Preparation of a Nanosheeted Uranyl-Organic Framework for Enhanced Photocatalytic Oxidation of Toluene.

Preparation of ultrathin metal-organic framework (MOF) nanosheets is an effective way to improve the catalytic efficiency of MOF photocatalysts owing to their superiority in reducing the recombination rate of photogenerated electrons and holes and enhancing charge transfer. Herein, a light-sensitive two-dimensional uranyl-organic framework named HNU-68 was synthesized. Due to its interlayer stacking structure, the corresponding ultrathin nanosheets with a thickness of 4.4 nm (HNU-68-N) can be obtained through ultrasonic exfoliation. HNU-68-N exhibited an enhanced ability to selectively oxidize toluene to benzaldehyde, with the value of turnover frequency being approximately three times higher than that of the bulk HNU-68. This enhancement is attributed to the smaller size and interface resistance of the layered HNU-68-N nanosheets, which facilitate more thorough substrate contact and faster charge transfer, leading to an improvement in the photocatalytic efficiency. This work provides a potential candidate for the application of ultrathin uranyl-based nanosheets.

Enhancement of Mass Transfer Process for Photocatalytic Reduction in Cr(VI) by Electric Field Assistance.

The removal of Cr(VI), a highly-toxic heavy metal, from industrial wastewater is a critical issue in water treatment research. Photocatalysis, a promising technology to solve the Cr(VI) pollution problem, requires urgent and continuous improvement to enhance its performance. To address this need, an electric field-assisted photocatalytic system (PCS) was proposed to meet the growing demand for industrial wastewater treatment. Firstly, we selected PAF-54, a nitrogen-rich porous organic polymer, as the PCS's catalytic material. PAF-54 exhibits a large adsorption capacity (189 mg/g) for Cr(VI) oxyanions through hydrogen bonding and electrostatic interaction. It was then coated on carbon paper (CP) and used as the photocatalytic electrode. The synergy between capacitive deionization (CDI) and photocatalysis significantly promotes the photoreduction of Cr(VI). The photocatalytic performance was enhanced due to the electric field's influence on the mass transfer process, which could strengthen the enrichment of Cr(VI) oxyanions and the repulsion of Cr(III) cations on the surface of PAF-54/CP electrode. In addition, the PCS system demonstrates excellent recyclability and stability, making it a promising candidate for chromium wastewater treatment.

An ultrasensitive photoelectrochemical assay for tumor necrosis factor-alpha based on hollow CdS cubes as a signal generator and NiCo2O4-Au as a signal extinguisher.

Sensitive detection of tumor necrosis factor-alpha (TNF-α) in human serum is beneficial for finding cancer patients early due to overexpressed TNF-α being related to some cancers. Here, a photoelectrochemical (PEC) aptasensor was constructed for ultrasensitive TNF-α assay based on the signal generator of hollow CdS cubes (H-CdS) and the signal extinguishing activity of NiCo2O4-Au. In this work, compared with traditional solid CdS, H-CdS could greatly promote the PEC signal because its hollow structure could accelerate the separation of photogenerated charges, which also possesses abundant active sites and high light absorption capability. Moreover, H-CdS can be prepared facilely with Cd-based Prussian blue analogs as the precursor. Meanwhile, NiCo2O4-Au was fabricated and utilized as a signal extinguisher. In the presence of TNF-α, NiCo2O4-Au could be introduced onto the H-CdS modified electrode, producing competitive consumption of the electron donor effect, the p-n semiconductor quenching effect, and the mimetic enzymatic catalytic precipitation effect, which all can significantly reduce the PEC signal. Based on the signal extinguishing activity of NiCo2O4-Au and the signal generator of H-CdS, TNF-α can be detected sensitively with a lower detection limit (0.63 fg mL-1) and a wide linear range (1 fg mL-1- to 1 ng mL-1), which may have a potential application in the PEC bioanalysis field and the disease diagnostics field.

Fluorescence Thermometers Involving Two Ranges of Temperature: Coordination Polymer and DMSP Embedding.

The measurement of temperature is indispensable in the fields of life, science, and industry. Fluorescence thermometers are attractive to researchers because of their advantages such as noncontact, high sensitivity, fast response, and excellent anti-interference. Here, a new coordination polymer (HNU-76) was synthesized by assembling Zn2+ with the H3TCA ligand, a fluorescent molecule with an AIE behavior, which can be used as a fluorescence thermometer. At 100-210 K, the fluorescence intensity ratio of HNU-76 versus temperature conforms to an Arrhenius-type decay relationship (R2 = 0.997), which can be the candidate for low-temperature sensing. In order to increase the sensing range, 4-[4-(dimethylamino)styryl] pyndine (DMSP) was successfully embedded on HNU-76, obtaining HNU-76⊃DMSP. The fluorescence intensity of HNU-76⊃DMSP conforms to an Arrhenius-type decay relationship (R2 = 0.997) at 270-360 K versus temperature. HNU-76 can be used for fluorescence detection at low temperatures, due to the DMSP loading, and HNU-76⊃DMSP can serve as the temperature thermometer in a range of temperatures common. Both materials show good cyclability and have the potential to be used in fluorescence thermometers.

