Zr Metal-organic Frameworks Research Articles

Parametric simulations of hierarchical core–shell MOF materials for direct air capture

Metal–organic frameworks (MOFs) can separate and adsorb specific gases from a gas mixture, making them an ideal candidate for direct air carbon capture. However, MOFs that adsorb CO2 well often competitively adsorb the more abundant H2O molecules in the atmosphere, degrading their adsorptive performance and operational longevity. MOF-contained-in-MOF (MOF⊂MOF) core–shell materials may resolve this issue if a shell can be synthesized to reject water while the core receives CO2. This paper builds on our team’s prior computational screening and experimental synthesis of individual and core–shell MOFs by performing multiphysics simulations on a spherical MOF⊂MOF core–shell pellet exposed to atmospheric air. This core–shell pellet is endowed with our previously calculated and experimentally measured constituent MOF properties to demonstrate a high throughput methodology for scale-up analysis on composite adsorbent structures. We simulate and screen five UiO-67(Zr) MOF variants for use as either the core or shell materials that lead to 25 MOF⊂MOF core–shell pellet combinations, five of which are pellets whose core and shell are the same MOF. The resulting rankings suggest that adding a shell MOF to a pellet does not necessarily improve the adsorptive performance of that pellet when using these UiO-67(Zr) variants. The highest-ranked core–shell pellet combination was a pellet whose core and shell were the same MOF material. However, when considering only the core domain of the pellet as a frame of reference, the ranking results suggest that using hydrophobic MOFs as the pellet core and hydrophilic MOFs as the pellet shell show improvement compared to without the shell MOF. Using this second frame of reference, we identify the MOF⊂MOF core–shell combination UiO-67(Zr)⊂2(NH2)-UiO-67(Zr) as the highest-performing pellet of those that show improvement over their homogeneous pellet counterparts. A set of parametric simulations are performed comparing the core–shell pellet UiO-67(Zr)⊂UiO-67(Zr) against that of UiO-67(Zr)⊂2(NH2)-UiO-67(Zr) to investigate the impact of air CO2 concentration, relative humidity, and shell thickness on each respective core MOF’s performance. From these studies, the largest improvement in the core MOF’s performance was observed when using elevated CO2 concentrations of 1000 ppm, reduced relative humidity levels of 10%, and an increased shell thickness of 0.03 cm on a pellet core 0.12 cm in radius. Together, these results suggest that additional UiO-67(Zr) MOF variants will need to be screened to determine the use cases where the use of a shell is of water-rejecting benefit to the pellet in the DAC setting. Further adsorption and porosimetry experimentation is necessary to replicate the proposed pellet under DAC conditions and establish a means of comparative analysis between the simulated and measured pellet properties.

MOF-Fabric Composites Based on a Multi-Functional MOF as Luminescent Sensors for a Neurotransmitter and an Anti-Cancer Drug.

A biocompatible, reliable, fast, and nanomolar-level dual-functional sensor for a neurotransmitter (e.g., adrenaline) and an anti-cancer drug (e.g., 6-mercaptopurine (6-MP)) is still far away from the hand of modern-day researchers. To address this issue, we synthesized an aqua-stable, bio-friendly, thiourea-functionalized Zr(IV) metal-organic framework (MOF) for selective, rapid sensing of adrenaline and 6-MP with ultra-low limit of detection (LOD for adrenaline = 1.9 nM and LOD for 6-MP = 28 pM). This is the first MOF-based fluorescent sensor of both the targeted analytes. The sensor not only can detect adrenaline in HEPES buffer medium but also in different bio-fluids (e.g., human urine and blood serum) and pH media. It also exhibited 6-MP sensing ability in aqueous medium and in various wastewater specimens and pH solutions. For the quick and on-site detection of this neuro-messenger (adrenaline) and the drug (6-MP), cost-effective sensor-coated cotton fabric composites were fabricated. The MOF@cotton fabric composite is capable of detecting both the analytes up to the nanomolar level by the naked eye under UV light. The sensor can be recycled up to five times without significantly losing its efficiency. The Förster resonance energy transfer in the presence of adrenaline and inner-filter effect in the presence of 6-MP are the most likely reasons behind the quenching of the MOF's fluorescence intensity, which were proved with the help of appropriate instrumental techniques.

