Farhat Nosheen

Hierarchical Zn/Ni‐MOF‐2 Nanosheet‐Assembled Hollow Nanocubes for Multicomponent Catalytic Reactions

Metal-organic frameworks (MOFs) are potentially useful molecular materials that can exhibit structure flexibilities induced by some external stimuli. Such structure transformations can furnish MOFs with improved properties. The shape-controlled growth of MOFs combined with crystal-structure transformation is rarely achieved. Herein, we demonstrate the synthesis of hierarchical Zn/Ni-MOF-2 nanosheet-assembled hollow nanocubes (NAHNs) by a facile surfactant-free solvothermal approach. The unique nanostructures undergo crystal-structure transformation from Zn/Ni-MOF-5 nanocubes to Zn/Ni-MOF-2 nanosheets, which is analogous to the dissolution and recrystallization of inorganic nanocrystals. The present synthetic strategy to fabricate isostructural MOFs with hierarchical, hollow, and bimetallic nanostructures is expected to expand the diversity and range of potential applications of MOFs.

Fine tuning of the structure of Pt-Cu alloy nanocrystals by glycine-mediated sequential reduction kinetics.

Uniform Pt-Cu alloy nanocrystals in the shape of dendrite, yolk-cage, and box structures are prepared via a facile wet-chemical reduction route in which glycine is demonstrated to alter the reduction kinetics of metal cations, critical to the morphology of the obtained product. These alloy nanocrystals exhibit superior specific activity and stability in the electro-oxidation of methanol.

Atomically thick Pt-Cu nanosheets: self-assembled sandwich and nanoring-like structures.

Atomically thick and flexible Pt-Cu alloy nanosheets are prepared and loaded with either Pd or Pt to produce sandwich structures or nanoring-like nanosheet structures, respectively. Core-shell alloy nanoparticles containing Rh, Ir, and Ru are also prepared. All of these structures exhibit superior specific and mass activities for the oxidation of formic acid for fuel cells for portable electronic devices as compared to commercial Pd/C catalyst.

Three dimensional hierarchical Pt-Cu superstructures

Three-dimensional (3D) hierarchical Pt-Cu tetragonal, highly branched, and dendritic superstructures have been synthesized by a facile template-free hydrothermal approach, showing growth patterns along (111, 110), (111), and (100) planes, respectively. These structures have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma optical emission spectrometry (ICP-OES) and a detailed formation mechanism has been developed, which shows that the in situ formed I2 and the galvanic replacement reaction between Cu and Pt4+ may guide the formation of these superstructures. The comparative electrocatalytic properties have been investigated for methanol and ethanol oxidation. Due to their interconnected arms, sufficient absorption sites, and exposed surfaces, these superstructures exhibit enhanced electrocatalytic performance for electro-oxidation of methanol and ethanol when compared with commercial Pt/C and Pt black.

Tuning the growth of metal-organic framework nanocrystals by using polyoxometalates as coordination modulators

Host-guest supramolecular interactions, which exist widely between diverse metal cations and polyoxometalate (POM) anions, have always been utilized to construct metal-organic frameworks (MOF) /POMs bulk composites. Actually, the interactions can also be found application in realizing shape-controlled synthesis of MOF nanocrystals (NCs). In this context, simply by introducing Keggin-type POMs into MOF precursors, various uniform [Cu3(BTC)2]n (BTC = benzene-1,3,5-tricarboxylate) NCs, including (truncated) octahedrons, hollow hierarchical spheres and octahedrons, are fabricated. Besides, such reaction system can be applied to construct noble metal@MOF nanocomposite, which significantly enhances the catalytic performance of the noble metal.摘要在金属阳离子和多酸阴离子之间广泛存在着一种超分子相互作用, 它经常被用来合成多酸基金属-有机骨架晶态材料. 这种相互作用还可以用来调控金属-有机骨架材料的成核生长过程, 从而实现其纳米晶体的可控制备. 本文将Keggin型多酸阴离子引入到金属-有机骨架材料的前驱体溶液中作为调节剂, 得到一系列形貌规则、尺寸均一的[Cu3(BTC)2]n (BTC = 1,3,5-苯三甲酸)纳米晶, 包括八面体、截角八面体、多级空心球、空心八面体等. 此外, 这种体系可以用于构建贵金属纳米晶@金属-有机骨架复合材料, 其催化性质相对于单纯的贵金属纳米晶有较大提高.