Defect Healing of Micro/Nanocrystals via the Coordination Competition of Rare Earth in Crystal Engineering.

Defect engineering has been generally observed and utilized in crystal materials including metal oxides, metal-organic frameworks, and so on; however, how to relate the defect formation and crystallization process is needed to be revealed clearly, and how to heal the defect is a big challenge. Herein, based on the new coordination complex (HNU-53), the crystal defects were created by increasing the reaction time and crystal size. Following the crystal growth process, the crystal color centers were simultaneously generated, resulting in fluorescence quenching. To heal the defect, the crystal growth was controlled by the introduction of rare earth ions. With the coordination competition of rare earth ions, the crystal defects were reduced and recovery of fluorescence emission was achieved.

Effects of non-invasive brain stimulation on motor function after spinal cord injury: a systematic review and meta-analysis.

BACKGROUND: In recent years, non-invasive brain stimulation (NIBS) has been used for motor function recovery. However, the effects of NIBS in populations with spinal cord injury (SCI) remain unclear. This study aims to conduct a meta-analysis of the existing evidence on the effects and safety of NIBS against sham groups for motor dysfunction after SCI to provide a reference for clinical decision-making. METHODS: Two investigators systematically screened English articles from PubMed, MEDLINE, Embase, and Cochrane Library for prospective randomized controlled trials regarding the effects of NIBS in motor function recovery after SCI. Studies with at least three sessions of NIBS were included. We assessed the methodological quality of the selected studies using the evidence-based Cochrane Collaboration's tool. A meta-analysis was performed by pooling the standardized mean difference (SMD) with 95% confidence intervals (CI). RESULTS: A total of 14 randomized control trials involving 225 participants were included. Nine studies used repetitive transcranial magnetic stimulation (rTMS) and five studies used transcranial direct current stimulation (tDCS). The meta-analysis showed that NIBS could improve the lower extremity strength (SMD = 0.58, 95% CI = 0.02-1.14, P = 0.004), balance (SMD = 0.64, 95% CI = 0.05-1.24, P = 0.03), and decrease the spasticity (SMD = - 0.64, 95% CI = - 1.20 to - 0.03, P = 0.04). However, the motor ability of the upper extremity in the NIBS groups was not statistically significant compared with those in the control groups (upper-extremity strength: P = 0.97; function: P = 0.56; and spasticity: P = 0.12). The functional mobility in the NIBS groups did not reach statistical significance when compared with the sham NIBS groups (sham groups). Only one patient reported seizures that occurred during stimulation, and no other types of serious adverse events were reported. CONCLUSION: NIBS appears to positively affect the motor function of the lower extremities in SCI patients, despite the marginal P-value and the high heterogeneity. Further high-quality clinical trials are needed to support or refute the use and optimize the stimulation parameters of NIBS in clinical practice.

Efficient Photocatalytic Oxidative Coupling of Benzylamine over Uranyl-Organic Frameworks.

Visible-light-driven organic transformation photocatalyzed by metal-organic frameworks (MOFs) under mild conditions is considered a feasible route to conserve energy and simplify synthesis. Herein, a light-sensitized, three-dimensional uranyl-organic framework (HNU-64) with twofold interpenetration and its derivatives HNU-64-CH3 and HNU-64-Cl with functionalized ligands of -CH3 and -Cl groups were obtained. These MOFs have broad optical absorption bands and suitable band energy levels in photooxidation, which makes them exhibit high activity and selectivity for the photooxidation of benzylamine to N-benzylbenzoimide under mild conditions. This work provides an efficient and simple synthetic option for oxidative coupling of amines to directly produce imines.

Dye-Encapsulated Lanthanide-Based Metal-Organic Frameworks as a Dual-Emission Sensitization Platform for Alachlor Sensing.

