He-Kuan Luo

Engineering organic macrocycles and cages: versatile bonding approaches.

The emergence of supramolecular chemistry has led to the discovery of a rising number of macrocycles and cages with a range of functionalities. Most of these supramolecular aggregates are metal coordination networks, whereas pure organic assemblies are less developed. Organic macrocycles and cages have the advantages of chemical robustness, processability in organic solvents, and suitability for pilot-scale applications. They are constructed primarily from covalent bonds, with irreversible and reversible bond types. We herein highlight the use of different versatile bonding approaches in engineering these soft materials, as well as their emerging applications, such as gas storage, thin films, liquid crystals, and catalysis.

Studies on highly efficient promoters for titanium-based Ziegler–Natta catalyst for ethylene polymerization

Abstract Three kinds of organohalides, including alicyclic halocarbons, aromatic halocarbons and aliphatic halocarbons, were studied as promoters for titanium-based Ziegler–Natta catalysts. The results showed that these three kinds of organohalides all have high activity promotion for titanium-based Ziegler–Natta catalyst. Chloro-cyclohexane (C 6 H 11 Cl), chlorobenzene (C 6 H 5 Cl), Cl–(CH 2 ) 5 –Cl, CF 2 ClCFCl 2 have very high promotion effect; with these as promoters the activity could be increased by over two times. The promoters could be added into the autoclave individually, or first blended with AlEt 3 solution, then added together into the autoclave.

Studies on new palladium(II) catalyst system for copolymerization of CO with ethylene

Abstract In this paper, a new class of four-membered catalyst system, PdCl2/MAn/DPPP1/CF3COOH, was firstly studied for copolymerization of CO with ethylene to prepare linear alternating polyketone, in which MAn component was mainly studied. The experimental results showed that this kind of new catalyst system exhibited highly efficient activity; especially when Cd(OAc)2·2H2O, Zn(OAc)2·4H2O, Fe(ClO4)3·9H2O, Pb(OAc)2·3H2O and Cu(OAc)2·H2O were used as MAn component, the corresponding catalyst system had very highly efficient activity of 8100, 7100, 6000, 6000 and 5800 g polyketone/(g Pd h), respectively, under conditions of 6.5 MPa and 110°C. The effects of MAn component were also investigated; the results showed that suitable MAn was probably a metal compound of weakly coordinating anions; Mn+ probably coordinated with Cl− more strongly than palladium(II); the stability of chelate complex (c) of Mn+ with DPPP was probably between mono-chelate ring and bis-chelate ring complexes of palladium(II) with DPPP. This new highly efficient catalyst system had the advantages of having high stability and low cost.

Amorphous ruthenium nanoparticles for enhanced electrochemical water splitting

This paper demonstrates an optimized fabrication of amorphous Ru nanoparticles through annealing at various temperatures ranging from 150 to 700 °C, which are used as water oxidation catalyst for effective electrochemical water splitting under a low overpotential of less than 300 mV. The amorphous Ru nanoparticles with short-range ordered structure exhibit an optimal and stable electrocatalytic activity after annealing at 250 °C. Interestingly, a small quantity of such Ru nanoparticles in a thin film on fluorine-doped tin oxide glass is also effectively driven by a conventional crystalline silicon solar cell that has excellent capability for harvesting visible light. Remarkably, it achieves an overall solar-to-hydrogen efficiency of 11.3% in acidic electrolyte.

Effect of La-Doping on optical bandgap and photoelectrochemical performance of hematite nanostructures

La-doped hematite nanotubes are fabricated by electrospinning of a sol–gel solution consisting of La(III) acetylacetonate hydrate/polyvinylpyrrolidone(PVP)/ferric acetylacetonate, and subsequent sintering at 500 °C for 5 h in air. Further grinding of these nanotubes affords La-doped hematite nanoparticles. FESEM EDX indicates that the La content is 3.66 mol% in La-doped hematite. HRTEM and XRD reveal that La3+ cations are doped into the hematite crystal lattice. UV-Vis diffuse reflectance shows increased light absorption for La-doped hematite, with the bandgap reduced from 2.58 eV to 2.46 eV. EIS and four-probe characterization demonstrate that La-doping reduces charge transfer resistance and increases the electrical conductivity, thus leading to improved charge transportation. Photoelectrochemical (PEC) water splitting studies show that under 100 mW cm−2 simulated solar irradiation, La-doped hematite nanoparticles demonstrate a net photocurrent density up to 0.112 and 0.270 mA cm−2 at 1.23 and 1.60 V vs. RHE, which are 187% and 63% higher than pristine hematite nanoparticles, respectively. The effect of La-doping on improving electrical conductivity, light absorption, and PEC performance is mainly attributed to the intensification of crystal orientation along the (110) plane and the lattice expansion caused by the La3+ cations, which have much larger radii and are more electron-rich than Fe3+.

