Preparation of MOF-derived ZnO/Co3O4 nanocages and their sensing performance toward H2S.

We report a type of micro-electro-mechanical system (MEMS) H2S gas sensors with excellent sensing performance at the ppb level (lowest detection limit is 5 ppb). The sensors were fabricated with ZnO/Co3O4 sensing materials derived from Zn/Co-MOFs by annealing at a suitable temperature of 500 °C. ZnO/Co3O4-500 exhibits the highest response when exposed to 10 ppb H2S gas at 120 °C, and the response/recovery times are 10 s/21 s. Moreover, it exhibits outstanding selectivity, long-term stability (retained 95% response after 45 days), and moisture resistance (only a minor fluctuation of 2% even at 90% RH). This can be ascribed to the fact that ZnO/Co3O4-500 has regular morphology, abundant oxygen vacancies (52.8%) and high specific surface area (96.5 m2 g-1). This work provides not only a high performance H2S MEMS gas sensor but also a systematic study of the effect of the annealing temperature on the sensing performance of ZnO/Co3O4 sensing materials derived from bimetal organic frameworks.

Tailoring the Ni-O Microenvironment in Amorphous-Dominated Highly Active and Stable Zn/NiO for Hydrogen Sulfide Detection.

Amorphous metal oxide semiconductor (MOS) materials are endowed with great promise to modulate electronic structures for gas-sensing performance improvement. However, the elevated-temperature requirement of gas sensors severely impedes the application of amorphous materials due to their low thermal stability. Here, a cationic-assisted strategy to tailor the Ni-O microenvironment in an amorphous-dominated Zn/NiO heterogeneous structure with high thermal stability was developed. It was found that 6 mol % Zn incorporation into amorphous NiO can effectively preserve the amorphous-dominated NiO phase even at high temperature. After calcination, the amorphous oxide can only be converted to crystals partly thus leading to the formation of amorphous/crystalline compounds, and the content of the amorphous phase can be adjusted by changing the calcination temperature. This amorphous/crystalline configuration can induce more electron transfer from Ni to Zn species, leading to the formation of active Niδ+ (δ>2) centers. Ex situ XPS and in situ Raman spectroscopy studies proved that the generated Niδ+ species pronouncedly promote the electron transfer during the H2S adsorption process. The amorphous/crystalline-6 mol % Zn/NiO sensor exhibits exceptional hydrogen sulfide response (2 ppm, 3.23), outstanding repeatability (as long as 5 weeks), and low limit of detection (as low as 50 ppb), surpassing most reported nickel-based gas sensors such as the crystal nickel oxide prepared in this work. The response and detection limit of the latter is only (2 ppm, 1.89) and (0.05 ppm) respectively. Our work thus opens up more opportunities for fundamental understanding and modulating of highly active amorphous sensing materials.

Building Feedback-Regulation System Through Atomic Design for Highly Active SO2 Sensing.

Reasonably constructing an atomic interface is pronouncedly essential for surface-related gas-sensing reaction. Herein, we present an ingenious feedback-regulation system by changing the interactional mode between single Pt atoms and adjacent S species for high-efficiency SO2 sensing. We found that the single Pt sites on the MoS2 surface can induce easier volatilization of adjacent S species to activate the whole inert S plane. Reversely, the activated S species can provide a feedback role in tailoring the antibonding-orbital electronic occupancy state of Pt atoms, thus creating a combined system involving S vacancy-assisted single Pt sites (Pt-Vs) to synergistically improve the adsorption ability of SO2 gas molecules. Furthermore, in situ Raman, ex situ X-ray photoelectron spectroscopy testing and density functional theory analysis demonstrate the intact feedback-regulation system can expand the electron transfer path from single Pt sites to whole Pt-MoS2 supports in SO2 gas atmosphere. Equipped with wireless-sensing modules, the final Pt1-MoS2-def sensors array can further realize real-time monitoring of SO2 levels and cloud-data storage for plant growth. Such a fundamental understanding of the intrinsic link between atomic interface and sensing mechanism is thus expected to broaden the rational design of highly effective gas sensors.

