MOFs@POMs-derived bimetallic oxide Fe2(MoO4)3 nanoparticles for sensitive colorimetric detection of salicylic acid in aspirin.

A colorimetric sensing method for salicylic acid (SA) was developed by designing and fabricating bimetallic oxide nanozymes. Firstly, by calcinating MIL-100(Fe)@PMo12 (MOFs@POMs) at different temperature, Fe2(MoO4)3-Ts (T = 400℃, 500℃, 600℃, 700℃) nanoparticles (NPs) were successfully prepared. Secondly, by evaluating the peroxidase-like activities, Fe2(MoO4)3-600 NPs shows the best peroxidase-like activity attributed to the Fenton-like effect and the synergistic coupling interaction between Mo and Fe. Finally, based on the specific complexation between SA and Fe3+, a sensitive colorimetric sensor for SA was established, which exhibits superior selectivity and interference with a detection limit of 0.11 µM and a linear range of 10 to 100 µM, the lowest LOD for SA to date, to the best of our knowledge.

Agar-Derived Slope-Dominated Carbon Anode with Puparium Like Nano-Morphology for Cost-Effective SIBs.

The microstructure of hard carbons (HCs) including interlayer distance and lateral ab direction and pore size distribution plays a key role in regulating the sodium ions storage performance. Herein, by employing the gelatinous agar as a model precursor, series P-doping HCs (P-HC-x, x = 1, 2, 3, 4) are facilely prepared in batches via controllably regulating its crosslinking state by phytic acid (PA) at a low carbonization temperature of 750 °C, in which PA plays three roles (acid, flame retardant, and P-doping precursor) in promoting the final structure of P-HC-x. Among those, the puparium like P-HC-2 with expanded carbon interlayer distance of 3.91 Å and shortened lateral ab direction of 9.4 nm delivers a high reversible capacity of 394 mAh g-1 at 0.1 A g-1 with high increased slope capacity of 363 mAh g-1 as well as an ultrafast charge-discharge feature and a superlong cycle life. Pairing with the Na3 V2 (PO4 )3 cathode, the fabricated sodium-ion full cells exhibit the 132 mAh g-1 reversible capacity at 0.1 A g-1 , and 86% capacity retention after 100 cycles. This work successfully develops slope-dominated high-performance carbon anode, which will provide new insights for the microstructure regulation and design of other precursor-derivedHCs.

Increasing the peroxidase-like activity of the MIL-100(Fe) nanozyme by encapsulating Keggin-type 12-phosphomolybdate and covering three-dimensional graphene.

To improve the peroxidase-like activities of metal-organic frameworks (MOFs) as nanozymes, a ternary MIL-100(Fe)@PMo12@3DGO nanocomposite was designed and fabricated by encapsulating Keggin-type H3PMo12O40 (PMo12) with fast and reversible multi-electron redox processes and an electron-rich structure into MIL-100(Fe), then being covered by three-dimensional graphene (3DGO) with higher conductivity, larger surface area, higher porosity, and better chemical stability. As a consequence, the as-prepared MIL-100(Fe)@PMo12@3DGO nanocomposite exhibits excellent peroxidase-like activities, namely, the lowest limit of detection (0.14 µM) in the range of 1-100 µM for glucose to date, to the best of our knowledge, attributed to the individual and synergistic effects of H3PMo12O40, 3DGO and MIL-100(Fe).

ZIF-67 on Sulfur-Functionalized Graphene Oxide for Lithium-Sulfur Batteries.

