Wenjun Dong

Synthesis of confined Ag nanowires within mesoporous silica via double solvent technique and their catalytic properties.

Ag nanowires within the channels of mesoporous silica have been successfully synthesized via a double solvent technique, in which n-hexane is used as a hydrophobic solvent to disperse mesoporous silica and an AgNO(3) aqueous solution is used as a hydrophilic solvent to fill mesochannels. The morphology of the obtained Ag (nanowires, nanoparticles or nanorods) can be controlled by adjusting the concentration of AgNO(3) solution and the template pore size. HRTEM images demonstrate extensive Ag nanowires with several to tens of hundreds nanometers in length are deposited along the long axis of mesochannels when the atomic AgNO(3)/Si ratio is 0.090. When the atomic AgNO(3)/Si ratio is 0.068 or 0.11, there is a combination of Ag nanoparticles and nanowires; nanoparticles are mainly formed when the atomic AgNO(3)/Si ratio is higher than 0.14. Further, the catalytic results of the oxidation of styrene show that styrene oxide and benzaldehyde are the main products of the reaction, and the morphology and diversity of Ag in Ag/mesoporous silica composites have an effect on the conversion of styrene and selectivity of styrene oxide.

Facile Hydrogen-Bond-Assisted Polymerization and Immobilization Method to Synthesize Hierarchical Fe3O4@Poly(4-vinylpyridine-co-divinylbenzene)@Au Nanostructures and Their Catalytic Applications

Hierarchical Fe3O4@poly(4-vinylpyridine-co-divinylbenzene)@Au (Fe3O4@P(4-VP-DVB)@Au) nanostructures were fabricated successfully by means of a facile two-step synthesis process. In this study, well-defined core-shell Fe3O4@P(4-VP-DVB) microspheres were first prepared with a simple polymerization method, in which 4-VP was easily polymerized on the surface of Fe3O4 nanoparticles by means of strong hydrogen-bond interactions between -COOH groups on poly(acrylic acid)-modified Fe3O4 nanoparticles and a 4-VP monomer. HAuCl4 was adsorbed on the chains of a P(4-VP) shell and then reduced to Au nanoparticles by NaBH4, which were embedded into the P(4-VP) shell of the composite microspheres to finally form the Fe3O4@P(4-VP-DVB)@Au nanostructures. The obtained Fe3O4@P(4-VP-DVB)@Au catalysts with different Au loadings were applied in the reduction of 4-nitrophenol (4-NP) and exhibited excellent catalytic activity (up to 3025 h(-1) of turnover frequency), facile magnetic separation (up to 31.9 emu g(-1) of specific saturation magnetization), and good durability (over 98 % of conversion of 4-NP after ten runs of recyclable catalysis and almost negligible leaching of Au).

Synthesis and self-assembly of large-area Cu nanosheets and their application as an aqueous conductive ink on flexible electronics.

Large-area Cu nanosheets are synthesized by a strategy of Cu nanocrystal self-assembly, and then aqueous conductive Cu nanosheet ink is successfully prepared for direct writing on the conductive circuits of flexible electronics. The Cu nanocrystals, as building blocks, self-assemble along the [111] direction and grow into large-area nanosheets approximately 30-100 μm in diameter and a few hundred nanometers in thickness. The laminar stackable patterns of the Cu nanosheet circuits increase the contact area of the Cu nanosheets and improve the stability of the conductor under stress, the result being that the Cu nanosheet circuits display excellent conductive performance during repeated folding and unfolding. Moreover, heterostructures of Ag nanoparticle-coated Cu nanosheets are created to improve the thermal stability of the nanosheet circuits at high temperatures.