Boosting Solid-State Luminescence of Thiazolothiazole Viologen by Incorporating Metal Halide Clusters to Hinder π-Stacking.

A new strategy is developed herein to improve the solid fluorescence of thiazolothiazole viologen by using the ZnCl42- cluster as a scaffold to hinder π-stacking. Importantly, the Cl···H bonds are formed in the solid state to sustain the framework and can be automatically dissociated when dissolved in H2O, thus having no impact on the strong emission in aqueous solution. As such, the first case of organic-inorganic viologen-zinc halide named 4PV·ZnCl4 was designed and synthesized, and a significant increase in photoluminescence quantum yield (ΦF) is realized from 4PV·2Br (ΦF = 0%) to 4PV·ZnCl4 (ΦF = 27.0%) in solid and from 97% to 98% in H2O. 4PV·ZnCl4 also displays pH stimuli-responsive naked-eye chromic behavior and photoluminescence with different coloring states and intensities. The multifunctional performance of 4PV·ZnCl4 provides a prerequisite for carrying different information, expanding their promising application in multilevel information encryption.

A Novel 3D-Morphology Pyrene-Derived Conjugated Fluorescence Polymer for Picric Acid Detection.

Aggregation-induced quenching (ACQ) is a hard problem in fluorescence material, leading to a poor utilization rate of fluorophores. In this work, 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) was synthesized and used as a precursor to build two kinds of fluorescence polymer. The TFFPy molecule with D2h symmetry can easily form polymers with C3 symmetry amines through the Schiff base reaction, making the resulting polymer a 3D amorphous material. Thus, ACQ of fluorophore can be reduced to minimum, making the most usage of the fluorescence of pyrene core. Fluorescence titration and DFT calculation can clearly prove this conclusion. The resulting CPs showed a highly sensitivity to picric acid, down to 3.43 ppm in solution, implying its potential in explosive detection.

Efficient Synthesis of Yellow-Green Carbon Quantum Dots as a Sensitive Fluorescent Probe of Folic Acid.

Bright yellow-green carbon quantum dots (YGCDs) have been successfully synthesized by a simple and efficient hydrothermal method. Their luminescent absolute quantum yield reached 30.0% in 4 h. Compared with commonly reported solvothermal methods, the synthesis time was reduced by more than 70% by using tin oxide nanoparticles as a catalyst. Moreover, the fluorescence of YGCDs could be selectively quenched by folic acid (FA) molecules, and the relative fluorescence intensities of F/F0 was fitted perfectly in line decay curve versus the concentration of FA in the range of 2.0×10-8  mol/l to 1.0×10-5  mol/l (R2 =0.9988). The detection limit of FA was below 2.0×10-8  mol/l, suggesting a promising fluorescent probe of folic acid.

[Preparation of luminescent silica nanoparticles with immobilized metal ion affinity for labeling phosphorylated proteins in Western Blot].