As an important factor affecting global agricultural output, pesticides have a significant impact on the ecosystem. It is an urgent task to accurately and conveniently detect pesticide residues after their application. Herein, a fluorescent dye@MOF platform was designed via the encapsulation of rhodamine B (RhB) into the MOF structure (named RhB@HNU-48), which can significantly enhance the sensing sensitivity of alachlor with an ultralow detection limit of 0.59 ppb. The improved sensitivity of RhB@HNU-48 to pesticides was attributed to the host-guest interactions that affect the excitation and emission spectra of the composites. Based on the sensing capability of RhB@HNU-48, a logic gate was built to evaluate the safety level of alachlor residues in rivers and soil. The preparation of photofunctionalized MOF composites through modulation of host-guest interactions offers a promising strategy for the construction of desired sensors for agricultural residues.

Modulation of the Host-Guest-Guest Interactions in a Metal-Organic Framework for Multiple Anticounterfeiting Applications.

Developing fluorescent materials with multiple and tunable emissions under different conditions is necessary to meet the growing demand for optical anticounterfeiting technology. Different modes of fluorescence emission can be obtained by loading multiple fluorescent components into metal-organic frameworks (MOFs) and modulating the interaction among them for multiple anticounterfeiting purposes. Herein, a Cd-based MOF (HNU-60) was constructed as a host to encapsulate both lanthanide ions and carbon quantum dots. Multiple fluorescence emissions can be achieved by modulation of host-guest and guest-guest interaction, which holds promise for multiple anticounterfeiting applications. This work opens the opportunity to construct the hybrid MOF-based materials with controlled fluorescence properties for emerging anticounterfeiting applications in various fields.

Synthesis of 4-dimethylaminobenzyl chrysin ester-Zn fluorescent chemical sensor for the determination of Cr(VI) in water.

Cr(VI) is a type of dangerous effluent that has caused great harm to human health and the environment. Recognition and perception of Cr(VI) by artificial receptors has attracted extensive attention. A novel fluorescent chemical sensor based on the 5,7-dihydroxyflavone skeleton was designed and synthesized for the selective recognition of Cr(VI). As confirmed by fluorescence technology, the fluorescent probe 4-dimethylaminobenzyl chrysin ester-Zn (DBC-Zn) showed high sensitivity and selectivity for dichromate and a fast response (less than 30 sec) recognition. The fluorescence intensity of DBC-Zn varies linearly with the concentration of Cr(VI) in the range 0.1-1 µM. The detection limit of Cr2 O7 2- by DBC-Zn is 2.3 nM, which is far lower than the national safe drinking water standard stipulated by the US Environmental Protection Agency (1.9 µM). The quenching mechanism of the probe can be attributed to the interaction of the dynamic quenching effect and the fluorescence internal filtration effect. In addition, the probe has good stability in both neutral and alkaline environments, and the accuracy of quantitative analysis of Cr2 O7 2- in lake water or tap water is more than 80%. The test paper based on DBC-Zn can effectively detect Cr2 O7 2- at the concentration of 100 ppb. This shows that the probe has a certain practical application value.

Enzyme-free fluorescence determination of uric acid by combining CdTe quantum dots with metal-organic framework for signal amplification.

The composite of CdTe quantum dots (QDs) with ZIF-8 was elaborately designed and synthesized as an enzyme-free fluorescent probe for the sensitive determination of uric acid (UA), based on the fluorescence detection property of CdTe QDs and the signal amplification function of ZIF-8. The structure and feature of the composite were characterized with transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, and fluorescence spectrometry. With adding UA to the composite, the emission of CdTe QDs reduced due to the inner filter and dynamic quenching effects of UA, and the adsorption ability of ZIF-8 toward UA promoted the response signal of CdTe QDs. On this basis, UA was quantified by the composite in the concentration range 0.05 to 10 µM with excitation/emission wavelength at 287/615 nm, and the detection limit of the composite toward UA was 32 nM. The reproducibility of the composite for determining UA was further evaluated, and the relative standard deviations were below 10.2%. The composite also exhibited the merits of enzyme-free analysis such as low testing cost, short analysis time (1 min), and loose pH condition (application in whole physiological pH range, 5.0 - 8.0). The composite was applied to the determination of UA in human urine with recoveries of spiked samples in the range 99 to 113%.

Highly Selective Gas Sensor Based on Litchi-like g-C3N4/In2O3 for Rapid Detection of H2.

