Metal-organic framework templated electrodeposition of functional gold nanostructures

Utilizing a pair of quick, scalable electrochemical processes, the permanently porous MOF HKUST-1 was electrochemically grown on a copper electrode and this HKUST-1-coated electrode was used to template electrodeposition of a gold nanostructure within the pore network of the MOF. Transmission electron microscopy demonstrates that a proportion of the gold nanostructures exhibit structural features replicating the pore space of this ∼1.4 nm maximum pore diameter MOF, as well as regions that are larger in size. Scanning electron microscopy shows that the electrodeposited gold nanostructure, produced under certain conditions of synthesis and template removal, is sufficiently inter-grown and mechanically robust to retain the octahedral morphology of the HKUST-1 template crystals. The functionality of the gold nanostructure within the crystalline HKUST-1 was demonstrated through the surface enhanced Raman spectroscopic (SERS) detection of 4-fluorothiophenol at concentrations as low as 1 μM. The reported process is confirmed as a viable electrodeposition method for obtaining functional, accessible metal nanostructures encapsulated within MOF crystals

Metal Organic and Covalent Triazine Frameworks as Templates for the Synthesis of Metallic Nanostructures and Doped Carbons

Metal Organic Frameworks (MOFs) are highly porous, crystalline frameworks composed of an organic linker and a metal oxide cluster. Covalent Triazine Frameworks (CTFs) are a subclass of MOFs and similarly are highly porous crystalline frameworks, but unlike MOFs, are composed of purely organic building units. Since the initial reports of a successful synthesis and characterization of MOF-5 in 1995, the interest in these frameworks has exploded. The ability to design the MOF properties and functionality by simply selecting the starting precursors make MOFs optimal materials for a multitude of fields. However, even with all of the research being conducted, there are many MOF applications yet to be discovered. In the first part of this thesis we explore the application of MOFs as templates for the synthesis of metallic nanostructures based on the size and the shape of the MOF pores. The limitless number of MOF structures with different pore shapes and sizes allow for the synthesis of nanostructures with any desired shape or size. It is shown that by using MOF-545 with one dimensional pores, well aligned, ultra-thin gold and platinum nanowires are grown. The nanowires inside the MOF pores are confirmed by imaging the focus-ion beam cross-section of the metal loaded MOF-545 using a transmission electron microscope. In the second part of this thesis, the use of MOFs as a precursor to fabricate nitrogen and metal co-doped carbons is discussed. MOF-545 is an excellent precursor for one-pot synthesis of metal and nitrogen co-doped carbon wires. Two different annealing methods are studied, either under pure argon or argon mixed with air impurities, and the resulting carbon wires are tested as an electro-catalyst for oxygen reduction reaction (ORR). Surprisingly, the air treated carbon wires show much higher ORR activity, comparable to that of platinum in basic electrolyte. Finally, the last part of this thesis will discuss controlling the surface area and porosity of carbon frameworks fabricated from CTFs. By using three different precursors, 12 carbon networks are synthesized and analyzed for porosity, surface area and capacitance. By varying the precursor composition and ratio, as well as the temperature, we are able to control the average pore size distribution between 1-17 nm, while the samples treated at 900�C show the best capacitance of 130 F/g

Synthesis, Structure, and Metalation of Two New Highly Porous Zirconium Metal–Organic Frameworks

Three new metal–organic frameworks [MOF-525, Zr₆O₄(OH)₄(TCPP-H₂)₃; MOF-535, Zr₆O₄(OH)₄(XF)₃; MOF-545, Zr₆O₈(H₂O)₈(TCPP-H₂)₂, where porphyrin H₄-TCPP-H₂ = (C₄₈H₂₄O₈N₄) and cruciform H₄-XF = (C₄₂O₈H₂₂)] based on two new topologies, <b>ftw</b> and <b>csq</b>, have been synthesized and structurally characterized. MOF-525 and -535 are composed of Zr₆O₄(OH)₄ cuboctahedral units linked by either porphyrin (MOF-525) or cruciform (MOF-535). Another zirconium-containing unit, Zr₆O₈(H₂O)₈, is linked by porphyrin to give the MOF-545 structure. The structure of MOF-525 was obtained by analysis of powder X-ray diffraction data. The structures of MOF-535 and -545 were resolved from synchrotron single-crystal data. MOF-525, -535, and -545 have Brunauer–Emmett–Teller surface areas of 2620, 1120, and 2260 m²/g, respectively. In addition to their large surface areas, both porphyrin-containing MOFs are exceptionally chemically stable, maintaining their structures under aqueous and organic conditions. MOF-525 and -545 were metalated with iron­(III) and copper­(II) to yield the metalated analogues without losing their high surface area and chemical stability

