Solvent-assisted Ligand Incorporation Research Articles

Functionalized Metal-Organic Framework for NADH Regeneration by Hydrogen in a Redox Flow Bioreactor.

The electrochemical regeneration of reduced nicotinamide adenine dinucleotide (NADH) using [Rh(Cp*)(bpy)Cl]+ holds significant promise for the industrial synthesis of chiral chemicals. However, challenges persist due to the high consumption of NADH and the limited efficiency of its cyclic regeneration, which currently hinder widespread application. To address these obstacles, based on in-situ growth of 3D ordered metal-organic framework (NU-1000) on the surface of graphite felt, [Rh(Cp*)(bpy)Cl]+ were immobilized on the Zr6 nodes of NU-1000 by solvent-assisted ligand incorporation (SALI), and applied in a flow bioreactor. Moreover, we employ a gas diffusion electrode (GDE) to oxidize H2, providing a clean proton source for the electrochemical regeneration of NADH. Consequently, highly efficient enzymatic electrocatalytic synthesis of L-lactate was achieved when coupled with L-lactate dehydrogenases (LDH) as a model reaction, and the total turnover number (TTN) reached 19600 and 1750 for [Rh(Cp*)(bpy)Cl]+ and NAD+ after 48 h, corresponding to a high turnover frequency (TOF) of 2350 h-1 and 210 h-1 for [Rh(Cp*)(bpy)Cl]+ and NAD+, respectively. This work provides new insights for the construction of efficient enzymatic electrosynthesis systems in industrial production.

Constructing perfluorinated UiO-67 for enrichment of polycyclic aromatic hydrocarbons in seawater and seabed sediments

To investigate the ocean contamination caused by polycyclic aromatic hydrocarbons (PAHs), UiO-67/perfluorooctanoic acid (UiO-67/PFOA) was synthesized through solvent-assisted ligand incorporation method. The UiO-67/PFOA was then served as an adsorbent in headspace solid-phase microextraction (HS-SPME) technology for collecting and concentrating trace PAHs. The addition of the PFOA improved the hydrophobicity and stability of the UiO-67/PFOA coating, and the C-F functional group in UiO-67/PFOA could form the pseudo hydrogen bonding with the C-H on the benzene ring of PAHs, which endowed the UiO-67/PFOA with 1.60-4.63 times enrichment performance for PAHs than UiO-67. Under optimal conditions, the wide linear ranges of PAHs (0.01-20 ng·mL−1) with good coefficients of determination (R2 ≥ 0.9950) and low limits of detection (LODs, 0.003-0.008 ng·mL−1) were obtained. The recoveries of five PAHs from spiked seawater and seabed sediment by the developed method ranged from 81.14% to 116.0% with satisfactory results. This work provided a good adsorbent for the enrichment of trace PAHs in complicated environments and a new approach for the subsequent synthesis of adsorbents with good enrichment performance.

Dual-functional porphyrinic zirconium-based metal-organic framework for the fluorescent sensing of histidine enantiomers and Hg2.

A novel fluorescence sensor based on a porphyrinic zirconium-based metal-organic framework, L-cysteine-modified PCN-222 (L-Cys/PCN-222), was developed to selectively recognize histidine enantiomers and sensitively detect Hg2+. The dual-functional sensor was successfully prepared via the solvent-assisted ligand incorporation method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), 1H nuclear magnetic resonance (1H NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption analyses. L-Cys/PCN-222 not only showed a higher quenching response for L-histidine than that for D-histidine with a fast fluorescent response rate of <40 s but also exhibited low detection limits for L- and D-histidine (2.48 μmol L-1 and 3.85 μmol L-1, respectively). Moreover, L-Cys/PCN-222 was employed as a fluorescent and visual sensor for the highly sensitive detection of Hg2+ in the linear range of 10-500 μmol L-1, and the detection limit was calculated to be 2.79 μmol L-1 in surface water. The specific and selective recognition of chiral compounds and metal ions by our probe make it suitable for real field applications.

Geometry and Chemistry: Influence of Pore Functionalization on Molecular Transport and Diffusion in Solvent-Filled Zirconium Metal-Organic Frameworks.

