Graphene oxide (GO) membranes represent a next generation of high-flux, ultra-lightweight and energy-efficient membranes for molecular and ionic separation in aqueous solution. In this work, we fabricate free-standing GO membranes with tunable thickness via facile vacuum filtration process. The effect of electrostatic interaction on the separation performance of GO membrane for organic dyes was demonstrated. It is observed that GO is negatively charged in a wide pH range of 1-12 and its surface charge density significantly varied with pH of aqueous solution. The electronegative GO membrane exhibits much higher rejection rate for electronegative organic dyes than that for electropositive molecules. Furthermore, the rejection rate and the strength of electrostatic interaction are directly related. In addition, the rejection behaviors of GO membranes for inorganic salts with different charge or ionic strength are explored as well. The experimental data are fitted well with the theoretical model based on Donnan equilibrium. Our results indicate that GO membranes could be promising candidate for water treatment and desalination application. And adjusting the surface charge density of GO and filtrated molecules is an effective way to achieve high separation performance (e.g. rejection rate).

A series of chromium­(III) complexes, LCrCl3 (Cr1–Cr4: L = 2-(N-R2-benz­imidazol-2-yl)-6-(3,5-R1-pyrazol-1-yl)­pyridine; Cr1: R1 = H, R2 = H; Cr2: R1 = Me, R2 = H; Cr3: R1 = Me, R2 = Me; Cr4: R1 = Me, R2 = Bn), were synthesized and characterized by IR spectroscopy and elemental analysis. The studies of the solid state of Cr2 and Cr3 revealed distorted octahedral geometries around the chromium centers by X-ray diffractions. In the presence of MAO, Cr1–Cr4 exhibited high activities toward ethylene oligomerization (up to 2.17 × 106 g·mol–1(Cr)·h–1) and ethylene polymerization (up to 6.78 × 105 g·mol–1(Cr)·h–1). The oligomers were produced with high selectivity for α-olefins (>99%), confirmed by FT-IR and 13C NMR, and the distributions followed the Schulz–Flory equation. Various reaction parameters including the amount of cocatalyst, reaction temperature, and time were evaluated in detail, and it was evident that the title complexes had good thermal stability and the substituents on imidazole-N of the ligands dramatically impacted the catalytic activities as well as the distribution of the products.

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ABSTRACT：N,N′-Bis(2,6-R-phenyl)-2,6-pyridinedicarboxamide (L: R = Cl, L1; R = F, L2; R = H, L3; R = Me, L4; R = Et, L5; R = i Pr, L6) were designed as neutral ligands, and the corresponding nickel complexes LNiBr 2 (Ni1-Ni6) were synthesized as precatalysts for ethylene oligomerization. All new ligands were fully characterized by NMR, FT-IR spectra, and elemental analysis, while the nickel complexes were examined by FT-IR spectra and elemental analysis. The coordination mode of ligand with nickel in complexes Ni5 and Ni6 was tridentate by O^N^O as established by single crystal X-ray diffractions. All the nickel complexes Ni1-Ni6 were tested for ethylene oligomerization with different alkylaluminums as cocatalysts, and diethylaluminum chloride (Et 2 AlCl) was proved to be the most effective. Upon activation with Et 2 AlCl, all nickel complexes showed high catalytic activity (up to 7.55 × 10 5 g·mol -1 (Ni)·h -1 ·atm -1 ) with good selectivity for α-C 4 .