uyi Li

Covalent Triazine-Based Frameworks as Visible Light Photocatalysts for the Splitting of Water.

Covalent triazine-based frameworks (CTFs) with a graphene-like layered morphology have been controllably synthesized by the trifluoromethanesulfonic acid-catalyzed nitrile trimerization reactions at room temperature via selecting different monomers. Platinum nanoparticles are well dispersed in CTF-T1, which is ascribed to the synergistic effects of the coordination of triazine moieties and the nanoscale confinement effect of CTFs. CTF-T1 exhibits excellent photocatalytic activity and stability for H2 evolution in the presence of platinum under visible light irradiation (λ ≥ 420 nm). The activity and stability of CTF-T1 are comparable to those of g-C3 N4 . Importantly, as a result of the tailorable electronic and spatial structures of CTFs that can be achieved through the judicial selection of monomers, CTFs not only show great potential as organic semiconductor for photocatalysis but also may provide a molecular-level understanding of the inherent heterogeneous photocatalysis.

Sulfur-doped covalent triazine-based frameworks for enhanced photocatalytic hydrogen evolution from water under visible light

Here, we show for the first time that the photocatalytic activity of covalent triazine-based frameworks (CTFs) can be efficiently improved using a facile sulfur-doping approach. The sulfur-doped CTFs show superior photocatalytic activity and stability in hydrogen evolution from water under visible light irradiation over pristine CTFs and g-C3N4. The significantly improved catalytic efficiency was attributed to sulfur-doping in the frameworks, which results in enhanced adsorption of visible light, reduced recombination of free charge carriers, and rapid separation and transportation of photogenerated electron–holes.

Click-based porous organic framework containing chelating terdentate units and its application in hydrogenation of olefins

Click reaction of 2,6-diethynylpyridine and tetrakis(4-azidophenyl)methane gave rise to a porous organic framework containing chelating terdentate 2,6-bis(1,2,3-triazol-4-yl)pyridyl units (BTP-POF). BTP can serve as a promising linkage of an organic framework and as an effective stabilizer of palladium nanoparticles (NPs) owing to its structural preference and strong chelating ability with palladium. The well-dispersed palladium NPs in interior pores and external surface of BTP-POF were readily obtained, the NPs in interior pores have a small size and narrow size distribution; they show excellent catalytic activity, high stability and good reusability in palladium-catalyzed hydrogenation of olefins at 25 °C. The mean diameter of palladium NPs was increased from 1.8 to 2.5 nm after recycling for seven runs, but no obvious loss of catalytic activity and agglomeration of palladium NPs was observed. Mercury drop test, filtration experiment and ICP analysis suggest that Pd/BTP-POF is a heterogeneous catalytic system in the hydrogenation of olefins.

Facile Synthesis and Tunable Porosities of Imidazolium-Based Ionic Polymers that Contain In Situ Formed Palladium Nanoparticles

A series of porous imidazolium‐based ionic polymers that contain in situ formed Pd nanoparticles (Pd@PIPs) was synthesized by a Suzuki–Miyaura cross‐coupling reaction in the presence of SiO2 particles. The hierarchical porosities of Pd@PIPs can be regulated well by adjusting the dosage of SiO2. Pd nanoparticles are formed concomitantly and encapsulated uniformly within the pores of the polymers. The appropriate usage of SiO2 templates results in a clear enhancement of the catalytic activity in the hydrogenation of nitroarenes without the addition of extra Pd species. The excellent catalytic performances are attributed to abundant meso‐ and macropores that facilitate the mass transfer of substrates during catalytic reactions.

Hollow click-based porous organic polymers for heterogenization of [Ru(bpy)3]2+ through electrostatic interactions

A facile approach for the heterogenization of transition metal catalysts using non-covalent interactions in hollow click-based porous organic polymers (H-CPPs) is presented. A catalytically active cationic species, [Ru(bpy)3]2+ (bpy = 2,2’-bipyridyl), was immobilized in H-CPPs via electrostatic interactions. The intrinsic properties of [Ru(bpy)3]2+ were well retained. The resulting Rucontaining hollow polymers exhibited excellent catalytic activity, enhanced stability, and good recyclability when used for the oxidative hydroxylation of 4-methoxyphenylboronic acid to 4-methoxyphenol under visible-light irradiation. The attractive catalytic performance mainly resulted from efficient mass transfer and the maintenance of the chemical properties of the cationic Ru complex in the H-CPPs.

Enhanced electrochemical lithium storage activity of LiCrO2 by size effect

Cr8O21 was chemically lithiated using a lithium–biphenyl–dimethoxyethane solution. Lithiated Cr8O21 shows a structure in which as-formed LiCrO2 units are sandwiched between Cr2O3 superlattice layers. Chemically lithiated Cr8O21 shows a delithiation capacity of 200 mAh g−1. It means that LiCrO2 units in lithiated Cr8O21 are electrochemically active. This finding is opposite to previous reports that LiCrO2 materials have very poor Li-storage capacities. Our new result implies that LiCrO2 with extremely small domain size could show enhanced reactivity. This proposal is proved unambiguously by the fact that LiCrO2 powder materials with smaller grain size ( 50 nm). In addition, it is found that the cation mixing is more significantly in LiCrO2 materials with smaller grain size, which seems a key factor for the storage and transport of lithium in layered Cr-based materials. The cation mixing may also explain the result that the lattice parameters of LiCrO2 do not change significantly upon lithium extraction and insertion, investigated by in situ and ex situXRD techniques.

