On-Off Ratiometric Fluorescence Europium(III) Metal-Organic Framework for Quantitative Detection of the Inflammatory Marker Neopterin.

Benefiting from the unique photoluminescence behavior of the lanthanide(III) ions and organic ligands, a lanthanide(III) metal-organic framework (Ln-MOF) material can simultaneously demonstrate photoluminescence of lanthanide(III) cations and organic molecules and endow its superior applications of fluorescence sensing behaviors. Herein, we present a europium(III) MOF material {[Eu2(BPTA)·(CH3COO)2·3DMA]·0.5DMA·3H2O}n (1) (where H4BPTA is 3,3',5,5'-biphenyltetracarboxylic acid) for photoluminescence performance of quantitatively sensing the inflammatory marker neopterin (Neo). The obtained 1 comprises Eu2(COO)4 paddlewheel secondary building units, which could be bridged by BPTA4- ligands to extend a 2D framework. The fluorescence titration indicates 1 can achieve simultaneous fluorescence behavior of Eu3+ ions and Neo via on-off ratiometric effects and thus could be exploited as the ratiometric fluorescence sensor matrix. Such a fluorescence phenomenon of 1 as a ratiometric sensor for quantitative detection of Neo via an on-off ratiometric effect is never observed in MOF chemistry. Moreover, naked-eye visible color variations of the fluorescence for 1 could be observed from red to blue with increasing concentrations of Neo, confirmed by fluorescent test strips as well as portable fluorescent hydrogels. And 1 also shows a low detection limit of 15.11 nM. A synergetic contribution of the competitive absorption, fluorescence resonance energy-transfer, and photoinduced electron-transfer mechanisms between Neo and the framework of 1 realizes the on-off ratiometric fluorescence behavior for Neo detection, supported by the UV-vis spectral overlap experiment and DFT calculations.

Exploring the structural stability and electrochemical performance of B doped T-graphene nanotubes from first-principles calculations.

The structural stability and electrochemical performance of intrinsic and B doped T-graphene nanotubes with different tube lengths are systematically studied by using first-principles calculations within the framework of density functional theory (DFT). The results show that with the increase of tube length, the adsorption energy of both intrinsic and B doped T-graphene nanotubes exhibits regular oscillations, and B doping is beneficial for elevating the adsorption ability of T-graphene nanotubes. The density of states show that intrinsic T-graphene nanotubes are zero band gap semiconductors, and the orbitals' electronic states cross the Fermi level to form a p-type semiconductor, indicating that B doping greatly improves the conductivity of the system. The results of migration behavior demonstrate that B doping can effectively reduce the diffusion barrier of lithium ions on their surface, especially in B doped T-graphene nanotubes with a tube length of N = 1, resulting in more effective migration behavior and excellent rate performance. These findings provide a theoretical basis for the development and application of negative electrode materials for lithium-ion batteries.

Elucidating the effects of B/Al doping on the structure stability and electrochemical properties of silicene using DFT.

Using first-principles calculation based on density functional theory, the effects of B, Al and B-Al doping on the structural stability and electrochemical properties of silicene were systematically studied, and their potential as anode materials for lithium ion batteries was evaluated. The calculated results of formation energy indicate that the doped system has good stability. The charge density difference and density of states show that doping can improve the conductivity of silicene, and enhance the interaction with Li. Moreover, on the surface of B, Al and B-Al doped silicene, the diffusion barriers of the most easily migrated path for Li ions are 0.22 eV, 0.19 eV, and 0.21 eV, respectively, suggesting that all doped systems have good Li ion migration rates. And the open circuit voltage is between 0.40 V and 0.54 V, which is relatively stable and low. Therefore, B, Al and B-Al doping can effectively regulate the structural stability and electrochemical performance of silicene, which provides a theoretical basis for the experimental preparation of excellent silicene anode materials.

Tuning the structural stability and electrochemical properties in graphene anode materials by B doping: a first-principles study.

The first-principles method of density functional theory (DFT) is used to study the structural stability and electrochemical properties of B doped graphene with concentrations of 3.125%, 6.25% and 18.75% respectively, and their lithium storage mechanism and characteristics are further studied. The results show that the doped systems all have negative adsorption energy, indicating that the structures can exist stably, and the adsorption energy of lithium ions on graphene decreases with the increase of B doping concentration. Among them, the B6C26 structure has the lowest adsorption energy and can adsorb more lithium ions. The density of states indicates that doping with B can increase the conductivity of graphene greatly. Subsequently, the CI-NEB method to search for the transition state of the doped structure is used, showing that the B6C26 structure has the lowest diffusion barrier and good rate performance. Therefore, these findings provide a certain research foundation for the development and application of lithium-ion battery anode materials.

A stochastic predator-prey model with Holling II increasing function in the predator.

This paper is concerned with a stochastic predator-prey model with Holling II increasing function in the predator. By applying the Lyapunov analysis method, we demonstrate the existence and uniqueness of the global positive solution. Then we show there is a stationary distribution which implies the stochastic persistence of the predator and prey in the model. Moreover, we obtain respectively sufficient conditions for weak persistence in the mean and extinction of the prey and extinction of the predator. Finally, some numerical simulations are given to illustrate our main results and the discussion and conclusion are presented.

Benefits of Ga, Ge and As substitution in Li2FeSiO4: a first-principles exploration of the structural, electrochemical and capacity properties.

Herein, the feasibility of Fe substitution by Ga, Ge and As in Li2FeSiO4 in modulating its structural, mechanical, electrochemical, capacity and electronic properties was systematically studied via first-principles calculations based on density functional theory within the generalized gradient approximation with Hubbard corrections (GGA+U). The calculated results show that Ga, Ge and As doping can effectively reduce the range of the cell volume change during Li+ removal, improving the Li+ detachment ability and cycle stability of the system. Meanwhile, the calculated mechanical properties including modulus ratio, B/G, and Poisson ratio, ν, indicate that the doped systems of Ga, Ge and As exhibit excellent mechanical properties. In addition, besides the increase in theoretical average deintercalation voltage induced by the Ga dopant when more than one Li+ ion is removed in the formula unit, the doping of Ga, Ge and As all reduce the theoretical average deintercalation voltage in the process of Li+ extraction. Especially in the case of doping of Ge, when 0.5 Li+ is removed from LiFe0.5Ge0.5SiO4, the theoretical average deintercalation voltage only increases by 0.19 V compared with the case of the removal of one Li+ in Li2Fe0.5Ge0.5SiO4, which causes the cathode material to have a longer and more stable discharge platform. Moreover, in the process of Li+ removal, the doping of Ga, Ge and As can effectively participate in the charge compensation of the system, and Ge and As can provide further charge, increasing the capacity of the Li2FeSiO4 cathode material considerably.