Cd-based Metal-organic Framework Research Articles

Synthesis and characterization of a β-cyclodextrin-MOF-based porous hydrogel for efficient adsorption of Au3+, Ag+, and Pb2+ ions

Wastewater containing heavy metal ions produced by electroplating, smelting and other industries poses a threat to human safety. Recently, metal–organic frameworks (MOFs) have emerged as porous crystalline adsorbents for the removal of heavy metal ions. Starch-derived cyclodextrins (CDs), a series of cyclic oligosaccharides, have been explored for fabrication of cost-efficient MOF materials. However, the coordination bonds in CD-based MOFs can be destroyed by water, which limits their application as absorbent materials for the removal of heavy metal ions from wastewater. In this work, a β-CD-MOF-based porous hydrogel was developed by incorporating a crosslinked hydrogel network based on acrylic acid (AA) and N,N’-methylenebis(acrylamide) (MBA) monomers into a β-CD-based MOF structure. The synthesized porous hydrogel, denoted A/M−CDMOF−gel, not only showed enhanced structural stability but also exhibited excellent properties for simultaneous adsorption of Au3+, Ag+, and Pb2+ ions. A kinetic study revealed that the A/M−CDMOF−gel had a satisfactory binding rate within 60 min of contact, and the higher fit coefficient from the pseudo-second-order model indicated its chemical adsorption property. Moreover, according to the Langmuir isotherm model fitting results, the maximum capacity of the A/M−CDMOF−gel reached 316.4, 60.9, and 414.2 mg/g for Au3+, Ag+, and Pb2+, respectively. Therefore, the regenerable A/M−CDMOF−gel adsorbent is expected to provide ideas for the development of renewable absorbent materials in the field of wastewater treatment and remediation.

Two new Cd-based metal–organic frameworks for afterglow detection of Fe3+ and NH3

The present study showcases two Cd-based MOFs that exhibit potential as afterglow probes for the “turn off” and “turn on” detection of Fe3+ ions and NH3, respectively.

A Cd-based MOF crystal vessel for the synthesis of interhalogens

As important halogenating and oxidant agents, the synthesis and utilization of interhalogens are plagued by their purity problem, strong volatility and high reactivity. Herein, a flexible Cd-based metal-organic framework (MOF), {[Cd(1,4-bdc)(4-bpa)]·DMF}n (1, where 4-bpa = 1,2-bis(4-pyridyl)acetylene), was prepared and its corresponding activation species, [Cd(1,4-bdc)(4-bpa)]n (2), with moderate pore size and shape, acting as a crystal vessel, was applied to synthesize and store pure interhalogens. The synthesis of interhalogen was realized by quantitive transformation of halogen molecules incorporated in the pores of 2, which was confirmed by single-crystal X-ray diffraction and other structural characterizations. The embedded interhalogen molecules were stabilized by their interactions with the inner groups of the porous framework of 2 and released in polar solvent and utilized in iodocyclization of organic alcohols with high selectivity. This work not only opens a new door to the synthesis of pure interhalogens but also demonstrates powerful applications of MOF crystal vessels in realizing classic but important inorganic and organic reactions.

Enhancement of catalytic activity for hydrogenation of nitroaromatic by anionic metal-organic framework

Nitroaromatic hydrogenation catalysis without precious metals remains a longstanding challenge. The rate of electron transfer is the crucial factor affecting hydrogenation catalysis. Herein, an ionic Cd-based metal-organic framework (I-Cd-MOF) exhibiting a unique structure with one-dimensional (1D) opening nanochannels and good electron transfer ability was synthesized for catalyzing hydrogenation of 4-nitrophenol (4-NP). The catalytic activity of the unique I-Cd-MOF without noble metals is detected, which is higher than most reported noble metal catalysts. Remarkably, the reaction rate of I-Cd-MOF (4.28 min−1) is about 47.6 times higher than that of the Cd-based neutral MOF (N-Cd-MOF) with the similar crystalline structure. Liquid chromatograph mass spectrometer (LC-MS) and theoretical results demonstrate that 4-NP and five intermediates are stabilized in the channels of I-Cd-MOF, which increases the possibility of contact with H* and H2 generated at the Cd sites. The I-Cd-MOF was extended to other nitroaromatic hydrogenation catalysis, which still displays excellent activity. More importantly, the I-MOF@Filter membrane was successfully constructed for continuous hydrogenation catalytic reactions, which maintains a high catalytic performance after 7 cycles of recycling without washing. This work fills in the application of the I-MOFs in hydrogenation catalytic reactions and provides an effective way for the rapid and green degradation of nitroaromatic compounds.

