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A novel UiO-66-NH2@calcein fluorescent material is constructed for the selective detection of Ca2+ ions in an aqueous system based on the turn-on effect.

Fluorescent probes designed to sense and image peroxynitrite (ONOO−).

Facile and rapid detection of residual organic pesticides on the fruits and vegetables has recently drawn increased attention in the food safety field. Herein, a surfactant-assisted solvothermal route with subsequent post-modification was designed for the preparation of Eu

Recently, much effort has been dedicated to ultra-thin two-dimensional metal–organic framework (2D MOF) nanosheets due to their outstanding properties, such as ultra-thin morphology, large specific surface area, abundant modifiable active sites, etc. However, the preparation of high-quality 2D MOF nanosheets in good yields still remains a huge challenge. Herein, we report 2D cadmium-based metal–organic framework (Cd-MOF) nanosheets prepared in a one-pot polyvinylpyrrolidone (PVP)-assisted synthesis method with high yield. The Cd-MOF nanosheets were characterized with good stability and dispersion in aqueous systems, and were highly selective and sensitive to the antibiotic metronidazole (MNZ) with low limit of detection (LOD: 0.10 μM), thus providing a new and promising fluorescent sensor for rapid detection of MNZ in aqueous solution.

A simple rhodamine-based compound CK was designed and synthesized as a fluorescent chemosensor for Sn

Two-dimensional (2D) Co-based MOF-on-MOF heterojunction nanostructures with improved electrocatalytic activity were successfully constructed via a mild two-step solution route, employing Co2+ ions as the center atoms, and 1,4-benzenedicarboxylate (BDC) and 4,4'-biphenyldicarboxylate (BPDC) as ligands. The as-obtained heterojunction nanostructures were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) technologies. Electrochemical measurements showed that as-prepared Co-BPDC/Co-BDC heterojunction nanostructures presented markedly enhanced OER electrocatalytic activity, compared with single Co-BPDC, Co-BDC, and/or their physical mixture. Also, the Co-BPDC/Co-BDC-3 heterojunction prepared after treatment for 3 h exhibited the strongest catalytic activity. To reach the current density jgeo = 10 mA cm-2, the Co-BPDC/Co-BDC-3 heterojunction-modified glassy carbon electrode required an overpotential of 335 mV in 1 M KOH, which was reduced by 57 and 93 mV, compared to the electrodes modified by Co-BDC and Co-BPDC, respectively. Simultaneously, the heterojunction catalyst also displayed better long-term stability. The improvement of the above performances should be attributed to the increased structure stability, BET surface area, ECSA, and electron transfer ability of the heterojunction.

Fe-Doped Co-Mo-S microtubes were successfully synthesized through a multistep synthetic route, employing MoO3 microrods as the sacrificial template, Co(NO3)2·6H2O and Fe(SO4)2·7H2O as the metal sources, 2-methylimidazole (2-MI) as the ligand and thioacetamide (TAA) as the S2- ion source. The as-prepared products were characterized by X-ray powder diffraction (XRD), energy dispersive spectrometry (EDS), inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), (high-resolution) transmission electron microscopy (TEM/HRTEM) and HAADF-STEM-EDS elemental mapping. Experiments showed that the as-obtained Fe-doped Co-Mo-S microtube catalyst demanded overpotentials of ∼105 and 268 mV to afford the current density of -10 mA cm-2 for hydrogen evolution reaction (HER) and 10 mA cm-2 for oxygen evolution reaction (OER) with a durability of 60 h in 1.0 M KOH solution, respectively. In a two-electrode water-splitting device, the as-prepared Fe-doped Co-Mo-S microtubes acted as both anode and cathode simultaneously. To deliver a current density of 10 mA cm-2, a cell voltage of 1.605 V was required in 1.0 M KOH solution. After continuously catalyzing the overall water splitting for 60 h, the overpotential hardly changed, implying remarkable long-term stability. Obviously, the present Fe-doped Co-Mo-S microtubes have potential applications as bifunctional catalysts for electrochemical water splitting.

