Hybrid Bimetallic Metal–Organic Frameworks: Modulation of the Framework Stability and Ultralarge CO2 Uptake Capacity

Construction of Zn-Cu bimetallic metal-organic frameworks for carbon dioxide capture

Bimetallic metal-organic frameworks (MOFs) have shown more impressive performance in gas adsorption compared with monometallic MOFs. Herein, a Cu-Zn bimetallic metal-organic framework (Zn/Cu-BTC) was synthesized via a one-pot method, and its structure, thermal stability and CO2 adsorption property were investigated and compared with those of corresponding monometallic Cu-BTC and Zn-BTC. The results showed that Zn/Cu-BTC has a specific ortho-octahedral crystal morphology with a unique X-ray diffraction peak, the atomic ratio of Zn to Cu is about 1 : 5, and it remained stable at a temperature up to 490 K. In Zn/Cu-BTC, Cu2+ played a role in increasing the specific surface area and porosity of the MOF and improving the gas adsorption performance. The CO2 adsorption of Zn/Cu-BTC is lower than that of Cu-BTC but much higher than that of Zn-BTC, and CO2 adsorption heat was 30.52 kJ mol-1, which indicated physical adsorption. In addition, Zn/Cu-BTC had higher CO2/N2 adsorption selectivity compared with Zn-BTC and Cu-BTC, with a maximum value of 17. This study can be a reference for the research on improving the adsorption selectivity of gases by constructing bimetallic MOFs.

Fe/Co-MOF Nanocatalysts: Greener Chemistry Approach for the Removal of Toxic Metals and Catalytic Applications

This study describes the preparation of new bimetallic (Fe/Co)-organic framework (Bi-MOF) nanocatalysts with different percentages of iron/cobalt for their use and reuse in adsorption, antibacterial, antioxidant, and catalytic applications following the principles of green chemistry. The prepared catalysts were characterized using several techniques, including X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy. These techniques proved the formation of MOFs, and the average crystallite sizes were 25.3-53.1, 27.6-67.2, 3.0-18.9, 3.0-12.9, and 3.0-23.6 nm for the Fe-MOF, Co-MOF, 10%Fe:90%Co-MOF, 50%Fe:50%Co-MOF, and 90%Fe:10%Co-MOF samples, respectively. The nanoscale (Fe/Co) Bi-MOF catalysts as efficient heterogeneous solid catalysts showed high catalytic activity with excellent yields and short reaction times in the catalytic reactions of quinoxaline and dibenzoxanthene compounds, in addition to their antioxidant and antibacterial activities. Furthermore, the nanoscale (Fe/Co) Bi-MOF catalysts efficiently removed toxic metal pollutants (Pb²⁺, Hg²⁺, Cd²⁺, and Cu²⁺) from aqueous solutions with high adsorption capacity.

The fabrication of a novel polyacrylonitrile/reduced graphene oxide-amino-halloysite/bimetallic metal–organic framework electrospun nanofiber adsorbent for the ultrasonic-assisted thin-film microextraction of fatty acid methyl esters in dairy products with gas chromatography-flame ionization detection