A 2D Cd-based metal organic framework: synthesis, structure, selectively and sensitive sensing of Fe3+

A Cd-based metal organic framework (Cd-MOF), {Cd2[H(t-4-cpp)]2(bibp)2}n, was constructed using 2,4,6-tri(4-carboxylphenyl)pyridine [H3(t-4-cpp)] and 4,4'-bis(imidazolyl)biphenyl (bibp) through the solvothermal method. Its structure was characterized by X-ray single-crystal diffraction. Cd-MOF crystallizes in the triclinic system, P-1 space group and features a two-dimensional (2D) framework. The fluorescence quenching results showed that Cd-MOF can selectively and sensitively sense Fe3+ with a detection limit of 0.993 μM.

Ferric ion substitution renders cadmium metal-organic framework derivatives for modulated Li storage based on local oxidation active centers.

In this work, a novel anionic Cd-MOF ([(CH3)2NH2]n[Cd(HL)DMF]n·2nH2O·nDMF, H4L = 1,2,4,5-tetrakis[(4-carboxy)phenoxymethyl]benzene) was synthesized for the first time. As a precursor, it was utilized to obtain Fe@Cd-MOF crystals via the substitution of Fe3+ ions due to a negatively charged framework and free-coordinated carboxyl group. Fe3O4/Fe-embedded carbon-based materials (Fe@Cd-MOFD) were further constructed by deriving Fe@Cd-MOF at high temperatures. The derived Fe@Cd-MOFD showed a structure resembling a central city with metal redox centers embedded into a carbon matrix. The introduced Fe3+ ions formed a local nano-sized metal oxide upon annealing, and these derived carbon materials offered high electronic conductivity. These pushed Fe@Cd-MOFD to remarkable electrochemical performance with an initial discharge capacity of 1703.8 mA h g-1. This work offers new insights into the fabrication of novel MOF-derived iron oxide hybrids for lithium storage.

Schiff Base-functionalized Metal-organic Frameworks for Selective Sensing of Chromate and Dichromate in Water.

In this research, Zn- or Cd-based metal-organic frameworks (coded ZnMOF-1 and CdMOF-1) containing benzene-1,4-dicarboxylic acid (H2bdc) and pyridyl-based Schiff base (4-pyridylcarboxaldehydeisonicotinoylhydrazone (L)) dual ligands were successfully assembled via a conventional solvothermal method. The photoluminescence quenching response of ZnMOF-1 and CdMOF-1 and their sensing sensitivity and selectivity towards various inorganic anions were evaluated in aqueous media. Crystallographic and thermogravimetric studies confirm the formation of both MOFs with good crystallinity and thermal stability. Photoluminescence studies also verify the selectivity of ZnMOF-1 and CdMOF-1 for efficient sensing of inorganic oxyanions (like chromate/dichromate: CrO42- and Cr2O72-). Further, it was noted that only chromate/dichromate (CrO42-/Cr2O72-) anions showed a significant turn-off quenching effect while other anions (like F-, Br-, I-, Cl-, ClO4-, SCN-, SO42-, NO3-, and NO2-) have a low/negligible effect on the photoluminescence intensity of both MOFs. The limit of detection (LOD) of chromate/dichromate by ZnMOF-1 and CdMOF-1 was 9.79/10.94µM and 2.68/1.48µM, respectively. A probable mechanism for turn-off quenching response towards chromate and dichromate anions could be attributed to the spectral overlap of both excitation and emission spectra of ZnMOF-1/CdMOF-1 with the absorption spectra ofchromate/dichromate anions. As a result, the energy transfer from ZnMOF-1 or CdMOF-1 to the target chromate and dichromate anions decreased fluorescence intensity (i.e., fluorescence quenching effect).