How to overcome the problem of fast capacity fading and low sulfur utilization is the key to promote the practical applications of lithium-sulfur (Li-S) batteries. Based on the fact that sulfur-functionalized graphene oxide (GO-S) can avoid the loss of sulfur/polysulfides through the strong C-S interaction, and the zeolitic imidazolate framework (ZIF-67) can capture sulfur and catalyze lithium polysulfide (Li2Sx, 4 ≤ x ≤ 8), the combination of ZIF-S (ZIF-67 after combining with sulfur) with GO-S can be expected to be an excellent electrode material for Li-S batteries due to the synergistic effect. Herein, ZIF-S@GO-S (n) nanocomposites (n = 1, 2, and 3 for the mass ratio of ZIF-67/GO of 4:1, 6:1, and 8:1, respectively) as the cathode materials in Li-S batteries were successfully fabricated, and ZIF-S@GO-S (2) showed better electrochemical performances and cycle stability with a high specific capacity of 1529.5 mA h g-1 at the initial cycle and 792 mA h g-1 after 500 cycles at 0.1 C (1 C = 1675 mA h g-1). The fact that ZIF-S@GO-S (n) can simultaneously improve the conductivity and utilization of S (C-S···S8 and C-S···SxLi2) and the conversion kinetics of Li2Sx (4 ≤ x ≤ 8) provides a new avenue for designing and fabricating promising cathodes for high-performance Li-S batteries.

An Unprecedented FeMo6 @Ce-Uio-66 Nanocomposite with Cascade Enzyme-Mimic Activity as Colorimetric Sensing Platform.

Introducing the idea of integrated design and cascade activity into nanozyme, the novel integrated nanozymes (INAzymes), FeMo6 @Ce-Uio-66 (FC-66(n)), were designed and synthesized by encapsulating iron-based polyoxometalates (FeMo6 ) into the ceria-based metal-organic framework (Ce-Uio-66). Due to the oxygen-driven reversible Ce3+ /Ce4+ couple sites, the "Fenton-like" effect by iron centers, the "nanoscale proximity" effects by nanocages, and their synergistic effects, FC-66(n) as INAzymes exhibit elegant cascade enzyme-mimic activities (oxidase-, peroxidase-, and Fenton-like activity), which realizes INAzyme activities based on polyoxometalates based metal-organic framework (POMOFs). By employing dopamine (DA) detection as a model reaction, a high-efficient fluorescent "turning-on-enhanced" platform under near neutral conditions was established.

Nanohybridization of CoS2 /MoS2 Heterostructure with Polyoxometalate on Functionalized Reduced Graphene Oxide for High-Performance LIBs.

To address the poor cycling stability and low rate capability of MoS2 as electrode materials for lithium-ion batteries (LIBs), herein, the CoS2 /MoS2 /PDDA-rGO/PMo12 nanocomposites are constructed via a simple hydrothermal process, combining the advantages of all three, namely, CoS2 /MoS2 heterojunction and polyoxometalates (POMs) provide abundant catalytically active sites and increase the multi-electron transfer ability, and the positively charged poly(diallyldimethylammonium chloride) modified reduced graphene oxide (PDDA-rGO) improve electronic conductivity and effectively prevent the aggregation of MoS2 , meanwhile stabilize the negatively charged [PMo12 O40 ]3- . After the electrochemical testing, the resulting CoS2 /MoS2 /PDDA-rGO/PMo12 nanocomposite achieved 1055 mA h g-1 initial specific capacities and stabilized at 740 mA h g-1 after 150 cycles at 100 mA g-1 current density. And the specific capacities of MoS2 , MoS2 /PDDA-rGO, CoS2 /MoS2 , and CoS2 /MoS2 /PDDA-rGO were 201, 421, 518, and 589 at 100 mA g-1 after 150 cycles, respectively. The fact of the greatly improving capacity of MoS2 -based nanocomposites suggests its potential for high performance electrode materials of LIBs. Moreover, the lithium storage mechanism of CoS2 /MoS2 /PDDA-rGO/PMo12 has been discussed on the basis of cyclic voltammetry with different scan rates.

A template-free assembly of Cu,N-codoped hollow carbon nanospheres as low-cost and highly efficient peroxidase nanozymes.

