High efficiency overall water splitting enabled by a hierarchical Ni–C structure derived from 2D MOF sheets without heteroatom doping.

No abstract

Water oxidation through the Mn4Ca-oxo complex in photosystem II has fascinated many researchers because of its high efficiency and low energy input; therefore, it has triggered great interest in various polymorphs of manganese oxides for electrocatalysis. Herein we report a facial ionic liquid (IL)-assisted [IL: 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4)] hydrothermal approach for tuning both crystallographic phase and nanostructure morphology of MnO2, enabling the excellent oxygen evolution reaction (OER) activity with an overpotential of 394 mV at 10 mA cm–2 and a Tafel slope of 49 mV dec–1. The roles of IL in the crystallographic and morphological transformation from β-MnO2 nanorods to α-MnO2 nanowires and in the OER are carefully scrutinized. TEM, EDX, FTIR, XPS characterizations all reveal the capping of IL cations on the surface of α-MnO2, where the amphiphilic nature, the electrostatic interaction, the steric hindrance, and the π–π stacking of IL cations collectively serve as entropic drivers for the templated growth of 2 × 2 tunnel structure incorporating K+ ions. This structure has been particularly beneficial for OER, owing to a concerted synergy from the nanostructured morphology, suitable tunnel structure with rich di-μ-oxo bridges, alkali-metal incorporation, as well as higher content of trivalent Mn3+. What’s more, our investigation indicates the surface-immobilized IL plays a crucial role toward efficient OER by facilitating the formation and stabilization of oxygen vacancies on the surface of α-MnO2 nanowires.

The adsorption behaviors of tea polyphenols (TP) on wool, silk, and nylon at pH 4.0 were investigated. The Langmuir-Nernst model had the best fitting to the adsorption isotherms. The analysis of adsorption mechanism suggested that the hydrogen bonding and electrostatic interactions operating between TP and fibers contribute to Langmuir adsorption, whereas other interactions (hydrophobic interaction and van der Waals forces) contribute to Nernst partition adsorption. Langmuir adsorption had greater contribution to total adsorption of TP on nylon, whereas partition adsorption imparted greater influence to TP adsorption on silk. In terms of the mordant dyeing of TP, silk and wool displayed much deeper color than nylon due to their higher content of the functional groups having the complex-forming ability, although they had lower adsorption capability for TP than nylon. The colors of the dyed fabrics mordanted with different metallic salts as well as their depth, were greatly dependent on the chemical nature of mordants and fibers, the metal ion-TP-fiber complexforming ability, and the related complex structure.

No abstract

The real-time conformational changes of cytosine (C)-rich ssDNA oligonucleotides upon binding with silver ions (Ag(+)) were studied using dual polarization interferometry (DPI). Upon the addition of Ag(+), Ag(+) selectively bound to cytosine-cytosine mismatches and formed C-Ag(+)-C complexes, inducing change of the structure of the C-rich ssDNA from random coil conformation to duplex conformation, whereas the control ssDNA without cytosine-cytosine mismatches had no such signal, which was consistent with circular dichroism (CD) characterization. The conformational change of DNA was reflected on the changes of the mass, thickness, and density values resolved by DPI. The calibration curves showed that as the concentration of Ag(+) increased from 10 nM to 8 μM, the thickness and mass values increased linearly while the density values decreased linearly. Other metal ions such as K(+), Ca(2+), Na(+), Mg(2+), Zn(2+), Mn(2+), Ni(2+), and Pb(2+) did not interfere with the interaction between Ag(+) and C-rich ssDNA, indicating that this method had a good selectivity. The practical application of this biosensor was also investigated in real samples such as drinking water. Besides, cysteine could specifically capture Ag(+) from C-Ag(+)-C complexes and transformed the structure of the C-rich DNA back from rigid double-stranded conformation to random coil conformation, which allowed cysteine to be detected selectively as well. It is expected that this biosensing strategy may be utilized to study the interaction of DNA with other molecules.

We realize the crossover from PTE to NTE by removing the excess fluorines in TiZrF7−x.

Scandium trifluoride (ScF3), adopting a cubic ReO3-type structure at ambient pressure, undergoes a pronounced negative thermal expansion (NTE) over a wide range of temperatures (10 K–1100 K). Here, we report the size effects on the NTE properties of ScF3. The magnitude of NTE is reduced with diminishing the crystal size. As revealed by the specific heat measurement, the low-energy phonon vibrations which account for the NTE behavior are stiffened as the crystal size decreases. With decreasing the crystal size, the peaks in high-energy X-ray pair distribution function (PDF) become broad, which cannot be illuminated by local symmetry breaking. Instead, the broadened PDF peaks are strongly indicative of enhanced atomic displacements which are suggested to be responsible for the stiffening of NTE-related lattice vibrations. The present study suggests that the NTE properties of ReO3-type and other open-framework materials can be effectively adjusted by controlling the crystal size.