Recent advances in continuous flow synthesis of metal-organic frameworks and their composites.

Metal-organic frameworks (MOFs) and their composites have garnered significant attention in recent years due to their exceptional properties and diverse applications across various fields. The conventional batch synthesis methods for MOFs and their composites often suffer from challenges such as long reaction times, poor reproducibility, and limited scalability. Continuous flow synthesis has emerged as a promising alternative for overcoming these limitations. In this short review, we discuss the recent advancements, challenges, and future perspectives of continuous flow synthesis in the context of MOFs and their composites. The review delves into a brief overview of the fundamental principles of flow synthesis, highlighting its advantages over batch methods. Key benefits, including precise control over reaction parameters, improved scalability and efficiency, rapid optimization capabilities, enhanced reaction kinetics and mass transfer, and increased safety and environmental sustainability, are addressed. Additionally, the versatility and flexibility of flow synthesis techniques are discussed. The article then explores various flow synthesis methods applicable to MOF and MOF composite production. The techniques covered include continuous flow solvothermal synthesis, mechanochemical synthesis, microwave and ultrasound-assisted flow synthesis, microfluidic droplet synthesis, and aerosol synthesis. Notably, the combination of flow chemistry and aerosol synthesis with real-time characterization is also addressed. Furthermore, the impact of flow synthesis on the properties and performance of MOFs is explored. Finally, the review discusses current challenges and future perspectives in the field of continuous flow MOF synthesis, paving the way for further development and broader application of this promising technique.

Quantifying thiolated chemical additives for copper electroplating process.

BACKGROUND: Copper foil, a thin layer of high-purity metallic copper, having excellent conductivity, ductility, and corrosion resistance, is extensively applied in various electronic applications. Thiolated (SH-containing) chemical additives (i.e., accelerator and inhibitor) in copper electroplating solution are known to be critical for optimizing the copper foil manufacturing processes. Due to the high ionic strength and acidity of copper electroplating solution, proper and accurate characterization of the thiolated chemical additives is a critical concern. RESULTS: In this study, a facile, accurate approach is developed for quantitative characterization of thiolated additives in the copper electroplating solution. Firstly, gold nanoparticles (AuNPs) were employed as an adsorbent for separating the thiolated chemical additives, namely, poly(ethylene glycol) methyl ether thiol (PEG-SH) as inhibitor, and 3-mercaptopropionic acid (MPA) as accelerator from other interfering chemicals present in the copper electroplating solution. Subsequently, quantitative analysis of the AuNPs in the form of thin particle film was performed using attenuated total reflection-Fourier transform infrared spectroscopy. Electrospray-differential mobility analyzer was employed orthogonally for the quantitative analysis of the amount of thiolated additives adsorbed on AuNP. Interestingly, the results indicated that the detection concentration ranges of 5 µM-100 µM for PEG-SH and 10 µM-200 µM for MPA, respectively. SIGNIFICANCE: Overall, this work demonstrates a successful separation and analysis methodology for the thiolated chemical additives in copper electroplating solution which enables the precise control over the copper foil manufacturing process.

Microfluidic-Aerosol Hyphenated Synthesis of Metal-Organic Framework-Derived Hybrid Catalysts for CO2 Utilization.

A new and efficient technique is developed by combining the hyphenated microfluidic- and aerosol-based synthesis with the coupled differential mobility analysis for the effective and continuous synthesis and simultaneous analysis of metal-organic frameworks (MOFs)-derived hybrid nanostructured products. HKUST-1, a copper-based MOF, is chosen as the representative to fabricate Cu-based hybrid catalysts for reverse water-gas shift (RWGS) reaction, an effective route for CO2 utilization. The effect of precursor concentration and carrier selection on the properties of the resulting products, including mobility size distribution, crystallization degree, surface area, and metal dispersion are investigated, as well as the correlation between the material properties of the synthesized catalysts and their catalytic performance in RWGS reaction in terms of conversion ratio/rate, selectivity, and operational stability. The results indicate that the continuous microfluidic droplet system can successfully synthesize MOF colloids, followed by the continuous production of MOF-derived hybrid materials through the tandem aerosol spray-drying-reaction system. High catalytic activity and low initiate temperature toward RWGS (turnover frequency = 0.0074 s-1; 450 °C) are achievable. The work facilitates the production and the designed concept of relevant MOF-derived hybrid nanostructured catalysts in the continuous synthesis system and the enhancement of applications in CO2 capture and utilization.