Developing carbon-based materials with high catalytic performance and sensitivity has significance in low-cost and highly efficient nanozymes. Herein, for the first time, Cu,N-codoped hollow carbon nanospheres (CuNHCNs) with highly active Cu-Nx sites were successfully assembled through a template-free strategy, in which Cu2+-poly(m-phenylenediamine) (Cu-PmPD) nanospheres were utilized as the source of Cu, N and C. Benefiting from the synergistic effect of the hollow spherical structure and optimized composition, the CuNHCN exhibits high affinity for 3,3',5,5'-tetramethylbenzidine and H2O2 with 0.0655 mM and 0.918 mM, respectively, which are superior to those of HRP and most metal-based nanozymes. Moreover, by employing glucose and ascorbic acid (AA) as biomolecule models, a CuNHCN-based colorimetric detection platform is developed. The CuNHCN exhibits superior peroxidase mimicking activity and sensitivity in detecting glucose and AA with a detection limit of 0.187 µM and 68.9 nM (S/N = 3), respectively. Also, the colorimetric detection based on the CuNHCN towards glucose and AA in human serum presents superior practicability and accuracy. The assay provides a new avenue for designing and fabricating low-cost peroxidase nanozymes with high performance in bioassays.

Hollow POM@MOF-derived Porous NiMo6 @Co3 O4 for Biothiol Colorimetric Detection.

Developing highly active and sensitive peroxidase mimics for L -cysteine (L -Cys) colorimetric detection is very important for biotechnology and medical diagnosis. Herein, polyoxometalate-doped porous Co3 O4 composite (NiMo6 @Co3 O4 ) was designed and prepared for the first time. Compared with pure and commercial Co3 O4 , NiMo6 @Co3 O4 (n) composites exhibit the enhanced peroxidase-mimicking activities and stabilities due to the strong synergistic effect between porous Co3 O4 and multi-electron NiMo6 clusters. Moreover, the peroxidase-mimicking activities of NiMo6 @Co3 O4 (n) composites are heavily dependent on the doping mass of NiMo6 , and the optimized NiMo6 @Co3 O4 (2) exhibits the superlative peroxidase-mimicking activity. More importantly, a sensitive L -Cys colorimetric detection is developed with the sensitivity of 0.023 µM-1 and the detection limit at least 0.018 µM in the linear range of 1-20 µM, which is by far the best enzyme-mimetic performances, to the best our knowledge.

Synthesis of POMOFs with 8-fold helix and its composite with carboxyl functionalized SWCNTs for the voltammetric determination of dopamine.

Although many satisfactory studies have been developed for biomolecule detection, the complexity of biofluids still poses a major challenge to improve the performance of nanomaterials as electrochemical sensors. Herein, unprecedented polyoxometalate-based metal-organic frameworks (POMOFs) with 8-fold meso-helical feature, [Ag5(trz)4]2[PMo12O40] (PAZ), were synthesized and explored as electrochemical sensors to detect dopamine (DA). To improve the conductivity of PAZ and the binding ability with single-walled carbon nanotubes (SWCNTs), the nanocomposite of carboxyl functionalized SWCNTs (SWCNTs-COOH) with nano-PAZ (NPAZ), NPAZ@SWCNTs-COOH, was fabricated, and transmission electron microscopy (TEM) shows that NPAZ can interact stably and uniformly with SWCNTs-COOH, owing to more defect sites on the surface of SWCNTs-COOH. The electrochemical result of NPAZ@SWCNTs-COOH/GCE towards detecting DA shows that the linear range was from 0.05 to 100 µM with a detection limit (LOD) of 8.6 nM (S/N = 3). A new electrochemical biosensing platform by combining 8-fold helical POMOFs with SWCNTs-COOH was developed for enhancing detection of dopamine for the first time, exhibiting the lowest detection limit to date.

Anderson polyoxometalates with intrinsic oxidase-mimic activity for "turn on" fluorescence sensing of dopamine.