Process intensification of synthesis of metal organic framework particles assisted by ultrasound irradiation

This study synthesized UiO-66, a typical Zr-Metal Organic Framework (MOF), by using an ultrasound-assisted synthesis method to reduce the synthesis time. This method was short-time ultrasound irradiation at the initial stage of the reaction. As compared with average particle size of conventional solvothermal method (=192 nm), averaged particle size by the ultrasound-assisted synthesis method showed particle sizes that were smaller on average, ranging from 56 to 155 nm. In order to compare the relative reaction rates of the solvothermal method and the ultrasound-assisted synthesis method, the cloudiness of the reaction solution in the reactor was observed with a video camera, and the luminance was calculated from the images obtained by the video camera. It was found that the ultrasound-assisted synthesis method showed a faster increase in luminance and shorter induction time than the solvothermal method. The slope of the luminance increase during the transient period was also found to become increase with the addition of ultrasound, which also affects the growth of particles. Observation of the aliquoted reaction solution confirmed that particle growth was faster in the ultrasound-assisted synthesis method than in the solvothermal method. Numerical simulations were also performed using MATLAB ver. 5.5 to analyze the unique reaction field generated by ultrasound. Bubble radius and temperature inside a cavitation bubble was obtained using the Keller-Miksis equation, which reproduces the motion of a single bubble. The bubble radius expanded and contracted repeatedly according to the ultrasound sound pressure, and eventually collapsed. The temperature at the time of collapse was extremely high, exceeding 17,000 K. It was confirmed that the high-temperature reaction field generated by ultrasound irradiation promoted nucleation, leading to a reduction in particle size and induction time.

Zr-metal–organic framework based cross-layer-connection additive for stable halide perovskite solar cells

The poor stability of metal halide perovskite seriously affects the large-scale commercial application of perovskite solar cells (PSCs). Here, a large-particle Zr-based metal–organic framework (Zr-MOF), e.g. UiO-66 (NH2), is added to the precursor solution of SnO2 electron transport layer (ETL), realizing a cross-layer modification of (1) ETL, (2) perovskite active layer and (3) theirs interface simultaneously. We find that the SnO2 particles are dispersed into the ordered porous scaffold of Zr-MOF, to form an ETL with improved crystallinity, reduced defect states and increased contact area with active perovskite film. For the subsequently deposited perovskite layer, the crystallization along the vertical direction is significantly optimized, and the defects are passivated by the bottom-up infiltrated Zr-MOF, so as to suppress the ion migration process. The power conversion efficiency (PCE) of one-step fabricated Zr-MOF-modified MAPbI3 based PSCs is optimized from 17.48% to 18.25%, and remaining 99% of its initial value after storage for 800 h under ambient conditions with the relative humidity over 60%. This work provides a simple cross-layer passivation strategy to improve the performance and stability of PSCs using highly designable MOF materials.

Synthetic Access to a Framework-Stabilized and Fully Sulfided Analogue of an Anderson Polyoxometalate that is Catalytically Competent for Reduction Reactions

Polyoxometalates (POMs) featuring 7, 12, 18, or more redox-accessible transition metal ions are ubiquitous as selective catalysts, especially for oxidation reactions. The corresponding synthetic and catalytic chemistry of stable, discrete, capping-ligand-free polythiometalates (PTMs), which could be especially attractive for reduction reactions, is much less well developed. Among the challenges are the propensity of PTMs to agglomerate and the tendency for agglomeration to block reactant access of catalyst active sites. Nevertheless, the pervasive presence of transition metal sulfur clusters metalloenzymes or cofactors that catalyze reduction reactions and the justifiable proliferation of studies of two-dimensional (2D) metal-chalcogenides as reduction catalysts point to the promise of well-defined and controllable PTMs as reduction catalysts. Here, we report the fabrication of agglomeration-immune, reactant-accessible, capping-ligand-free CoIIMo6IVS24n- clusters as periodic arrays in a water-stable, hierarchically porous Zr-metal-organic framework (MOF; NU1K) by first installing a disk-like Anderson polyoxometalate, CoIIIMo6VIO24m-, in size-matched micropores where the siting is established via difference electron density (DED) X-ray diffraction (XRD) experiments. Flowing H2S, while heating, reduces molybdenum(VI) ions to Mo(IV) and quantitatively replaces oxygen anions with sulfur anions (S2-, HS-, S22-). DED maps show that MOF-templated POM-to-PTM conversion leaves clusters individually isolated in open-channel-connected micropores. The structure of the immobilized cluster as determined, in part, by X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) analysis, and pair distribution function (PDF) analysis of total X-ray scattering agrees well with the theoretically simulated structure. PTM@MOF displays both electrocatalytic and photocatalytic competency for hydrogen evolution. Nevertheless, the initially installed PTM appears to be a precatalyst, gaining competency only after the loss of ∼3 to 6 sulfurs and exposure to hydride-forming metal ions.