A water-stable Cd-MOF and corresponding MOF@melamine foam composite for detection and removal of antibiotics, explosives, and anions

Water pollution has become one of the most worrisome environmental problems due to its harmful to human health and environmental safety. Thus, the design and development of robust and porous materials for detection and removal of pollutants from wastewater is extremely significant. Herein, a water-stable urea-containing 3D Cd-based metal-organic framework (MOF), {[Cd(L)0.5(bpe)0.5(H2O)]·x(solv)}n (MOF-1) (H4L = 5,5′-(((1,4-phenylenebis(azanediyl))bis(carbonyl))bis(azanediyl))diisophthalic acid) was prepared using urea-functionalized tetracarboxylate H4L ligand. The activated MOF-1 (MOF-1a) showed fast, sensitive, selective, and recyclable discrimination of nitrofurazone (NFZ) and nitrofurantoin (NFT) antibiotics, 2,4,6-trinitrophenol (TNP) explosive, as well as Cr2O72− by strong luminescence quenching and obvious red-shift of maximum emission. Unfortunately, MOF-1a has low adsorption capacity for the above pollutants owing to its small pore. To improve this disadvantage, MOF-1 crystals were in situ grown on the macroporous melamine foam (MF) by a facile one-pot solvothermal method, generating a MOF-1@MF composite with stability and high voids. The MOF-1@MF exhibited rapid, enhanced, and recyclable adsorption capacity toward NFZ, NFT, TNP, and Cr2O72− in water or even aqueous solutions with different pH values. Combination of the accessible functional sites in MOF-1 and macroporous structure of MF makes MOF-1@MF composite stand out as an excellent adsorbent in wastewater treatment. This work not only presents a water-stable MOF for selective recognition of NFZ, NFT, TNP, and Cr2O72−, but also provides a facile one-pot strategy to prepare MOF-based composites for high-performance removal of above pollutants from water, promoting their practical application in water quality monitoring and wastewater purification.

Acid-directed synthesis of three Cd-based metal–organic frameworks with luminescence and catalytic CO2transformation properties

This paper shows an example of acid-directed hydrothermal synthesis of three different Cd(ii)-MOFs based on the same mixed ligands. Two of them show blue fluorescence emissions and high activities in the CO2cycloaddition with epoxybutanes.

Modulation of the Host-Guest-Guest Interactions in a Metal-Organic Framework for Multiple Anticounterfeiting Applications.

Developing fluorescent materials with multiple and tunable emissions under different conditions is necessary to meet the growing demand for optical anticounterfeiting technology. Different modes of fluorescence emission can be obtained by loading multiple fluorescent components into metal-organic frameworks (MOFs) and modulating the interaction among them for multiple anticounterfeiting purposes. Herein, a Cd-based MOF (HNU-60) was constructed as a host to encapsulate both lanthanide ions and carbon quantum dots. Multiple fluorescence emissions can be achieved by modulation of host-guest and guest-guest interaction, which holds promise for multiple anticounterfeiting applications. This work opens the opportunity to construct the hybrid MOF-based materials with controlled fluorescence properties for emerging anticounterfeiting applications in various fields.

A Stable Cd(II)-Based Metal-Organic Framework: Synthesis, Structure, and Its Eu3+ Functionalization for Ratiometric Sensing on the Biomarker 2-(2-Methoxyethoxy) Acetic Acid.

A novel two-dimensional Cd-based metal-organic framework (MOF), [Cd(pddb)H2O]n (Cd-MOF), has been hydrothermally synthesized using the V-shaped ligand 4,4'-(pyridine-2,6-diyl)-dibenzoic acid (H2pddb) and structurally characterized. The framework exhibits fascinating one-dimensional in-plane channels functionalized with active pyridine-N sites. The as-synthesized Cd-MOF exhibits excellent water and chemical stability. Furthermore, a simple and nondestructive coordinated postsynthetic modification method has been applied to Cd-MOF to obtain a class of MOF hybrids functionalized by lanthanide ions. More interestingly, Eu3+@Cd-MOF can act as a dual-emissive ratiometric fluorescent probe for 2-(2-methoxyethoxy) acetic acid (MEAA), a metabolite of 2-(2-methoxyethoxy) ethanol, which could result in DNA damage and teratogenic and developmental toxicity. During the sensing process, the fluorescence sensor exhibits notable water tolerance, reusability, and a low detection limit (8.5 μg mL-1). In addition, the chemical substances in human urine and serum do not interfere with the fluorescence quenching process, which makes it possible for the fluorescent probe to be applied in the detection of MEAA in human urine and serum systems. The possible sensing mechanism is also studied and discussed in detail.

