Eu(III)-Functionalized MOF-Based Dual-Emission Ratiometric Sensor Integrated with Logic Gate Operation for Efficient Detection of Hippuric Acid in Urine and Serum.

With the introduction of Eu3+ ions as the secondary fluorescent signal reporter and sensing active sites, a dual-emission ratiometric sensor of Eu3+@NiMOF (Eu3+ functional NiMOF) for hippuric acid (HA) detection in urine and serum was fabricated via the postsynthetic encapsulating strategy. Based on the two emission signals at 441 nm (turn-on) and 628 nm (turn-off), the produced Eu3+@NiMOF ratiometric sensor provided enhanced sensitivity, higher selectivity, and 9.7 times lower limits of detection (LOD) for the detection of HA (2.38 µM, 0.42 µg·mL-1) than that of the pristine NiMOF. Considering the high sensitivity and visualization results, further exploration of intelligent applications in the HA sensing process was carried out by constructing a tandem combinational logic gate to improve the practicability and convenience with the help of a smartphone. This work provides a promising approach for developing MOF-based ratiometric sensors to detect biomarkers.

In situ generated Cu-Co-Zn trimetallic sulfide nanoflowers on copper foam: a highly efficient OER electrocatalyst.

The electrocatalytic oxygen evolution reaction (OER) is an integral part and a stepping stone to various electrochemical technologies in the field of electrochemical energy conversion. The development of OER catalysts with low-cost materials, industry-related activity and long-term durability is highly needed, but remains challenging at this stage. In this paper, Cu ions in a copper foam (CF) substrate were replaced with Cu(OH)2 grown on CF to participate in the subsequent reaction, and then a subsequent two-step hydrothermal method was used to obtain the nanoflower-like Cu-Co-Zn trimetallic sulfide (named CuCoZn-S-3) catalyst, whose unique flower structure ensures that the catalyst surface exhibits a larger electrochemical active area, so as to expose plentiful active sites. The synergism between metals regulates the electron environment and accelerates the charge transfer rate, greatly improving the electrocatalytic activity of the catalyst. The prepared CuCoZn-S-3 exhibits excellent OER performance under alkaline conditions. It requires overpotentials of only 175 mV and 242 mV to drive current densities of 10 mA cm-2 and 100 mA cm-2, respectively. The Tafel slope of CuCoZn-S-3 is 62.3 mV dec-1. This study may provide a viable strategy for the rational preparation of low-cost and efficient OER electrocatalysts in alkaline medium.

Ionic Self-Assembled Luminescent Nanospheres from Cationic Polyelectrolyte and Eu-Containing Polyoxometalate.

Using the ionic self-assembly (ISA) strategy to combine Eu-containing polyoxometalates (Eu-POMs) and organic molecules mainly through noncovalent electrostatic interactions can protect Eu-POMs from solvent quenching of luminescence and enhance their processability. For this reason, a cationic polyelectrolyte, branched polyethyleneimine (PEI), and a Eu-POM, Na9(EuW10O36)·32H2O (EuW10), were used here to construct luminescence-enhanced spherical aggregates with diameters ranging from 50 to 200 nm. At a fixed concentration of EuW10, the phase behavior and luminescence properties of the mixture could be modulated by the PEI concentration. Such ISA-induced aggregates could effectively shield water molecules and result in better photophysical properties. Compared to bare EuW10, the absolute quantum yield and lifetime of luminescence for aggregates increased 10 and 5 times, respectively. Meanwhile, the sensitivity of the EuW10 coordination structure to the environment made it possible for obtained aggregates being used to detect either copper cations or permanganate anions due to their strong specific quenching effects to luminescence. Such a new type of luminescent soft material not only provided a reference for exploring the luminescence enhancement mechanism of lanthanide through self-assembly in aqueous solution but also exhibited potential in detection by luminescence analysis.

Phthalocyanine-sensitized evolution of hydrogen and degradation of organic pollutants using polyoxometalate photocatalysts.

In this study, 2 (3), 9 (10), 16 (17), 23 (24)-tetrakis-(8-quinoline-oxy) phthalocyanine zinc(II) (ZnQPc) was prepared and then quaternized to obtain water soluble zinc phthalocyanine (ZnQPc4+). Then, ZnQPc4+ was used as a photosensitizer for a series of POM catalysts, including Dawson type K6[α-P2W18O62]·14H2O (P2W18) and K10[α-P2W17O61]·20H2O (P2W17) and Keggine type H3PW12O40·xH2O (PW12). The Keggin type PW12 showed higher efficiency with 18.2 µmol of H2 evolution (turnover number (TON) = 14,550) for 6 h upon ZnQPc4+ sensitization in relation to two Dawson P2W17 and P2W18 in a visible light-driven water-soluble system with isopropanol and H2PtCl6·6H2O. In addition, the complexes of ZnQPc4+ with a series of POM catalysts (P2W17, P2W18, and PW12) were also used as photocatalysts for the degradation of methylene blue (MB) in water, and it was found that the complexes of ZnQPc4+ with P2W17 and PW12 showed improved photocatalytic activity, and the degradation rates of MB reached 100% at a small dosage under natural pH and visible light. The high efficacy of POM catalysts for H2 evolution and the degradation of MB were attributed to the sensitization of POMs by ZnQPc4+, which was enabled by the transfer of photogenerated electrons of ZnQPc4+ to the lowest unoccupied molecular orbital (LUMO) of POM.

