Self-Assembled Polyoxometalate Nanodots as Bidirectional Cluster Catalysts for Polysulfide/Sulfide Redox Conversion in Lithium-Sulfur Batteries.

Polyoxometalates (POMs) are a class of discrete molecular inorganic metal-oxide clusters with reversible multielectron redox capability. Taking advantage of their redox properties, POMs are thus expected to be directly involved in the lithium-sulfur batteries (Li-S, LSBs) system as a bidirectional molecular catalyst. Herein, we design a three-dimensional porous structure of reduced graphene-carbon nanotube skeleton supported POM catalyst as a high-conductive and high-stability host material. Based on various spectroscopic techniques and in situ electrochemical studies together with computational methods, the catalytic mechanism of POM clusters in Li-S battery was systematically clarified at the molecular level. The constructed POM-based sulfur cathode delivers a reversible capacity 1110 mAh g-1 at 1.0 C and cycling stability up to 1000 cycles at 3.0 C. Furthermore, Li-S pouch/beaker batteries with a POM-based cathode were successfully demonstrated. This work provides essential inputs to promote molecular catalyst design and its application in LSBs.

Controllable Supramolecular Chiral Twisted Nanoribbons from Achiral Conjugated Oligoaniline Derivatives.

The fabrication of supramolecular chiral nanostructures from achiral materials without the need of pre-existing chirality is a major challenge associated with the origin of life. Herein, supramolecular chiral twisted nanoribbons of achiral oligoaniline derivatives were prepared via simply performing the chemical oxidation of aniline in an alcohol/water mixed solvent. In particular, the supramolecular chirality of the twisted nanoribbons could be controlled by facilely tuning the alcohol content in the mixed solvent. A tetra-aniline derivative C24H20O3N4 was attested to be the major component of the obtained nanoribbons. The main driving forces for the assembly of the oligoaniline derivative into twisted nanoribbons might be the π-π stacking and hydrogen bonding interactions among the chains which could be modulated by the alcohol content in the mixed solvent. The single-handed twisted nanoribbons could be used to separate chiral phenylalanine from a racemic mixture. Thus, it is highly anticipated that the supramolecular chirality endows π-conjugated molecules with potential application in chiral recognition.

Uptake of Cd(II) Onto Raw Crab Shells: Isotherm, Kinetic, Adsorption Properties And Mechanisms.

This study focuses on the uptake of cadmium (Cd(II)) ion from water onto raw crab shells acting as a biosorbent. Experimental data were perfectly fitted to the Langmuir and Dubinin-Radushkevich models, while the uptake kinetics are well-described using the pseudo-second-order model. The effects of experimental conditions on the uptake isotherms and kinetics are discussed in detail. A study of uptake thermodynamics has indicated that the Cd(II) uptake onto the crab shell is an endothermic and spontaneous process. For further understanding of this process, possible mechanisms of Cd(II) uptake onto crab shell have been deduced from experimental results. Desorption experiment shows that 93.7% of adsorbed Cd(II) could be recovered with a 0.1 M HNO3 solution. The inhibitory effects of other metal co-ions on the Cd(II) uptake on the crab shell are also discussed.

Core-Shell Structure and Interaction Mechanism of γ-MnO2 Coated Sulfur for Improved Lithium-Sulfur Batteries.

Lithium-sulfur batteries have attracted worldwide interest due to their high theoretical capacity of 1672 mAh g-1 and low cost. However, the practical applications are hampered by capacity decay, mainly attributed to the polysulfide shuttle. Here, the authors have fabricated a solid core-shell γ-MnO2 -coated sulfur nanocomposite through the redox reaction between KMnO4 and MnSO4 . The multifunctional MnO2 shell facilitates electron and Li+ transport as well as efficiently prevents polysulfide dissolution via physical confinement and chemical interaction. Moreover, the γ-MnO2 crystallographic form also provides one-dimensional (1D) tunnels for the Li+ incorporation to alleviate insoluble Li2 S2 /Li2 S deposition at high discharge rate. More importantly, the MnO2 phase transformation to Mn3 O4 occurs during the redox reaction between polysulfides and γ-MnO2 is first thoroughly investigated. The S@γ-MnO2 composite exhibits a good capacity retention of 82% after 300 cycles (0.5 C) and a fade rate of 0.07% per cycle over 600 cycles (1 C). The degradation mechanism can probably be elucidated that the decomposition of the surface Mn3 O4 phase is the cause of polysulfide dissolution. The recent work thus sheds new light on the hitherto unknown surface interaction mechanism and the degradation mechanism of Li-S cells.

Removal of Pb(II) and Zn(II) from Aqueous Solutions by Raw Crab Shell: A Comparative Study.

Removals of Pb(II) and Zn(II) ions from water using crab (Clistocoeloma sinensis) shell particles as biosorbent have been compared in this study. Uptake equilibriums for two ions well described by Langmuir isotherm revealed that crab shell possessed higher uptake capacity for Pb(II) (709 mg/g) than that for Zn(II) (117 mg/g). Kinetics data for the uptake of the two metals were successfully modeled using the pseudo-second-order model, where the initial uptake rate of Pb(II) was much faster than that of Zn(II). Dubinin-Radushkevick modeling and thermodynamic parameters hinted at different uptake mechanisms of Pb(II) and Zn(II) removal by crab shell, attested by FTIR, XRD, FESEM analysis. Pb(II) ion was removed mainly through the chemical reaction, while the uptake of Zn(II) ion onto crab shell was attributed to the chelation and coordination interactions. The polluted river water and laboratory wastewater both satisfied the standards for drinking and irrigation/fishery water, respectively, after being treated with crab shell particles.

Ethanol vapor-induced fabrication of colloidal crystals with controllable layers and photonic properties.

A novel fabrication method for colloidal crystals has been proposed for the first time in this research. In this method, a suspension droplet containing colloidal particles was first spread onto a glass substrate placed in an ethanol vapor environment, and then the droplet was extracted from its center. In that case, the contact angle of the droplet reduced and the contact line receded toward the center, during which the colloidal particles self-assembled and immobilized forming a 2D colloidal crystal film on the substrate upon drying the liquid film. Alternately spreading and drying of suspension films could construct fine multi-layers of colloidal crystals, while the ethanol fraction in the suspension would be used to control roughly but rapidly the layer numbers of colloidal crystals. It was also found that the photonic properties of resultant colloidal crystal films were elevated by increasing their thickness.