A tetraphenylborate-based anionic metal-organic framework as a versatile solid electrolyte for fast Li+, Na+, K+, Mg2+, Ca2+, and Zn2+ transportation.

Tetraphenylborate (BPh4 -) has been widely employed in the field of electrolytes and displayed better ionic conductivities in polymer solid-state Li+ conductors. However, the fabrication of tetraphenylborate monomers into metal-organic frameworks (MOFs) and the exploration of their potential in solid-state electrolytes have never been reported. In this work, carboxylic acid functionalized lithium tetraphenylborate was purposefully synthesized and employed to construct an anionic MOF as a solid electrolyte. The counter cation Li+ was encapsulated into the anionic channel to become the free mobile charge carrier that produced a lithium-ion solid electrolyte with outstanding ion conductivity (2.75 × 10-3 S cm-1 at 25 °C), an impressively high lithium-ion transference number (t Li+ = 0.89), and low activation energy (0.15 eV). Acting as a solid electrolyte, the anionic MOF-based lithium iron phosphate battery delivered an initial specific capacity of 135 mA h g-1 and retained 95% capacity after 220 charge-discharge cycles with a coulombic efficiency close to 100%. Moreover, by exchanging the free Li+ with Na+, K+, Mg2+, Ca2+, and Zn2+, our anionic MOF is also available for other types of solid electrolytes with the corresponding conductivities all above that of the functional battery electrolyte. Our work provided a convenient and tunable route to prepare conducting MOFs for alkali metal ions, alkaline earth metal ions, and other possible metal cations of interest, which could be used in solid-state electrolytic devices in the future.

Mechanistic insights into aggregation process of graphene oxide and bacterial cells in microbial reduction of ferrihydrite.

Microbial reduction of ferrihydrite is prevalent in natural environments and plays an important role in reductive dissolution of Fe(III) minerals. With consistent release of anthropogenic graphene oxide (GO) into water bodies, new changes in the Fe(III)-reducing microorganisms/ferrihydrite binary system demand attention. Herein, we focused on the interaction of GO and bacterial cells in view of colloidal stability and interfacial forces, and on the consequences for microbial ferrihydrite reduction. The results showed that the addition of GO decreased the bioreduction efficiency of ferrihydrite down to 1/15 of the control. Meanwhile, the GO nanosheets were found not depositing on ferrihydrite but spontaneously aggregating with Shewanella spp., the representative dissimilatory Fe(III) reduction bacterial species. Using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and atomic force microscopy (AFM), the aggregation process can be interpreted in three steps according to the interaction energy calculation, namely, colloidal instability, reversible aggregation and irreversible aggregation. The motility of living cells seems the reason inducing the colloidal instability between GO and bacteria. While, the aggregation remains reversible even the secondary minimum achieved at the separation distance of 8.74-9.24 nm from XDLVO. When the separation distance <5.74-6.01 nm, the adhesion work predominates and causes irreversible aggregation, validated by AFM. Additionally, the probable ecological risks raised by this aggregation behavior for the imbalance of iron biogeochemical cycle were demonstrated.

Stochastic response analysis for nonlinear vibration systems with adjustable stiffness property under random excitation.

Nonlinear vibration systems with adjustable stiffness property have attracted considerable attentions for their prominent broadband performances. In the present manuscript, we consider the stochastic dynamical systems with adjustable stiffness and proposed a numerical method for the random responses analysis of the Gaussian white noise excited systems. A multi-dimensional Fokker-Plank-Kolmogorov equation governing the joint probability density of the mechanical states is derived according to the theory of diffusion processes. We solve the multi-dimensional equation using a splitting method and obtained the stationary probability densities and the mean-square responses directly. Two classical nonlinear vibration systems with adjustable stiffness, including the energy harvesting system and the Duffing system with Dahl friction, are presented as examples. Their comparisons with the results from Monte-Carlo simulations illustrate the effectiveness of the proposed procedure for both monostable and bistable cases, even for cases with strong excitation. In addition, the splitting method is efficient for higher-dimensional problem and has advantages of simple implementation, less storage of intermediate values and so on. Hence, in terms of the application scope, the proposed procedure is superior to the current mainstream methods for the random response evaluation of nonlinear vibration systems with adjustable stiffness.