Postsynthetic modification (PSM) of metal-organic frameworks (MOFs) enables incorporation of diverse functionalities in pores for chemical separations, drug delivery, and heterogeneous catalysis. However, the effect of PSM on molecular transport, which is essential for most applications of MOFs, has been rarely studied. In this paper, we used perfluoroalkane-functionalized Zr-MOF NU-1008 as a platform to systematically interrogate transport processes and mechanisms in solvated pores. We anchored perfluoroalkanes onto NU-1008 nodes by solvent-assisted ligand incorporation (SALI-n, with n = 3, 5, 7, and 9 denoting the number of fluorinated carbons). Transport of a luminescent molecule, BODIPY, through individual crystallites of four versions of methanol-filled SALI-n was monitored by confocal fluorescence microscopy as a function of time and location. In comparison with the parent NU-1008, the diffusivity of the probe molecules within SALI-n declined by 2- to 7-fold depending on chain length and loading, presumably due to the reduction in pore diameter or adsorptive interactions with perfluoroalkyl chains. Atomistic simulations were performed to uncover the microscopic behavior of the BODIPY diffusion in SALI-n. The perfluoroalkyl chains are observed to stay close to the pore walls, instead of extending toward the pore center. BODIPY molecules, which preferably interact with linkers, were pushed to the interior of the channels as the chain length increased, resulting in solvated diffusion and minor differences in the short-time mobility of BODIPY in SALI-n. This suggested that the observed decline of transport diffusivity in SALI-n mainly stemmed from the reduction in the pore size when these flexible chains are present. We anticipate that this proof of concept will assist in understanding how pore functionalization can physically and chemically affect mass transport in MOFs and will be useful in further guiding the design of PSM to realize the optimal performance of MOFs for various applications.

Immobilization of Gold Nanoparticles on Postsynthetically Modified NU-1000 for Hydrogen Evolution Reaction

NU-1000, being a hydrothermally stable metal-organic framework (MOF), with structural robustness is viable for functionalization with various entities. A postsynthetic modification strategy called solvent-assisted ligand incorporation (SALI) is chosen for functionalizing NU-1000 with thiol moieties using 2-mercaptobenzoic acid. In accordance with soft acid-soft base interactions, the thiol groups on NU-1000, as a scaffold, can immobilize the gold nanoparticles without much aggregation. The catalytically active gold sites on thiolated NU-1000 are utilized for hydrogen evolution reaction (HER). The catalyst delivered an overpotential of 101 mV at a current density of 10 mAcm-2 in 0.5 M H2SO4. The faster charge transfer kinetics determined from the Tafel slope of 44 mV/dec enhances the HER activity. The sustainable performance of the catalyst for 36 h proves its utility as a potential catalyst to produce neat hydrogen.

Metal-organic framework functionalized bipolar electrodes for bulk electroenzymatic synthesis

Electrochemical regeneration of the cofactor nicotinamide adenine dinucleotide (NADH) is crucial for the enzymatic synthesis of a variety of valuable chemicals. [Rh(Cp*)(bpy)Cl]+ has been reported as one of the most efficient non-enzymatic catalysts for electrochemical regeneration of NADH, but the efficiency of the existing systems is still far from satisfying. Here we propose to suspend metal–organic framework functionalized glassy carbon beads in a bipolar electrochemical cell under mechanical stirring for bulk electroenzymatic synthesis. The beads are modified with a metal–organic framework NU-1000 shell, in which [Rh(Cp*)(bpy)Cl]+ catalyst is incorporated via the solvent-assisted ligand incorporation approach. Enzymatically active 1,4-NADH is electrochemically regenerated, and finally bipolar electrochemical bulk conversion of pyruvate into L-lactate is performed in the presence of NADH dependent L-lactate dehydrogenase as a model system. The very high turnover frequency (TOF) of 3100 ± 106 h−1 opens up promising perspectives for employing this concept also for various other electroenzymatic bulk processes.

