Structural Engineering of BiVO4 /CoFe MOF Heterostructures Boosting Charge Transfer for Efficient Photoelectrochemical Water Splitting.

Boosting charge separation and transfer of photoanodes is crucial for providing high viability of photoelectrochemical hydrogen (H2 ) generation. Here, a structural engineering strategy is designed and synthesized for uniformly coating an ultrathin CoFe bimetal-organic framework (CoFe MOF) layer over a BiVO4 photoanode for boosted charge separation and transfer. The photocurrent density of the optimized BiVO4 /CoFe MOF(NA) photoanode reaches a value of 3.92 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE), up to 6.03 times that of pristine BiVO4 , due to the greatly increased efficiency of charge transfer and separation. In addition, this photoanode records one onset potential that is considerably shifted negatively when compared to BiVO4 . Transient absorption spectroscopy reveals that the CoFe MOF(NA) prolongs charge recombination lifetime by blocking the hole-transfer pathway from the BiVO4 to its surface trap states. This work sheds light on boosting charge separation and transfer through structural engineering to enhance the photocurrent of photoanodes for solar H2 production.

Catalytic Conversion of Carbohydrates into 5-Hydroxymethylfurfural by Phosphotungstic Acid Encapsulated in MIL-101 (Cr, Sn) Catalyst in Deep Eutectic Solvents.

Herein, we report the synthesis of bimetal-organic frameworks (BMOFs) with both Brønsted and Lewis acidities, in which phosphotungstic acid (PTA) was encapsulated in BMOFs. It is efficient in converting starch to 5-hydroxymethyl-furfural (HMF) in deep eutectic solvents (DESs) such as choline chloride and formic acid. The highest yield of HMF (37.94%) was obtained using P0.5/BMOFs1.0 to catalyze starch in a mixed solvent system comprising DESs and ethyl acetate (EAC) (v/v; 2:3) at 180 °C and a reaction time of 10 min. Employing a DES as a cocatalyst and solvent reduced the use of organic solvents. The catalyst showed adequate reusability, and the HMF yield only decreased by 2.88% after six cycles of reuse compared with that of the initial catalyst. This study demonstrates the application potential of BMOFs in the conversion of biomass to useful molecules with commercial and/or research value.

Exceptional removal and immobilization of selenium species by bimetal-organic frameworks.

Binary metallic organic frameworks can always play excellent functions for pollutants removal. One binary MOFs, UiO-66(Fe/Zr)), was newly synthesized and applied to remove aquatic selenite (SeIV) and selenate (SeVI). The adsorption behaviors and mechanisms were investigated using batch experiments, spectroscopic analyses, and theoretical calculations (DFT). The characterization results showed that the material inherited the topological structure of UiO-66 and excellent thermal stability. The large specific surface area (467.52 m2/g) and uniform mesoporous structures of the synthesized MOFs resulted in fast adsorption efficiency and high adsorption capacity for selenium species. The adsorbent kept high adsorption efficiency in a wide pH range from 2 to 11 with good anti-interference ability. The maximum adsorption capacity for Se(IV) and Se(VI) reached as high as 196 mg/g at pH 3 and 258 mg/g at pH 5, respectively. The process was conformed to fit pseudo-second-order kinetics and Langmuir isotherm, and could be explained by the formation of Fe/Zr-O-Se bond on the material surface, which was interpreted by the results of XPS, FTIR and DFT calculation. The regeneration and TCLP experiments demonstrated that UiO-66(Fe/Zr) could be regenerated for five cycles without obvious decrease of efficiencies, and the leaching rate of the adsorbed Se(IV) and Se(VI) in the spent adsorbent were only 4.8% and 2.3%. More than 99% of original Se(IV) and Se(VI) in the lake and tap water samples (1.0 mg/L of Se) could be removed in 2.0 h.

Antiblocking Heterostructure to Accelerate Kinetic Process for Na-Ion Storage.

Heterostructures are attracting increasing attention in the field of sodium-ion batteries. However, it is still unclear whether any two monophase components can be used to construct a high-performance heterostructure for sodium-ion batteries, as well as the kind of heterostructures that can boost electrochemical performances. In this study, based on classical semiconductor theories on antiblocking and blocking interfaces, attempts are made to answer the abovementioned queries. For this purpose, NiTe2 -ZnTe antiblocking and CoTe2 -ZnTe blocking heterostructures are synthesized through a bimetal-hexamine framework-derived strategy. The NiTe2 -ZnTe antiblocking heterostructure exhibits excellent high-rate and cycling performances, while the CoTe2 -ZnTe blocking heterostructure performs poorly, even compared to their monophase components. Further, kinetic measurements and theoretical calculation confirm that antiblocking heterointerfaces can boost Na-ion diffusion efficiency and decrease the diffusion barrier, which can be attributed to the highly conductive antiblocking heterointerfaces generated due to electron transfer from NiTe2 to ZnTe. Therefore, this study provides a new perspective to design heterostructures more efficiently, with significantly better Na-ion storage performance.