The cooperation effect in the Au–Pd/LDH for promoting photocatalytic selective oxidation of benzyl alcohol

Materials with different Au–Pd ratios bimetallic alloy nanoparticles (NPs) supported on MgAl–LDH (Au–Pd/LDH) were prepared by an impregnation–reduction method and developed as photocatalysts for the selective oxidation of benzyl alcohol to benzaldehyde under visible light irradiation. A typical sample (Au9–Pd1/LDH) showed efficient photocatalytic activity with 91.1% conversion and 99% selectivity. The conversion was greatly increased from 3.6% for Au/LDH and 1.5% for Pd/LDH, respectively. Moreover, it was four times higher than that for Au9–Pd1/TiO2. The ESR spectrum demonstrated that the main reactive species were superoxide radicals (O2˙−) generated by the transfer of hot electrons from the Au–Pd alloy NPs to the surface adsorbed molecular oxygen. The formation of hot electrons was attributed to localized surface plasmon resonance (LSPR) of the alloy NPs. Based on XPS analysis, a synergistic electron effect in the Au–Pd alloy was observed due to the transfer of electrons from Pd to Au atoms. This effect enhances the adsorption ability of Pd atoms to oxygen molecules and facilitates the formation of O2˙−. The results from CO2-TPD and in situ FT-IR analyses indicated that benzyl alcohol could be efficiently activated at the surface base sites on the LDH via surface coordination to form a metal-alkoxide intermediate. Here, the intermediate could be more easily oxidized by O2˙− to form benzaldehyde. Finally, a possible mechanism based on the cooperation effect between the alloy NPs and the surface basic sites on the LDH was proposed to illustrate the photocatalytic process.

Thin CuOx-based nanosheets for efficient phenol removal benefitting from structural memory and ion exchange of layered double oxides

Despite extensive efforts dedicated to researching two-dimensional (2D) transition metal oxides (TMOs), significant challenges still remain to simplify their synthesis and improve the activity and reusability of these materials. In this work, we prepared a 2D Cu-containing layered double oxide (CuLDO) under mild conditions. Only via stirring LDO in diluted Cu solution at room temperature could ion exchange between Mg in LDO and Cu ions from that solution allow fixing of Cu onto the surfaces of LDO nanosheets with good dispersion at a high density. The obtained CuLDO was then annealed to give CuOx-rich nanosheets (denoted as c-CuLDO), which maintained a thin thickness of 5–9 nm with a flowers-like architecture thanks to the structural memory of the source materials. The excellent morphology of CuOx-based nanosheets helped to avoid the restacking of nanosheets. Such a c-CuLDO outperformed many other reported Cu-based nanomaterials as a catalyst in phenol degradation (k = 0.335 min−1) because c-CuLDO could efficiently activate persulfate to generate abundant amounts of sulfate radical (SO4˙−). Furthermore, the catalytic activity of used c-CuLDO could be restored by a simple hydrothermal treatment. The developed chemistry could also be used to remove copper ions from wastewater, generating value-added Cu-based nanomaterials and eliminating waste at the same time. The current results may inspire the design of novel low dimensional nanomaterials that are difficult to synthesize directly by conventional bottom-up strategies.

MoS2 Quantum Dots-Modified Covalent Triazine-Based Frameworks for Enhanced Photocatalytic Hydrogen Evolution

MoS2 quantum dots (QDs)-modified covalent triazine-based framework (MoS2 /CTF) composites are synthesized through an in situ photodeposition method. MoS2 QDs are well distributed and stabilized on the layers of CTFs by coordination of the frameworks to MoS2 . The QDs-sheet interactions between MoS2 and CTFs facilitate interfacial charge transfer and separation. As a consequence, the composites exhibit outstanding photocatalytic activity and stability for hydrogen evolution under visible light irradiation (λ≥420 nm), that exceed those over pristine CTFs and MoS2 -modified g-C3 N4 (MoS2 /g-C3 N4 ) composite, making them promising materials for solar energy conversion.

Macromol. Rapid Commun. 20/2015

Frontispiece: A covalent triazine-based framework (CTF) possessing a graphene-like layered morphology demonstrates excellent photocatalytic activity and stability in splitting water under visible light irradiation. Due to the tailorable electronic and spatial structures of CTFs, they not only show great potential as organic semiconductors for photocatalysis but also provide a molecular-level understanding of the inherent heterogeneous photocatalysis. Further details can be found in the article by J. Bi,* W. Fang, L. Li, J. Wang, S. Liang, Y. He, M. Liu, and L. Wu* on page 1799.