In this work, electrospun polyacrylonitrile/reduced graphene oxide-amino-halloysite/bimetallic metal–organic framework (PAN/rGO-amino-HNT/Co_0.5Zn_0.5(MeIm)₂) nanofiber film was synthesized and investigated as a novel adsorbent for the ultrasonic-assisted thin-film microextraction (UA-TFME) of fatty acid methyl esters (FAMEs), including palmitic methyl ester (PAME), oleic methyl ester (OAME), stearic methyl ester (SAME), and linoleic methyl ester (LAME), from dairy products. The hybrid nanocomposite was obtained via bonding halloysite nanotubes to reduced graphene oxide, followed by loading with bimetallic metal–organic frameworks. The determination of FAMEs with nanofiber film was performed in two stages of desorption and absorption where, initially, the analytes were adsorbed onto the nanofiber film and then desorbed with organic solvent. In this study, ultrasound was used for both the adsorption and desorption stages. The advantages of ultrasonication are extensive, overcoming the shortcomings of conventional techniques in terms of energy consumption and solvent use, allowing a shorter treatment time with a low cost of implementation. Based on PAN/rGO-amino-HNT/Co_0.5Zn_0.5(MeIm)₂ thin film, a microextraction-gas chromatography-flame ionization detection (TFME-GC-FID) method was developed. Experimental parameters affecting the extraction and desorption steps were optimized. The desorption parameters, including desorption time and the properties of the desorption solvent, were investigated one factor at a time. Then, effective parameters in the adsorption step were optimized using a Box–Behnken design and Design-Expert 7 software. Under the optimal conditions, the method detection limits (S/N = 3) were in the range of 0.03–0.06 μg L⁻¹ and the limits of quantification (S/N = 10) were within 0.11–0.23 μg L⁻¹. The relative standard deviations for intra-day and inter-day precision were 2.4–4.7% and 2.6–3.4%, respectively. In the present work, the UA-TFME method was successfully applied for the quantification of fatty acid methyl esters in dairy products (milk, yogurt, cheese, yogurt soda and butter samples) for the first time. The fatty acids were transesterified using standard procedures and were subjected to UA-TFME treatment prior to GC-FID determination. The developed method possesses the advantages of simplicity, rapidity, cost-effectiveness, sensitivity, and non-invasiveness.

Electrospun polyacrylonitrile/reduced graphene oxide-amino-halloysite/bimetallic metal–organic framework nanofiber film was synthesized and successfully applied to the ultrasonic-assisted thin-film microextraction (UA-TFME) of fatty acid methyl esters from dairy products.

Three-dimensional Co/Ni bimetallic organic frameworks for high-efficient catalytic ozonation of atrazine: Mechanism, effect parameters, and degradation pathways analysis

Herein, the potential of bimetallic MOFs in catalytic ozonation was investigated for the first time. Three novel ozonation catalysts, i.e. cobalt-based, nickel-based and cobalt/nickel-based metal-organic frameworks (Co-MOF, Ni-MOF and Co/Ni-MOF), were synthesized, characterized by XRD, SEM, N₂ sorption-desorption isotherms, FTIR and XPS, and applied in catalytic ozonation for atrazine removal. It was found that the catalysts showed outstanding performance in the catalytic ozonation, especially Co/Ni-MOF which was attributed to multiple metal sites, higher coordination unsaturation, metal centers with larger electron density, and better efficiency in electron transfer than its single-metal counterparts. Under specific experimental conditions, 47.8%, 67.0%, 75.5%, and 93.9% of atrazine were removed after adsorption and degradation in the ozonation system without catalyst, and the catalytic ozonation systems with Co-MOF, Ni-MOF and Co/Ni-MOF, respectively. Higher removal rates could be achieved by growing initial pH, increasing oxidant dosage and reducing pollutant concentration, while an excess of Co/Ni-MOF was not favorable for the catalytic ozonation. Surface hydroxyl groups and acid sites were considered as the critical catalytic sites on Co/Ni-MOF. From the results of EPR tests, O₂·^-, ¹O₂ and ·OH were ascertained as the main reactive species in the degradation. It was suspected that O₂·^- and H₂O₂ played important roles in the formation of ·OH and the cycle of Co(II)/Co(III) and Ni(II)/Ni(III). Additionally, Co/Ni-MOF displayed good stability and reusability in cycling experiments, ascribed to the enhancement of the porosity and pore hydrophobicity. Finally, based on MS/MS analysis at different reaction times, major degradation pathways for atrazine were proposed.

Bimetallic metal-organic frameworks and their derivatives

Bimetallic metal-organic frameworks (MOFs) have two different metal ions in the inorganic nodes. According to the metal distribution, the architecture of bimetallic MOFs can be classified into two main categories namely solid solution and core-shell structures. Various strategies have been developed to prepare bimetallic MOFs with controlled compositions and structures. Bimetallic MOFs show a synergistic effect and enhanced properties compared to their monometallic counterparts and have found many applications in the fields of gas adsorption, catalysis, energy storage and conversion, and luminescence sensing. Moreover, bimetallic MOFs can serve as excellent precursors/templates for the synthesis of functional nanomaterials with controlled sizes, compositions, and structures. Bimetallic MOF derivatives show exposed active sites, good stability and conductivity, enabling them to extend their applications to the catalysis of more challenging reactions and electrochemical energy storage and conversion. This review provides an overview of the significant advances in the development of bimetallic MOFs and their derivatives with special emphases on their preparation and applications.