Protein phosphorylation is an important type of post-translational protein modification. In Western Blot experiment, the assay of phosphoproteins need special phospho antibodies, which are expensive, difficult to preserve, poorly reproducible. To this end, the immobilized metal ion affinity luminescent silica nanoparticles for instead of phospho antibodies were prepared. A layer of polymer was created on the surface of the silica nanoparticles via co-polymerization to protect the nanoparticles and to functionalize them with the immobilized metal ion affinity property to specifically label the phosphorylated proteins in Western Blot assays. The affinity luminescent silica nanoparticles were prepared with the following procedure. First, the sol-gel precursor fluorescein isothiocyanate-3-aminopropyltriethoxysilane (FITC-APTES) with the fluorescent moiety was prepared by modifying APTES with FITC. The luminescent silica nanoparticles (FITC@SiO2) were synthesized using the Stöber synthesis method in a reversed microemulsion. Briefly, 123.2 mL of cyclohexane, 25.6 mL of n-hexanol, and 5.44 mL of deionized water were ultrasonically mixed, and then 28.3 g of Triton X-100 were added and the mixture was magnetically stirred for 15 min to form a clear and transparent microemulsion system. Within 10 min, 0.8 mL of FITC-APTES precursor, 1.6 mL of tetraethoxysilane (TEOS), and 0.96 mL of concentrated ammonia (25%-27%, mass fraction) were added to the microemulsion, and the mixture was stirred at 24 ℃ for 24 h. After the reaction, the microemulsion system was destroyed by adding 200 mL of ethanol. The resulting FITC@SiO2 luminescent silica nanoparticles were centrifuged, and washed three times with ethanol. After dryness, the FITC@SiO2 nanoparticles were modified with methacryloxy-propyltrimethoxysilane (MPS) to introduce the double bonds for further modification. The functional monomer nitrilotriacetic acid (NTA) and glycidyl methacrylate (GMA) were copolymerized on the surface of the nanoparticles to convert FITC@SiO2-MPS to FITC@SiO2-MPS-GMA-NTA. The polymer coating of the silica nanoparticles was not only able to protect the silica from hydrolysis, but also to introduce the functional groups of nitrilotriacetic acid, which can chelate with metal ions. Elemental analysis demonstrated that the NTA groups had been bonded to the surface of the nanoparticles via copolymerization. The polymerization did not affect the morphology and fluorescence properties of the nanoparticles. The FITC@SiO2-MPS-GMA-NTA nanoparticles were activated with three different metal ions Zr4+, Fe3+, and Ti4+, for the enrichment of phosphorylated peptides derived form α-casein tryptic digestion. HPLC-MS analysis indicated that the FITC@SiO2-MPS-GMA-NTA-Ti 4+ nanoparticles are the best for the enrichment of phosphorylated peptides. The FITC@SiO2-MPS-GMA-NTA-Ti4+ nanoparticles were used for labelling the phosphorylated proteins in Western Blot experiment. The electrophoretic band of α-casein could be clearly labeled with the FITC@SiO2-MPS-GMA-NTA-Ti 4+ nanoparticles, while the bovine albumin band could not be labelled. This indicates that the luminescent FITC@SiO2-MPS-GMA-NTA-Ti4+nanoparticles can be used to label the phosphorylated proteins in Western Blot experiments.

5,5'-(p-Phenyl-ene)di-1H-tetra-zole.

Crystals of the title organic compound, C(8)H(6)N(8), were generated in situ through the [2 + 3]-cyclo-addition reaction involving the precursor 1,4-dicyano-benzene and azide in water with Zn(2+) as Lewis acid. The asymmetric unit consists of one half-mol-ecule, and a twofold axis of symmetry passes through the centre of the benzene ring. There is an inter-molecular N-H⋯N hydrogen bond. The mol-ecules are assembled into a three-dimensional supra-molecular framework by π-π stacking inter-actions, with a perpendicular distance of 3.256 Š[centroid-centroid = 3.9731 (8) Å] between two tetra-zole ring planes, and 3.382 Šbetween the benz-ene ring and tetra-zole ring planes [centroid-centroid = 3.5010 (9) Å].

Synthesis and luminescence of a novel conjugated europium complex with 6-aniline carbonyl 2-pyridine carboxylic acid.

A novel organic ligand, 6-aniline carbonyl 2-pyridine carboxylic acid (HAP), and the corresponding europium complex, tris(6-aniline carbonyl 2-pyridine carboxylato) europium (III) (Eu-AP) have been designed and synthesized. The results showed that Eu-AP was a conjugated complex, emitting strong red luminescence. The lifetimes of (5)D(0) of Eu(3+) in the complex were examined using time-resolved spectroscopic analysis, and the lifetime value was 0.55 +/- 0.01 ms for solid Eu(AP)(3). Thermogravimetric analysis showed that the europium complex had good thermal stability.