Co( ii ) complexes loaded into metal–organic frameworks as efficient heterogeneous catalysts for aerobic epoxidation of olefins

A series of efficient cobalt(II)-anchored Cr-MOF (Cr-MIL-101-NH2) catalysts, such as Co(II)@Cr-MIL-101-Sal, Co(II)@Cr-MIL-101-P2I and Co(II)@Cr-MIL-101-P3I, have been successfully synthesized by one-pot modification of the terminal amino group with salicylaldehyde, pyridine-2-aldehyde or pyridine-3-aldehyde and anchoring of Co(II) ions into the mesoporous Cr-MOF supports. The Co(II)@Cr-MIL-101-P2I catalyst exhibited high catalytic performance for epoxidation of olefins with air as an oxidant due to the nitrogen atom in the pyridine ring as a strong electron-withdrawing substituent, high dispersion of Co(II) species and high surface area for sufficient contact between the substrate and active sites. The strong coordination interaction between the Co(II) ions and chelating groups in the Co(II)@Cr-MIL-101-P2I catalyst guaranteed the excellent recycling performance. Furthermore, the synthesized Co(II)@Cr-MIL-101-P2I catalyst realized its general applicability towards various olefins, such as cyclic olefins, tri-substituted olefins, aliphatic olefins and aromatic olefins.

Heterogeneous Fe-MIL-101 catalysts for efficient one-pot four-component coupling synthesis of highly substituted pyrroles

Four-component coupling reactions (4CRs) of 1,3-dicarbonyl compounds, amines, aldehydes and nitromethane have been carried out for substituted pyrroles using iron-containing metal organic frameworks (MOFs) as heterogeneous catalysts. Due to its higher surface area and larger pore size, the Fe-MIL-101 catalyst exhibits higher activity than that of Fe-MIL-88B and Fe-MIL-53. The reusability and heterogeneity of the Fe-MIL-101 catalyst was investigated, and no significant reduction of its catalytic activity was observed over five cycles reaction.

Highly efficient sulfonated-polystyrene–Cu(II)@Cu3(BTC)2 core–shell microsphere catalysts for base-free aerobic oxidation of alcohols

A novel catalyst consisting of a functional sulfonated-polystyrene (SPS) core, a porous Cu3(BTC)2 shell and an active Cu(II) interface between the core and shell was developed via a facile step-by-step assembly method. The polystyrene core was sulfonated first to achieve functional –SO3H groups on its surface. The main function of the –SO3H groups was to graft Cu(II) ions to generate an active Cu(II) interface, and the excess –SO3H could provide acid conditions for the catalytic reaction. The Cu(II) interface along with the acid conditions and the co-catalyst 2,2,6,6-tetramethyl-piperidyl-1-oxy (TEMPO) enhanced the catalytic activity for the aerobic oxidation of alcohols to aldehydes by molecular oxygen under base-free conditions. A portion of Cu(II) ions on the SPS surface was then coordinated with H3BTC (1,3,5-benzenetricarboxylic acid) to form a porous Cu3(BTC)2 shell, which could protect the active metal from leaching as well as provide porous channels for mass transfer, resulting in high stability and recyclability in the catalysis procedure. The SPS–Cu(II)@Cu3(BTC)2 catalyst could be recycled ten times without a significant loss in its activity and selectivity. Furthermore, the SPS–Cu(II)@CuBDC (BDC = 1,4-benzenedicarboxylate) composite was also synthesized and showed high efficiency for catalyzing the aerobic oxidation of alcohols and aerobic homocoupling of arylboronic acids, suggesting that the unique nanostructure of SPS–Cu(II)@MOFs can be easily extended to design complex catalysts with high efficiency and good stability for different catalytic reactions.

A facile in situ self-assembly strategy for large-scale fabrication of CHS@MOF yolk/shell structure and its catalytic application in a flow system.

A hierarchical yolk/shell copper hydroxysulfates@MOF (CHS@MOF, where MOF = metal-organic frameworks) structure was fabricated from a homogeneous yolk/shell CHS template composed of an active shell and a stabilized core via a facile self-template strategy at room temperature. The active shell of the template served as the source of metal ion and was in situ transformed into a well-defined MOF crystal shell, and the relatively stabilized core retained its own nature during the formation of the MOF shell. The strategy of in situ transformation of CHS shell to MOF shell avoided the self-nucleation of MOF in the solution and complex multistep procedures. Furthermore, a flow reaction system using CHS@MOF as self-supported stationary-phase catalyst was developed, which demonstrated excellent catalytic performance for aldehyde acetalization with ethanol, and high yields and selectivities were achieved under mild conditions.