A dual-mode pH sensor film based on the pyrene-based Zr-MOF self-destruction with fluorescence turn-on effect

Rapid detection of on-the-spot water sample pH has become an urgent problem to resolve, and developing a method with the characters of fast, convenient and low-cost is significant. In this study, an amino functionalized pyrene-based Zr-MOF (NU-1000-NH2) was synthesized by solvent-assisted ligand incorporation (SALI) method, in which the Zr6 metal cluster, fluorescent pyrene-based H4TBAPy and p-aminobenzoic acid were acted as node, linker and modulator, respectively. The as-synthesized NU-1000-NH2 possessed the pH-dependent fluorescence enhancement property at 450 nm emission under alkaline condition, thus a convenient fluorescence “turn-on” pH sensor was fabricated. Upon introduction of OH–, the carboxylate groups in NU-1000-NH2 could react with it, and the deprotonation and gradual collapse of the NU-1000-NH2 crystal were occurred, resulting in the release of the fluorescent H4TBAPy ligand and fluorescence enhancement. Moreover, to solve the difficulties of on-the-spot pH detection, the solid-phase pH film sensor was successfully constructed by embedding the NU-1000-NH2 particles into the polyvinyl alcohol (PVA), combining with the RGB model and smartphone detector. The proposed fluorescent MOF-based pH sensor with dual-mode detection is expected to achieve on-the-spot pH monitoring in the field of environmental monitoring.

Porphyrin-Moiety-Functionalized Metal–Organic Layers Exhibiting Catalytic Capabilities for Detoxifying Nerve Agent and Blister Agent Simulants

The development of very efficient bifunctional catalysts for the simultaneous detoxification of two kinds of the deadliest chemical warfare agents (CWAs), nerve agent and blister agent, is highly desirable. In this study, two porphyrin-based ligands [tetrakis(4-carboxyphenyl) porphyrin (TCPP) and protoporphyrin IX (PPIX)] are introduced into 2D Zr-1,3,5-tris(4-carboxyphenyl)benzene (BTB) metal-organic layers (MOLs), composed of six-connected Zr6 nodes and the tritopic carboxylate ligand BTB, by a solvent-assisted ligand incorporation method. The loads of TCPP and PPIX are 6.4 and 10.9 wt %, respectively. The detoxification of simulants of the nerve agent and the blister agent was conducted to investigate the catalytic activity of porphyrin-moiety-functionalized MOLs. The reaction half-life of optimal TCPP-functionalized MOL catalyzing the hydrolysis of a nerve agent simulant is only 2.8 min, meanwhile, the half-life of the selective catalytic oxidation of a blister agent simulant is only 1.2 min under LED illumination. More importantly, such a degradation half-life is only about 4 min under natural sunlight (∼60 mW/cm2). To our knowledge, TCPP-functionalized MOL is by far the most efficient catalyst for blister agent simulant degradation under solar light. Therefore, 2D ultrathin MOLs on demand appear to be a promising and efficient material platform for the development of bifunctional catalysts for CWA protection.

Precisely introducing active sites into NU-1000 through linker incorporation for degrading sulfamethoxazole under visible-light photo-Fenton process

Combining adsorption and catalytic degradation to remove micropollutants in water has become a scientific challenge. However, the current material possessing both suitable pore size and evenly distributed active sites together is less common. Herein, we synthesized stable mesoporous metal–organic framework (MOFs) with Zr6 clusters and carboxylate linkers using solvent-assisted linker incorporation and post-synthetic metalation (NU-1000-Fe). A terpyridine-iron (II/III)-based metal–ligand was introduced into the porous channels successfully in Zr-MOFs without changing the mesoporous skeleton. The remained mesoporosity of the framework facilitated the adsorption of sulfamethylthiazole (SMX) in water (adsorption efficiency ∼ 40 %). Besides, it is verified that efficient p-n heterojunctions were successfully constructed by terpyridine-iron (II/III) and NU-1000. Results show that the accelerated charge transfer and photo-generated electron-hole separation abilities through introducing terpyridine-iron (II/III) facilitate the elimination of SMX in the process of visible-light photo-Fenton (removal efficiency > 90 %). Our findings offer a facile solvent-assisted ligand incorporation strategy for introducing additional active sites into MOFs to promote the degradation of micropollutants in water.

Fine-Tuning the Electrocatalytic Regeneration of NADH Cofactor Using [Rh(Cp*)(bpy)Cl]+-Functionalized Metal-Organic Framework Films.