Fabrication of novel electrochemical sensor based on bimetallic Ce-Ni-MOF for sensitive detection of bisphenol A

In this paper, a novel bimetallic Ce-Ni metal-organic frameworks (Ce-Ni-MOF) are synthesized by hydrothermal reaction, using 1,3,5-benzenetricarboxylic acid as a ligand. In particular, the bimetallic Ce-Ni-MOF with the largest specific surface area and catalytic sites was synthesized when the molar ratio of Ce³⁺ to Ni²⁺ was 3:7. Bimetallic Ce-Ni-MOF is added to the traditional conductive material of multiwall carbon nanotubes (MWCNTs) to play their synergistic effect, improve the conductivity, specific surface area, and catalytic site of the MWCNTs. A novel bisphenol A (BPA) sensor was successfully prepared by a self-assembled multilayer strategy of Ce-Ni-MOF/MWCNTs modified glassy carbon electrodes (GCE). Field emission scanning electron microscopy, powder X-ray diffraction, and transmission electron microscope were carried out to characterize the Ce-Ni-MOF/MWCNTs. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used as a sensitive analytical method for the determination of BPA, and a wider linear dynamic range of BPA determination in 0.1 μmol·L^-1 to 100 μmol·L^-1 with a detection limit of 7.8 nmol·L^-1 (S/N = 3). The proposed method was applied to measure the content of BPA in different brands of drinking water with satisfying recovery from 97.4 to 102.4%. Graphical abstract.

Recent highlights and future prospects on mixed-metal MOFs as emerging supercapacitor candidates

Mixed-metal metal-organic frameworks (M-MOFs) consist of at least two different metal ions as nodes in the same framework. The incorporation of a second or more metal ions provides structural/compositional diversity, multi-functionality and stability to the framework. Moreover, the periodical array of different metal ions in the framework may alter the physical/chemical properties of M-MOFs and result in fascinating applications. M-MOFs with exciting structural features offer superior supercapacitor performances compared to single metal MOFs due to the synergic effect of different metal ions. In this review, we summarize several synthetic methods to construct M-MOFs by employing various organic ligands or metalloligands. Further, we discuss the electrochemical performance of several M-MOFs and their derived composite materials for supercapacitor applications.

Composition-tuned metal-organic thin-film structures based on photoswitchable azobenzene by ALD/MLD

We demonstrate the fabrication of in-situ crystalline thin films of various azobenzene (AZO) based metal-organic structures using the atomic/molecular layer deposition (ALD/MLD) technique; these are highly intriguing materials as azobenzene is one of the prototype organic molecules experiencing photoisomerization. Our Li-, Ca and Fe-AZO thin films deposited from Li(thd) (thd = 2,2,6,6-tetramethyl-3,5-heptanedione), Ca(thd)2, FeCl3 and azobenzene-4,4'-dicarboxylic acid precursors in the temperature range of 250-360 °C exhibit metal-AZO structures not known from bulk samples. In all these structures, the AZO linker molecules are free to undergo the characteristic trans-cis photoisomerization reaction upon UV (360 nm) irradiation. However, this lowers the degree of crystallinity. To address the issue, we investigate hetero-organic structures where TPA (terephthalic acid) is used as another linker component together with AZO. This allows the trans-cis reaction of the AZO moieties to occur without compromising the film crystallinity. Finally, we demonstrate the growth of MOF-on-MOF type Ca-ADA@Ca-TPA thin films also showing the efficient photoisomerization reaction.