Highly porous carbons derived from MOFs for shape-stabilized phase change materials with high storage capacity and thermal conductivity

Highly porous carbons (HPCs) are successfully prepared using a controlled carbonization of metal organic frameworks (MOFs) method. New micropores and mesoporous channels are produced during the migration and aggregation of small ZnO particles in the carbon matrix, while larger nanocavities are created after the evaporation of ZnO particles. The HPCs with high surface area (up to 2551 m2 g−1) and large total pore volume (up to 3.05 cm3 g−1) have high adsorption of polyethylene glycol (PEG) (up to 92.5 wt%) for shape-stabilized phase change materials (ssPCMs). In the PEG@HPCs composites, the nanocavities with a large mesopore volume guarantee the high storage of PEG molecules, and the micropores and mesoporous channels induced surface tension and capillary force to ensure the high thermal stability of the composites. With a high content of PEG and good shape-stabilities, the PEG@HPCs show high phase change enthalpy, which is close to or even higher than that of pure PEG. The thermal conductivity of PEG can also be improved by HPCs.

Hierarchically nanostructured MnCo2O4 as active catalysts for the synthesis of N-benzylideneaniline from benzyl alcohol and aniline

A facile and scaled-up synthesis route to hierarchically nanostructured transition metal oxides with desirable properties is of great practical importance because of their excellent performance as heterogeneous catalysts in organic synthesis. In this work, hierarchically nanostructured MnCo2O4 nanorods with multi-nanopores have been prepared by a facile co-precipitation method using oxalic acid as a precipitant and through their consequent removal by calcination. When evaluated as catalysts for the synthesis of N-benzylideneaniline from benzyl alcohol and aniline, the as-prepared hierarchically nanostructured MnCo2O4-500 nanorods possessed high conversion (90.9%) of benzyl alcohol and selectivity (95.4%) of N-benzylideneaniline at 60 °C even under air for 15 h, which can be attributed to the appropriate and similar ratios of Mn2+/Mn3+ (1.36:1) and Co2+/Co3+ (1.35:1) with excellent synergistic effects. The proposed mechanism reveals that the benzyl alcohol is initially dehydrogenated to benzaldehyde which then reacts with another molecule of aniline to form N-benzylideneaniline. The MnCo2O4-500 nanorods can also be easily recycled without significant loss in catalytic activity for at least 4 cycles. Our findings could provide some guidance on the design of nanostructured spinel-type metal oxide catalysts with better synergistic effects in organic synthesis.

Fabrication of Hierarchical Fe3O4@SiO2@P(4VP-DVB)@Au Nanostructures and Their Enhanced Catalytic Properties†

Hierarchical Fe3O4@SiO2@P(4VP-DVB)@Au nanostructures were prepared in which the slightly cross-linked, thin poly(4-vinylpyridine-co-divinylbenzene) (P(4VP-DVB)) shells were constructed onto Fe3O4@SiO2 nanospheres, followed by in situ embedding of gold nanocrystals homogeneously into the P4VP chains. These slightly cross-linked chains, easily swollen by the reactants, make the gold nanocrystals accessible to the reactants, and the thin shell (about 15 nm) reduces the diffusion distance of the reactants to the active gold nanocrystals (about 5 nm), thereby enhancing their catalytic activity and utility. At the same time, confinement of gold nanocrystals within the P4VP shells prevents their migration and coagulation during catalytic transformations. Hence the nanocomposites exhibit high activity (up to 4369.5 h(-1) of turnover frequency (TOF)) and controllable magnetic recyclability without any significant loss of gold species after ten runs of catalysis in the reduction of 4-nitrophenol.