Electrochemical regeneration of the reduced form of the nicotinamide adenine dinucleotide (NADH) cofactor catalyzed by immobilized [Rh(Cp*)(bpy)Cl]+ is a promising approach for the enzymatic synthesis of many valuable chemicals with NAD-dependent dehydrogenases. However, rational control of the efficiency is often limited by the irregular structure of the electrode/electrolyte interface and the accessibility of the molecular catalyst. Here, we propose an electrochemical system for NADH cofactor regeneration, based on highly ordered three- dimensional (3D) metal-organic framework (NU-1000) films. [Rh(Cp*)(bpy)Cl]+ is incorporated at the zirconium nodes of NU-1000 via solvent-assisted ligand incorporation (SALI), leading to a diffusion-controlled behavior, associated with an electron hopping mechanism. Varying the ratio of redox-active [Rh(Cp*)(bpy)Cl]+ and inactive postgrafting agents enables the elaboration of functional electrodes with tunable electrocatalytic activity for NADH regeneration. The exceptionally high faradic efficiency of 97%, associated with a very high turnover frequency (TOF) of ∼1400 h-1 for NADH regeneration, and the total turnover number (TTN) of over 20000 for the enzymatic conversion from pyruvate to l-lactate, when coupled with l-lactate dehydrogenases (LDH) as a model reaction, open up promising perspectives for employing these electrodes in various alternative bioelectrosynthesis approaches.

Ferrocene-boosting Zr-MOFs for efficient photocatalytic CO2 reduction: A trade-off between enhancing LMCT and frustrating Lewis acid

The introduction of rich-electron ligands is a promising strategy to improve the ligand-to-metal charge transfer (LMCT) ability of metal–organic frameworks (MOFs) for efficient photocatalytic CO2 reduction reactions (CO2RR), while the resulting impaired Lewis acid sites go against stable bonding with CO2 and hinder the electron transfering to CO2. It is thus the key to search a trade-off between increasing LMCT and frustrating Lewis acid. Herein, the ferrocene (Fc) modified UiO-66 series MOFs, NH2-UiO-66-Fc, have been prepared to optimize LMCT for boosting CO2RR through a simple solvent-assisted ligand incorporation (SALI) method. Theoretical calculation and systematic experiments, including photoelectrochemical measures, in situ electron paramagnetic resonance, fluorescence probe analysis and X-ray photoelectron spectroscopy indicate that with increasing Fc content, the LMCT energy of MOFs significantly decreases from 2.66 to 2.10 eV based on the established electron transfer double-channel mechanism, while the Lewis acidity of Zr sites reduces with the CO2 adsorption energy (Ead) ranging from −1.061 to −0.632 eV. Through introducing an optimal Fc content, NH2-UiO-66-Fc(2.0) integrating satisfactory LMCT ability and Lewis acidity shows superior photocatalytic CO2RR performance (CO yield: 90.65 μmol·g−1·h−1), about 13 times higher than that of the unmodified MOF and superior to most reported pristine MOF photocatalysts. DFT calculation demonstrates that the excellent performance of NH2-UiO-66-Fc(2.0) is attributed to the lowest energy barrier of 1.50 eV for the rate-limiting step of *COOH formation. In this work, such a simple post-modification strategy for facilitating the whole electron transfer path of photocatalytic CO2RR will provide a new way to construct high-performance MOFs-based CO2RR photocatalysts.

Redox-Hopping-Based Charge Transport Mediated by Ru(II)-Polypyridyl Species Immobilized in a Mesoporous Metal-Organic Framework

Electronic charge transport through crystalline metal-organic frameworks (MOFs) can be accomplished by site-to-site electron (or hole) hopping, provided that redox-active sites, such as easily reducible or oxidizable MOF linkers, are present. If the framework itself is redox-inert, solvent-assisted ligand incorporation of redox-active moieties can serve to enable hopping-based charge transport. Here we have studied the redox hopping process within Ru-bpy@NU-1008, where Ru-bpy is a carboxylate-functionalized derivative, i.e., a node-ligating derivative, of the well-known chromophore Ru(2,2′-bipyridine)32+, and NU-1008 is a redox-inert MOF featuring hierarchical porosity and csq topology. Chronoamperometry experiments with electrode-supported thin films of Ru-bpy@NU-1008 show that charge transport is feasible through portions of the MOF, with other portions being inaccessible. Possible confounding features are the undersized c-pores that cross-connect 1D mesoporous channels, as ingress and egress of charge-compensating anions is believed to accompany the net oxidation of Ru(II) to Ru(III) and the reduction of Ru(III) to Ru(II). Phenomenologically, transport through the electroactive portion of the films is diffusion-like, with the magnitude of the apparent diffusion coefficient being 6 × 10−12 cm2/s.