Removal of diclofenac by adsorption process studied in free-base porphyrin Zr-metal organic frameworks (Zr-MOFs).

As the world population continues to grow, there is also a rising concern regarding water pollution since this condition could negatively impact the supply of clean water. One of the most recent concerns is related to the pollution that comes from various pharmaceuticals, in particular non-steroidal anti-inflammatory drugs (NSAIDs) since they have been industrially produced at large scale and can be easily purchased as an over-the-counter medicine. Diclofenac is one of the most popular NSAIDs because of its high-effectiveness, which leads to its excessive consumption. Consequently, its presence in water bodies is also continuously increasing. An adsorption process could then be employed as a highly effective method to address this issue. In comparison to other conventional adsorbents such as activated carbon, the use of metal-organic frameworks (MOFs) as an alternative adsorbent is very attractive since it can offer various advantages such as tailorability and high adsorption capacity. In this study, the performance of three water-stable, free-base porphyrin MOFs assembled using zirconia-based nodes, namely MOF-525, MOF-545, and NU-902, for diclofenac adsorption was thoroughly investigated. Interestingly, although all three free-base porphyrin MOFs are assembled using the same building block and have a similar specific surface area (based on the experimental argon physisorption and calculation based on non-localized density functional theory), their diclofenac adsorption capacity is substantially different from one another. It is found that the highest diclofenac adsorption capacity is shown by MOF-525, which has maximum capacity around 792 mg g-1. This is then followed by MOF-545 and NU-902 that have adsorption capacities around 591 and 486 mg g-1, respectively. Some possible adsorption mechanisms are then thoroughly discussed that might contribute to this phenomenon. Lastly, their performance is also compared with other MOFs that are also studied for this purpose to show their performance superiority not only in terms of adsorption capacity but also their affinity towards the diclofenac molecule, which might be useful as an adsorption performance indicator in the real condition where the contaminant concentration is considerably low.

Aptasensors with palladium nanoparticle-modified hemin-containing metal-organic frameworks as the signal marker for detection of exosomes.

Zr-metal-organic frameworks (Zr-MOFs) have received increasing interest for their use as the signal marker in the development of sandwich-structured aptasensors for the detection of exosomes. However, Zr4+ ions of the Zr-MOFs can interact with not only the exosomes, but also the aptamers, leading to possible false positives and a large background response. In the present study, we report for the first time aptasensors with Pd nanoparticle (NP)-decorated and hemin-embedded UiO-66 MOFs serving as the signal amplification marker to eliminate false positives and decrease the background response of aptasensors. To construct aptasensors for detection of exosomes, CD63-specific aptamers were tethered onto magnetic Fe3O4 particles coated with polydopamine (PDA) and UiO-66-NH2 using glutaraldehyde crosslinking for capturing the exosomes. To prepare highly catalytic Zr-MOF-based signal markers, UiO-66 MOFs were modified with hemin followed by Pd NPs. The as-prepared Pd-decorated hemin-embedded MOFs showed high catalytic activity towards the chromogenic oxidation reaction of TMB by H2O2. Moreover, the decoration with Pd NPs led to the change of the surface charge state of the catalytic hemin-embedded UiO-66 MOFs from positive to negative, weakening the interaction between the signal marker and the negatively charged aptamers. Therefore, the as-prepared aptasensors showed an improved sensing performance towards exosomes with a linear concentration range from 4.28 × 102 to 4.28 × 105 and a limit of detection (LOD) of 86.2 particles per μL. The as-prepared aptasensors also showed high sensitivity and selectivity to the exosomes from different origins including the HeLa cell line and MCF-7 cell line.