NiMo-MOF-Derived Carbon-Armored Ni4Mo Alloy of an Interwoven Nanosheet Structure as an Outstanding pH-Universal Catalyst for Hydrogen Evolution Reaction at High Current Densities.

Development of highly efficient and stable non-precious metal-based pH-universal catalysts for hydrogen evolution reaction (HER) at high current densities remains challenging for water electrolysis-based green hydrogen production. Herein, a simple solvothermal process was developed to synthesize a NiMo metal-organic framework (MOF), from which a carbon-armored Ni4Mo alloy of an interwoven nanosheet structure was derived with a two-stage thermal treatment, to serve as a high-performance pH-universal HER catalyst. It requires low overpotentials of 22, 48, and 98 mV to achieve a current density of -10 mA cm-2 and 192, 267, and 360 mV to deliver an ultrahigh current density of -500 mA cm-2 in alkaline, acidic, and neutral media, respectively, and exhibits remarkable operational stability at an ultrahigh initial current density of -500 mA cm-2 for over 50 h, making it promising for applications in large-scale green hydrogen production. The success can be attributed to the unique catalyst design of a carbon-armored, composition-optimized NiMo alloy of an advantageous nanostructure of interwoven nanosheets for enhanced utilization of active sites and mass transfer of electrolytes and gaseous products, made possible with a MOF-derivation fabrication approach.

Nitrogen-doped carbon armored Cobalt oxide hollow nanocubes electrochemically anchored on fluorine-doped tin oxide substrate for acidic oxygen evolution reaction.

Developments of non-precious metal based active and stable catalysts are of great importance and challenge to green hydrogen production from acidic electrocatalytic water splitting. Design of composite catalysts with synergy between active and stable components proves to be a promising approach. Herein, N-doped carbon armored Co3O4 hollow nanocubes electrochemically anchored on fluorine-doped tin oxide (FTO) substrates are developed as efficient and stable catalysts for acidic oxygen evolution reactions. Co3O4 acts as the active component with N-doped carbon coating layer serving as the stable protection component, shielding Co3O4 from direct attack of anodic dissolution. Electrochemical fixation offers firm holding of the composite catalyst onto acid-tolerant FTO substrates and hollow nanocubes serve as nano-reactors for confined fast reactions. Under optimal conditions, the composite catalyst achieves an overpotential of 465 mV at 10 mA cm-2 in 0.5 M H2SO4, and stays stable for 12 hr with a 10% increment in applied potentials.

Label-Free Bimetallic In Situ-Grown 3D Nickel-Foam-Supported NH2-MIL-88B(Fe2Co)-MOF-based Impedimetric Immunosensor for the Detection of Cardiac Troponin I.

In this study, a simple and competent metal-organic framework (MOF)-based nickel foam (NF)-supported three-dimensional (3D) immunosensor (Ab-NH2-MIL-88B(Fe2Co)-MOF/NF) was constructed and utilized for the specific recognition of the biomarker cardiac troponin (I) (cTnI). In the present work, biosensor fabrication was progressed through the modification of the NF substrate with the MOF material (NH2-MIL-88B(Fe2Co)-MOF) to enable an amine-functionalized electrode. This amine-functionalized NF electrodes (NH2-MIL-88B(Fe2Co)-MOF/NF) were then biointerfaced with anti-cTnI antibodies, which ended up as Ab-NH2-MIL-88B(Fe2Co)-MOF/NF electrodes. Analytical executions of the constructed bioelectrode were investigated for the quantitative analysis of cTnI in both buffered and serum solutions. Then, the electrochemical studies were carried out using the electrochemical impedance spectroscopy (EIS) method by monitoring changes concerning the charge transfer resistance (Rct) characteristics. The limit of detection (LOD) of the Ab-NH2-MIL-88B(Fe2Co)-MOF/NF immunosensor was achieved to be 13 fg/mL with great specificity. This kind of immunosensor imparts a new platform for the construction and application of MOF-hybrid 3D electrode materials with enhanced electrochemical behavior in cTnI sensing for the first time.