Bimetal MOFs catalyzed Fenton-like reaction for dual-mode detection of thiamphenicol.

In this work, we used a simple ultrasonic stripping method to synthesize a bimetal MOFs at room temperature as a nanoenzyme with peroxidase-like (POD-like) activity. Through bimetal MOFs catalytic Fenton-like competitive reaction, thiamphenicol can be quantitatively dual-mode detected by fluorescence and colorimetry. It realized the sensitive detection of thiamphenicol in water, and the limits of detection (LOD) were 0.030 nM and 0.031 nM, and the liner ranges were 0.1-150 nM and 0.1-100 nM, respectively. The methods were applied to river water, lake water and tap water samples, and with satisfactory recoveries between 97.67% and 105.54%.

Fluorinated magnetic porous carbons for dispersive solid-phase extraction of perfluorinated compounds.

Novel magnetic and fluorinated porous carbons (M-FPCs) with high fluorine content, large pore volume and specific surface area were first prepared by carbonizing and further fluorinating Fe-Zr bimetal-organic frameworks. The M-FPCs exhibit excellent adsorption performance toward perfluorinated compounds (PFCs), and the maximal adsorption capacity ranges from 518.1 to 919.3 mg g-1 for various PFCs. Based on this property, an environmental analytical method of dispersive solid-phase extraction (DSPE) using M-FPCs as adsorbents coupled with ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS) was developed for the detection of trace PFCs. The linear range was as wide as 10-200 ng L-1, and low limit of detection (0.02-0.16 ng L-1) and good precision (relative standard deviation less than 6.11% for intra-day and inter-day) were achieved. This method was applied to the detection of trace PFCs in environmental water and soil samples with satisfactory results.

Bimetallic molecularly imprinted nanozyme: Dual-mode detection platform.

Molecularly imprinted polymer nanozyme (MIL-101(Co,Fe)@MIP) with bimetallic active sites and high-efficiency peroxidase-like (POD-like) activity were synthesized for the ratiometric fluorescence and colorimetric dual-mode detection of vanillin with high selectivity and sensitivity. Compared with the monometallic nanozyme, the POD-like activity of bimetallic nanozyme was greatly enhanced by changing the electronic structure and surface structure. Ratiometric fluorescence and colorimetric dual-mode detection of vanillin in aqueous solution was realized by vanillin entering specific imprinted cavities and blocking the molecular channels on the surface of MIL-101(Co,Fe)@MIP and the dual-mode visual detection was also realized. The limits of detection were as low as 104 nM and 198 nM, respectively. The method proposed in this paper was applied to the real samples of ice cream and candy. And the recoveries were between 93.3% and 105.5%, which also reached a satisfactory degree. The further detection of dexamethasone and prednisone, two drugs belonging to glucocorticoid, proved that the nanozyme analysis method based on MIL-101(Co,Fe)@MIP could be developed into a sensing platform.

Multishelled NiO/NiCo2O4 hollow microspheres derived from bimetal-organic frameworks as high-performance sensing material for acetone detection.

Recently, tremendous research interest was stimulated to obtain advanced function materials with hierarchical structure and tailored chemical composition from metal-organic frameworks (MOFs) based precursors. Herein, Bimetal-organic frameworks of Ni-Co-BTC solid microspheres synthesized through hydrothermal method were acted as template to induce multishelled NiO/NiCo2O4 hollow microspheres by annealing treatment. When evaluated as gas sensing material, the optimal hybrid of NiO/NiCo2O4 (the molar ration of NiCo=1.5) multishelled hollow microspheres endowed a high sensitivity (17.86) to 100 ppm acetone with rapid response/recovery time (11/13 s) under low working temperature (160 °C) and the low detection limit reached 25 ppb. The enhanced mechanism was originated from the following aspects: the multishelled hollow architecture provided efficient diffusion path for gas molecules and sufficient active site for gas sensing reaction; the nanoscale p-p heterojunction created at NiO and NiCo2O4 nanoparticles interface amplified the resistance variation by tuning the potential barrier; the potent combination of the "chemical catalytic" effect of NiO and the "electrical catalytic" effect of NiCo2O4 improved the selective acetone detection.

Synergistic effect of dual sites on bimetal-organic frameworks for highly efficient peroxide activation.

