IL-COOH/Fe₃O₄@Zr-MOFs were fully studied by IR, HNMR, XRD, N₂ adsorption-desorption isotherms, TEM, EDS mapping, VSM, and so on. Then, they were employed for the selective adsorption and detection of fluoroquinolone antibiotics (FQs). The adsorption isotherms and kinetics demonstrated that the adsorption process followed a pseudo-second-order kinetic model and the Langmuir isotherm model. Among them, IL-COOH/Fe₃O₄@UiO-67-bpydc showed the best adsorption performance, and the maximum adsorption capacity of ofloxacin was 438.5 mg g^-1. Coupled magnetic solid-phase extraction with HPLC-DAD, a convenient, sensitive, and efficient method for extraction and detection of FQs in environmental water, was developed based on IL-COOH/Fe₃O₄@UiO-67-bpydc. The recoveries of environmental water were ranging from 90.0 to 110.0%, and the detection limits were lower than 0.02 μg L^-1. The novel functionalized composites served as solid-phase adsorbents and liquid-phase extractants. This study also provided a promising strategy for designing and preparing multi-functionalized nanocomposites for the removal or detection of pollutants in environmental samples.

Metal-Organic Frameworks Based on Group 3 and 4 Metals

Metal-organic frameworks (MOFs) based on group 3 and 4 metals are considered as the most promising MOFs for varying practical applications including water adsorption, carbon conversion, and biomedical applications. The relatively strong coordination bonds and versatile coordination modes within these MOFs endow the framework with high chemical stability, diverse structures and topologies, and interesting properties and functions. Herein, the significant progress made on this series of MOFs since 2018 is summarized and an update on the current status and future trends on the structural design of robust MOFs with high connectivity is provided. Cluster chemistry involving Y, lanthanides (Ln, from La to Lu), actinides (An, from Ac to Lr), Ti, and Zr is initially introduced. This is followed by a review of recently developed MOFs based on group 3 and 4 metals with their structures discussed based on the types of inorganic or organic building blocks. The novel properties and arising applications of these MOFs in catalysis, adsorption and separation, delivery, and sensing are highlighted. Overall, this review is expected to provide a timely summary on MOFs based on group 3 and 4 metals, which shall guide the future discovery and development of stable and functional MOFs for practical applications.

One-step synthesis of functional metal organic framework composite for the highly efficient adsorption of tylosin from water

Functional metal organic framework composite can effectively remove antibiotics from environmental water samples. However, designing excellent adsorbents with multiple active sites via a rapid one-step method is still a challenging problem. A novel metal organic framework composite (UiO-66-NH₂-AMPS) was synthesized through one-step polymerization by adding functional monomer 2-acrylamide-2-methylpropanesulfonic acid (AMPS) during the preparation of UiO-66-NH₂. The microstructure and morphology of the UiO-66-NH₂-AMPS composite were characterized, and the adsorption performance towards tylosin (TYL) in water was explored by equilibrium adsorption experiment. The results illustrated that the adsorption equilibrium can be reached within 1 h, and the maximum binding amount of UiO-66-NH₂-AMPS for TYL was 161.60 mg g^-1, which was approximately 2.1-329 times of that of the other adsorbents. The pseudo second-order kinetic and Liu isotherm model were suitable for the adsorption process, and thermodynamic study displayed that the adsorption of UiO-66-NH₂-AMPS composite for TYL is spontaneous and endothermal. The infrared and X-ray photoelectron spectra exhibited that hydrogen bond and electrostatic interaction were the primary recognition force for TYL. The UiO-66-NH₂-AMPS composite have been successfully applied to remove TYL from environmental water. After 5 cycles, the removal efficiency of UiO-66-NH₂-AMPS was still above 91.30%.