Highly ordered nanotubes titanium dioxide (NTs-TiO2) array was fabricated and used as the support of Pt nanoparticles for the selective aqueous phase of glycerol (GLY) electrooxidation. The structure and morphology of the NTs-TiO2/Pt were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, etc. The electrooxidation GLY properties of NTs-TiO2/Pt were investigated by cyclic voltammetry, linear sweep voltammetry, and accelerated service life test. The results show that, compared with bulk Pt and nano-TiO2/Pt, the NTs-TiO2/Pt have the highest service life and electrooxidation activity and selection for GLY. At the reaction condition of 1.2 V potential, the NTs-TiO2/Pt catalyst afforded 67.1% selectivity for the glyceric acid.

Two-dimensional Cd-MOF/Tb

The pyrolysis characteristics and kinetics of lignocellulosic biomass (cotton stalk) and seaweed (Gracilaria lemaneiformis) were studied comparatively. Results of the thermal degradation processes showed that the pyrolysis occurence of G. lemaneiformis is easier than that of cotton stalk. However, G. lemaneiformis released less volatile components and produced more solid residues. As the heating rate increased, the maximum mass loss rates for cotton stalk were decreased, while those for G. lemaneiformis were increased. Results of the kinetic analysis by Popescu method indicated that the pyrolysis mechanism of cotton stalk is three-dimensional diffusion, which can be described by Zhuralev, Lesokin, and Tempelmen (Z–L–T) equation $$(G(\alpha ) = \{ [1/(1 - \alpha )]^{1/3} - 1\}^{2} )$$ , whereas that of G. lemaneiformis is random nucleation and nuclei growth, which can be described by Avrami–Erofeev equation $$(G(\alpha ) = [ - \ln (1 - \alpha )]^{1/4} )$$ . The average activation energy values (192.17 and 146.11 kJ mol−1, respectively) of cotton stalk and G. lemaneiformis obtained by Popescu method are similar with those (189.88 and 153.79 kJ mol−1, respectively) calculated by Flynn–Wall–Ozawa (FWO) method. Moreover, the average activation energy of G. lemaneiformis is lower than that of cotton stalk.

Nitroxyl (HNO), a kind of active nitrogen species, plays a vital role in particular physiological and pathological process. Urgent detection of HNO and understanding its biological roles in living systems is indispensable. Herein, we presented a novel dansyl-naphthalimide fluorescent sensor, NA-PA, for the selective response for HNO with remarkable fluorescence enhancement (ΦF = 32.5%) due to the hydrolysis of boronic pinacol ester. The proposed probe exhibited the desirable prominent features of high sensitivity, fast response, excellent selectivity and low cytotoxicity. Importantly, the probe works well in visualizing HNO in HepG-2 cells and live mice, illuminating that NA-PA would be a powerful tool to evaluate the physiological and pathological functions of HNO in life.

It has drawn extensive research interest to integrate luminescent ligands into metal-organic frameworks as luminescent materials due to striking luminescent properties. In this work, a Co-MOF with weak fluorescence emission, [Co(OBA)(2,2′-BPY)], was synthesized by a mixed solvothermal route with Co(NO3)2 as the Co2+ ion source, 4,4′-Oxybis(benzoic acid) (OBA) and 2,2′-Bipyridyl (2,2′-BPY) as the ligands. Its fluorescence was obviously enhanced through integrating a small amount of luminescent ligands: 2-aminoterephthalic acid. Interestingly, the above enhanced fluorescence could be selectively quenched by the organophosphorus pesticides with p-nitrophenyl group such as p-nitrophenyl phosphate (PNPP) and bis(p-nitrophenyl) phosphate (BNPP) in water systems. As a case, the detection limit towards PNPP was up to 352 nM (0.07 mg kg−1), which is far lower than the standards for similar pesticide residues in fruits in China (0.1–0.6 mg kg−1) [ 1 ]. At the same time, the above phenomenon of the fluorescence quenching was not interfered from some other pesticides, metallic ions, amino acids and aromatic nitrocompounds, implying the present fluorescent material has potential application as a highly selective probe for detecting PNPP pesticide residues in food and domestic water. Furthermore, a possible quenching mechanism was discussed.

