Preparation of Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> by Electrospinning: Researching Their Synthesis Mechanism and Photocatalytic Activity

The novel Bi₂WO₆ nanomaterials, which consist of nanosheets and nanoparticles, were successfully synthesized by a combination of electrospinning and calcining processes. The Bi₂WO₆ with different morphologies and microstructures had been obtained in the same experimental conditions. The growth mechanism of such special nanostructures was investigated, and citric acid played an important role in the formation of Bi₂WO₆ nanostructures. The Bi₂WO₆ nanomaterials exhibited excellent photocatalytic property in the photodegradation of the pulping and papermaking wastewater under visible light irradiation. Besides, preparation of the photocatalyst using electrospinning was beneficial for separation and recycling. So, the Bi₂WO₆ nanomaterials have a great potential in application for wastewater treatment in the future.     

Chiral salen-metal derivatives of polyoxometalates with asymmetric catalytic and photocatalytic activities

Immobilization of the chiral salen-metal complex [Mn(III)(salen)(H(2)O)(2)ClO(4)] on the Keggin-type polyoxometalate (POM) skeletons leads to the isolation of POM derivatives functionalized with chiral salen-metal complexes, which represent the first examples of introducing chiral salen-metal complexes into the POM systems.     

An interesting molecular-assembly of β-cyclodextrin pipelines with embedded hydrophilic nickel maleonitriledithiolate

A unique tubular molecular-assembly, constructed by β-cyclodextrin and Na[Ni(mnt)(2)], was identified by X-ray crystallography. Inclusion complex Na[Ni(mnt)(2)]@β-cyclodextrin (1) crystallized in space group P2(1)2(1)2 as hydrated head-to-head, tail-to-tail, and head-to-tail host pipelines with negatively charged [Ni(mnt)(2)](-) guests included, exhibiting a 3?:?1 (host?:?guest) stoichiometry. The hydrophilic transition-metal coordination compound (Na[Ni(mnt)(2)]) was embedded within a hydrophobic cyclodextrin cavity, which resulted in a β-cyclodextrin trimer motif and one-third "empty" host packing model in the crystal. Induced circular dichroism (ICD) spectra of inclusion complex 1 was investigated, which indicated the same penetration pattern of the guests in host cavities in solution phase as that discovered in the crystal structure. In addition, PM3 quantum chemistry calculations strongly supported the co-conformational alignments of inclusion complex 1 that was identified in the crystal as well as in the solution.     

Pathwise Estimation of Stochastic Differential Equations with Unbounded Delay and Its Application to Stochastic Pantograph Equations

The existence and uniqueness of the global solution of stochastic differential equations with discrete variable delay is investigated in this paper, and the pathwise estimation is also done by using Lyapunov function method and exponential martingale inequality. The results can be used not only in the case of bounded delay but also in the case of unbounded delay. As the applications, this paper considers the pathwise estimation of solutions of stochastic pantograph equations.     

Long term behaviors of stochastic single-species growth models in a polluted environment

Thresholds for extinction and persistence are important for assessing the risk of mortality in systems exposed to toxicant. In this paper, three single-species models with random perturbation in a polluted environment are proposed and investigated. One is the generalized logistic model and the other two are the stochastic resource–consumer models of Leslie and Gallopin. For each model, the survival threshold is obtained in some cases. In general, each threshold is determined by intensity of the random noise, the mean stress measure in organisms, the population intrinsic growth rate and the stress response rate.     

Controlling the transmission of stereochemical information through space in terphenyl-edged Fe4L6 cages

A series of terphenyl-edged Fe(4)L(6) cages were synthesized from substituted 4,4'-diamino-p-terphenyls, 2-formylpyridine, and iron(II). For the parent diaminoterphenyl, all three possible diastereomers, with T, S(4), and C(3) point symmetries, were formed in nearly equal amounts, as determined by (1)H and (13)C NMR. When 2,2″-dimethylterphenylenediamine was used, the T-symmetry diastereomer was observed to predominate. The use of 2',3',5',6'-tetramethylterphenylenediamine generated predominantly the S(4) cage diastereomer, whereas 2',5'-dimethylterphenylenediamine produced the C(3)-symmetric cage to a greater degree than the other two diastereomers. The factors contributing to the transfer of chiral information between metal vertices were analyzed, and the general principles underlying the delicately balanced thermodynamics were determined.     

Rational solution growth of α-FeOOH nanowires driven by screw dislocations and their conversion to α-Fe2O3 nanowires

We report the rational synthesis of α-FeOOH (goethite) nanowires following a dislocation-driven mechanism by utilizing a continuous-flow reactor and chemical equilibria to maintain constant low supersaturations. The existence of axial screw dislocations and the associated Eshelby twist in the nanowire product were confirmed using bright-/dark-field transmission electron microscopy imaging and twist contour analysis. The α-FeOOH nanowires can be readily converted into semiconducting single-crystal but porous α-Fe(2)O(3) (hematite) nanowires via topotactic transformation. Our results indicate that, with proper experimental design, many more useful materials can be grown in one-dimensional morphologies in aqueous solutions via the dislocation-driven mechanism.     

A potential fluorescence detection approach to trace hexachlorobenzene via disaggregating with ethanol

A potential ultra-sensitive detection approach for hexachlorobenzene (HCB), based on the measurement of the intrinsic fluorescence of well-separated HCB molecules in ethanol, has been proposed. Owing to the strong intermolecular π-π stacking interaction of the planar aromatic rings, self-aggregated HCB shows almost no fluorescence. However, the intrinsic emission of HCB can readily be detected in ethanol due to the enhanced emission from the disaggregated HCB, which is related to the hydrogen bond formation between ethanol and HCB. By simply measuring the HCB intrinsic fluorescence, a HCB concentration a little bit higher than 10(-14) M (~0.001 ppt) in ethanol can be detected; moreover, the fluorescence intensity of the HCB increases linearly with the HCB concentration ranging from 10(-10) to 10(-7) M. The approach might provide a simple, fast and efficient method for HCB quantification.     

Highly selective in situ metal ion determination by hybrid electrochemical "adsorption-desorption" and colorimetric methods

A novel and facile hybrid analytical method coupling electrochemical “adsorption–desorption” and colorimetric analyses was developed to detect heavy metal ions in turbid water samples. The target metal ions were deposited onto an electrode inserted into the original sample, which was referred to as the “adsorption” process. After changing the medium, the concentrated target metal ions were dissolved in a new, clean buffer (blank buffer), which was referred to as the “desorption” process. The concentrations of the target metal ions were measured by colorimetric analyses after the addition of specific indicator amounts. We demonstrated the applicability of this method by detecting Cd²⁺, Pb²⁺ and Cu²⁺ with co-depositing Bi³⁺ on portable screen-printed electrodes (SPEs). A good correlation (correlation coefficient of R = 0.997) was observed between concentrations ranging from 1 to 200 μM and absorbance values. After the multiple “desorption” process, the even better detection limits as low as 10, 10 and 100 nM were achieved for Cd²⁺, Pb²⁺ and Cu²⁺, respectively. The practicality of this hybrid method was confirmed by the detection of Cd²⁺, Pb²⁺ and Cu²⁺ in wastewater samples, and these results were in agreement with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Overall, this hybrid method provides a simple, selective and effective technique for environmental pollutant analyses.