Active site engineering is of significant importance for developing high activity metal-organic frameworks (MOFs) for catalytic applications. Herein, we develop a one-pot strategy to construct bimetal organic frameworks with Fe-Co dual sites for Fenton-like catalysis. Density functional theory (DFT) demonstrated that the introducing Co heteroatoms into MIL-101(Fe) (MIL represents Matérial Institute Lavoisier) was favorable for the formation of electron-deficient centers around benzene rings and electron-rich centers around Fe/Co. This synergistic effect could effectively decrease the energy barrier of H2O2 activation. Due to the facilitated charge transfer in the coordinated structures, MIL-101(Fe,Co) with engineered dual sites exhibited exceptionally high efficiency for the degradation of ciprofloxacin (CIP). The reaction rate of MIL-101(Fe,Co)/H2O2 system was 0.12 min-1, which was nearly 7.5 times higher than that of pristine MIL-101(Fe). The reaction mechanism of heterogeneous Fenton-like catalysis was fundamentally investigated by series of in-situ techniques, such as DRIFTS and Raman. ·OH radicals generated by H2O2 activation endowed the inspiring ability of MIL-101(Fe,Co) for water decontamination. This work offers a facile principle of exploring MOFs-based Fenton-like catalysts with a wide working pH range for environmental applications.

Controlled formation of porous CuCo2O4 nanorods with enhanced oxidase and catalase catalytic activities using bimetal-organic frameworks as templates.

Porous structures with highly dispersed and active catalytic sites are vital to improve the catalytic activity and stability of artificial enzyme-related catalytic reactions. Herein, a novel nanorod-like bimetal-organic framework serving as porous support and supplier of Co2+ and Cu2+ was used to prepare a beneficial porous metal oxide. By optimizing the calcination temperature, the composition of calcined product can be controlled and the nanorods with isolated and highly active CuCo2O4 nanoparticles were obtained. The porous CuCo2O4 nanorods exhibit a pH-dependent catalytic property, that is, they behave as oxidase in acid conditions and catalase in alkaline conditions. The CuCo2O4 nanorods perform dual-enzyme catalytic activity superior to monometallic oxides. What's more, compared with the reported Co3O4 nanoparticles, Co3O4/CuO hollow nanocage hybrids and NiCo2O4 mesoporous spheres, the porous CuCo2O4 nanorods show higher affinity to 3,3',5,5'-tetramethylbenzidine with a lower Km value. The superior dual-enzyme catalytic activities of CuCo2O4 nanorods benefit from the high catalytic activity of binary metal oxides and structural stability. After incubating in a wide range of pHs, temperatures and ionic strengths, the catalytic activity of CuCo2O4 nanorods can be maintained. The oxidase activity of CuCo2O4 nanorods can be inhibited in the presence of ascorbic acid, which can be applied in effective detection of ascorbic acid. This study opens a new path to prepare stable and highly active porous artificial enzymes.

Porous Microrod Arrays Constructed by Carbon-Confined NiCo@NiCoO2 Core@Shell Nanoparticles as Efficient Electrocatalysts for Oxygen Evolution.

The study of cost-efficient and high-performance electrocatalysts for oxygen evolution reaction (OER) has attracted much attention. Here, porous microrod arrays constructed by carbon-confined NiCo@NiCoO2 core@shell nanoparticles (NiCo@NiCoO2 /C PMRAs) are fabricated by the reductive carbonization of bimetallic (Ni, Co) metal-organic framework microrod arrays (denoted as NiCo-MOF MRAs) and subsequent controlled oxidative calcination. They successfully combine the desired merits including large specific surface areas, high conductivity, and multiple electrocatalytic active sites for OER. In addition, the oxygen vacancies in NiCo@NiCoO2 /C PMRAs significantly improve the conductivity of NiCoO2 and accelerate the kinetics of OER. The above advantages obviously enhance the electrocatalytic performance of NiCo@NiCoO2 /C PMRAs. The experimental results demonstrate that the NiCo@NiCoO2 /C PMRAs as electrocatalysts exhibit high catalytic activity, low overpotential, and high stability for OER in alkaline media. The strategy reported will open up a new route for the fabrication of porous bimetallic composite electrocatalysts derived from MOFs with controllable morphology for electrochemical energy conversion devices.

Bimetal-Organic Framework Derived CoFe2 O4 /C Porous Hybrid Nanorod Arrays as High-Performance Electrocatalysts for Oxygen Evolution Reaction.

Porous CoFe2 O4 /C NRAs supported on nickel foam@NC (denoted as NF@NC-CoFe2 O4 /C NRAs) are directly fabricated by the carbonization of bimetal-organic framework NRAs grown on NF@poly-aniline(PANI), and they exhibit high electrocatalytic activity, low overpotential, and high stability for the oxygen evolution reaction in alkaline media.