Cd(II)-based metal–organic framework-derived CdS photocatalysts for enhancement of photocatalytic activity

CdS with band gaps of 2.4 eV is an essential semiconductor for optoelectronic and photocatalytic devices. In this study, Cd(II)-based metal–organic framework (MOF)-derived CdS photocatalysts are successfully synthesized using a facile chemical bath deposition method. CdS precursors are derived from Cd-based MOFs that H2S gas was bubbled into as S source. Four kinds of CdS nano-photocatalyst are obtained through controlling the thermal annealing process of CdS precursors. The excellent photocatalytic performance of CdS and the benefits of the porous and molecular sieving properties of MOFs are well integrated. The evolution of the morphology, microstructure, and optical properties are investigated by various characterization methods. The results indicate that the sample with an annealing temperature of 500 °C is primarily nanosheet structures with sizes ranging from 20 to 30 nm, which construct a porous network structure, Moreover, the best photodegradation activity is obtained by illuminating the catalyst in rhodamine-B dye solution for 80 min and reducing the absorption intensity to nearly zero. Finally, the pollutant degradation mechanism was analyzed in detail.

Anion-directed two cadmium(II) metal–organic frameworks based on bis(imidazol-1-yl)methane with diverse supramolecular structures and luminescence properties

Two Cd-based metal-organic frameworks derived from bis(imidazol-1-yl)methane (BIM), [Cd(BIM)2(NO3)2]n (complex 1) and {[Cd(BIM)2Cl2]•2H2O}n (complex 2), can be prepared and controlled by using different metal-dependent anions. BIM and Cd(NO3)2 can form a 1D framework based on CdN4(NO3)2 node. Cd(NO3)2 is replaced by CdCl2 to construct another 1D structure based on CdN4Cl2. It is notable that diverse structures of both complexes are mainly attributed to the metal-dependent anion effect during the assembly of metal cations and organic ligands. Meanwhile, complex 1 is used as a mode to explore the luminescent performance for nitrofurantoin (NFT) with preferable detectable ability and good reusability.

A porous Cd-based metal-organic framework for sensitive and selective detection of aspartic acid/Ag+ in aqueous medium

The development of a fast and stable luminescence detection method is of great significance to people's health and the protection of the ecological environment. In this work, a porous three-dimensional (3D) Cd-based metal-organic framework (MOF1) has been synthesized by the reaction of tri(p-carboxyphenyl)phosphane oxide (H3L) and 1,4-bis(pyrid-4-yl)benzene (1,4-bpb) with Cd2+ ions based on the mixed-ligand strategy, and characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and scanning electron microscope (SEM), etc. The luminescence experiments of MOF1 for amino acids and cations showed that MOF1 has highly sensitive and selective recognition for aspartic acid/Ag+ in aqueous medium. Meanwhile, the recognition mechanism of MOF1 for aspartic acid/Ag+ was analyzed by a series of experiments, the results indicate that the energy gap between HOMO energy values of H3L and aspartic acid/Ag+ is recognition impetus of MOF1 for aspartic acid by enhancement luminescence and for Ag+ by luminescence quenching, the sensing processes of MOF1 for aspartic acid and Ag+ ions are dynamic and static respectively by fluorescence lifetimes. Furthermore, the cycle and anti-interference experiments indicate that MOF1 has good luminescence stability and high sensing selectivity for aspartic acid and Ag+. The above results indicate that MOF1 has potential applications in recognizing aspartic acid and Ag+ in aqueous medium.

Cd-Based Metal-Organic Framework Containing Uncoordinated Carbonyl Groups as Lanthanide Postsynthetic Modification Sites and Chemical Sensing of Diphenyl Phosphate as a Flame-Retardant Biomarker.

With the judicious selection of an appropriate semirigid polycarboxylate, 2,5-bis(3',5'-dicarboxylphenyl)benzoic acid (H5bdba), and an inorganic metal ion, a novel anionic framework, {[NH2(CH3)2]2·[Cd3.5(bdba)(Hbdba)(H2O)1.5]}n (Cd-MOF), has been synthesized solvothermally. Single-crystal measurement results show that the prepared Cd-MOF features a three-dimensional structure containing two types of one-dimensional channels, and as we expected, there exist accessible uncoordinated -COOH groups on Hbdba pointing toward the rhombus channels. Powder X-ray diffraction and thermogravimetric analysis measurements were performed for the thermal and chemical stability analysis of Cd-MOF. In addition, the lanthanide(III)-functionalized hybrids, Ln(III)@Cd-MOF, were initially prepared by coordinated postsynthetic modification to incorporate luminescent Ln(III) ions into the structure. The luminescence properties of the hybrids are studied, and the results show notable and specialized fluorescent sensitization of Cd-MOF to Tb(III) ions. Moreover, the Tb(III)@Cd-MOF hybrid with outstanding fluorescence properties was developed as a highly sensitive and selective luminescent probe for the biomarker diphenyl phosphate (DPP) based on multiquenching effects. Tb(III)@Cd-MOF is the first case to realize the detection of urinary DPP through lanthanide metal-organic framework fluorescence spectrometry and shows practical detection potential.