Hierarchical MnO2/SnO2 Heterostructures for a Novel Free-Standing Ternary Thermite Membrane

We report the synthesis of a novel hierarchical MnO2/SnO2 heterostructures via a hydrothermal method. Secondary SnO2 nanostructure grows epitaxially on the surface of MnO2 backbones without any surfactant, which relies on the minimization of surface energy and interfacial lattice mismatch. Detailed investigations reveal that the cover density and morphology of the SnO2 nanostructure can be tailored by changing the experimental parameter. Moreover, we demonstrate a bottom-up method to produce energetic nanocomposites by assembling nanoaluminum (n-Al) and MnO2/SnO2 hierarchical nanostructures into a free-standing MnO2/SnO2/n-Al ternary thermite membrane. This assembled approach can significantly reduce diffusion distances and increase their intimacy between the components. Different thermite mixtures were investigated to evaluate the corresponding activation energies using DSC techniques. The energy performance of the ternary thermite membrane can be manipulated through different components of the MnO2/SnO2 heterostructures. Overall, our work may open a new route for new energetic materials.

Growth of Concave Polyhedral Pd Nanocrystals with 32 Facets Through In Situ Facet-Selective Etching

The control over crystal-plane exposure of nanoparticles in a variety of shapes and material types (such as metals and metal oxides) has attracted much attention because fascinating properties might be accomplished. In the case of metallic nanocrystals (NCs), it has been demonstrated that the exposed crystal facets of metallic NCs have a large influence on their catalytic reactivity and selectivity. Recent studies indicate that high-index facets of a face-centered cubic (fcc) metal (e.g. , Pd, Pt, and Au) generally exhibit significantly enhanced catalytic activity toward specific reactions compared to low-index facets because of a high density of low-coordinated surface atoms. However, up to date, studies on the design and synthesis of metallic nanostructures enclosed by high-index facets are still insufficient. High-index facets usually disappear during the growth of NCs due to their high surface energies. However, recent studies have shown that the exposure of high-index facets could be realized by tuning the growth kinetics, 16] the selective adsorption of specific chemical species, and their epitaxial growth from seeds terminating in high-index facets. 22] Herein, we report a synthetic strategy that allows the highyield fabrication of concave polyhedral Pd NCs with 32 facets that are rich in atomic steps and defects on the surface. This nanostructure was successfully prepared through an in situ facet-selective etching growth route. The vital role that iodide ions (I ) together with ethanolamine as the surface controller play in the formation of concave polyhedral Pd NCs having catalytic active sites is demonstrated. The concave polyhedral Pd NCs exhibit significantly enhanced specific and mass activities towards the electrooxidation of ethanol in comparison to truncated octahedral Pd NCs and commercial Pd black catalysts with low-index facets. In a typical synthesis of concave polyhedral Pd NCs, poly(vinyl pyrrolidone) (PVP, MW = 30 000), NaI, and an aqueous Na2PdCl4 solution were mixed together with ethanolamine. The resulting homogeneous solution was transferred to a Teflon-lined stainless-steel autoclave with a capacity of 12 mL. The sealed vessel was then heated at 200 8C for 6 h before it was cooled to room temperature (see the Experimental Section for synthesis details). The resulting products were collected by centrifugation and washed several times with water and ethanol. The representative electron microscopic images of the asobtained Pd NCs are shown in Figure 1. As depicted by transmission electron microscopic (TEM) images in Figure 1 a and Figure S1 c and d in the Supporting Information, the product consists of well-shaped NCs with a yield above 90 % and an average apex-to-apex distance of 50 nm. The nanoparticles display a darker contrast in the center compared to the edges, indicating the possible presence of concave features in the NCs. The scanning electron microscopic (SEM) images shown in Figure 1 b and Figure S1 a,b in the Supporting Information reveal that the nanoparticles have the same geometrical characteristics and can be regarded as an octapod, which is confirmed by high-angle annular dark-field scanning TEM (HAADF-STEM)