Novel Au/La-SrTiO3 microspheres: Superimposed Effect of Gold Nanoparticles and Lanthanum Doping in Photocatalysis

Novel multielement Au/La-SrTiO(3) microspheres were synthesized by a solvothermal method using monodisperse gold and La-SrTiO(3) nanocrystals as building blocks. The porous Au/La-SrTiO(3) microspheres had a large surface area of 94.6 m(2)  g(-1). The stable confined Au nanoparticles demonstrated strong surface plasmon resonance effect, leading to enhanced absorption in a broad UV/Vis/NIR range. Doping of rare-earth metal La also broadened the absorption band to the visible region. Both the conduction and valence bands of Au/La-SrTiO(3) microspheres thus show favorable potential for proton reduction under visible light. The superimposed effect of Au nanoparticles and La doping in Au/La-SrTiO(3) microspheres led to high photocurrent density in photoelectrochemical water splitting and good photocatalytic activity in photodegradation of rhodamine B. The photocatalytic activities are in the order of the following: Au/La-SrTiO(3) microspheres>Au/SrTiO(3) microspheres>La-SrTiO(3) microspheres>SrTiO(3) microspheres.

A binary catalyst system of a cationic Ru-CNC pincer complex with an alkali metal salt for selective hydroboration of carbon dioxide

Binary catalyst systems comprising a cationic Ru-CNC pincer complex and an alkali metal salt were developed for selective hydroboration of CO2 utilizing pinacolborane at r.t. and 1 atm CO2, with the combination of [Ru(CNCBn)(CO)2(H)][PF6] and KOCO2tBu producing formoxyborane in 76% yield. A bicyclic catalytic mechanism was proposed and discussed.

How Does Substitutional Doping Affect Visible Light Absorption in a Series of Homodisperse Ti11 Polyoxotitanate Nanoparticles—A Comment on the Band Gap Determination of the FeII Cages (Chem. Eur. J. 2015, 21, 11538)

There is no experimental support for the conclusion by Coppens and Chen in a recent paper that the (HOMO-LUMO) band gaps in a series of Fe(II) polyoxotitanate cages are in the range 1.43-1.59 eV.

2,5-dimethyl-3,6-bis[(2,6-diisopropylphenylimino)methyl]- and 2,6-bis[(2,6-diisopropylphenylimino)methyl]pyrazine: Two new chelating ligands for transition metal complexes

The reaction of tetramethylpyrazine with SeO2 yields 2,5-dimethylpyrazine-3,6-dicarboxaldehyde (1) from which the 2,5-dimethyl-3,6-bis[(2,6-diisopropylphenylimino)methyl]pyrazine (2) was synthesized by treatment with 2 equivalents of 2,6-diisopropylaniline. 2,6-Dimethylpyrazine reacts with benzaldehyde to give 2,6-distyrylpyrazine (3). Ozonolysis of 3, followed by treatment with Na2SO3 and 2,6-diisopropylaniline resulted in the formation of 2,6-bis[(2,6-diisopropylphenylimino) methyl]pyrazine (5) together with [(2,6-diisopropylphenylimino)methyl]benzene (6).

Transformation of CO2 to Value-Added Materials

Carbon dioxide (CO2) is an attractive C1 resource because it is cheap and abundant and its more extensive use would be beneficial for the environment. However, its high thermodynamic stability and poor reactivity have seriously limited its utilization as a ready carbon source. The scientific challenges facing CO2 transformation are accordingly very attractive. This paper summarizes recent advances made in transformation of CO2 to value-added high-molecular-weight materials such as polymers, star-shaped molecules and nanocarbons.