Dairong Chen

LDH nanocages synthesized with MOF templates and their high performance as supercapacitors.

Layered double hydroxides (LDHs) are currently attracting intense research interest for their various applications. Three LDH hollow nano-polyhedra are synthesized with zeolitic imidazolate framework-67 (ZIF-67) nanocrystals as the templates. The nanocages well inherit the rhombic dodecahedral shape of the ZIF-67 templates, and the shell is composed of nanosheets assembled with an edge-to-face stacking. This is the first synthesis of the LDH non-spherical structures. And the mechanism of utilizing metal-organic framework (MOF) nanocrystals as templates is explored. Control of the simultaneous reactions, the precipitation of the shells and the template etching, is extremely crucial to the preparation of the perfect nanocages. And the Ni-Co LDH nanocages exhibit superior pseudocapacitance property due to their novel hierarchical and submicroscopic structures.

Synthesis of amorphous cobalt sulfide polyhedral nanocages for high performance supercapacitors

Amorphous cobalt sulfide polyhedral nanocages are synthesized by utilizing zeolitic imidazolate framework-67 (ZIF-67) nanocrystals as templates. Electrochemical characterization shows that CoS nanocages exhibit high specific capacitances, owing to their amorphous phase and novel structures.

Electrospun flexible self-standing γ-alumina fibrous membranes and their potential as high-efficiency fine particulate filtration media

Novel self-standing γ-alumina fibrous membranes with good flexibility have been successfully fabricated for the first time using an electrospinning technique. The γ-alumina membranes were composed of randomly arranged nanofibers with a high aspect ratio and small diameter (ca. 230 nm). The γ-alumina membranes show high tensile strength (2.98 MPa) and thermal stability (up to 900 °C), which favor their applications in high temperature conditions. Furthermore, the γ-alumina membranes exhibit good filtration performance for 300 nm dioctyl phthalate fine particulate gas filtration. The filtration efficiency is 99.848% and the pressure drop is 239.12 Pa for the membrane calcined at 700 °C with a basis weight of 9.28 g m−2; and the filtration efficiency could be over 99.97% when the basis weight is over 11.36 g m−2, suggesting that the γ-alumina fibrous membrane is a promising candidate for high temperature, fine particulate filtration applications. This work also provides a novel insight into the electrospinning of flexible self-standing inorganic membranes for applications in the separations field.

Hydrothermal synthesis and selective photocatalytic properties of tetragonal star-like ZrO2 nanostructures

Tetragonal star-like ZrO2 nanostructures were prepared using ZrOCl2·8H2O and CH3COONa as raw materials via a hydrothermal process. The zirconia nanostructures were investigated in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), infrared (IR) spectrum, thermal-gravimetry (TG) and other techniques, and possible formation mechanism was proposed. In the formation of the tetragonal star-like zirconia nanostructures, acetate played an important role due to the adsorption on certain of the crystals facets. Tetragonal star-like zirconia showed excellent selective photocatalytic activity for the photodegradation of anionic dyes (methyl orange, congo red and rhodamine B) in acidic, neutral and weak basic aqueous solutions.

Facile synthesis of sheet-like N–TiO2/g-C3N4 heterojunctions with highly enhanced and stable visible-light photocatalytic activities

Sheet-like N–TiO2/g-C3N4 heterojunctions with well-controlled structures as high-efficiency visible-light photocatalysts were synthesized by direct co-calcination of preformed N–TiO2 nanoparticles and g-C3N4 nanosheets. The composition, structure, morphology, and optical absorption properties of the as-prepared g-C3N4 nanosheets and N–TiO2/g-C3N4 heterojunctions were thoroughly investigated with XRD, FT-IR, SEM, TEM, XPS, and UV-vis DRS, respectively. The visible-light photocatalytic activity of the heterojunctions with different N–TiO2/g-C3N4 mass ratios was evaluated by photodegradation of rhodamine B dye and the highest enhancement was attained at a mass ratio of 1u2006:u20063, which was 19 and 5.3 times as high as that of the individual N–TiO2 nanoparticles and g-C3N4 nanosheets, respectively. The photocatalytic activity of the composites originating from nanosheets is 11 times as high as that of the bulk g-C3N4/N–TiO2 heterojunctions. Moreover, the sheet-like N–TiO2/g-C3N4 photocatalyst exhibits excellent stability against repeated use and could still retain over 98.8% of the initial activity after seven cycles. Such a good visible-light photocatalytic performance is mainly due to the effective structure and chemical composition provided by the present method, which endow the as-prepared heterojunctions with exceptionally high specific surface area (>80 m2 g−1) as well as efficient charge transfer at the heterojunction interfaces. The charge separation mechanism during the photodegradation process was also studied and a possible photocatalytic mechanism was proposed.

