Panpan Su

Nitrogen-doped carbon nanotubes derived from Zn–Fe-ZIF nanospheres and their application as efficient oxygen reduction electrocatalysts with in situ generated iron species

Nitrogen-doped carbon nanotubes (NCNTs) have been successfully synthesized via the direct solid pyrolysis of Zn–Fe-ZIF and the N content, N doped state, diameter and formation temperature of the NCNTs can be finely tuned by mixing Zn–Fe-ZIF with proper amounts of dicyandiamide (DCDA). DCDA serves as the extra nitrogen supplier and favors the formation of NCNTs at relatively low temperature due to its inducing effect for graphitic structure. The synthesized NCNTs, with iron species and high amounts of graphitic N, exhibit higher catalytic activity than commercial Pt/C as oxygen reduction electrocatalysts in alkaline solution.

Spinel ZnMn2O4 nanoplate assemblies fabricated via "escape-by-crafty-scheme" strategy

A two-step process that differs in important details from previous methods used to prepare ZnMn2O4 nanoplate assemblies has been reported. This material was prepared by thermal transformation of metal–organic nanoparticles into metal–oxide nanoparticles based on the “escape-by-crafty-scheme” strategy. Firstly, the nanoscale mixed-metal–organic frameworks (MMOFs) precursor, ZnMn2–ptcda (ptcda = perylene-3,4,9,10-tetracarboxylic dianhydride), containing Zn2+ and Mn2+, was prepared by the designed soft chemical assembly of mixed metal ions and organic ligands at a molecular scale. In a second step, the MMOFs are thermally transformed into spinel structured ZnMn2O4 with morphology inherited from the MMOFs precursors. The well-crystallized spinel structure can be formed by thermal treatment of ZnMn2–ptcda at 350 °C, and is formed at temperatures ≥450 °C using the co-precipitation method. This “escape-by-crafty-scheme” strategy can be extended to the preparation of other spinel metal–oxide nanoparticles, e.g. CoMn2O4, and NiMn2O4, with well-defined morphology inherited from the metal–organic precursors. The ZnMn2O4 nanoplate assemblies thermally treated at 450 °C have potential application in lithium ion batteries as anode materials, which show high specific capacity and good cyclability.

Enhanced lithium storage capacity of Co3O4 hexagonal nanorings derived from Co-based metal organic frameworks

Co3O4 with high capacities and energy density has potential applications to be electrode materials for lithium ion batteries, one of the most important power sources. For improving the cycling stability, the Co3O4 nanostructures are required. Herein, we report successful construction of Co3O4 hexagonal nanorings and nanoplates/nanoparticles via treating Co-based metal organic frameworks (MOFs) with organic amine. The studies show that the release rate of Co(II) to the reaction system and the spatial hindrance of the organic linkers of MOFs determine the final morphology of Co3O4. As an anode for lithium ion batteries, Co3O4 hexagonal nanorings with 1370 mA h g−1 specific capacity after 30 cycles displayed higher reversible capacity and better stability than commercial Co3O4 particles with only 117 mA h g−1 specific capacity after 30 cycles. The improved performance of Co3O4 hexagonal nanorings could be attributed to the shortened transfer path for Li+ afforded by the special morphology. It is expected that plentiful metal oxide nanostructures could be constructed from MOFs due to the available versatile categories of MOFs.

Metal-Oxide Nanoparticles with Desired Morphology Inherited from Coordination-Polymer Precursors

The “escape-by-crafty-scheme” strategy is an efficient approach to prepare metal-oxide nanomaterials with desirable morphology and crystal planes inherited from coordination-polymer nanoparticle pr ...

CNTs@Fe–N–C core–shell nanostructures as active electrocatalyst for oxygen reduction

The development of non-precious metal catalysts for oxygen reduction reactions (ORRs) is of extreme importance for the construction of efficient H2/O2 polymer electrolyte membrane fuel cells (PEMFCs), one of the most promising clean energy technologies. Herein, we report the fabrication of core–shell structured CNTs@Fe–N–C composites with a Fe–N–C shell closely wrapped around a core of CNTs (carbon nanotubes) as efficient catalysts for ORR. CNTs@Fe–N–C composites afford comparable activity to commercial Pt/C catalysts with a loading of 20 μg Pt cm−2 towards ORR in alkaline media. The results of XRD, TEM, XPS and 57Fe Mossbauer characterizations suggest that the high ORR activity of CNTs@Fe–N–C composites are mainly attributed to the combined advantages of the unique core–shell nanostructure allowing close contact between Fe–N–C and CNTs, uniformly distributed FeN4/C species, and the presence of pyridine and graphitic nitrogen.