Synthesis, Structure, and Metalation of Two New Highly Porous Zirconium Metal–Organic Frameworks

Three new metal–organic frameworks [MOF-525, Zr₆O₄(OH)₄(TCPP-H₂)₃; MOF-535, Zr₆O₄(OH)₄(XF)₃; MOF-545, Zr₆O₈(H₂O)₈(TCPP-H₂)₂, where porphyrin H₄-TCPP-H₂ = (C₄₈H₂₄O₈N₄) and cruciform H₄-XF = (C₄₂O₈H₂₂)] based on two new topologies, <b>ftw</b> and <b>csq</b>, have been synthesized and structurally characterized. MOF-525 and -535 are composed of Zr₆O₄(OH)₄ cuboctahedral units linked by either porphyrin (MOF-525) or cruciform (MOF-535). Another zirconium-containing unit, Zr₆O₈(H₂O)₈, is linked by porphyrin to give the MOF-545 structure. The structure of MOF-525 was obtained by analysis of powder X-ray diffraction data. The structures of MOF-535 and -545 were resolved from synchrotron single-crystal data. MOF-525, -535, and -545 have Brunauer–Emmett–Teller surface areas of 2620, 1120, and 2260 m²/g, respectively. In addition to their large surface areas, both porphyrin-containing MOFs are exceptionally chemically stable, maintaining their structures under aqueous and organic conditions. MOF-525 and -545 were metalated with iron­(III) and copper­(II) to yield the metalated analogues without losing their high surface area and chemical stability

Tuning the Catalytic Activity of a Metal–Organic Framework Derived Copper and Nitrogen Co-Doped Carbon Composite for Oxygen Reduction Reaction

An efficient non-noble metal catalyst for the oxygen reduction reaction (ORR) is of great importance for the fabrication of cost-effective fuel cells. Nitrogen-doped carbons with various transition metal co-dopants have emerged as attractive candidates to replace the expensive platinum catalysts. Here we report the preparation of various copper- and nitrogen-doped carbon materials as highly efficient ORR catalysts by pyrolyzing porphyrin based metal organic frameworks and investigate the effects of air impurities during the thermal carbonization process. Our results indicate that the introduction of air impurities can significantly improve ORR activity in nitrogen-doped carbon and the addition of copper co-dopant further enhances the ORR activity to exceed that of platinum. Systematic structural characterization and electrochemical studies demonstrate that the air-impurity-treated samples show considerably higher surface area and electron transfer numbers, suggesting that the partial etching of the carbon by air leads to increased porosity and accessibility to highly active ORR sites. Our study represents the first example of using air or oxygen impurities to tailor the ORR activity of metal and nitrogen co-doped carbon materials and open up a new avenue to engineer the catalytic activity of these materials

General synthesis and definitive structural identification of MN4C4 single-atom catalysts with tunable electrocatalytic activities

Single-atom catalysts (SACs) have recently attracted broad research interest as they combine the merits of both homogeneous and heterogeneous catalysts. Rational design and synthesis of SACs are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report a general approach to a series of monodispersed atomic transition metals (for example, Fe, Co, Ni) embedded in nitrogen-doped graphene with a common MN4C4 moiety, identified by systematic X-ray absorption fine structure analyses and direct transmission electron microscopy imaging. The unambiguous structure determination allows density functional theoretical prediction of MN4C4 moieties as efficient oxygen evolution catalysts with activities following the trend Ni &gt; Co &gt; Fe, which is confirmed by electrochemical measurements. Determination of atomistic structure and its correlation with catalytic properties represents a critical step towards the rational design and synthesis of precious or nonprecious SACs with exceptional atom utilization efficiency and catalytic activities