Hexing Li

Synthesis of Ultralong Copper Nanowires for High-Performance Transparent Electrodes

Cu nanowires hold great promise for the fabrication of low-cost transparent electrodes. However, their current synthesis is mainly performed in aqueous media with poor nanowire dispersibility. We report herein the novel synthesis of ultralong single-crystalline Cu nanowires with excellent dispersibility, providing an excellent candidate material for high-performance transparent electrode fabrication.

High‐Performance Energy‐Storage Architectures from Carbon Nanotubes and Nanocrystal Building Blocks

High-performance energy-storage architectures are fabricated by forming conformal coatings of active nanocrystal building blocks on preformed carbon nanotube conductive scaffolds for lithium ion electrodes. This unique structure offers effective pathways for charge transport, high active-material loading, structure robustness, and flexibility. This general approach enables the fabrication of a new family of high-performance architectures for energy storage and many other applications.

Aqueous medium Ullmann reaction over a novel Pd/Ph-Al-MCM-41 as a new route of clean organic synthesis

By using the Ph- and Al-functionalized MCM-41 (Ph–Al-MCM-41) as a support, a new and powerful Pd/Ph–Al-MCM-41 catalyst was designed and used in iodobenzene (Ar–I) Ullmann coupling reaction with the attempt to develop new routes of clean organic synthesis by using water instead of organic solvents as the reaction medium. The as-prepared Pd/Ph–Al-MCM-41 exhibited higher activity, better selectivity to biphenyl (Ar–Ar) and stronger durability than other supported Pd catalysts and the maximum Ar–Ar yield reached 79.8% at the optimum Ph/Al/Si molar ratio (15/1/60). Meanwhile, the Pd/Ph–Al-MCM-41 catalyst could be recycled 5 times, indicating the good stability, especially good hydrothermal stability. According to various characterizations, such as FTIR, XRD, TEM, ICP, NMR, N2 sorption isotherms, the correlation of the catalytic performance to the structural characteristics of the Pd/Ph–Al-MCM-41 was discussed. Besides the high dispersion of Pd active sites on the surface and the easy diffusion in the pore channels of the Ph–Al-MCM-41 owing to the mesoporous structure, the higher activity of the Pd/Ph–Al-MCM-41 could be attributed to the increase of both the surface hydrophobicity resulting from Ph-modification and the surface Lewis acidity owing to the Al-modification, which were favorable for the adsorption of the Ar–I molecules, and thus enhanced the activity. The surface hydrophobicity could also account for the promotion on the selectivity to Ar–Ar by the Ph-modification, since less water could enter the pore channels, which was favorable for Ar–I dehalogenation to form the Ar–H byproduct. The promoting effect of the Al-modification on the selectivity was limited since the Lewis acidic site could adsorb Ar–I molecules in two modes, which were favorable for both the coupling reaction to form Ar–Ar and dehalogenation to form Ar–H. The hydrothermal stability test demonstrated that both the Ph-groups and Al-dopants could stabilize the mesoporous structure in aqueous solution, which could account for the strong durability of the Pd/Ph–Al-MCM-41 catalyst.

Water-medium isomerization of homoallylic alcohol over a Ru(II) organometallic complex immobilized on FDU-12 support

A novel Ru(II) organometallic catalyst with highly ordered cage-like mesoporous structure was prepared by coordinating the Ru(II) with the PPh2-ligand incorporated into the FDU-12 support (Ru–PPh2-FDU-12). During water-medium isomerization of 1-phenyl-3-buten-1-ol, the Ru–PPh2-FDU-12 exhibited almost the same activity and selectivity as the corresponding RuCl2(PPh3)3 homogenous catalyst and could be used for at least 5 repetitions, showing good potential for industrial application. The excellent performance of the Ru–PPh2-FDU-12 could be attributed to the high and uniform dispersion of the Ru(II) active sites on the FDU-12 support, the large size of both the pore entrance and pore cages, which facilitated the diffusion, the adsorption and the transformation of organic substrates on the catalyst surface. The decrease in the activity of the Ru–PPh2-FDU-12 after being used for 5 times could be mainly attributed to the decrease in the pore entrance size and the pore cage size rather than the leaching of the Ru(II) active species from the FDU-12 support.

Water-medium ullmann reaction over a highly active and selective Pd/Ph-SBA-15 catalyst

A series of Pd/Ph-SBA-15 catalysts with ordered mesoporous structure are designed by using the phenyl-functionalized SBA-15 (Ph-SBA-15) as supports. These catalysts exhibit higher activity and selectivity toward biphenyl than Pd/SiO2, Pd/MCM-41, Pd/Ph-MCM-41 and Pd/SBA-15 in a water-medium iodobenzene Ullmann coupling reaction. The promoting effects on the activity and selectivity could be mainly attributed to the high dispersion of Pd active sites, the ordered mesoporous channels and the strong surface hydrophobocity which facilitate the diffusion and/or adsorption of organic reactant molecules, especially in aqueous media. Meanwhile, the relatively large pore channels are favorable for the coupling of iodobenzene to form biphenyl, which is much bigger than the byproduct benzene resulting from the dehalogenation of iodobenzene. The Pd/Ph-SBA-15 catalyst could be separated easily from reaction products and used repetitively several times, showing the superiority over the homogeneous catalysts for industrial applications.

Self‐Assembly of Palladium Nanoparticles on Periodic Mesoporous Organosilica Using an In Situ Reduction Approach: Catalysts for Ullmann Reactions in Water

A Si--H functionalized phenyl-bridged periodic mesoporous organosilica [H-PMO(Ph)] is synthesized via a surfactant-directed assembly approach. Pd nanoparticles are then immobilized onto the PMO catalyst [Pd/H-PMO(Ph)] by a Si--H in situ reduction method. The Ullmann reaction, in water as medium, is used to investigate the catalytic performance of Pd/H-PMO(Ph). The results show that the Pd/H-PMO(Ph) catalyst has excellent catalytic activity and selectivity, which can be attributed to synergetic effects derived from the highly dispersed catalytic species and the hydrophobic microenvironments. Furthermore, the catalyst could be conveniently recovered and recycled five times without significant loss of activity and selectivity.