Towards the fastest kinetics and highest uptake of post-functionalized UiO-66 for Hg2+ removal from water.

Recent advances in adsorbents have improved the removal of mercury ions from wastewater. Metal-organic frameworks (MOFs) have been increasingly used as adsorbents due to their high adsorption capacity and ability to adsorb various heavy metal ions. UiO-66 (Zr) MOFs are mainly used because they are highly stable in aqueous solutions. However, most functionalized UiO-66 materials are unable to achieve a high adsorption capacity because of the undesired reactions that occur during post-functionalization. Herein, we report a facile post-functionalization method to synthesize a MOF adsorbent with fully active amide- and thiol-functionalized chelating groups, termed UiO-66-A.T. UiO-66-A.T. was synthesized via a two-step reaction by crosslinking with a monomer containing a disulfide moiety, followed by disulfide cleavage to activate the thiol groups. UiO-66-A.T. removed Hg2+ from water with a maximum adsorption capacity of 691 mg g-1 and a rate constant of 0.28 g mg-1 min-1 at pH 1. In a mixed solution containing 10 different heavy metal ions, UiO-66-A.T. has a Hg2+ selectivity of 99.4%, which is the highest reported to date. These results demonstrate the effectiveness of our design strategy for synthesizing purely defined MOFs to achieve the best Hg2+ removal performance to date among post-functionalized UiO-66-type MOF adsorbents.

Mobility and separation of linear and branched C5 alkanes in UiO-66 (Zr) probed by 2H NMR and MD simulations.

The UiO-66 (Zr) metal-organic framework (MOF) is of notable interest due to its facile synthesis, robustness under a wide range of chemical and physical conditions and its capability to separate industrially relevant hydrocarbons mixtures. However, the knowledge of the molecular mechanisms behind these process remains limited. Here, we present a combined experimental (2H NMR) and computational study of the molecular mobility, transport and adsorption of C5 alkanes isomers in a dehydroxylated UiO-66 (Zr) MOF. We show that the tetrahedral cages of the MOF are the preferred adsorption location for both n-pentane and isopentane. In a binary mixture of the isomers, isopentane interacts more strongly with the material leading it to occupy more of the tetrahedral cages than n-pentane, resulting in an isopentane/n-pentane adsorption selectivity of αads = 2 (at 373 K). At the same time, the microscopic diffusivity for n-pentane, Dn (En = 18 kJ mol-1), is significantly lower than for isopentane, Diso (Eiso = 28 kJ mol-1), which results in a high separation selectivity for a n-pentane/isopentane mixture of α ≈ 13 (at 300 K). This shows that the UiO-66 MOF is indeed a promising active material for use in light hydrocarbon separation processes.

Programmable T-Junction Structure-Assisted CRISPR/Cas12a Electrochemiluminescence Biosensor for Detection of Sa-16S rDNA

Herein, a strand displacement amplification (SDA)-assisted CRISPR/Cas12a (LbCpf1) electrochemiluminescence (ECL) biosensor was fabricated for ultrasensitive identification of Staphylococcus aureus (Sa)-16S rDNA. A porphyrinic Zr metal-organic framework (MOF) (PCN-224) nanomaterial was prepared as the coreactant accelerator, which promoted the conversion of S2O82- and SO4*-, thus enhancing the reaction with CdS quantum dots (QDs) and amplifying the ECL emission signal. Meanwhile, with the presence of Sa-16S rDNA, the auxiliary probes and primers stimulated the SDA reaction under the action of Klenow fragment (3'-5' exo-) and Nt. BbvCI specifically recognized Sa-16S rDNA to form a defective T-junction structure and generated second primers to initiate the cycles. Such a structure transformed the input signal (Sa-16S rDNA) into substantial single-stranded DNA products (SP) through SDA. SP acted as activators and activated arbitrary side chain cleavage of CRISPR/Cas12a (trans-cleavage) and further realized effective annihilation of ECL signals. This ECL platform demonstrated desirable assay performance for Sa-16S rDNA with a wide response range of 1 fM to 10 nM, and the limit of detection was 0.437 fM (S/N = 3), showing good sensitivity and specificity. Therefore, the method not only expanded the applications of CRISPR/Cas12a but also opened up a novel strategy for clinical diagnosis.