Synthesis of metal sulfide nanoboxes based on Kirkendall effect and Pearson hardness

The monodisperse metal sulfide (Ag2S, CdS, PbS, ZnS, and AgInS2) yolk–shell nanoboxes with sizes of about 220 nm were synthesized through a sacrificial template-directed method based on the Kirkendall effect. In a typical synthetic process for nanoboxes, there were two steps of ion-exchange. The first anion exchange was based on the control of solubility product rule, halide ions in silver halide were replaced by chalcogenide ions, following this a series of metal chalcogenide nanoboxes were obtained based on Pearson hard–soft acids and bases (HSAB) of various metal ions. The obtained CdS showed preferable absorption in the visible light region. This facile method is expected to obtain other nanostructures with preserved morphology.

Solvothermal Preparation of Pd Nanostructures under Nitrogen and Air Atmospheres and Electrocatalytic Activities for the Oxidation of Methanol

Monodispersed Pd nanoparticles and their porous spherelike aggregates with different lattice parameters were solvothermally prepared under nitrogen and air atmospheres. Here PdCl(2) acted as Pd precursor and hexadecylamine played the roles of solvent, reductant, and surface capping agent. Oxygen existing in air resulted in the change of surface capping agent, which then induced the aggregation of Pd nanoparticles, and the incorporation of oxygen led to the expansion of its lattice parameter to 0.398 nm, whereas the standard lattice parameter in metallic Pd is 0.389 nm. The monodispersed nanoparticles presented better catalytic activity and stability for the oxidation of methanol than the sphere-like Pd aggregates.

Hollow CeO2 dodecahedrons: one-step template synthesis and enhanced catalytic performance

Novel hollow CeO2 dodecahedrons were synthesized using ZIF-67 nanocrystals as templates via a one-step liquid phase reaction for the first time. The structure, composition, morphology, surface chemical states, and band gap of the as-prepared hollow CeO2 dodecahedrons were thoroughly investigated with XRD, SEM, TEM, HR-TEM, XPS, Raman, UV-Vis and ICP-AES. The hollow structures, with a specific BET surface area as high as 128 m2 g−1, are composed of small CeO2 nanocrystallites less than 5 nm. The formation mechanism of hollow CeO2 dodecahedrons was proposed, and the relative rate between Ce3+ hydrolysis and template dissolution was found to be the key to the successful formation of well-defined hollow dodecahedrons. The CO oxidation catalytic activities of hollow CeO2 dodecahedrons revealed an excellent performance with a complete CO conversion at 170 °C and a superior catalytic stability, which was attributed to the synergistic effect of large surface area, small crystallites, hollow structure, large amount of oxygen vacancies, and the containing Co species. This work provides a rapid and cost-efficient approach to synthesize a new dodecahedral CeO2 hollow structure, which broadens the way to synthesize crystalline metal oxide with controllable morphologies in mild solution conditions.

Enhanced Catalytic Activity in Liquid-Exfoliated FeOCl Nanosheets as a Fenton-Like Catalyst.

A facile liquid-phase exfoliation method to prepare few-layer FeOCl nanosheets in acetonitrile by ultrasonication is reported. The detailed exfoliation mechanism and generated products were investigated by combining first-principle calculations and experimental approaches. The similar cleavage energies of FeOCl (340u2005mJu2009m(-2) ) and graphite (320u2005mJu2009m(-2) ) confirm the experimental exfoliation feasibility. As a Fenton reagent, FeOCl nanosheets showed outstanding properties in the catalytic degradation of phenol in water at room temperature, under neutral pH conditions, and with sunlight irradiation. Apart from the increased surface area of the nanosheets, the surface state change of the nanosheets also plays a key role in improving the catalytic performance. The changes of charge density, density of states (DOS), and valence state of Fe atoms in the exfoliated FeOCl nanosheets versus plates illustrated that surface atomistic relationships made the few-layer nanosheets higher activity, indicating the exfoliation process of the FeOCl nanosheets also brought about surface state changes.

Flexible Pd/CeO2–TiO2 nanofibrous membrane with high efficiency ultrafine particulate filtration and improved CO catalytic oxidation performance

Flexible CeO2–TiO2 fibrous membrane was prepared by an electrospinning combined sol–gel method. The composition, structure, and morphology of the membrane were thoroughly investigated with XRD, FT-IR, N2 adsorption–desorption, SEM and TEM. The tensile-strength of the TiO2–CeO2 was evaluated with a tensile tester and the highest strength (1.38 MPa) was attained at a Ce and Ti molar ratio of 5u2006:u2006100, which was 3 times as high as that of pure TiO2. After Pd was loaded on the fibers, the strength of fibrous membrane (1.28 MPa) stayed almost the same. Moreover, the Pd/CeO2–TiO2 fibrous membrane exhibits high thermal stability against long time usage and retains its strength up to 1.22 MPa after 400 °C for 20 h. Strength performance is mainly due to effective size control of the particles composing the nanofibers; this endows the fibrous membrane with application potential for high efficiency particle filtration. The best filtration performance had an efficiency of 99.86% and a corresponding pressure drop of 178 Pa. At the same time, the fibrous membrane also exhibits good low-temperature CO oxidation performance with a complete conversion of CO to CO2 at 200 °C and no decrease of catalytic activity over 30 h. The excellent properties of this Pd/CeO2–TiO2 fibrous membrane enrich the applications of inorganic fibrous membranes simultaneously for air filtration and catalysis.