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.

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.

Electron delocalization of robust high-nuclear bismuth-oxo clusters for promoted CO2 electroreduction.

The integration of high activity, selectivity and stability in one electrocatalyst is highly desirable for electrochemical CO2 reduction (ECR), yet it is still a knotty issue. The unique electronic properties of high-nuclear clusters may bring about extraordinary catalytic performance; however, construction of a high-nuclear structure for ECR remains a challenging task. In this work, a family of calix[8]arene-protected bismuth-oxo clusters (BiOCs), including Bi4 (BiOC-1/2), Bi8Al (BiOC-3), Bi20 (BiOC-4), Bi24 (BiOC-5) and Bi40Mo2 (BiOC-6), were prepared and used as robust and efficient ECR catalysts. The Bi40Mo2 cluster in BiOC-6 is the largest metal-oxo cluster encapsulated by calix[8]arenes. As an electrocatalyst, BiOC-5 exhibited outstanding electrochemical stability and 97% Faraday efficiency for formate production at a low potential of -0.95 V vs. RHE, together with a high turnover frequency of up to 405.7 h-1. Theoretical calculations reveal that large-scale electron delocalization of BiOCs is achieved, which promotes structural stability and effectively decreases the energy barrier of rate-determining *OCHO generation. This work provides a new perspective for the design of stable high-nuclear clusters for efficient electrocatalytic CO2 conversion.

Single-phase white light material and antibiotic detection of lanthanide metal-organic frameworks.

WLEDs have been widely used in lighting and display equipment due to their energy-saving and environment-friendly advantages, but it is still a great challenge to construct high-quality single-phase white light materials for the preparation of WLEDs. In this work, three Ln-MOFs (HNU-82-84) with the same structure were synthesized by assembling rare earth ions (Tb3+, Eu3+, La3+) and 4,4',4''-nitrilotribenzoic acid (H3TCA) ligands. The structure and optical properties of the three compounds were investigated. Under the ultraviolet lamp, HNU-82-84 displays green light, red light, and blue light emission, respectively. Based on the RGB principle, aiming at the single-phase white material, the proportion of adding rare earth ions is reasonably adjusted to design and synthesize the Ln-MOF (Eu0.015Tb0.037La0.148-TCA) with CIE chromaticity coordinates of (0.319, 0.344). In addition, the WLED was prepared by Eu0.015Tb0.037La0.148-TCA and commercial LED lamps. Furthermore, HNU-82 has strong fluorescence emission and good water stability and can be used to detect nitrofurazone (NZF) and nitrofurantoin (NFT). The concentrations of the aqueous solutions of NZF and NFT had a well correlated linear relationship with the fluorescence quenching effect of HNU-82, and the detection limits were 6.60 × 10-7 mol L-1 and 4.62 × 10-7 mol L-1, respectively. Hence, HNU-82 also has potential as a fluorescent sensor for the detection of NZF and NFT in the aquatic environment.

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.

Detection of organic arsenic based on acid-base stable coordination polymer.

Organic arsenic, usually found in animal feed and livestock farm wastewater, is a carcinogenic and life-threatening substance. Hence, for the rapid and sensitive detection of organic arsenic, the development of new fluorescent sensors is quite essential. Here, an acid-base stable coordination polymer (HNU-62) was constructed by the introduction of hydrophobic fluorescence ligand, which can be used as a highly selective sensor for the detection of roxarsone (ROX) in water. The limit of detection (LOD) of HNU-62 for ROX was 4.5 × 10-6 M. Furthermore, HNU-62 also exhibits good anti-interference and recyclability, which can be used in detecting ROX in real samples of pig feed. This work provides an alternative approach for the construction of water-stable coordination polymer-based fluorescence sensors.

Light-driven uranyl-organic frameworks used as signal-enhanced photoelectrochemical sensors for monitoring anthrax.

The semiconductor-like characteristics and light absorption ability of metal-organic frameworks (MOFs) make it have the potential for photoelectrochemical sensing. Compared with composite and modified materials, the specific recognition of harmful substances directly using MOFs with suitable structures can undoubtedly simplify the fabrication of sensors. Herein, two photosensitive uranyl-organic frameworks (UOFs) named HNU-70 and HNU-71 were synthesized and explored as the novel "turn-on" photoelectrochemical sensors, which can be directly applied to monitor the biomarker of anthrax (dipicolinic acid). Both sensors have good selectivity and stability towards dipicolinic acid with the low detection limits of 1.062 and 1.035 nM, respectively, which are far lower than the human infection concentration. Moreover, they exhibit good applicability in the real physiological environment of human serum, demonstrating a good application prospect. Spectroscopic and electrochemical studies show that the mechanism of photocurrent enhancement results from the interaction between dipicolinic acid and UOFs, which facilitates the photogenerated electron transport.