Production of Levulinic Esters by Heterogeneous Catalysis with Zr Metal–Organic Frameworks in Pressure Reactors

Production of Levulinic Esters by Heterogeneous Catalysis with Zr Metal–Organic Frameworks in Pressure Reactors

Synthesis and application of Zr-metal–organic framework for simultaneous detection and rapid adsorption of p-nitrophenol from water

Synthesis and application of Zr-metal–organic framework for simultaneous detection and rapid adsorption of p-nitrophenol from water

Ti(IV) immobilized bisphosphate fructose-modified magnetic Zr metal organic framework (MOF) for specific enrichment of phosphopeptides

Highly selective enrichment of low abundance phosphopeptides from intricate biological samples before mass spectrometry detection is a vital prerequisite for in-depth phosphoproteomics. Herein, a magnetic material mMOF-FBP-Ti4+ is fabricated by grafting UiO-66-NH2 metal–organic framework (Zr-MOF) onto the surface of Fe3O4, and subsequently immobilizing Ti(IV) on the mMOF with fructose 1,6-bisphosphate as chelating ligands. The obtained mMOF-FBP-Ti4+ showed large specific surface area (202.4 m2 g−1) and superparamagnetism (47.5 emu/g). The intrinsic Zr − O clusters of mMOF and the immobilized Ti(IV) ions on the surface of mMOF could interact with phosphopeptides as metal oxide affinity chromatography (MOAC) and immobilized metal affinity chromatography (IMAC), respectively. The introduction of fructose 1,6-bisphosphate also improved the hydrophilicity of the material, which enhanced the hydrophilic chromatography interaction (HILIC) between mMOF-FBP-Ti4+ and phosphopeptides. The above strong affinities provided low limit of detection (0.2 fmol μL−1), high selectivity (α-/β-casein/BSA tryptic digests with a mass ratio of 1:1:500), great reusability (three times circles) and good postenrichment recovery (90.2 %) towards phosphopeptides. Furthermore, the mMOF-FBP-Ti4+ was successfully applied to capture phosphopeptides from non-fat milk tryptic digest and human saliva, indicating its great potential for highly efficient enrichment of low-abundance phosphopeptides in complex biological samples.

Highly Stable and End‐group Tuneable Metal–Organic Framework/Polymer Composite for Superior Triboelectric Nanogenerator Application

AbstractTriboelectric nanogenerators (TENGs) are receiving significant attention lately as efficient mechanical energy harvesting devices. They are finding multiple uses in numerous low‐power applications. Current TENG designs, although innovative, fall short on practical demands like performance tunability, modulatory, and stability. This invites further research in the use of new materials for TENGs. Metal‐organic frameworks (MOFs) offer a unique feature of molecular tunability to optimize energy conversion which has been exploited in this study. Prototypal hybridization strategy is deployed on underexplored isoreticular subfamily UiO‐66(Zr) MOFs through UiO‐66‐X/PVDF (X = H or Br) composites for TENG output tuning and amplification. UiO‐66‐X/PVDF exhibits good aquatic and thermal stability accompanying substantial boost in TENG power. Functionalized H2BDC linker improved surface roughness and potential. UiO‐66‐Br encased in PVDF matrix boosted charge and TENG performance by enhancing electrification. Computational details support observations. Device captures waste energy in a vertical contact‐separation mode and functions consistently amidst diverse environmental settings. Functionalized TENG‐2 delivers a Vp–p of 110.41 V, which is 2.92 times and 14.12 times higher than unfunctionalized TENG‐1 and PVDF film, respectively. Findings reveal maiden example of ligand‐mediated functional group‐driven performance tuning of TENG and mechanistic insight using isoreticular MOFs/PVDF composites.

Metal-Organic Framework UiO-66-Mediated Dual-Signal Ratiometric Electrochemical Sensor for microRNA Detection with DNA Walker Amplification.

