Macro-meso damage characteristics of coal body under different pressure relief conditions.

The mining of the protective coal seam usually produces different pressure relief effects on the different areas of protected coal seam, the reason is that the stress paths of protected seam coal body in different areas caused by mining effect are different. In order to explore the differential pressure relief damage effect of coal body under different pressure relief conditions, the stress evolution path of coal body in different areas of the protected coal seam is obtianed by using theoretical analysis and the macro-micro damage characteristics of coal body under different stress paths by using numerical simulation in this paper. The results show that: The damage characteristics of the sample models are basically the same in the in-situ stress recovery stage and the mining disturbance stage of the two stress paths. With ith the sequence of stress stages experienced by the sample model, the distribution of acoustic emission events concentrates in the high-intensity area and the porosity continues to decrease. The number of cracks increases slowly in the stage of in-situ stress recovery stage, most of which are tensile cracks, while the number of cracks increases sharply in the mining disturbance stage, most of which are shear cracks. The difference of the deformation and macro meso damage characteristics of the sample models under the two stress paths is mainly reflected in the post mining pressure relief stage. At the post mining pressure relief stage of path 1, the number of cracks in the sample has little growth, and most of them are small energy tensile cracks, and the porosity increases, which verifies its obvious pressure relief activation antireflection effect; At this stage of path 2, the crack growth of the sample is obvious, and most of them are high-energy shear cracks, and the porosity continues to decrease. Compared with path 1, the pressure relief expansion effect of the sample model is suppressed and the compression damage continues to develop in this stage of path 2.

Single-strand DNA-scaffolded copper nanoclusters for the determination of inorganic pyrophosphatase activity and screening of its inhibitor.

A fluorescence method for the determination of inorganic pyrophosphatase (PPase) activity has been established based on copper nanoclusters (CuNCs). The polythymine of 40 mer (T40) acts as a template for the reduction reaction from Cu2+ to Cu0 by ascorbic acid (AA). This reaction leads to the formation of fluorescent CuNCs with excitation/emission peaks at 340/640 nm. However, the higher binding affinity between inorganic pyrophosphate (PPi) and Cu2+ hinders the effective formation of CuNCs. This shows low fluorescence intensity. PPase catalyzes the hydrolysis of PPi into Pi during which free Cu2+ ions are produced. This facilitates the formation of fluorescent CuNCs. Thus, the fluorescence intensity was restored. The fluorescence enhancement of the system has a linear relationship with PPase activity in the range 0.3 to 20 mU·mL-1, and the detection limit is0.2 mU·mL-1. The relative intensity (I/I0) at 640 nm for the analytical solution versus system is also employed to screen the inhibitor for PPase with high efficiency. Graphical abstract Schematic representation of a fluorescent assay for the determination of inorganic pyrophosphatase activity and screening its inhibitor based on single-strand polythymine-scaffolded copper nanoclusters.

DNA-scaffold copper nanoclusters integrated into a cerium(III)-triggered Fenton-like reaction for the fluorometric and colorimetric enzymatic determination of glucose.

A fluorometric and colorimetric method are described for the determination of hydrogen peroxide and glucose by integrating copper nanoclusters (CuNCs) into a Fenton-like reaction. The mechanism mainly depends on the fast formation of long-strand DNA-templated CuNCs with strong red fluorescence (with excitation/emission maxima at 340/640 nm) in the absence of H2O2. The DNA can be cleaved into short-oligonucleotide fragments by hydroxy radicals as formed in the Ce(III)-triggered Fenton-like reaction in the presence of H2O2. As a result, short-strand DNA loses the ability as a template for the formation of CuNCs. This leads to a decrease of fluorescence. The colorimetric assay, in turn, is based on the oxidation of colorless Ce(III) ions to the distinctly yellow Ce(IV) ions (with an absorption maximum at 400 nm) by H2O2. Compared with those assays based on the use of enzyme mimics, this method does not require any chromogenic substrates such as ABTS and TMB. Based on the dual-signal readout platform, we successfully achieved the detection of H2O2 and glucose. LODs are as low as 0.266 µM and 2.92 µM. The methods were applied to the sensitive determination of glucose by using glucose oxidase (GOx) which catalyzes the oxidization of glucose to produce H2O2. The practical application was demonstrated by determination of glucose in human serum, with apparent recoveries of 98.4-101.9% and 99.1-105.6%, respectively. The concentration of glucose ranges from 1 to 500 µM and 50 to 600 µM based on the dual-signal readout platform, respectively. This fluorometric and colorimetric dual-mode strategy will pave a new avenue for constructing effective assays for H2O2-related analytes in biochemical and clinical applications. Graphical abstractSchematic representation of a fluorometric and colorimetric dual-readout strategy for the sensitive determination of hydrogen peroxide and glucose. The assay has been designed by integrating copper nanoclusters into a Ce(III)-triggered Fenton-like reaction.

Iodide-assisted silver nanoplates for colorimetric determination of chromium(III) and copper(II) via an aggregation/fusion/oxidation etching strategy.

