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Recently, the composite of spinel-type manganese oxide (λ-MnO 2 )/graphene has drawn wide attention because of its good electrochemical adsorption selectivity for low concentrations of Li + ions from lake brine or seawater to cope with the fast-rising demand of lithium resources. In this composite, the synergistic effect between the good selectivity of λ-MnO 2 for Li + ions and the excellent conductivity of graphene play an important role for the electrochemical adsorption of Li + ions. In order to reveal the synergistic mechanism in the electronic conductivity, the ionic conductivity and the ion selectivity of the λ-MnO 2 /graphene composite, density functional theory (DFT) calculations combined with electrochemical adsorption experiments were carried out. The calculation results show that the enhanced electronic conductivity of the composite is due to the decrease of the band gap (E g ) in the λ-MnO 2 /graphene composite compared with pure λ-MnO 2 . Meanwhile, the graphene composited with λ-MnO 2 decreased the diffusion energy barrier of Li + ions in λ-MnO 2 . In addition, the competitive adsorption of Li + , Na + and Mg 2+ ions were investigated by the nudged elastic band (NEB) method and charge distribution analysis. The results show that Li + ions in λ-MnO 2 exist in their pure ion state and have the lowest diffusion energy barrier compared with Na + and Mg 2+ . The results of the DFT calculations were validated by cyclic voltammetry, electrochemical impedance spectroscopy and electrochemical adsorption experiments.

The remarkable effect of divalent transition metal ions on the electrochemical performance of transition metal-based layered double hydroxides (LDHs) was systematically investigated via computational and experimental approaches. Ni3-xCoxAl-LDHs (x = 0, 1, 2, and 3) were synthesized on carbon paper by a unipolar pulse electrodeposition (UPED) method and used as electrodes in energy storage systems. The structures were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Their electrochemical performance was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The mechanism of different electrochemical performances with various divalent transition metal ions was investigated by the density functional theory (DFT) plus U method and molecular dynamics (MD) simulations. The computational and experimental data demonstrated that the electronic and ionic conductivity and deprotonation of NiAl-LDHs were improved by doping Co species, and the incorporation of Co and Ni cations enabled LDHs to exhibit a larger interlayer spacing which can facilitate the diffusion of OH- ions, indicating that NiCo2Al-LDHs had the highest specific capacitance.

The development of heterogeneous catalysts for the epimerization of sugars has received much less attention than that for the isomerization of sugars. To date, molybdates are the most effective catalysts for the epimerization of sugars, although they lack stability toward hydrolysis of their active sites in water. To solve the issue of the formation of a highly water-soluble heteropolyblue (PMo red ) for phosphomolybdates (PMos) in aqueous reaction systems, herein, a 1-butyl-3-methylimidazolium phosphomolybdate ([BMIM] 3 PMo 12 O 40 ) was synthesized through an ion-exchange method. This catalyst was effective and selective for the C2-epimerization of sugars under mild reaction conditions (<100 °C; 1-2 h) with good water-tolerant properties. The reaction was confirmed to occur in a heterogeneous manner and no leaching of PMo red was detected by means of UV/Vis spectroscopy. Moreover, the catalyst can be simply separated by filtration and reused for at least eight cycles without a drop in catalytic activity. XRD, FTIR, and X-ray photoelectron spectroscopy measurements indicate that the catalyst is stable under the reaction conditions. In a comparison of the catalytic activity and surface wettability with those of other PMo salts, that is, 1-ethyl-3-methylimidazolium phosphomolybdate ([EMIM] 3 PMo 12 O 40 ), 1-hexyl-3-methylimidazolium ([HexMIM] 3 PMo 12 O 40 ), [choline] 3 PMo 12 O 40 , and cetyltrimethylammonium phosphomolybdate ([CTA] 3 PMo 12 O 40 ), it is found that [BMIM] 3 PMo 12 O 40 has more appropriate hydrophobic-hydrophilic balance, which should be responsible for better catalytic activity and stability., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of new hydroxypyridine-based ionic liquids (ILs) are synthesized and applied in CO 2 capture through chemical absorption, in which one IL, i.e., tetrabutylphosphonium 2-hydroxypyridine ([P 4444 ][2-Op]), shows a viscosity as low as 193 cP with an absorption capacity as high as 1.20 mol CO 2 per mol IL. Because the traditional anion-CO 2 absorption mechanism cannot provide an explanation for the influences of cations and temperature on CO 2 absorption capacity, herein, a novel cation-participating absorption mechanism based on the proton transfer is proposed to explain the high absorption capacity and the existence of a turning point of absorption capacity with the increase of temperature for the capture of CO 2 using [P 4444 ][n-Op] (n = 2, 3, 4) ILs. Also, the relationship between the viscosity of ILs and the linear interaction energy is proposed for the first time, which can guide how to design and synthesize ILs with low viscosity. Quantum chemistry calculations, which are based on the comprehensive analysis of dipole moment, cation-anion interaction energy and surface electrostatic potential, indicate that the different viscosities of hydroxypyridine-based ILs and the changes after CO 2 absorption mainly resulted from the different distribution of negative charges in the anion.