Hydrogen (H2) has gradually become a substitute for traditional energy, but its potential danger cannot be ignored. In this study, litchi-like g-C3N4/In2O3 composites were synthesized by a hydrothermal method and used to develop H2 sensors. The morphology characteristics and chemical composition of the samples were characterized to analyze the gas-sensing properties. Meanwhile, a series of sensors were tested to evaluate the gas-sensing performance. Among these sensors, the sensor based on the 3 wt% g-C3N4/In2O3 (the mass ratio of g-C3N4 to In2O3 is 3:100) showeds good response properties to H2, exhibiting fast response/recovery time and excellent selectivity to H2. The improvement in the gas-sensing performance may be related to the special morphology, the oxygen state and the g-C3N4/In2O3 heterojunction. To sum up, a sensor based on 3 wt% g-C3N4/In2O3 exhibits preeminent performance for H2 with high sensitivity, fast response, and excellent selectivity.

Modulation of High-Spin Co(II) in Li/Co-MOFs as Efficient Fenton-like Catalysts.

Developing high-performance catalysts toward the Fenton reaction is important for environmental protection and sustainable development, yet it is still challenging. The high-spin states of first-row transition metal atoms with tetrahedral coordination provide a flexible electronic environment to activate the catalyst and elevate its catalytic activity. As a type of material with adjustable structures, metal-organic frameworks (MOFs) are excellent candidate catalysts as they can accurately regulate the coordination configurations of metal ions. In this paper, we investigate and summarize the direct formation of bimetallic carboxylate Li/Co-MOFs with tetrahedral coordination metal centers in a mixed H2O/polar organic solvent system. The induction of Li(I) ions is manifested in the generation of hydroxides during the dissociation of the Co(II) solvation structure to trigger the tetrahedral coordination behavior of Co(II). These Li/Co-MOFs containing high-spin Co(II) centers can serve as highly efficient Fenton-like catalysts for organics. This study provides a promising strategy for rational design of MOF-based catalysts with high-spin metal centers for application in environment governance.

A Zinc Metal-Organic Framework for Concurrent Adsorption and Detection of Uranium.

Uranium is one of the principal raw materials in the nuclear industry, but if released into the natural environment, it also poses latent health risks to mankind. Therefore, there is an urgent need to develop a strategy that can concurrently detect and adsorb uranium to realize the sustainable development of nuclear power and protect the environment. In this work, a fluorescent zinc-based metal-organic framework (HNU-50) was designed and synthesized for the effective detection and extraction of U(VI). The amide groups on N-pyridin-4-ylpyridine-4-carboxamide ligands and two uncoordinated carboxyl oxygen atoms on pyromellitic acid ligands in HNU-50 provide potential uranium-binding sites. Consequently, HNU-50 is competent of selectively and efficiently catching uranyl ions, achieving an optimum adsorption capacity of 632 mg/g. Additionally, the adsorption of U(VI) results in fluorescence quenching of HNU-50, thus allowing sensitive and selective detection of U(VI) by fluorescence change. Note that HNU-50 exhibits a considerably low detection limit of 1.2 × 10-8 M for U(VI) in aqueous solution, which is below the World Health Organization maximum pollution standards for potable water (6.3 × 10-8 M).

In Situ Ligand Formation-Driven Synthesis of a Uranyl Organic Framework as a Turn-on Fluorescent pH Sensor.

A uranium-based metal-organic framework, [(UO2)(H2DTATC)] (HNU-39, H4DTATC = 5,5'-(9,10-dihydroxy-4a,9,9a,10-tetrahydroanthracene-9,10-diyl)diisophthalic acid) was successfully prepared by a hydrothermal method. The structure of HNU-39 comprises UO8 hexagonal bipyramids linked by doubly protonated DTATC ligands, forming a ribbon arrangement. It is worth noting that the DTATC ligand was transformed in situ from 5,5'-(anthracene-9,10-diyl)diisophthalic acid (H4DPATC) during the synthesis of HNU-39. Research on fluorescence properties has shown that HNU-39 exhibits fluorescence turn-on response under alkaline conditions and could be used as a potential pH sensor. Moreover, HNU-39 can also be successfully applied for pH sensing in real samples from a sewage treatment plant. The sensing mechanism can be interpreted as OH- ions reacting with the protons in the organic ligand of HNU-39.

Face-Directed Assembly of Molecular Cubes: In Situ Substitution of a Predetermined Concave Cluster.

Systematic design and self-assembly of metal-organic polyhedra with predictable configurations has been a long-standing challenge in crystal engineering. Herein a concave polyoxovanadate cluster, [V6 O6 (OCH3 )9 (SO4 )4 ]5- , which can be generated in situ under specific reaction conditions, is reported. Based on this cluster, a potential trivalent molecular building block, [V6 O6 (OCH3 )9 (SO4 )(CO2 )3 ]2- , can be obtained by the bridging-ligand-substitution strategy and it possesses appropriate angle information for the design of molecular cubes. Utilizing the face-directed assembly of the trivalent molecular building block and a diverse set of tetratopic carboxylate linkers, a series of metal-organic cubes (VMOC-1-VMOC-5) with the same topology but different functionalities and dimensions were designed and constructed. An inclusion study using VMOC-3 shows that they are potential molecular receptors for selective capture of size-matching polycyclic aromatic hydrocarbon guest molecules.