Bimetallic Metal-Organic Framework-Derived Hybrid Nanostructures as High-Performance Catalysts for Methane Dry Reforming.

Syngas, consisting of equimolar CO and H2, is an important feedstock for large-scale production of a wide range of commodity chemicals including aldehyde, methanol, ammonia, and other oxygenated chemicals. Dry reforming of methane (DRM), proceeding by reacting greenhouse gases, CO2 and CH4, at high temperatures in the presence of a metal catalyst, is considered one of the most environmentally friendly routes for syngas production. Nevertheless, nonprecious metal-based catalysts, which can operate at relatively low temperatures for high product yields and selectivities, are required to drive the DRM process for industrial applications effectively. Here, we developed NiCo@C nanocomposites from a corresponding NiCo-based bimetallic metal-organic framework (MOF) to serve as high-performance catalysts for the DRM process, achieving high turnover frequencies (TOF) at low temperatures (>5.7 s-1 at 600 °C) and high product selectivities (H2/CO = 0.9 at 700 °C). The incorporation of Co in Ni catalysts improves the operation stability and light-off stability. The present development for MOF-derived nanocomposites opens a new horizon for design of DRM catalysts.

Microwave-Assisted Synthesis of Nanoporous Aluminum-Based Coordination Polymers as Catalysts for Selective Sulfoxidation Reaction.

A series of aluminum-based coordination polymers or metal⁻organic frameworks (Al⁻MOFs), i.e., DUT-4, DUT-5, MIL-53, NH2-MIL-53, and MIL-100, have been facile prepared by microwave (MW)-assisted reactions and used as catalysts for selective sulfoxidation reactions. The MW-assisted synthesis drastically reduced the reaction time from few days to hours. The prepared MOFs have smaller and uniform particle sizes and better yield compared to conventional hydrothermal method. Furthermore, the Al⁻MOFs have been successfully demonstrated as catalysts in oxidation reaction of methyl phenyl sulfide with H2O2 as oxidant, even under mild conditions, with more than 95% conversion.

Waste polyethylene terephthalate (PET) materials as sustainable precursors for the synthesis of nanoporous MOFs, MIL-47, MIL-53(Cr, Al, Ga) and MIL-101(Cr).

In our novel green approach, the waste polyethylene terephthalate (PET) bottle material has effectively been used as the starting precursor instead of terephthalic acid for the synthesis of five terephthalate based nanoporous trivalent metal-organic frameworks (MOFs) namely MIL-47, MIL-53(Cr), MIL-53(Al), MIL-53(Ga), and MIL-101(Cr). The optimum reaction parameters to achieve the green synthesis were studied. These MOFs were structurally identified by using powder X-ray diffraction (PXRD) measurements. Scanning electron microscopy (SEM) images confirm the particle nature and size of the synthesized MOFs. Nitrogen gas sorption measurements have been done for some of the MOFs to check their porous properties. All the characterization techniques strongly supported that the synthesized MOFs using PET are similar to their literature reports. The gas adsorption studies for the synthesized MIL-53(Cr) and MIL-101(Cr) showed their significant gas uptake capability towards CO2 and H2 gases. Further, the synthesized MIL-47 and MIL-101(Cr) have been tested for their catalytic ability in chemical fixation of CO2 gas through the conversion of CO2 and epoxides to the corresponding cyclic carbonates which shows promising results to use them as catalysts.

Multidimensional (0D to 3D) Alkaline-Earth Metal Diphosphonates: Synthesis, Structural Diversity, and Luminescence Properties.