Anderson-type polyoxometalate containing Fe3+ and Mo6+, (NH4)3[H6Fe(III)Mo6O24] (FeMo6), was found to work as an oxidase-mimicking nanoenzyme for the first time, exhibiting the ability of catalytic oxidation of o-phenylenediamine (OPD), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTs), and 3,3',5,5'-tetramethylbenzidine (TMB), which features easy synthesis, low cost, simple operation, and low consumption. Attributed to the nature of FeMo6 and Fenton-like effect, a novel sensor based on two consecutive "turn on" fluorescence was developed for detecting dopamine (DA) by employing the FeMo6-OPD system, and the linear range was from 1 to 100 µM with the detection limit 0.0227 µM (3σ/s). Moreover, to increase oxidase-mimic activity of FeMo6, reduced graphene oxide (rGO) loading FeMo6 composites (FeMo6@rGO (n), n = 5%, 10%, 15%) was fabricated, and results show that oxidase-like activities of FeMo6@rGO (n) are dependent on the mass ratio of FeMo6/rGO, and FeMo6@rGO (10%) exhibits the highest oxidase-mimic activity and the fastest respond time (4 min) among all reported oxidase mimic of DA to date. Graphical abstract Anderson-type Mo-POMs FeMo6 was found to work as an oxidase-mimicking nanoenzyme for the first time and was used to detect DA for two consecutive "turn on" fluorescence sensor modes.

A polypyrrole-coated eightfold-helical Wells-Dawson POM-based Cu-FKZ framework for enhanced colorimetric sensing.

To explore a novel colorimetric biosensor with high sensibility and selectivity, a new Wells-Dawson-type polyoxometalate (POM)-based metal-organic framework (MOF) with an eightfold helix, [Cu9(FKZ)12(H2O)8][H3P2W18O62]2·4H2O (CuFKZP2W18) (HFKZ = 1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-1-yl)methyl] ethanol), was successfully synthesized; then, polypyrrole (PPy) was introduced to fabricate CuFKZP2W18/PPy(n) nanocomposites (n = 7%, 15%, 30%) via a facile in situ oxidation polymerization process. All the results indicate that CuFKZP2W18/PPy(15%) as a colorimetric biosensor exhibits lower limits of detection (0.07 µM towards H2O2 and 0.627 µM towards ascorbic acid), smaller Km values (0.106 mM for H2O2 and 0.042 mM for o-phenylenediamine) and higher sensitivity (0.0227 1 µM-1 towards H2O2 and 0.0025 1 µM-1 to ascorbic acid) than most reported enzyme mimetics to the best of our knowledge.

Effects of Polyoxometalates on the Hydroxylation of N-Heterocyclic Ligands.

Four polyoxometalate (POM)-based Cu complexes with the hydroxylated pyridine analogue 3-(2-hydroxylpyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl (btpo), H3{[Cu2(btpo)2](PW12O40)}·2H2O (1), H3{[Cu2(btpo)2](PMo12O40)}·2H2O (2), H2{[Cu2(btpo)2](SiW12O40)·SO4 (3), and H4{[Cu4(btpo)4](SiW12O40)}·8H2O (4), were synthesized hydrothermally under acid conditions. Single-crystal X-ray structural analysis reveals that 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl was hydroxylated into btpo in compounds 1-4, again providing structural evidence for the Gillard mechanism, in which H2O as a weak nucleophile can attack the α-C atom of N-heterocyclic molecules at a lower pH value (ca. 1.0) with the help of POMs.

Assembly of 12-Tungstovanadate-Templated Nanocage and Nanocomposites with Single-Walled Carbon Nanotubes as Anodes in Lithium-Ion Batteries.

A new 12-tungstovanadate-templated 3D nanocage framework, Ag10(µ4-ttz)4(H2O)4(VW12O40) (VW12@MOCF), was designed based on a "molecular library", hydrothermally synthesized, structurally characterized, and explored as anode material for lithium-ion batteries (LIBs). Combination of the structural superiority of VW12@MOCF with the good electrical conductivity of the single-walled carbon nanotubes (SWNTs) renders the VW12@MOCF/SWNT-2 nanocomposite reasonable electrochemical performance and stability as anode materials of LIBs. The successful cooperative fabrication of nanocages and polyoxometalate (POMs) must initiate extensive research interests.

Enhancing the colorimetric detection of H2O2 and ascorbic acid on polypyrrole coated fluconazole-functionalized POMOFs.