Step-by-Step Assembly of Metal-Organic Frameworks from Trinuclear Cu3 Clusters.

Two novel metal-organic frameworks (MOFs), HBNU-1 and HBNU-2, have been synthesized successfully. We adopt a step-by-step assembly strategy, which first synthesize the Cu3 cluster Cu3(µ3-OH)(pz)3(CH3COO)2(Hpz), and then react it with H2BDC under different conditions to form final frameworks. In both MOF structures, the Cu3 clusters are maintained, although certain differences are observed. Compared with HBNU-1, the Cu3 cluster dimerizes into Cu6 cluster in HBNU-2. With this step-by-step cluster assembly strategy, MOF structure predicting becomes possible and may give some reference for MOF structure designing.

In situ synthesis of luminescent dsDNA-Cu NCs stained with a dsDNA-lighted fluorophore for rapid and stable detection of histamine in food.

Poisonous histamine is accumulated in stale meat and fermented foods. The rapid and stable detection of histamine is essential for food safety. Herein, a ratiometric fluorometric method for histamine detection was designed through in situ preparing double-stranded DNA­copper nanoclusters (dsDNA-Cu NCs) stained with 4',6-diamidino-2-phenylindole (DAPI). dsDNA-Cu NCs with red emission were rapidly synthesized via mixing Cu2+, ascorbate and dsDNA at room temperature for 5 min. When DAPI was added during preparation, DAPI coordinated with the Cu element accompanied by the quenched red emission of dsDNA-Cu NCs, and DAPI bound to dsDNA together with the enhanced blue emission of DAPI. Upon adding DAPI and histamine simultaneously, the coordination of histamine with the Cu element further decreased the red emission of dsDNA-Cu NCs, and drove the movement of DAPI from the Cu element to dsDNA along with the enhanced blue emission of DAPI. Significantly, ratiometric fluorescence was insensitive to variations in instrument and environment, causing stable measurement. Meanwhile, in situ synthesis integrated probe preparation with analyte detection, reducing time consumption. Additionally, this method quantified histamine in the concentration range of 7-50 µM with a detection limit of 3.6 µM. It was applied to determining histamine in food with satisfactory accuracy and precision.

Controllable Synthesis of Sheet-Flower ZnO for Low Temperature NO2 Sensor.

ZnO is a wide band gap semiconductor metal oxide that not only has excellent electrical properties but also shows excellent gas-sensitive properties and is a promising material for the development of NO2 sensors. However, the current ZnO-based gas sensors usually operate at high temperatures, which greatly increases the energy consumption of the sensors and is not conducive to practical applications. Therefore, there is a need to improve the gas sensitivity and practicality of ZnO-based gas sensors. In this study, three-dimensional sheet-flower ZnO was successfully synthesized at 60 °C by a simple water bath method and modulated by different malic acid concentrations. The phase formation, surface morphology, and elemental composition of the prepared samples were studied by various characterization techniques. The gas sensor based on sheet-flower ZnO has a high response value to NO2 without any modification. The optimal operating temperature is 125 °C, and the response value to 1 ppm NO2 is 125. At the same time, the sensor also has a lower detection limit (100 ppb), good selectivity, and good stability, showing excellent sensing performance. In the future, water bath-based methods are expected to prepare other metal oxide materials with unique structures.

Space-confined growth of nanoscale metal-organic frameworks/Pd in hollow mesoporous silica for highly efficient catalytic reduction of 4-nitrophenol.

The development of confined growth of metal-organic frameworks (MOFs) in a nano-space remains a challenge mainly due to the spatial size randomness and inhomogeneity of host materials and the limitation of MOF species. In this study, we developed a general "stepwise vacuum evaporation" strategy, which allows the nano-confined growth of MOFs in hollow mesoporous silica nanospheres (HMSN) by the vacuum forces and the capillary effect. A series of nanoscale MOFs including ZIF-8, ZIF-90, HKUST-1, MIL-53(Cr) and UiO-66-NH2 were confinely synthesized inside the cavities of HMSN, resulting in hierarchically porous composites with core-shell structures. Further functionalization was studied by anchoring Pd to obtain UiO-66-NH2/Pd@HMSN catalyst, which exhibited excellent activity in the catalytic reduction of 4-nitrophenol to 4-aminophenol under ambient condition.