Confinement Effect and 3D Design Endow Unsaturated Single Ni Atoms with Ultrahigh Stability and Selectivity toward CO2 Electroreduction.

Developing single-atomic catalysts with superior selectivity and outstanding stability for CO2 electroreduction is desperately required but still challenging. Herein, confinement strategy and three-dimensional (3D) nanoporous structure design strategy are combined to construct unsaturated single Ni sites (Ni-N3) stabilized by pyridinic N-rich interconnected carbon nanosheets. The confinement agent chitosan and its strong interaction with g-C3N4 nanosheet are effective for dispersing Ni and restraining their agglomeration during pyrolysis, resulting in ultrastable Ni single-atom catalyst. Due to the confinement effect and structure advantage, such designed catalyst exhibits a nearly 100% selectivity and remarkable stability for CO2 electroreduction to CO, exceeding most reported state-of-the-art catalysts. Specifically, the CO Faradaic efficiency (FECO) maintains above 90% over a broad potential range (-0.55 to -0.95 V vs. RHE) and reaches a maximum value of 99.6% at a relatively low potential of -0.67 V. More importantly, the FECO is kept above 95% within a long-term 100 h electrolyzing. Density functional theory (DFT) calculations explain the high selectivity for CO generation is due to the high energy barrier required for hydrogen evolution on the unsaturated Ni-N3. This work provides a new designing strategy for the construction of ultrastable and highly selective single-atom catalysts for efficient CO2 conversion.

Preparation and Adsorption Properties of MCM-41 with Novel Gemini Ionic Liquid Surfactants as Template.

A mesoporous molecular sieve was prepared by the hydrothermal synthesis method with symmetric Gemini surfactant 1,3-bis(hexadecyldimethylammonio)-propane dibromide, symmetric Gemini ionic liquid surfactant 1,3-bis(3-hexadecylimidazolium-1-yl) propane dibromide and self-designed asymmetric Gemini ionic liquid surfactant 1-(3-(hexadecyldimethylammonio)prop-1-yl)-3-hexadecylimidazolium dibromide as the template agent. The structure characterization results for mesoporous molecular sieves show that the material possesses a hexagonal pore structure with uniform channels. The mesoporous silica that was synthesized with self-designed asymmetric Gemini ionic liquid surfactant as the template agent possesses the largest surface area and its pore size and specific surface area are, respectively, 3.28 nm and 879.37 m2/g. The adsorption properties of the prepared MCM-41 for crystal violet were investigated, and the adsorption thermodynamics and kinetics were investigated. The results show that adsorption equilibrium can be reached under pH = 9 and 35 °C for 50 min, and the quantity of adsorption can reach up to 464.21 mg/g. The adsorption process belongs to Langmuir isothermal adsorption, conforming to second-order adsorption kinetics, and the adsorption process is an endothermic process.

{4-Bromo-2-[2-(piperidin-1-ium-1yl)ethyl-iminometh-yl]phenolato}diiodido-zinc(II).

In the title complex, [ZnI(2)(C(14)H(19)BrN(2)O)], the Zn(II) atom is four-coordinated by the imine N and phenolate O atoms of the Schiff base ligand and by two iodide ions in a distorted tetra-hedral coordination. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming chains running along the b axis.

Diiodido[N'-(2-methoxy-benzyl-idene)-N,N-dimethyl-ethane-1,2-diamine]zinc(II).

In the title complex, [Zn(C(12)H(18)N(2)O)I(2)], the Zn(II) ion is four-coordinated by the imine N and amine N atoms of the Schiff base ligand and by two iodide ions in a distorted tetra-hedral coordination.

{4-Bromo-2-[3-(diethyl-ammonio)propyl-imino-meth-yl]phenolato}diiodidozinc(II) methanol solvate.

In the title complex, [ZnI(2)(C(14)H(21)BrN(2)O)]·CH(3)OH, the asymmetric unit consists of a mononuclear zinc(II) complex mol-ecule and a methanol solvent mol-ecule. The compound was derived from the zwitterionic form of the Schiff base 4-bromo-2-[3-(diethyl-amino)propyl-imino-meth-yl]phenol. The Zn(II) atom is four-coordinated by the imine N and phenolate O atoms of the Schiff base ligand and by two iodide ions in a distorted tetra-hedral coordination. In the crystal structure, the methanol mol-ecules are linked to the Schiff base mol-ecules through N-H⋯O and O-H⋯O hydrogen bonds. One I atom is disordered over two positions in a 0.702 (19):0.298 (19) ratio.

Diiodido{4-nitro-2-[2-(piperidin-1-yl)ethyl-imino-meth-yl]phenolato}zinc(II).

In the title complex, [ZnI(2)(C(14)H(19)N(3)O(3))], the Zn(II) atom is four-coordinated by the imine N and phenolate O atoms of the Schiff base ligand, and by two iodide ions in a distorted tetra-hedral coordination. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming dimers.

{(E)-2-[3-(Dimethyl-ammonio)propyl-iminometh-yl]phenolato}diiodidozinc(II).

The title complex, [ZnI(2)(C(12)H(18)N(2)O)], is a mononuclear zinc(II) compound derived from the zwitterionic form of the Schiff base (E)-2-[(3-dimethyl-amino-propyl-imino)meth-yl]phenol. The Zn(II) atom is four-coordinated by the imine N and phenolate O atoms of the Schiff base ligand, and by two iodide ions in a tetra-hedral coordination geometry. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming chains running along the b axis.