Electrochemical nanotags with strong signal input are necessary for a ratiometric electrochemical sensor to overcome the drawbacks of inaccurate detection results. In this paper, the metal-organic framework (MOF) UiO-66 was utilized as an electrochemical signal tag. A stable and strong current response at +0.9 V can be detected in neutral conditions. MicroRNA (miRNA) was employed as the model analyte. Herein, an enzyme-free DNA-walker-based ultrasensitive ratiometric electrochemical biosensor in combination with Zr MOF (UiO-66) signal tags to detect miRNA was demonstrated. In the presence of miRNA, the autonomous walker movement can be initiated by miRNA, leading to the release of biotin-modified fragments. Thus, streptavidin-labeled UiO-66 nanomaterials were not bound to the electrode, generating a low signal response of UiO-66 at +0.9 V. However, the current signal of electrolyte solution as reference at +0.2 V was increased due to the enhancement of electrode conductivity. This ratiometic sensor demonstrated high sensitivity, selectivity, and reproducibility. It can eliminate the disturbance of environmental factors and basic electrode characteristics, providing more accurate signals. A limit of detection (LOD) of 0.17 fM was achieved. Moreover, the method was also used to detect miRNA-21 spiked in real serum samples.

Tunable Competitive Absorption-Induced Signal-On Photoelectrochemical Immunoassay for Cardiac Troponin I Based on Z-Scheme Metal-Organic Framework Heterojunctions.

Recently emerged Z-scheme heterostructure-based immunoassays have presented new opportunities for photoelectrochemical (PEC) biosensing development. Here, we described a tunable signal-on PEC biosensor for the detection of cardiac troponin I (cTnI), which exploited a competitive absorption effect between Cu(II) ions and a Zr metal-organic framework (Zr-MOF) constructed on TiO2 nanorods (Cu2+@Zr-MOF@TiO2 NRs). Water-stable Zr-MOF was coated onto TiO2 NRs on fluorine-doped tin oxide to form a Z-scheme heterostructure substrate (Zr-MOF@TiO2 NRs), which exhibited a high photoelectric response. Cu2+@Zr-MOF@TiO2 NRs, constructed by loading Cu(II) ions onto the architecture of Zr-MOF by electrostatic interaction, demonstrated a low background signal. After sandwich immunorecognition within a 96-well plate, H2S, generated by confined alkaline phosphatase on zeolitic imidazolate framework-8, was directed to react with Cu(II) ions to form CuS. This resulted in an in situ change in the photoelectrode and an enhanced photoelectric signal. The developed PEC biosensing platform exhibited high sensitivity and selectivity for the cTnI immunoassay with a detection limit of 8.6 pg/mL. The Z-scheme-based competition absorption modulation of photoelectrochemistry provides a new strategy for general PEC biosensing development.

Label-free fluorescence aptasensor for the detection of patulin using target-induced DNA gates and TCPP/BDC-NH2 mixed ligands functionalized Zr-MOF systems

Patulin (PAT) is an unsaturated lactone mycotoxin primarily produced by Penicillium expansum and Aspergillus clavatus. Given the potential health risks and economic losses associated with PAT, the rapid detection of PAT using fluorescent aptasensors is of significant importance in evaluating food safety. However, it easily increases the cost and complexity caused by signal labeling. We combined TCPP/BDC-NH2 mixed ligands functionalized Zr metal–organic frameworks (Zr-MOFmix) and terminated three-stranded DNA gates (ttsDNA gates) to fabricate a label-free fluorescent aptasensor for PAT detection. The Zr-MOFmix system was synthesized via a one-pot strategy and could be used to address the problem of pore size limitation and increase the loading amounts of dyes. TtsDNA gate was integrated into the Zr-MOFmix system to control the release of dyes, exhibiting a high signal-to-background ratio. The single-stranded aptamer region in ttsDNA gate situated away from the surface of the Zr-MOFmix, resulting in a natural release of dyes in the absence of PAT. While binding to PAT resulted in target-induced conformational changes that helped form the hairpin structure of the aptamer. This structure hindered the release of dyes from the pores of Zr-MOFmix, thus reducing the fluorescence signals intensity. The stimuli-responsive DNA-gated material provides a platform for PAT analysis under conditions of a low limit of detection (0.871 pg/mL). Furthermore, the excellent specificity and anti-interference of the fluorescent aptasensor make the system suitable for the analysis of apple juice samples. This label-free strategy is cheaper and simper compared with labeled detection, especially for the development of multi-target-detection.

