Abstract
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 ∼1.4nm 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 1μM. The reported process is confirmed as a viable electrodeposition method for obtaining functional, accessible metal nanostructures encapsulated within MOF crystals.
Highlights
Metal-organic frameworks (MOFs) are a well-established family of nanoporous material whose framework is constructed from metal based inorganic clusters connected by heteroatomcontaining organic linker molecules
The powder X-ray diffraction (PXRD) patterns of the HKUST-1 coated Cu foil before and after Au electrodeposition are shown in Fig. 2 and show that both potentiostatic and potentiodynamic deposition techniques resulted in the reduction of Au3+ to Au metal
The far larger full widths at half maxima of the Au diffraction peaks in comparison to those derived from the HKUST-1 template indicate that the sizes of the crystalline domains of the Au are of the order of nanometers
Summary
Metal-organic frameworks (MOFs) are a well-established family of nanoporous material whose framework is constructed from metal based inorganic clusters connected by heteroatomcontaining organic linker molecules. A diverse range of different techniques have been employed in the synthesis of a variety of different encapsulated nanostructured metal/MOF composites [12,13,14,15,16,17,18,19], for application in areas such as substrates for surface enhanced Raman spectroscopy (SERS) [12] and catalysis [16,17,18]. The random nature of the pores of the mesoporous silica resulted in relatively poor alignment of the nanowires[22] in contrast to those formed in the well aligned pores of the anodized alumina [21] These two porous materials were combined to achieve the templated electrodeposition of well aligned nanowires, $10 nm in diameter and hundreds of nm long, of Ag, Cu and Te [23]. The high surface area, rough nature of the HKUST-1 encapsulated gold nanostructure is shown to act as an ideal surface enhanced Raman spectroscopic (SERS) substrate
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