Zinc-cobalt oxides as efficient water oxidation catalysts: the promotion effect of ZnO

Herein, we report the promotion effect of ZnO in water oxidation catalyzed by Co. Zinc–cobalt oxides—ZnCoxOy were prepared via the calcination of Zn–Cox-coordination polymers. The results of XRD, Co K-edge XANES and EXAFS show that the Co/Zn ratio greatly affected the oxidation state of Co and local structure of the ZnCoxOy oxides. With a Co/Zn ratio higher than 3.0, Zn(II) prefers to substitute in the lattice of Co3O4. The integrated ZnO and Co3O4 composites were formed at a Co/Zn ratio less than 2.0. The HR-TEM images show that ZnO and Co3O4 compactly contact to form the interfaces in the composites. In both the chemical water oxidation and the visible-light-driven photocatalytic water oxidation ([Ru(bpy)3]2+–persulfate system), Zn substituted in the spinel structured Co3O4 oxide cannot significantly improve the water oxidation activity and only the integrated ZnO and Co3O4 composites afford much higher TOFs than Co3O4. This suggests the existence of the cooperation effect between ZnO (water adsorption site) and Co3O4 (water oxidation site). Our results provide a facile approach to design composite catalysts for the water oxidation reaction.

Bifunctionalized Hollow Nanospheres for the One-Pot Synthesis of Methyl Isobutyl Ketone from Acetone

Pd-doped propyl sulfonic acid-functionalized hollow nanospheres proved to be efficient bifunctionalized catalysts for the one-pot synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen in liquid phase. These hollow nanospheres exhibited a higher activity than their bulk mesoporous counterparts (SBA-15 or FDU-12), mainly due to the short diffusion resistance of hollow nanospheres. Hollow nanospheres with silica frameworks showed higher activity and selectivity for MIBK than those with ethane-bridged frameworks, suggesting that hollow nanospheres with hydrophilic surface properties favor the formation of MIBK. This is probably due to the increased affinity of the hydrophilic surface towards acetone and its decreased affinity towards MIBK, which precludes deep condensation of MIBK with acetone. Under optimal conditions, up to 90 % selectivity for MIBK can be obtained with conversions of acetone as high as 43 %. This result is among the best reported so far for mesoporous silica-based catalysts. The control/fine-tuning of morphology and surface properties provides an efficient strategy for improving the catalytic performance of solid catalysts.

Systematic morphology and phase control of Mg-ptcda coordination polymers by Ostwald ripening and self-templating

Mg-ptcda (ptcda = perylene-3,4,9,10-tetracarboxylic dianhydride) coordination polymer particles (CPPs) with special hexagonal tubes morphology were manufactured by a self-assembly and hydrothermal method. The growth process from unstable nanoribbons to metastable hexagonal rods to a core–shell structure and finally to the stable hexagonal tubes was achieved and investigated by SEM and XRD characterizations. The morphology of Mg-ptcda is mainly controlled by Ostwald ripening and self-templating mechanism. Mg-ptcda CPPs with various morphologies, such as hexagonal rings and snowflakes, and particle sizes from micro to nanoscale can be finely tuned using organic solvent as additives. The optical properties of Mg-ptcda CPPs show that incorporation of ptcda dyes in coordination polymers can efficiently reduce their aggregation and interaction in the solid state. Furthermore, porous MgO nanomaterials with various morphologies can be fabricated from Mg-ptcda CPP precursors by a simple thermal treatment process.

Preparation of Zn–Co–O mixed-metal oxides nanoparticles through a facile coordination polymer based process

This paper reports a facile process that starts from the coordination polymers (CPs) precursor for the preparation of mixed-metal oxides. Firstly, a series of CPs, Zn–Co–ptcda (ptcda = perylene-3,4,9,10-tetracarboxylic dianhydride) with different molar ratios of Zn2+ and Co2+, were prepared by self-assembly of metal ions and organic ligands at the molecular scale. Based on the scanning electron microscopy, X-ray diffraction and thermogravimetric analysis, Zn–Co–ptcda takes both the advantages of Zn–ptcda and Co–ptcda. After a simple thermal treatment, the mixed-metal CPs are transformed into mixed-metal oxides with morphology and composition inherited from the CPs precursor. Binary-phase oxide Co3O4/ZnO and single-phase spinel ZnxCo3−xO4 (0 < x < 1) can be successfully prepared by this strategy.

Fabrication of ZnO with tunable morphology through a facile treatment of Zn-based coordination polymers

The morphology and structure of zinc oxide (ZnO), one of the important semiconductors, are relevant to its properties and applications. The preparation of ZnO with tunable morphology and desired structure is an attractive topic in the field of material synthesis. This work reports a facile method for the synthesis of ZnO with controllable morphology and crystal orientation using Zn-based coordination polymer particles (Zn-CPP) as precursors. Using hydrothermal method, Zn-CPP with morphologies of microrod, nanoplate, flower-like, arrow-tipped microsheet, and square cylinder were successfully synthesized via the coordination between metal ions Zn2+ and organic ligand 1,4,5,8-naphthalenetetracarboxylic dianhydride in aqueous solution. Subsequent thermal treatment of the Zn-CPP successfully resulted in the formation of porous ZnO with similar morphology to Zn-CPP. It is also found that the ZnO with enhanced (002) orientation could be obtained from Zn-CPP with preferred (002) orientation. This strategy could be extended for the preparation of other metal oxides with desired shape and structure.