A series of new alkaline-earth metal diphosphonate frameworks were successfully synthesized under solvothermal reaction condition (160 °C, 3 d) using 1-hydroxyethylidene-1,1-diphosphonic acid (CH3C(OH)(H2PO3)2, hedpH4) as a diphosphonate building block and Mg(II), Ca(II), Sr(II), or Ba(II) ions as alkaline-earth metal ion centers in water, dimethylformamide, and/or EtOH media. These diphosphonate frameworks, (H2NMe2)4[Mg(hedpH2)3]·3H2O (1), (H2NMe2)2[Ca(hedpH2)2] (2), (H2NMe2)2[Sr3(hedpH2)4(H2O)2] (3), and [Ba3(hedpH2)3]·H2O (4) exhibited interesting structural topologies (zero-, one-, two-, and three-dimensional (0D, 1D, 2D, and 3D, respectively)), which are mainly depending on the metal ions and the solvents used in the synthesis. The single-crystal analysis of these newly synthesized compounds revealed that 1 was a 0D molecule, 2 has 1D chains, 3 was a 3D molecule, and 4 has 2D layers. All compounds were further characterized using thermogravimetric analysis, solid-state (31)P NMR, powder X-ray diffraction analysis, UV-vis spectra, and infrared spectroscopy. In addition, Eu(III)- and Tb(III)-doped compounds of 1-4, namely, (H2NMe2)4[Ln(x)Mg(1-x)(hedpH2)2(hedpH(2-x))]·3H2O (1Ln), (H2NMe2)2[Ln(x)Ca(1-x)(hedpH2)(hedpH(2-x))] (2Ln), (H2NMe2)2[Ln(x)Sr(3-x)(hedpH2)3(hedpH(2-x))(H2O)2] (3Ln), and [Ln(x)Ba(3-x)(hedpH2)2(hedpH(2-x))]·H2O (4Ln) (where Ln = Eu, Tb), were synthesized, and their photoluminescence properties were studied. The quantum yield of 1Eu-4Eu was measured with reference to commercial red phosphor, Y2O2S:Eu(3+) (YE), and the quantum yield of terbium-doped compounds 1Tb-4Tb was measured with reference to commercial green-emitting phosphor CeMgAl10O17:Tb(3+). Interestingly, the compound 2Eu showed very high quantum yield of 92.2%, which is better than that of the reference commercial red phosphor, YE (90.8%).

Carbonization and oxidation of metal-organic frameworks based on 1,4-naphthalene dicarboxylates.

Three new isostructural metal-organic frameworks (MOFs), [V(OH)(NDC)] (1), [Cr(OH)(NDC)] (2), and [Ga(OH)(NDC)] (3) have been synthesized hydrothermally using 1,4-naphthalene dicarboxylate (NDC) as the linker. These MOFs (1, 2 and 3) have been used as a template for the synthesis of metal-oxide-inserted nanoporous carbon materials. The newly synthesized MOFs and the resulting porous carbon hybrid functional materials have been characterized using powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopic analysis. Results show that compounds 2 and 3 form their respective metal oxide nanoparticles on the surface of the carbon materials during carbonization at 800 °C. The gas sorption properties of the new MOFs and their corresponding carbon frameworks have been reported.

Synthesis, structure and in vitro pharmacological evaluation of a novel 2-oxo-1,2-dihydroquinoline-3-carbaldehyde (2'-methylbenzoyl) hydrazone bridged copper(II) coordination polymer.

A novel ligand bridged copper(II) coordination polymer, [Cu(HL)(NO3)]n has been synthesized by reacting 2-oxo-1,2-dihydroquinoline-3-carbaldehyde (2'-methylbenzoyl) hydrazone (H2L) with Cu(NO3)2·3H2O, and characterized by X-ray diffraction studies. The DNA interaction studies revealed that the compounds could interact with CT-DNA through intercalation. A gel electrophoresis assay demonstrated the ability of the complex to cleave the pBR322 plasmid DNA. The protein binding studies indicated that the complex exhibited strong binding affinities. Investigations of antioxidative properties showed that the polymeric Cu(II) complex has strong radical scavenging potencies. The cytotoxic effect of the compounds showed that the polymeric complex exhibited excellent anticancer activity against Hep G2, and A431 cells which is six to ten times better than that of well-known commercial anticancer drug, cisplatin.