Xylenol orange-modified CdTe quantum dots as a fluorescent/colorimetric dual-modal probe for anthrax biomarker based on competitive coordination.

Bacillus anthracis spores can make humans infected with vicious anthrax, so it is significant to detect their biomarker 2,6-pyridinedicarboxylic acid (DPA). The development of dual-modal methods for DPA detection that are more flexible in practical applications remains a challenge. Herein, colorimetric xylenol orange (XO) was modified on fluorescent CdTe quantum dots (QDs) for dual-modal detection of DPA through competitive coordination. After the binding of XO on CdTe QDs via coordination with Cd2+, CdTe QDs displayed quenched red fluorescence and the bound XO was presented as red color. The competitive coordination of DPA with Cd2+ made XO released from CdTe QDs, causing the enhanced red fluorescence of CdTe QDs and the yellow color of free XO. On this basis, DPA was rapidly (1 min) quantified through fluorescent and colorimetric modes within the ranges of 0.1-5 µM and 0.5-40 µM, respectively. The detection limits for DPA were calculated as low as 42 nM and 240 nM, respectively assigned to fluorescent and colorimetric modes. The level of urinary DPA was further measured. Satisfactory relative standard deviations (fluorescent mode: 0.1%-10.2%, colorimetric mode: 0.8%-1.8%) and spiked recoveries (fluorescent mode: 100.0%-115.0%, colorimetric mode: 86.0%-96.6%) were obtained.

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.

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.

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.

Bifunctional ratiometric fluorescent probe for sensing anthrax spore biomarker and tetracycline at different excitation channels.

Multifunctional fluorescent probes have received increasing attention for the sake of atom economy and high-density integration. Herein, CdTe quantum dots (QDs) modified with Eu3+ were synthesized as the bifunctional ratiometric fluorescent probe for sensing two hazardous substances tetracycline (TC) and anthrax spore biomarker 2,6-dipicolinic acid (DPA) at different excitation channels, based on the discrepant excitation wavelengths of Eu3+ and the fluorescence quenching of CdTe QDs after interaction with them. Both DPA and TC enhanced the red emission of Eu3+ via antenna effect but caused the green emission of CdTe QDs to quench. Interestingly, the excitation wavelengths of Eu3+ after coordinating with DPA and TC were 275 and 386 nm, respectively. On this basis, CdTe QDs-Eu3+ achieved the bifunctional ratiometric detection of DPA (λex = 275 nm) and TC (λex = 386 nm) with different excitation channels. Both DPA and TC were selectively detected by CdTe QDs-Eu3+ with rapid response (DPA-1 min, TC-1 min) and high sensitivity (DPA-LOD 0.3 µM, TC-LOD 2.2 nM). CdTe QDs-Eu3+ were applied to analyzing DPA and TC in food, biological and environmental samples. Satisfactory spiked recoveries (80.0-119.0 %) and relative standard deviations (0.5-8.4 %) were obtained for measuring DPA and TC in these samples.

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.

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%.

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.

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.

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.

CdTe QDs@ZIF-8 composite-based recyclable ratiometric fluorescent sensor for rapid and sensitive detection of chlortetracycline.

The residue problem in animal food products caused by the abuse of chlortetracycline (CTC) is one of the food safety issues that have attracted much attention. Herein, a composite was generated by embedding CdTe quantum dots (QDs) into ZIF-8 for ratiometric fluorescent analysis of CTC. With adding CTC, the green luminescence of CTC appeared under the sensitization effect of Zn2+ in ZIF-8, but the red luminescence of CdTe QDs was reduced by the inner filtration effect of CTC. On this basis, CTC was detected by the composite with a short response time of 1 min, and the limit of detection was calculated to be 37 nM that was 17 times lower than the maximum residue limit of CTC in animal food products (626 nM). Excellent recyclability of the composite was also observed, and CTC was consecutively measured at least six times. The composite was used to determine CTC in basa fish and pure milk with satisfactory recoveries (91.0-110.0%). Portable test strips were further manufactured and the visual determination of CTC was obtained. These results convictively demonstrate that CdTe QDs@ZIF-8 composite as a recyclable ratiometric fluorescent sensor achieves the rapid and sensitive measurement of CTC residue in animal food products.