Dibromido{(E)-2-eth-oxy-6-[3-(methyl-ammonio)propyl-iminometh-yl]phenol-ato}zinc(II).

The title complex, [ZnBr(2)(C(13)H(20)N(2)O(2))], is a mononuclear zinc(II) compound derived from the zwitterionic form of the Schiff base (E)-2-eth-oxy-6-((3-(methyl-amino)propyl-imino)meth-yl)phenol. The Zn(II) atom is four-coordinated by the imine N and phenolate O atoms of the Schiff base ligand, and by two bromide ions, in a tetra-hedral coordination geometry. Adjacent mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming chains running along the b axis.

Dibromido[N-propyl-N'-(2-pyridylmethyl-idene)ethane-1,2-diamine]zinc(II).

The title complex, [ZnBr(2)(C(11)H(17)N(3))], is a mononuclear zinc(II) compound derived from the Schiff base N-propyl-N'-(1-pyridin-2-ylmethyl-idene)ethane-1,2-diamine. The Zn(II) atom is five-coordinate, binding to the imine N, pyridine N, and amine N atoms of the Schiff base ligand and to two bromide anions in a distorted trigonal-bipyramidal coordination geometry. Adjacent mol-ecules are linked through inter-molecular N-H⋯Br hydrogen bonds, forming dimers.

Bis{(E)-2-eth-oxy-6-[2-(ethyl-ammonio)ethyl-iminometh-yl]phenolato}nickel(II) bis(perchlorate).

In the title centrosymmetric mononuclear nickel(II) complex, [Ni(C(13)H(20)N(2)O(2))(2)](ClO(4))(2), the Ni(II) atom is four-coordinated by the imine N and phenolate O atoms of the zwitterionic forms of two Schiff base ligands in a square-planar coordination geometry. In the crystal structure, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming chains running along the a axis.

Synthesis and properties of novel ammonium-based room-temperature gemini ionic liquids.

Ammonium-based room-temperature asymmetrical gemini ionic liquids, 1-trimethylammonium-3-(pyridinium)propane bisdicyanamide ([N111C3Py][DCA]2) and 1-trimethylammonium-3-(1-methylpiperidinium)propane bisdicyanamide ([N111C3MPi][DCA]2) were respectively synthesized and structurally characterized by 1H NMR and 13C NMR. Thermal stability of the gemini ionic liquids was determined by thermogravimetric analysis under a pure nitrogen atmosphere. Densities and viscosities of pure GILs and their binary mixtures with acetonitrile (MeCN) were investigated over the entire range of mole fractions at various temperatures, from 288.15 to 333.15 K, under atmospheric pressure. Moreover, the excess molar volumes (V E m) and the viscosity deviations (Δη) of the binary mixtures were evaluated and well fitted to the Redlich-Kister polynomial expression. The negative values of V E m and Δη result from strong self-association and interaction between the gemini ionic liquid molecules and MeCN. Results are discussed in terms of molecular interactions and structures.

[Determination of solubility parameters for asymmetrical dicationic ionic liquids by inverse gas chromatography].

Inverse gas chromatographic (IGC) technology was used to determine the solubility parameters of three asymmetrical dicationic ionic liquids ([ PyC5Pi] [ NTf2]2, [MpC5Pi] [NTf2]2 and [PyC6Pi] [NTf2]2) at 343.15-363.15 K. Five alkanes were applied as test probes including octane (n-C8) , decane (n-C10), dodecane (n-C12), tetradecane (n-C14), hexadecane (n-C16). Some thermodynamic parameters were obtained by IGC data analysis, such as the specific retention volumes of the solvents (V0(g)), the molar enthalpies of sorption (ΔHs(1)), the partial molar enthalpies of mixing at infinite dilution (ΔH∞91)), the molar enthalpies of vaporization (ΔH)v)), the activity coefficients at infinite dilution (Ω∞(1)), and Flory-Huggins interaction parameters (χ∞(12)) between ionic liquids and probes. The solubility parameters (δ2) of the three dicationic ionic liquids at room temperature (298.15 K) were 28.52-32.66 (J x cm(-3)) ½. The solubility parameters (δ2) of cationic structure with 4-methyl morpholine are bigger than those of the cationic structure with pyridine. The bigger the solubility parameter (δ2) is, the more the carbon numbers of linking group of the ionic liquids are. The results are of great importance to the study of the solution behavior and the applications of ionic liquid.

[Determination of solubility parameter for dicationic ionic liquid by inverse gas chromatography].

An inverse gas chromatographic method has been used to measure the solubility parameter of the dicationic ionic liquid, 1,10-bis(3-methylimidazolium-1-yl) decane hexafluorophosphate [C10(MIM)2][PF6]2, at the absolute temperatures from 343.15 K to 363.15 K. The test probe solvents were n-octane, n-dodecane, n-tetradecane, and n-hexadecane. The specific retention volumes of the solvents (Vg(0)), the molar enthalpy of sorption (DeltaH1(S)), the partial molar enthalpy of mixing at infinite dilution (DeltaH1(infinity)), the molar enthalpy of vaporization (DeltaHv), the activity coefficients at infinite dilution (gamma12(infinity)), Flory-Huggins interaction parameters (chi12(infinity)) between [C10(MIM)][PF6]2 and probe solvents were obtained. parameter (delta2) of [C10(MIM)2][PF6]2 was determined as 15.01 (J x cm(-3))(1/2), which was of great importance to the study of the solution behavior and application for ionic liquid.