Synthesis, characterization and in vitro pharmacological evaluation of new water soluble Ni(II) complexes of 4N-substituted thiosemicarbazones of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde.

Four new Ni(II) complexes of general formula [Ni(H2-Qtsc-R)2](NO3)2 (H2-Qtsc-R = 4N-substituted thiosemicarbazones of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde, where R = H (1), Me (2), Et (3), or Ph (4)) have been synthesized and characterized. The geometry of the complexes was confirmed by single crystal X-ray crystallography for one of the complexes (3). The binding affinity of the complexes with DNA and protein have been studied which indicate that they could interact with calf thymus DNA and bovine serum albumin protein. Investigations of antioxidative properties showed that all the complexes have strong radical scavenging properties. Cytotoxic studies showed that the complexes exhibited effective cytotoxic activity against a panel of human cancer cells without affecting the normal cells much.

Role of substitution at terminal nitrogen of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde thiosemicarbazones on the coordination behavior and structure and biological properties of their palladium(II) complexes.

A series of four new palladium(II) complexes of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde thiosemicarbazones with triphenylphosphine as coligand have been synthesized and characterized by the aid of various spectral techniques. The single-crystal X-ray diffraction studies revealed that the unsubstituted thiosemicarbazone ligand acted as monobasic tridentate (ONS(-)) in the cationic [Pd(H-Qtsc-H)(PPh(3))]Cl complex, whereas the monosubstituted thiosemicarbazone ligands acted as monobasic bidentate (NS(-)) in their respective complexes, [PdCl(H-Qtsc-R)(PPh(3))] (R = Me (2), Et (3), Ph (4)). To ascertain the potentials of the above Pd(II) complexes toward biomolecular interactions, additional experiments involving interaction with calf thymus DNA and bovine serum albumin were carried out. Moreover, all the palladium(II) complexes have been screened for their radical scavenging activity toward DPPH, O(2)(-), OH, and NO radicals. The efficiency of the complexes in arresting the growth of human cervical cancer cells (HeLa), human laryngeal epithelial carcinoma cells (HEp-2), human liver carcinoma cells (Hep G2), and human skin cancer cells (A431) has also been studied along with the cell viability test against the noncancerous NIH 3T3 mouse embryonic fibroblasts cell lines under in vitro conditions. All the in vitro pharmacological evaluation results clearly revealed the relationship between the structure and the activity of the new Pd(II) complexes.

Syntheses, structures, and properties of multidimensional lithium coordination polymers based on aliphatic carboxylic acids.

Three lithium coordination polymers, [Li4(H2O)2(EDTA)] (1), [Li4(H2O)4(BTCA)] (2), and (H2NMe2)2[Li2(H2O)2(BTCA)] (3) (H4EDTA = ethylenediaminetetraacetic acid, H4BTCA = 1,2,3,4-butane tetracarboxylic acid, H2NMe2 = dimethyl amine), have been synthesized by reacting lithium salts with aliphatic carboxylic acids using a solvothermal method. The structures of all the three complexes have been determined by single crystal X-ray diffraction studies. The single crystal structure analysis revealed that complex 1 has a three-dimensional framework, whereas complex 2 has 2D sheets and complex 3 has 1D chains. In addition, these lithium complexes contain various inorganic motifs with a tetramer in 1 and 2, and discrete tetrahedra in 3 and have further been connected through organic ligands to construct multidimensional structures. Further, the electrochemical properties of complexes 1­3 have been studied to evaluate these compounds as electrode materials for lithium ion batteries with discharge capacities of around 100 mA h g(-1) in the first thirty cycles.

Mixed ligand palladium(II) complexes of 6-methoxy-2-oxo-1,2-dihydroquinoline-3-carbaldehyde 4N-substituted thiosemicarbazones with triphenylphosphine co-ligand: synthesis, crystal structure and biological properties.