Catalytically active silver nanoparticles stabilized on a thiol-functionalized metal-organic framework for an efficient hydrogen evolution reaction.

A post-synthetic technique, Solvent Assisted Ligand Incorporation (SALI), was used for thiol functionalization in the zirconium-based metal-organic framework NU-1000. This thiol-functionalized MOF was employed as a support for the growth of silver nanoparticles (Ag NPs) through coordination of a Ag(I) complex with a node-anchored thiol-ligand, followed by the reduction of Ag(I) to Ag(0). X-ray photoelectron spectroscopy revealed that the ratio of Ag(0) to Ag(I) proportionally increased with the loading of silver ions. The HER activity increased with the enhancement of Ag(0) in the system and the best efficiency was observed for the composite with ∼95% Ag(0). This composite displayed an overpotential of 165 mV in an acidic medium at 10 mA cm-2 and a Tafel slope of 53 mA dec-1. The loading of silver beyond the optimum value led to the aggregation of the particles which affected the overpotential substantially. The catalyst demonstrated appreciable static stability for 24 h, which promotes the use of the material as an HER catalyst. Therefore, these results emphasized that Ag NPs embedded onto a thiol-functionalized MOF is a propitious material for developing a clean and renewable energy source.

L-Cysteine modified metal-organic framework as a chiral stationary phase for enantioseparation by capillary electrochromatography.

A new kind of chiral zirconium based metal–organic framework, l-Cys-PCN-222, was synthesized using l-cysteine (l-Cys) as a chiral modifier by a solvent-assisted ligand incorporation approach and utilized as the chiral stationary phase in the capillary electrochromatography system. l-Cys-PCN-222 was characterized by X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, Fourier-transform infrared spectra, nitrogen adsorption/desorption, circular dichroism spectrum, zeta-potential and so on. The results revealed that l-Cys-PCN-222 had the advantages of good crystallinity, high specific surface area (1818 m2 g−1), thermal stability and chiral recognition performance. Meanwhile, the l-Cys-PCN-222-bonded open-tubular column was prepared using l-Cys-PCN-222 particles as the solid phase by ‘thiol–ene’ click chemistry reaction and characterized by scanning electron microscopy, which proved the successful bonding of l-Cys-PCN-222 to the column inner wall. Finally, the stability, reproducibility and chiral separation performance of the l-Cys-PCN-222-bonded OT column were measured. Relative standard deviations (RSD) of the column efficiencies for run-to-run, day-to-day, column-to-column and runs were 1.39–6.62%, and did not obviously change after 200 runs. The enantiomeric separation of 17 kinds of chiral compounds including acidic, neutral and basic amino acids, imidazolinone and aryloxyphenoxypropionic pesticides, and fluoroquinolones were achieved in the l-Cys-PCN-222-bonded OT column. These results demonstrated that the chiral separation system of the chiral metal–organic frameworks (CMOFs) coupled with capillary electrochromatography has good application prospects.

Temperature-Dependent Nitrous Oxide/Carbon Dioxide Preferential Adsorption in a Thiazolium-Functionalized NU-1000 Metal-Organic Framework.