A novel fluorescent Zn(II)-based metal-organic framework (Zn-MOF), [Zn2(oba)4(4,4′-bpy)2]n, was successfully synthesized through a simple solvothermal route at 130 °C for 48 h, employing Zn(NO3)2·6H2O, 4,4′-Oxybis(benzoic acid) (oba) and 4,4′-Bipyridine (4,4′-bpy) as the initial reactants, dimethylacetamide (DMA) as the reaction medium. The as-obtained Zn-MOF was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrum (FTIR), Thermogravimetric analysis (TGA) and elemental analysis. The fluorescence tests showed that the as-obtained Zn-MOF emit a strong violet light centered at 445 nm under the excitation of 323 nm UV light. Intriguingly, the above strong violet emission could be highly selectively quenched by aromatic nitrophenols or antibiotic metronidazole (MET) in aqueous systems with fairly low detection limits. Other substituted phenols and antibiotics, as well as some cations, anions, amino acids and small organic molecules hardly affected the violet emission of the as-obtained Zn-MOF, indicating that this novel Zn-MOF could be prepared as a selective fluorescent probe for detections of aromatic nitrophenols and MET antibiotic in water solutions.

Ultrathin Tb3+-doped Zinc metal-organic-framework two-dimensional (2D) nanosheets (Tb3+@Zn-AIP-NS, AIP = 5-aminoisophthalic acid) were synthesized by an ultrasonic exfoliation method at room temperature, employing Tb3+@Zn-AIP microrods prepared in advance as the raw material. Experiments revealed that the as-prepared ultrathin Tb3+@Zn-AIP-NS could be dispersed homogeneously in deionized water to obtain a stable sol, and emit the strong characteristic fluorescence of Tb3+ ions. Since the above strong luminescence of Tb3+ ions was quenched by nitrofurazone (NFZ) antibiotic without the interference from other antibiotics, anions, cations and amino acids in aqueous systems, the ultrathin Tb3+@Zn-AIP-NS could be employed as a sensitive probe for visualized fluorescence detection of NFZ with a high Ksv of 4.59 × 105 M−1, a low LOD of 0.24 μM and a quick response time of 20 s. Systematic investigations on the sensing mechanism suggested that the synergistic action between the inner filter effect and the fluorescence resonance energy transfer resulted in the selective detection of NFZ. Moreover, the practical application of the present Tb3+@Zn-AIP-NS sensor was also investigated.

Mesoporous composite TiO2-ZrO2 (TZ) having enhanced surface area was synthesized by sol-gel process. The structure of the prepared samples was characterized by X-ray diffraction, transmission electron microscope, energy dispersive spectrometer, scanning electron microscope, N2 sorption techniques, etc. Electrocatalytic reduction of 2-pyridinaldehyde in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) on the mesoporous TZ composite film electrode was investigated by cyclic voltammetry (CV). A comparison of the CV recorded in the absence and presence of 2-pyridinaldehyde confirmed the catalytic reduction of 2-pyridinaldehyde produced 2-piperidinemethanol by Ti(III)/Ti(IV) redox couple on the surface of mesoporous TZ composite film. The mechanism of this electrode reaction is called catalytic (EC′) mechanism.