A series of new 6-methoxy-2-oxo-1,2-dihydroquinoline-3-carbaldehyde 4N-substituted thiosemicarbazone ligands (H2L1­H2L5) and their corresponding palladium(II) complexes [Pd(L1)(PPh3)] (1), [Pd(L2)(PPh3)] (2), [Pd(HL3)(PPh3)]Cl (3), [Pd(L4)(PPh3)] (4) and [Pd(L5)(PPh3)] (5), have been synthesized in order to evaluate the effect of terminal N-substitution in thiosemicarbazone moiety on coordination behaviour and biological activity. The new ligands and their corresponding complexes were characterized by analytical and various spectral techniques. The molecular structure of the complexes 2­5 were characterized by single crystal X-ray diffraction studies which revealed that the ligands H2L2, H2L4 and H2L5 are coordinated to palladium(II) as binegative tridentate (ONS2−) by forming six and five member rings whereas, the ligand H2L3 coordinated to Pd(II) as uninegative tridentate (ONS−). The interactions of the new complexes with calf thymus DNA (CT-DNA) have been evaluated by absorption and ethidium bromide (EB) competitive studies which revealed that complexes 1­5 could interact with CT-DNA through intercalation. Further, the interactions of the complexes with bovine serum albumin (BSA) were also investigated using UV-visible, fluorescence and synchronous fluorescence spectroscopic methods, which showed that the new complexes could bind strongly with BSA. Antioxidant studies showed that all the complexes have a strong antioxidant activity against 2-2'-diphenyl-1-picrylhydrazyl (DPPH) radical and 2,2'-azino-3-ethylbenzthiazoline-6-sulfonic acid diammonium salt (ABTS) cation radical. In addition, in vitro cytotoxicity of the complexes against human lung cancer (A549) cell line was assayed which showed that 4 has higher cytotoxic activity than the rest of the complexes and cisplatin.

Synthesis, crystal structure and pharmacological evaluation of two new Cu(II) complexes of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde (benzoyl) hydrazone: a comparative investigation.

Two new copper(II) complexes have been synthesized by reacting 2-oxo-1,2-dihydroquinoline-3-carbaldehyde (benzoyl) hydrazone (H(2)L) with CuCl(2)·2H(2)O or Cu(NO(3))(2)·3H(2)O. The structures of the complexes have been determined by single crystal X-ray diffraction studies. Results obtained using spectroscopic methods strongly suggested that the ligand and its Cu(II) complexes could interact with calf thymus DNA through intercalation. In the case of protein binding, the obtained results indicated that all the three compounds could quench the intrinsic fluorescence of bovine serum albumin through static quenching process. In addition, antioxidant activity tests showed that H(2)L and its copper(II) complexes possess significant scavenging effect against free radicals. Further, the two copper(II) complexes exhibited effective cytotoxic activity against a panel of human cancer cell lines.

Biological evaluation of a novel water soluble sulphur bridged binuclear copper(II) thiosemicarbazone complex.

The reaction of 2-oxo-1,2-dihydroquinoline-3-carbaldehyde 4(N,N)-dimethylthiosemicarbazone (HL) with copper(II) nitrate in methanol yielded water soluble [{Cu(L)(CH(3)OH)}(2)](NO(3))(2) · H(2)O. Structural analysis revealed that the complex consists of centrosymmetric binuclear entities containing square-pyramidal copper(II) ions bridged through the sulfur atoms. The spectroscopic experimental evidences strongly suggested that the ligand and complex could interact with calf thymus DNA (CT-DNA) through intercalation. A gel electrophoresis assay demonstrated the ability of the complex to cleave the pBR322 plasmid DNA. The complex also exhibited a strong binding to bovine serum albumin (BSA) over the ligand. Investigations of antioxidative properties showed that the complex has strong radical scavenging properties. Further, the cytotoxic effect of the complex was examined on HeLa, Hep G2, and HEp-2, which showed that the complex exhibited substantial cytotoxic specificity on HeLa over the other two.