A new fluconazole-functionalized polyoxometalate-based metal-organic framework (POMOF) [Ag3(FKZ)2(H2O)2][H3SiW12O40] (AgFKZSiW12) was successfully constructed, and its polypyrrole (PPy) coated composite AgFKZSiW12@PPy was also obtained via a facile 'in situ' oxidation polymerization process. The peroxidase-like activity evaluation indicates that the maximized synergistic effect from the integration of PPy, SiW12 clusters, HFKZ drug molecules, and Ag ions deeply enhanced the overall performance. More importantly, AgFKZSiW12@PPy exhibits the fastest response time (30 s) among all the reported peroxidase mimics to date, including the pristine AgFKZSiW12 (2 min). Moreover, the AgFKZSiW12@PPy-based colorimetric biosensing platform towards H2O2 and ascorbic acid (AA) exhibits limits of detection (LOD) as low as 0.12 µM and 2.7 µM, respectively. This work reveals a promising prospect in medical diagnosis and biotechnology for colorimetric biosensor fabrication with high performance through the introduction of PPy.

FeOCl/POM Heterojunctions with Excellent Fenton Catalytic Performance via Different Mechanisms.

To enhance the Fenton catalytic performance in a neutral solution under indoor sunlight, a novel FeOCl/polyoxometalate (POM) (FeOCl/POM-W and FeOCl/POM-Mo) composite was successfully synthesized for the first time, which shows significantly improved Fenton catalytic activity and stability for phenol degradation compared with FeOCl. Furthermore, the degradation constants ( k) of FeOCl/POM-Mo (0.08 min-1) and FeOCl/POM-W (0.06 min-1) are a factor of 4 and 3 times greater than that of FeOCl (0.02 min-1), respectively. The enhanced catalytic activity is attributed to the formation of FeOCl/POM heterojunctions, which results in efficient separation of photoinduced electron-hole pairs and electron transfer from POM to FeOCl. Density functional theory calculations indicate a strong interface interaction of Fe-O-Mo and Fe-O-W in the FeOCl/POM heterojunctions. A Z-scheme mechanism for FeOCl/POM-Mo and a double-transfer mechanism for FeOCl/POM-W are proposed for the enhanced catalytic performance. This study sheds new light on the design and fabrication of high-performance photo-Fenton catalysts to overcome the environmental crisis.

Assembly of Multifold Helical Polyoxometalate-Based Metal-Organic Frameworks as Anode Materials in Lithium-Ion Batteries.

For exploring the multifold helical fabrication of polyoxometalate (POM)-based hybrid compounds, four POM-based crystalline compounds with different meso-helices, H3[Ag27(trz)16(H2O)6][SiW12O40]2·5H2O (1), H[Ag27(trz)16(H2O)4][PW12O40]2·2H2O (2), [Ag23(trz)14(H2O)2][HSiW12O40] (3), and [Ag23(trz)14(H2O)2][PW12O40] (4), were successfully isolated by using the delicate 1,2,3-triazole ligand and silver ions in this work. Crystal analysis reveals that compounds 1 and 2 and compounds 3 and 4 are isomorphous and display 2-/4-fold mixed meso-helices and simple 2-fold meso-helices, respectively. In addition, due to the reversible multielectron redox behavior and electron storage functions of POMs, compounds 1 and 3 were studied as anode materials in lithium-ion batteries (LIBs). Compounds 1 and 3 show very high lithiation capacities (1356 and 1140 mAh g-1, respectively) in the initial cycle, which are much higher than those of (NBu4)4[SiW12O40] and commercial graphite at the current density of 100 mA g-1. More importantly, both compounds also show good stable performance after 100 cycles.

Polyoxometalates Templated Metal Ag-Carbene Frameworks Anodic Material for Lithium-Ion Batteries.

A POMs templated 3D Ag-carbene framework with lvt-a topology was hydrothermally synthesized. The POMs templated MCF combining the advantages of POMs, MOFs, and carbene not only shows excellent thermal and chemical stabilities but also possesses a good discharge capacity of 481 mAh·g-1 after 100 cycles applied as anode material in LIBs.