Solvent-assisted ligand incorporation (SALI) of the ditopic linker 5-carboxy-3-(4-carboxybenzyl)thiazolium bromide [(H2PhTz)Br] into the zirconium metal–organic framework NU-1000 [Zr6O4(OH)8(H2O)4(TBAPy)2, where NU = Northwestern University and H4TBAPy = 1,3,6,8-tetrakis(p-benzoic-acid)pyrene], led to the SALIed NU-1000-PhTz material of minimal formula [Zr6O4(OH)6(H2O)2(TBAPy)2(PhTz)]Br. NU-1000-PhTz has been thoroughly characterized in the solid state. As confirmed by powder X-ray diffraction, this material keeps the same three-dimensional architecture of NU-1000 and the dicarboxylic extra linker bridges adjacent [Zr6] nodes ca. 8 Å far apart along the crystallographic c-axis. The functionalized MOF has a BET specific surface area of 1560 m2/g, and it is featured by a slightly higher thermal stability than its parent material (Tdec = 820 vs. 800 K, respectively). NU-1000-PhTz has been exploited for the capture and separation of two pollutant gases: carbon dioxide (CO2) and nitrous oxide (N2O). The high thermodynamic affinity for both gases [isosteric heat of adsorption (Qst) = 25 and 27 kJ mol–1 for CO2 and N2O, respectively] reasonably stems from the strong interactions between these (polar) “stick-like” molecules and the ionic framework. Intriguingly, NU-1000-PhTz shows an unprecedented temperature-dependent adsorption capacity, loading more N2O in the 298 K ≤ T ≤ 313 K range but more CO2 at temperatures falling out of this range. Grand canonical Monte Carlo simulations of the adsorption isotherms confirmed that the preferential adsorption sites of both gases are the triangular channels (micropores) in close proximity to the polar pillar. While CO2 interacts with the thiazolium ring in an “end-on” fashion through its O atoms, N2O adopts a “side-on” configuration through its three atoms simultaneously. These findings open new horizons in the discovery of functional materials that may discriminate between polluting gases through selective adsorption at different temperatures.

Photoinduced Charge Transfer with a Small Driving Force Facilitated by Exciplex-like Complex Formation in Metal-Organic Frameworks.

Photoinduced charge transfer (PCT) is a key step in the light-harvesting (LH) process producing the redox equivalents for energy conversion. However, like traditional macromolecular donor-acceptor assemblies, most MOF-derived LH systems are designed with a large ΔG0 to drive PCT. To emulate the functionality of the reaction center of the natural LH complex that drives PCT within a pair of identical chromophores producing charge carriers with maximum potentials, we prepared two electronically diverse carboxy-terminated zinc porphyrins, BFBP(Zn)-COOH and TFP(Zn)-COOH, and installed them into the hexagonal pores of NU-1000 via solvent-assisted ligand incorporation (SALI), resulting in BFBP(Zn)@NU-1000 and TFP(Zn)@NU-1000 compositions. Varying the number of trifluoromethyl groups at the porphyrin core, we tuned the ground-state redox potentials of the porphyrins within ca. 0.1 V relative to that of NU-1000, defining a small ΔG0 for PCT. For BFBP(Zn)@NU-1000, the relative ground- and excited-state redox potentials of the components facilitate an energy transfer (EnT) from NU-1000* to BFBP(Zn), forming BFBP(Zn)S1* which entails a long-lived charge-separated complex formed through an exciplex-like [BFBP(Zn)S1*-TBAPy] intermediate. Various time-resolved spectroscopic data suggest that EnT from NU-1000* may not involve a fast Förster-like resonance energy transfer (FRET) but rather through a slow [NU-1000*-BFBP(Zn)] intermediate formation. In contrast, TFP(Zn)@NU-1000 displays an efficient EnT from NU-1000* to [TFP(Zn)-TBAPy], a complex that formed at the ground state through electronic interaction, and thereon showed the excited-state feature of [TFP(Zn)-TBAPy]*. The results will help to develop synthetic LHC systems that can produce long-lived photogenerated charge carriers with high potentials, i.e., high open-circuit voltage in photoelectrochemical setups.

Chiral fluorescence recognition of glutamine enantiomers by a modified Zr-based MOF based on solvent-assisted ligand incorporation.

In this study, three types of chiral fluorescent zirconium-based metal–organic framework materials were synthesized using l-dibenzoyl tartaric acid as the chiral modifier by the solvent-assisted ligand incorporation method, which was the porous coordination network yellow material, denoted as PCN-128Y. PCN-128Y-1 and PCN-128Y-2 featured unique chiral selectivity for the Gln enantiomers amongst seven acids and the highly stable luminescence property, which were caused by the heterochiral interaction and aggregation-induced emission. Furthermore, a rapid fluorescence method for the chiral detection of glutamine (Gln) enantiomers was developed. The homochiral crystals of PCN-128Y-1 displayed enantiodiscrimination in the quenching by d-Gln such that the ratio of enantioselectivity was 2.0 in 30 seconds at pH 7.0, according to the Stern–Volmer quenching plots. The detection limits of d- and l-Gln were 6.6 × 10−4 mol L−1 and 3.3 × 10−4 mol L−1, respectively. Finally, both the maximum adsorption capacities of PCN-128Y-1 for the Gln enantiomers (Qe(l-Gln) = 967 mg g−1; Qe(d-Gln) = 1607 mg g−1) and the enantiomeric excess value (6.2%) manifested that PCN-128Y-1 had strong adsorption capacity for the Gln enantiomers and higher affinity for d-Gln.