Two-dimensional Cd-MOF/Tb3+ (Cd-MOF = [Cd (μ-2,3-pdc) (H2O)3]n (2,3-pdc = 2,3-pyridine dicarboxylic acid)) fluorescent nanosheets with the thickness of 1.4 nm were successfully synthesized by a simple solution route with subsequent ultrasonic exfoliation at room temperature. It was found that as-obtained Cd-MOF/Tb3+ ultrathin nanosheets could be homogeneously dispersed in aqueous system to form a sol with excellent stability. Also, the fluorescence intensity of nanosheets remarkably increased to almost 12 times higher than that of Cd-MOF/Tb3+ microsheets before exfoliation. Further investigations uncovered that the above strong fluorescence of Cd-MOF/Tb3+ nanosheets could be highly sensitively quenched by Cefixime antibiotic in aqueous solution without interference from other antibiotics, amino acids and pesticides. Hence, the as-obtained ultrathin Cd-MOF/Tb3+ nanosheets could be prepared as a highly selective and sensitive fluorescence probe for the detection of Cefixime in aqueous system. Compared with the bulk Cd-MOF/Tb3+ sensor, the Cd-MOF/Tb3+ ultrathin nanosheets sensor exhibited a far lower detection limit down to 26.7 nM for CFX. Also, the as-obtained nanosheets sensor presented satisfactory recovery ranging from 98.07% to 103.01% and acceptable repeatability (RSD

Hierarchical core-shell NiCo2S4@CoNi-LDH nanoarrays grown on carbon cloth (CC) with outstanding electrocatalytic activity for oxygen evolution reaction (OER) were successfully constructed by a three-step hydrothermal strategy. The as-prepared hierarchical core-shell NiCo2S4@CoNi-LDH nanoarrays were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS) and EDS mapping technologies. Electrochemical measurements showed that the OER catalytic activity of as-obtained NiCo2S4@CoNi-LDH catalyst could be tuned by the molar ratio of Co/Ni in CoNi-LDH. Experiments uncovered that NiCo2S4@Co1Ni4-LDH catalyst prepared at the Co/Ni molar ratio of 1:4 exhibited the strongest OER electrocatalytic activity. To deliver the current densities of 100 mA cm−2, the as-obtained NiCo2S4@Co1Ni4-LDH catalyst required the overpotential of 337 mV in 1.0 M KOH solution. After continuously catalyzing for 40 h, the voltage curve hardly waved, presenting excellent long-term stability. The present work is a useful attempt for constructing highly active and cost-effective OER catalyst.

The electrocatalytic synthesis of low-density polyethylene (LDPE) from carbon dioxide on a nanostructured (ns)TiO2 film electrode was investigated by controlled potential electrolysis in a solvent mixture of water and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI]BF4) at room temperature under ambient pressure. Under these conditions, the nsTiO2 film is remarkably efficient and selective for the electroreduction of CO2. The current efficiency for the formation of the electrolytic product is about 8-14% at -1.50 V (vs SCE). The electrocatalytic activity of the electrode in the electrochemical reduction of CO2 was investigated by cyclic voltammetry (CV), and the probable electrode reaction mechanism is discussed.

Nanoporous TiO2 having enhanced surface area was synthesized by sol–gel method. On the nanoporous TiO2 film electrode, electrocatalytic reduction of the 2-pyridineethanol in the ionic liquid electrolyte of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI]BF4) was investigated by cyclic voltammetry (CV). It was found that the indirect electroreduction of 2-pyridineethanol produced 2-piperidinoethanol by Ti(IV)/Ti(III) redox system on the nanoporous TiO2 film surface. The current of cathodic reduction peak increased along with the increase of reactant concentration. The electrode reaction mechanism is called catalytic (EC′) mechanism.

In this paper, we have demonstrated that carbon-doped nanostructured TiO2 (CD ns-TiO2) films could be prepared simply and cheaply with oxalic acid and tetrabutylammonium bromide (Bu4N·Br) as the carbon sources. The surface morphology of the films was a multiple-porous network structure.The average size of nanoparticle was about 40 nm. Carbon doped into substitutional sites of TiO2 has also proven to be indispensable for band-gap narrowing and photovoltaic effect. Carbon doping lowered the band gap of n-TiO2 to 1.98, 1.64, and 1.26 eV. The CD ns-TiO2 film was first used as photoanode for solar cells, exhibiting high photocurrent densities (l.34 mA/cm2) and yielding an overall conversion efficiency (η) of 4.42 %.