Huaixia Zhao

Facile Fabrication of Ultrafine Palladium Nanoparticles with Size- and Location-Control in Click-Based Porous Organic Polymers

Two click-based porous organic polymers (CPP-1 and CPP-2) are readily synthesized through a click reaction. Using CPP-1 and CPP-2 as supports, palladium nanoparticles (NPs) with uniform and dual distributions were prepared through H2 and NaBH4 reduction routes, respectively. Ultrafine palladium NPs are effectively immobilized in the interior cavities of polymers. The coordination of 1,2,3-triazolyl to palladium and the confinement effect of polymers on palladium NPs are verified by solid-state (13)C NMR and IR spectra, XPS analyses, EDX mapping, and computational calculation. The steric and electronic properties of polymers have a considerable influence on the interaction between polymers and palladium NPs, as well as the catalytic performances of NPs. The ultrafine palladium NPs with uniform distribution exhibit superior stability and recyclability over palladium NPs with dual distributions and palladium on charcoal in the hydrogenation of nitroarenes, and no obvious agglomeration and loss of catalytic activity were observed after recycling several times. The excellent performances mainly result from synergetic effects between palladium NPs and polymers.

Shape-Controllable Formation of Poly-imidazolium Salts for Stable Palladium N -Heterocyclic Carbene Polymers

The imidazolium-based main-chain organic polymers are one of promising platforms in heterogeneous catalysis, the size and outer morphology of polymer particles are known to have important effects on their physical properties and catalytic applications, but main-chain ionic polymers usually generate amorphous or spherical particles. Herein, we presented a versatile and facile synthetic route for size- and shape-controllable synthesis of main-chain poly-imidazolium particles. The wire-shaped, spherical and ribbon-shaped morphologies of poly-imidazolium particles were readily synthesized through quaternization of bis-(imidazol-1-yl)methane and 2,4,6-tris(4-(bromomethyl)phenyl)-1,3,5-triazine, and the modification of their size and morphology were realized through adjusting solvent polarity, solubility, concentration and temperatures. The direct complexation of the particles with Pd(OAc)2 produced ionic polymers containing palladium N-heterocyclic carbene units (NHCs) with intactness of original morphologies. The particle morphologies have a significant effect on catalytic performances. Wire-shaped palladium-NHC polymer shows excellent catalytic activity and recyclabilty in heterogeneous Suzuki-Miyaura cross-coupling reaction.

Spatial control of palladium nanoparticles in flexible click-based porous organic polymers for hydrogenation of olefins and nitrobenzene

Two flexible click-based porous organic polymers (CPP-F1 and CPP-F2) have been readily synthesized. SEM images show CPP-F1 is a 3D network, while CPP-F2 exhibits a granular morphology. Pd(OAc)2 can be easily incorporated into CPP-F1 and CPP-F2 to form Pd@CPP-F1 and Pd@CPP-F2, respectively. The interactions between the polymers and palladium are confirmed by solid-state 13C NMR, IR and XPS. Palladium nanoparticles (NPs) are formed after hydrogenation of olefins and nitrobenzene. Palladium NPs in CPP-F1 are well dispersed on the external surface of the polymer, while palladium NPs in CPP-F2 are located in the interior pores and on the external surface. In comparison with NPs in CPP-F1, the dual distribution of palladium NPs in CPP-F2 results in higher selectivity in the hydrogenation of 1,3-cyclohexadiene to cyclohexane. The catalytic systems can be recycled several times without obvious loss of catalytic activity or agglomeration of palladium NPs. Hot filtration, mercury drop tests and ICP analyses suggest that the catalytic systems proceed via a heterogeneous pathway.

A durable luminescent ionic polymer for rapid detection and efficient removal of toxic Cr2O72

A durable luminescent imidazolium-based main-chain ionic polymer (IMIP-Br) was prepared by a facile quaternization reaction of tri(4-imidazolylphenyl)amine and 1,2,4,5-tetrakis(bromomethyl)benzene. IMIP-Br can not only detect Cr2O72− rapidly and estimate its concentration in water, but also capture Cr2O72− quickly via anion exchange. The tremendous exchange capacity of 318 mg g−1 and remarkable efficiency of 92.6% are achieved using an equivalent amount of IMIP-Br. The separation and recycling procedures are simplified by the integration of Fe3O4 particles and IMIP-Br. The resultant IMIP-Fe shows outstanding enrichment ability, good regenerative ability and superior recyclability for removal of Cr2O72−. The combination of promising removal performances and simple magnetic separation endows IMIP-Fe with great promises for capture and separation of Cr2O72− from contaminated water systems.

Solvent-mediated crystal-to-crystal transformations from a cationic homometallic metal–organic framework to heterometallic frameworks

Two unprecedented heterometallic metal–organic frameworks (MOFs), Ag2(btr)2Cr2O7·0.5H2O (1) and Ag9(btr)6(Cr2O7)4·PF6·6H2O (2) [btr = 4,4′-bis(1,2,4-triazole)], were synthesized through crystal-to-crystal transformation when the monometallic MOF Ag2(btr)2·2ClO4·3H2O was immersed in the aqueous solutions of KPF6–K2Cr2O7 and NaBF4–K2Cr2O7, respectively. The transformation follows a solvent-mediated anion-induced mechanism through the dissolution–reaction–crystallization process. Single-crystal X-ray diffraction analyses reveal that both 1 and 2 are three-dimensional structures based on Ag+, Cr2O72− and btr. In 1, Cr2O72− adopts a bidentate bridging mode, and Ag+ ions are linked by Cr2O72− and btr into a neutral framework. However, Cr2O72− in 2 exhibits two types of unprecedented bridging modes through bridging four and five Ag+ ions. Ag+ ions in 2 are bridged by Cr2O72− and btr to form a cationic framework. The non-coordinated BF4−/PF6− anions show a structure-directing effect during the crystal-to-crystal transformations and can be considered as structure-directing agents. The second-harmonic-generation (SHG) measurement shows that 1 is a non-linear optical complex.

Solvent‐Induced Facile Synthesis of Cubic‐, Spherical‐, and Honeycomb‐Shape Palladium N‐Heterocyclic Carbene Particles and Catalytic Applications in Cyanosilylation

The facile synthesis of palladium N-heterocyclic carbene (NHC) particles with spherical, cubic, and honeycomb morphologies is accomplished. The structures of cubic and honeycomb particles are defined as an unprecedented trinuclear palladium-NHC complex. An obvious effect of particle morphologies on catalytic activity and recyclability is observed in hetero-geneous cyanosilylation.