Post-Synthetic Defunctionalization of Ammonium-Functionalized Zr-Based Metal-Organic Framework MIP-202 for Knoevenagel Condensation Reaction

ABSTRACT A new recyclable and stable catalyst based on a Zr metal-organic framework, namely MIP-202 has been constructed through a simple post‐synthetic modification strategy as an extremely efficient and applied heterogeneous catalyst for Knoevenagel condensation reaction between benzaldehyde and ethyl cyanoacetate under mild reaction conditions. The principal purpose of this study is to reduce the amount of the protonated amine functional groups (NH3 +) in the pores of MIP-202 using the solvent assisted ligand exchange (SALE), in order to achieve an optimal structure to obtain higher efficiencies in Knoevenagel condensation reaction. The resultant catalyst is characterized via various techniques including PXRD, FT-IR, FE-SEM, EDX, BET, AAS, CHN, and TG analyses. The post-modified catalyst exhibited high catalytic performance with 90% efficiency, which is an enhanced activity compared to the pristine MIP-202 MOF, and also four recycling stability without a significant decrease in catalytic activity. Therefore, it was proved that the adjustment of functional groups is an effective method for the improvement of the reaction process. The catalytic mechanism has also been investigated.

Dual-wavelength electrochemiluminescence biosensor based on a multifunctional Zr MOFs@PEI@AuAg nanocomposite with intramolecular self-enhancing effect for simultaneous detection of dual microRNAs

Rapid parallel detection of multi-targets has always been an exploration aim in electrochemiluminescence (ECL) assays. Herein, a multifunctional nanocomposite of Zr metal-organic frameworks (MOFs) @PEI@AuAg nanoclusters (NCs) with intense and stable dual-wavelength ECL was synthesized for the first time, and used to construct a new ECL biosensor for rapid simultaneous detection of dual targets. Notably, the novel ECL emitter Zr MOFs with high-performance was not only integrated with a co-reactant polyethyleneimine (PEI) to form a unique intramolecular self-enhancing structure, but also loaded a large number of another ECL emitter AuAg NCs, furthermore, AuAg NCs with superior electron transfer property can much enhance the electrical conductivity of the composites, thus achieving the goal of “killing three birds with one stone”. Moreover, a unique stable and rigid three-dimensional DNA tetrahedron (TDN) structure was connected with two quenching probes BHQ1 and BHQ3 and immobilized on the composites-modified electrode, so ECL emission of the nanocomposites at two wavelengths of 535 nm and 644 nm were both quenched by resonance energy transfer (RET). In the presence of target miRNAs, the efficient DNA cycling double-amplification processes were performed by using exonuclease (T7 Exo) combined with DNA Walker, thus both quenching groups were separated to restore the ECL at two wavelengths, achieving simultaneous and rapid ECL detection of two miRNAs. Therefore, this present work not only opens a unique nanocomplex with dual wavelength ECL and self-enhancing performance, but also develops a highly sensitive ECL biosensor with promising value for rapid multi-target analysis in clinical fields.

A new aminobenzoate-substituted s-triazin-based Zr metal organic frameworks as efficient catalyst for biodiesel production from microalgal lipids

In order to solve problems that large molecules of microalgal lipids were difficult to access active sites in micropore structures of traditional metal organic frameworks (MOF), a novel two-dimensional nanosheet catalyst (aminobenzoate-substituted s-triazin-based Zr metal organic frameworks, Zr-TATAB) that exposed more active sites with stronger acidity was synthesized through replacement of trimesate linker in water/acid-resistant Zr-based MOF-808 with 4,4 ́,4 ́ ́-s-triazine-1,3,5-triyltri-p-aminobenzoate (H3TATAB) to promote catalytic conversion efficiency of microalgal lipids to biodiesel. The binding energy of Zr increased by 0.2 eV due to electronic shift caused by triazine ring and imine groups in H3TATAB ligand, which led to more exposed Zr4+ active sites in Zr-TATAB catalyst. Due to increase of charge on crystal edges, dissociation of terminal hydroxyl groups was inhibited and Coulomb repulsion was increased. Therefore, Zr-TATAB catalyst possessed higher dispersion to avoid from pore blocking and catalytic deactivation, which enhanced recycling performance of catalyst. Compared with MOF-808, the total number of acid and base sites in Zr-TATAB catalyst increased from 6.0 mmol g−1 to 8.0 mmol g−1, while strength of acid sites increased with an increased ammonia desorption temperature by 150 °C, which led to an increased catalytic conversion efficiency of microalgal lipids to biodiesel to 98.2%.