Thiol-functionalized PCN-222 MOF for fast and selective extraction of gold ions from aqueous media

With the growing demand of gold for research laboratories and industrial technologies, there is high needed to extract gold from related waste other than natural resources. Herein, we designed a novel adsorbent denoted as PCN-222-MBA (Thiol-functionalized PCN-222), by functionalizing Zr6-nodes of PCN-222 (PCN = Porous Coordination Network) with 4-mercaptobenzoic acid (MBA) through solvent-assisted ligand incorporation (SALI) approach for selective and facile extraction of gold ions from aqueous media. The mesoporous MOF was characterized by different techniques. The performance of PCN-222-MBA as solid adsorbent was assessed under batch conditions, with significant parameters studied and optimized. The maximum adsorption capacity of the respective adsorbent was 714.3 mg/g at pH 6.1 and 1 min. PCN-222-MBA exhibited high affinity for Au(III) than other coexisting ions and could be regenerated at least six cycles. Gold ions were also extracted and determined in real samples.

Regioselective Functionalization of the Mesoporous Metal-Organic Framework, NU-1000, with Photo-Active Tris-(2,2'-bipyridine)ruthenium(II).

Solvent-assisted ligand incorporation is an excellent method for the post-synthetic functionalization of Zr-based metal–organic frameworks (MOFs), as carboxylate-derivative functionalities readily coordinate to the Zr6 nodes by displacing node-based aqua and terminal hydroxo ligands. In this study, a photocatalytically active ruthenium complex RuII(bpy)2(dcbpy), that is, bis-(2,2′-bipyridine)-(4,4′-dicarboxy-2,2′-bipyridine)ruthenium, was installed in the mono-protonated (carboxylic acid) form within NU-1000 via SALI. Crystallographic information regarding the siting of the ruthenium complex within the MOF pores is obtained by difference envelope density analysis. The ruthenium-functionalized MOF, termed Ru-NU-1000, shows excellent heterogeneous photocatalytic activity for an oxidative amine coupling reaction.

A porous multifunctional and magnetic layered graphene oxide/3D mesoporous MOF nanocomposite for rapid adsorption of uranium(VI) from aqueous solutions

A novel adsorbent, GO/Fe3O4/OPO3H2/PCN-222, was successfully synthesized via graphene oxide (GO) modification with magnetic particles, phosphorous-containing groups, and a mesoporous Zr-MOF, PCN-222 (PCN stands for Porous Coordination Network), respectively, to give the nominal composite. The last step was through a solvent-assisted ligand incorporation technique. Morphological, structural, and physicochemical properties of the hybrid material was assessed by FT-IR, PXRD, SEM/EDX, BET surface area, VSM, TGA/DSC, UV–vis DRS, and ICP-OES analyses. This solid was then used for dispersive solid phase extraction of uranium ions dissolved in water. Several parameters including pH of solution, extraction and desorption times, amount of adsorbent, and type and concentration of elution solvent were investigated and optimized. The maximum adsorption capacity of adsorbent was found to be 416.7mgg−1 (pH, 6.2; amount of adsorbent, 5.0mg; extraction time, 3.0min) beyond what was achievable with the individual components. In addition, various coordination modes between the multifunctional adsorbent and uranyl ions were investigated by DFT calculations in details, revealing some favorable non-covalent cation–π interaction and strong binding of free-base porphyrin, carboxyl and phosphorous-containing groups to the uranium ions. Under optimized conditions, high determination coefficient (R2=0.9994) was obtained and limit of detection and relative standard deviation were found 0.9μgL−1 and 2.7%, respectively.