Polyoxometalate-Incorporated Metallapillararene/Metallacalixarene Metal-Organic Frameworks as Anode Materials for Lithium Ion Batteries.

A series of remarkable crystalline compounds containing metallapillararene/metallacalixarene metal-organic frameworks (MOFs), [Ag5(pyttz)3·Cl·(H2O)][H3SiMo12O40]·3H2O (1), [Ag5(trz)6][H5SiMo12O40] (2), [Ag5(trz)6][H5GeMo12O40] (3), and [Ag5(trz)6][H4PW12O40] (4) (pyttz = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, trz = 1,2,4-triazole), have been obtained by using a simple one-step hydrothermal reaction of silver nitrate, pyttz for 1 and trz for 2-4, and Keggin type polyoxometalates (POMs). Crystal analysis reveals that Keggin POMs have been successfully incorporated in the windows of the metallapillararene/metallacalixarene MOFs in compounds 1-4. In addition, the Keggin silicomolybdenate-based hybrid compounds 1 and 2 were used as anode materials in lithium ion batteries (LIBs), which exhibited promising electrochemical performance with the first discharge capacities of 1344 mAh g-1 for 1 and 1452 mAh g-1 for 2, and this stabilized at 520 mAh g-1 for 1 and 570 mAh g-1 for 2 after 100 cycles at a current density of 100 mA g-1. The performances are better than that of (NBu4)4[SiMo12O40] matrix and commercial graphite anodes.

Construction of a 12-Phosphomolybdate-based Coordination Polymer@Crumpled Graphene Balls Composite as Anode for Lithium Batteries.

To address the poor electronic conductivity and easily dissolved in electrolyte of polyoxometalates (POMs), and considering the high electrical conductivity and configuration advantages of crumpled graphene balls (CGBs), herein, a series of POM-based coordination polymers [Cu(pyttz)2 ]PMo12 @CGB (n, n=1, 2, 3) were successfully synthesized, and electrochemical lithium storage performance and lithium ion diffusion kinetics were comprehensively investigated. Galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) study confirm that [Cu(pyttz)2 ]PMo12 @CGB (n, n=1, 2, 3) integrates the advantage of high electronic conductivity of CGB and excellent Li+ migration kinetics of POMs, which greatly ameliorates the electrochemical performances of POMs, among [Cu(pyttz)2 ]PMo12 @CGB (2) exhibits an excellent reversible specific capacity of around 941.4 mA h g-1 at 0.1 A g-1 after 150 cycles and admirable rate performance. This work will promote the development of POMCP anodes, thus fulfilling their potential in high-performance LIBs.

Oxygen-powered flower-like FeMo6@CeO2 self-cascade nanozymes: a turn-on enhancement fluorescence sensor.

Enzyme cascade reactions in organisms have sparked tremendous interest for their coupled catalysis-facilitated efficient biochemical reactions. However, multi-enzyme cascade nanozymes remain largely unused. In the work, flower-like porous ceria-based integrated enzymes (INAzyme), FeMo6@CeO2 (FMC-n), were readily prepared using an efficient thermally induced process. Owing to a larger specific surface area and excellent adsorption, the flower-like matrix (CeO2) can serve as not only an effective sorbent for the conversion of dissolved oxygen in solution but also an excellent support for self-cascade reactions with FeMo6. Based on the electron transfer through Fe and Ce cycles, FMC-n INAzyme exhibits intrinsic oxidase-, peroxidase- and Fenton-like activities. Moreover, by assessing the Vo mobility and F-Vo relative content of FMC-2 and FC-66, we found that the contribution of enhanced accessibility through the specific surface area (SSA) to the activity of the INAzyme is significantly higher than the active sites. Finally, a fluorescence turn-on enhancement sensing platform based on self-cascade FMC-n for the detection of Cys was established, culminating in a LOD of as low as 0.014 µM in the range of 1-100 µM.