Zinc-based metal-organic frameworks as nontoxic and biodegradable platforms for biomedical applications: review study

Development of biomedical systems for controllable drug delivery systems and construction of biosensors is imperative to reduce side effects of common treatment techniques and enhance the therapeutic efficacy. To address this issue, metal-organic frameworks (MOFs) as hybrid porous polymeric structures have attracted worldwide attention due to their unprecedented opportunities in vast range of applications in diverse fields including chemistry, biological, and medicinal science as gas storage/separation, sensing, and drug delivery systems. Recently, biomedical application has become an interesting and promising issue for development and usage of multi-functional MOFs. Flexible chemical composition and versatile porous structure of MOFs enable the engineering and enhancement of their medical formulation and functionality as practical carriers for whether therapeutic or imaging agents. One important point in this domain is the efficient delivery of drugs in the body using nontoxic and biodegradable carriers. This review brings together the literatures that addressing the biomedical applications of Zinc-based MOFs (i.e. as drug delivery systems or nontoxic agent in matter of therapeutic applications) to present recent achievements in this interesting field.

Mixed-metal metal–organic frameworks

Mixed-metal MOFs contain at least 2 different metal ions presenting promising potential in heterogeneous catalysis, gas sorption/separation, luminescence and sensing.

Core-Shell Zeolitic Imidazolate Frameworks for Enhanced Hydrogen Storage

Core-shell ZIF-8@ZIF-67- and ZIF-67@ZIF-8-based zeolitic imidazolate frameworks (ZIFs) were synthesized solvothermally using a seed-mediated methodology. Transmission electron microscopy-energy-dispersive X-ray spectrometry, line scan, elemental mapping, X-ray photoelectron spectroscopy, and inductively coupled plasma-atomic emission spectroscopy analyses were performed to confirm the formation of a core-shell structure with the controlled Co/Zn elemental composition of ∼0.50 for both the core-shell ZIFs. The synthesized core-shell ZIF-8@ZIF-67 and ZIF-67@ZIF-8 frameworks conferred enhanced H₂ (2.03 and 1.69 wt %) storage properties at 77 K and 1 bar, which are ca. 41 and 18%, respectively, higher than that of the parent ZIF-8. Notably, the distinctly remarkable H₂ storage properties shown by both the core-shell ZIFs over the bimetallic Co/Zn-ZIF and the physical mixture of ZIF-8 and ZIF-67 clearly evidenced their unique structural properties (confinement of porosity) and elemental heterogeneity due to the core-shell morphology of the outperforming core-shell ZIFs. Moreover, H₂ adsorption isotherm data of these frameworks are best fitted with the Langmuir model (R ² ≥ 0.9999). Along with the remarkably enhanced H₂ storage capacities, the core-shell ZIFs also displayed an improved CO₂ capture behavior. Hence, we demonstrated here that the controlled structural features endorsed by the rationally designed porous materials may find high potential in H₂ storage applications.

Formation of bimetallic metal–organic framework nanosheets and their derived porous nickel–cobalt sulfides for supercapacitors

Bimetallic metal–organic frameworks (Ni/Co-MOFs) with nanosheet-assembled flower-like structures as well as their derived Ni–Co–S electrode showed higher specific capacitances and excellent cycling stability.

Microwave induced “egg yolk” structure in Cr/V-MIL-53

Using a one pot microwave procedure, mixed-metal “egg yolk” MOFs are created, with a core of (Cr/V)-MIL-53 and a shell of Cr-MIL-53.

Application of Ni/Co-based metal–organic frameworks (MOFs) as an advanced electrode material for supercapacitors

A Ni/Co–MOF-based supercapacitor electrode exhibited high specific capacitance, and good rate and cycling performance.

Facile water-stability evaluation of metal–organic frameworks and the property of selective removal of dyes from aqueous solution

A facile method was developed to evaluate the relative water stability of MOFs by controlling the volume ratio of DMF and H₂O.

Assembly of a series of d10 coordination polymers of pamoic acid through a mixed-ligand synthetic strategy: syntheses, structures and fluorescence properties

Eight fluorescent coordination compounds were obtained based on H₂PA and N-donor ligands through a mixed-ligand synthetic strategy.