The authors have studied the role of different ligands on the surfaces of silver nanoplates for regulating their analytical applications. Citrate-capped silver nanoplates are applied for the detection of chromium ions (Cr3+) based on aggregation of silver nanoplates. Cr3+ can cause aggregation through high affinity between Cr3+ and carboxylate groups of citrates, resulting in a color change from dark yellow to purple and at last colorless. The detection limit is 8.0 nM. This system shows excellent selectivity in the presence of a variety of other metal ions. Further, silver nanoplates coupled with iodide ions are employed for the colorimetric determination of copper ions (Cu2+) based on a new strategy of fusion/oxidation etching nanoplates. When Cu2+ is introduced into this silver nanoplate system, Cu2+ can oxidize I- to iodine (I2), which can further oxidize silver to form silver iodide (AgI). Simultaneously, the solution color changes from dark yellow to colorless. The lower limit detection is 0.27 µM. This assay exhibits excellent selectivity for Cu2+ over other environmental metal ions. It is perceived that this design concept will open up a fresh insight of simple, rapid and reliable detection of other heavy metal ions in drinking water and environmental samples. Graphical abstract Iodide-assisted silver nanoplates can be used for the colorimetric and visual ldetermination of Cr3+ and Cu2+ based on an aggregation/fusion/oxidation etching mechanism. These systems allows selective and sensitive determination of the ions in real samples.

DNA-templated copper nanoclusters as a fluorescent probe for fluoride by using aluminum ions as a bridge.

A selective fluorescent on-off-on probe has have designed for the detection of fluoride (F-) ions based on DNA-templated copper nanocluster (CuNCs) and by using aluminum(III) ions as a bridge. A 40-mer polythymine acts as a template for the reduction of Cu(II) to Cu(0) by ascorbic acid. This result is the formation of red fluorescent CuNCs, with excitation/emission peaks at 340/640 nm. After addition of Al3+ ions, the fluorescence of CuNCs is quenched because the interaction of Al3+ and DNA disturbs the formation of DNA-templated CuNCs. Fluorescence is restored on addition of fluoride to the system. This is due to the desorption of Al3+ from the DNA and the formation of the Al(OH)3F- complex. This system displays a fast fluorometric response to fluoride, with high selectivity over other anions. Fluorescence increases linearly in the 2 to 150 µM F- concentration range, and the detection limit is 1.0 µM. This probe has been successfully used for the detection of F- ions in four brands of toothpaste. The method is rapid, cost-effective, selective, and does not require toxic solvents and reagents. Graphical abstract Schematic presentation of a method for fluorometric determination of fluoride by using DNA-templated copper nanoclusters (CuNCs) and using aluminum(III) as a bridge. The red fluorescence of the CuNCs is quenched in the presence of Al(III) ions but restored after addition of fluoride.

On-off-on luminescent pyrophosphate probe based on the use of Mn-doped ZnS quantum dots and using Eu(III) as a mediator.

A selective phosphorescent on-off-on probe with long decay lifetime has been designed for the detection of pyrophosphate ions (PPi). The detection scheme is based on the use of europium(III)-modulated Mn(II)-doped ZnS quantum dots capped with N-acetyl-L-cysteine. Both the aggregation of quantum dots and electron transfer induced by Eu(III) ions cause phosphorescence to be quenched ("off" state). Phosphorescence is, however, restored on addition of PPi to the system ("on" state). The effect is attributed to the removal of Eu(III) from the carboxy groups on the surface of the quantum dots owing to the stronger interaction between PPi and Eu(III). A linear relationship exists between phosphorescence intensity (best measured at excitation/emission wavelengths of 316/594 nm) and PPi concentration in the 400 nM to 6000 nM with a detection limit of 145 nM. An additional attractive feature is provided by the long-lived phosphorescence (1920 µs) of the quantum dots. It can be used to eliminate interference by short-lived fluorescence in biological samples by performing time resolved measurements. The probe was applied to the determination of PPi in spiked in urine samples and gave recoveries in the range from 98 to 105% with RSDs of <2.0%. Graphical abstract Schematic of a long-lived phosphorescent on-off-on probe for the sensitive and selective detection of pyrophosphate ions (PPi). It is based on the use of Eu(III)-modulated Mn(II)-doped ZnS quantum dots (QDs). Phosphorescence is quenched of QDs after the addition of Eu3+but restored after the addition of PPi.

Synthesis of Unique Flowerlike Bi2 O2 (OH)(NO3 ) Hierarchical Microstructures with High Surface Area and Superior Photocatalytic Performance.

Unique flowerlike Bi2 O2 (OH)(NO3 ) (denoted as BION) hierarchical microstructures assembled by ultrathin nanosheets were hydrothermally synthesized from incomplete hydrolysis of anhydrous bismuth nitrate (Bi(NO3 )3 ) after adsorption of glacial acetic acid (HAc). The structure, composition, and optical properties of the products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, etc. The as-prepared flowerlike BION possessed an ultra-high surface area and thus exhibited exceptional photocatalytic activity for rhodamine B (RhB) degradation under UV light irradiation with an efficiency of about 17; 6 and 2.5 times higher than spherical, aggregated sheet-like BION and P25 TiO2 , respectively, and also superior to the reported sheet-like BION. It also showed good photocatalytic activity for crystal violet (CV) degradation. This work opens new routes for the rational design and synthesis of nontoxic basic bismuth nitrates with a facile synthetic approach, controllable morphology, and excellent photoreactivity.