Luminescent Sodium Deoxycholate Ionogel Induced by Eu3+ in Ethylammonium Nitrate.

Hydrogels based on bile salts and lanthanide ions have been reported for their easy gelation. However, the weak mechanical properties and water quenching to luminescence of lanthanide ions limit their applications in practice. Hence, a supramolecular ionogel has been prepared here through simply mixing of sodium deoxycholate and europium nitrate in a protic ionic liquid, ethylammonium nitrate (EAN). The prepared ionogel was characterized by scanning electron microscopy, X-ray energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, fluorescence spectroscopy, and rheological measurements. Such an ionogel resulted synergistically from metal coordination and hydrogen bonding. The effect of the solvent structure on gel properties was also explored by comparison with those formed in alkylammonium nitrates with longer chains. EAN was found to behave more effectively both as a solvent and a bridge to enhance the ionogel mechanical strength. The ionogels also exhibited better fluorescent properties than those of the corresponding hydrogels. The obtained results should expand the applications of lanthanide-containing luminescent soft materials in nonaqueous media. It is expected to apply in the fields of solid electrolytes, biosensors, and optics response.

Zwitterionic Surfactant Micelle-Directed Self-Assembly of Eu-Containing Polyoxometalate into Organized Nanobelts with Improved Emission and pH Responsiveness.

Recently, hybrid coassembly between polyoxometalates (POMs) and cationic building blocks provides an efficient strategy to greatly optimize POMs' functionality as well as their aggregate structural diversity. Adaptive hybrid supramolecular materials with enhanced luminescence have then been obtained from lanthanide-containing POMs. In this work, a commercially available and pH-switchable zwitterionic surfactant, tetradecyldimethylamine oxide (C14DMAO), was chosen to coassemble with a lanthanide-containing anionic POM [Na9(EuW10O36)·32H2O, abbreviated as EuW10] in water. The much improved red-emitting luminescent nanobelts at a C14DMAO/EuW10 molar ratio ( R) of 20 were obtained, which exhibited longer luminescence lifetime and higher quantum yield compared with EuW10 aqueous solution. After careful characterization of morphology and structure of nanobelts, an unusual axial lamellar aggregation arrangement mechanism was proposed. It was the partial protonation of C14DMAO at the solution pH of about 6.5 that led to positively charged micelles, being bridged by anionic EuW10 clusters to aggregate into such novel nanobelts under the synergetic effects of appropriate electrostatic, hydrogen-bonding, and hydrophobic interactions. The resulted pH-responsive luminescent nanobelts and their aggregation model should offer attractive references for preparing smart optical supramolecular materials.

Highly luminescent and multi-sensing aggregates co-assembled from Eu-containing polyoxometalate and an enzyme-responsive surfactant in water.

Hybrid co-assembly of polyoxometalates (POMs) with cationic organic matrices offers a preferable way to greatly enhance POM functionality as well as processability. Thus, multi-stimulus responsive supramolecular materials based on lanthanide-containing POMs with improved luminescence may be fabricated from appropriate components through this convenient strategy. Herein, we reported that the co-assembly of Na9(EuW10O36)·32H2O (EuW10) and a commercially available cationic surfactant, myristoylcholine chloride (Myr), in water could produce enhanced red-emitting luminescent aggregates, with their photophysical properties highly dependent on the molar ratio (R) between Myr and EuW10. The R of 36 was finally selected owing to the displayed superior luminescence intensity and good aggregate stability. The Myr/EuW10 hybrids induced by electrostatic and hydrophobic forces presented practically as multilamellar spheres with diameters varying from 80 to 300 nm. Compared to an aqueous solution of EuW10 nanoclusters, a 12-fold increase in absolute luminescence quantum yield (∼23.3%) was observed for the hybrid spheres, which was ascribed to the efficient shielding of water molecules. An unusual aggregation arrangement mechanism and the excellent photophysical properties of these aggregates were thoroughly investigated. Both the enzyme substrate character of Myr and the sensitive coordination structure of EuW10 to the surrounding environment made Myr/EuW10 aggregates exhibit multi-stimulus responsiveness to enzymes, pH, and transition metal ions, thus providing potential applications in fluorescence sensing, targeted-release, and optoelectronics.

Flexible and enhanced multicolor-emitting films co-assembled by lanthanide complexes and a polymerizable surfactant in aqueous solution.