A new Cd-based metal organic framework derived nitrogen doped nano-porous carbon for high supercapacitor performance

A new cadmium metal–organic framework [Cd(NIPA)(CH3CH2OH)3] (NIPA = 5-nitroisophthalic acid) has been assembled and served as precursor to fabricate nanoporous nitrogen doped carbon material via carbonization process under 900 °C (NC900). The obtained NC900 shows high capacitance (367 F g−1 at 1 A/g), good cycling life (95% of initial capacitance after 3000 cycles). Moreover, NC900//NC900 supercapacitor device is assembled and shows energy density of 6.3 Wh kg−1 with a current density of 1 A/g and the capacitance retention maintains 65% at 0.5 A g−1 after 3000 cycles). The results obtained provide a facile way to prepare carbon material (MOF is used as precursor) for energy-storage devices. For the first time, the heteroatom doped nanoporous carbon material based on a new Cd MOF is served as supercapacitor materials.

A multifunctional 3D Cd-based metal-organic frameworks for the highly luminescence sensitive detection of CrO42−/Cr2O72− and nitro aromatic compounds

A novel 3D Cd(II)-based luminescent metal-organic framework {[Cd(L)(bpe)0.5]·H2O}n (1) [L = 6-(3-pyridyl)isophthalic acid and 1,2-bis(4-pyridyl)ethane], has been successfully assembled by a solvothermal reaction. The structure displays 4,5-connnected framework and exhibits solvent stability. More importantly, the excellent sensitivity and selectivity of compound 1 as luminescence probes for detecting CrO42−/Cr2O72− and a wide range of nitro aromatic compounds (NACs).

Pore modulation of guest photophysics in metal organic frameworks: Photophysical studies of meso-tetra (N-methyl-4-pyridyl) porphine encapsulated within MOM-11 and MOM-12

The ability of metal organic frameworks (MOFs) to modulate the photophysical properties of encapsulated guests is of importance for the applications of these materials in light harvesting and photocatalysis. Here, the photophysical properties of tetra (N-methyl-4-pyridyl)-21H,23H porphine (TMPyP) encapsulated within two Cd-based MOFs (MOM-11 and MOM-12) are reported. It is shown that the pores of CdTMPyP@MOM-11and CdTMPyP@MOM-12 fix the orientation of the porphyrin peripheral pyridinium groups relative to the porphyrin plane. These fixed orientations have a significant effect on the porphyrin S1-CT coupled excited state leading to differences in steady state emission, emission lifetimes, and absorption properties. In addition, it is observed that the pores ofCdTMPyP@MOM-11and CdTMPyP@MOM-12 also restrict out of plane porphyrin ring distortions associated with sit-atop porphyrins resulting in extended triplet state lifetimes. The results demonstrate that specific pore structures can systematically modulate the excited state properties of TMPyP type porphyrins by regulating accessible guest conformations.

Two tetranuclear Cd-based metal–organic frameworks for sensitive sensing of TNP/Fe3+ in aqueous media and gas adsorption

Two Cd-MOFs were solvothermally synthesized by mixed-ligand strategy. 1 has the largest adsorption selectivity for CO2. Furthermore, 1 and 2 present sensitive sensing for TNP/Fe3+ in water or soil samples.

Nonvolatile Electrical Bistability Behaviors Observed in Au/Ag Nanoparticle-Embedded MOFs and Switching Mechanisms.

Electrically bistable devices play an important role in the next generation of information materials. Plasmonic noble metal nanoparticles (Au and Ag NPs) with diameters <6 nm were embedded into 3-D Cd-based metal-organic framework (MOF) matrixes via the photoreduction method to generate Au (Ag) NPs@MOF composites. Electrical bistability measurements on the sandwiched ITO/NPs@MOF/silver devices indicate that two switchable conductivity states with nonvolatile memory behaviors can be observed. The ITO/Au NP@2/Ag device with neutral matrix possesses the highest ON/OFF current ratio of 104, which can be attributed to its higher electron tunneling efficiency because of the better dispersity of Au NPs in the MOF matrix. A mechanism regarding the electric-field-induced charge-transfer process assisted by conformational change in the active layer was proposed.