Lanthanide complex doped lyotropic liquid crystals (LLCs) are soft materials which are impressive due to their excellent luminescence efficiencies and stabilities. The introduction of lanthanide complexes into polymerizable LLCs, however, may produce organized films with better optical and mechanical properties through in situ photopolymerization. An environmentally friendly strategy to fabricate flexible multicolor-emitting films has been developed through co-assembling red-/green-emitting trisdipicolinate lanthanide complexes [choline]3[Ln(DPA)3] (Ln-DPA, Ln = Eu, Tb) into LLC matrices mainly via electrostatic interaction and further photopolymerization. The LLCs were constructed from a polymerizable surfactant, 3-dodecyl-1-vinylimidazolium bromide (C12VIMBr), in aqueous solution. The maintenance of the well-defined LLC nanostructures in the luminescent films was validated by small-angle X-ray scattering (SAXS) as well as scanning electron microscopy (SEM) measurements. Remarkably, the lifetime and absolute luminescence quantum efficiency of such films have been improved significantly compared with those of the corresponding solid Eu-DPA complex or in aqueous solution and LLC matrices. Through tuning the molar ratio of Eu-DPA to Tb-DPA complexes, the emission color of the films could be finely-tailored between red and green in the CIE chromaticity diagram. Furthermore, the films also possessed certain mechanical strength and stability against pH, metal ions, and temperature, indicating their potential application as robust luminescent materials.

Enhanced full color tunable luminescent lyotropic liquid crystals from P123 and ionic liquid by doping lanthanide complexes and AIEgen.

HYPOTHESIS: The soft materials from ionic liquid mediated lyotropic liquid crystals (LLCs) containing europium complexes have exhibited enhanced luminescence efficiencies and photo-stabilities. The combination with aggregation-induced emissive compounds (AIEgens), however, may produce multicolor and even white emitting LLCs. EXPERIMENTS: Here, we have fabricated highly luminescent hexagonal (H1) LLC containing a red-emitting trisdipicolinate lanthanide complex [choline]3[Eu(DPA)3] (Eu-DPA) from Pluronic 123 and 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6). Then, a typical AIEgen, tetrakis(4-hydroxyphenyl)ethane (TPE-OH) showing blue light was doped into H1 matrix, accompanying with a green-emitting Tb-DPA. FINDINGS: The emission color of such LLCs could be finely-tuned through changing the molar ratio of Eu-DPA to Tb-DPA. Remarkably, the white emitting H1 LLC with CIE coordinate of (0.328, 0.315) has been prepared by accurately adjusting the relative contents of TPE-OH, Eu-DPA and Tb-DPA. Further, the emission color could be switched between bright white and blue upon tuning UV light from 254 to 365 nm repeatedly. To our best knowledge, such full color tunable luminescent LLCs with improved luminescent performances for both AIEgen and lanthanide complexes have not been reported. This facile approach is universal and various kinds of luminophores can be thus encapsulated into LLC matrices to fabricate soft materials with rich luminescent properties.

Phase behaviours of a cationic surfactant in deep eutectic solvents: from micelles to lyotropic liquid crystals.

In recent years, aggregates formed in deep eutectic solvents (DESs), especially micelles, have attracted much attention. In this study, the phase behaviours of a cationic surfactant, cetylpyridinium bromide (CPBr), in two DESs, choline chloride + glycerol (ChG) and choline chloride + ethylene glycol (ChEG), were investigated in wide concentration and temperature ranges. With the help of small angle X-ray scattering, polarized optical microscopy and rheological measurements, the structures and properties of various aggregates were characterized. The micelles, hexagonal phase, bicontinuous cubic phase and lamellar phase were observed with the increase of CPBr concentration. Such rich phase behaviours were due to the large cohesive energy densities of DESs. Comparative studies in water and ethylammonium nitrate were carried out to explore how well DESs acted as self-assembly media.

Unusual Aggregation Arrangement of Eu-Containing Polyoxometalate Hybrid in a Protic Ionic Liquid with Improved Luminescence Property.

Hybridization of polyoxometalates (POMs) with cationic surfactants offers the opportunity to greatly improve their functionalities as well as processabilities. Here, a surfactant-encapsulated Eu-containing POM complex (SEP) was formed via electrostatic interaction between 1-octadecyl-3-methylimidazolium bromide (OB) and Na9(EuW10O36)·32H2O (EuW10). SEP was first self-assembled in a protic ionic liquid to prepare the soft aggregates to fundamentally avoid the fluorescence quenching by water molecules. The structures and photophysical properties of SEP or aggregates were investigated thoroughly by NMR and FTIR spectroscopy, optical and electron microscopy, small-angle X-ray scattering, and fluorescence measurements. The formed gel-like aggregates were found to compose of three-dimensional networks of microribbons with an interdigitated layered molecular packing of SEP, which was different from the usual inverse bilayer model of POM hybrids in common organic solvents. Compared to EuW10 solid or its aqueous solution, both SEP and its aggregates exhibited intense red luminescence with much improved lifetime and quantum efficiency. In addition, the soft aggregates exhibited an efficient energy transfer and an obviously enhanced monochromaticity, owning to the organized arrangement of EuW10 units and a confined microenvironment to isolate them from each other between adjacent layers. The obtained results will not only present a useful reference to the aggregation behavior of POM hybrids in ionic liquids, but also provide an easy way to design EuW10 luminescent soft materials based on the nonaqueous media.