Metal-organic frameworks (MOFs) are a novel type of nanoporous materials that have attracted widespread attention over the past two decades [1]. Cu-based metal-organic frameworks such as Cu₃(BTC)₂ (also known as HKUST-1) are one of the most famous MOF representatives, which exhibit a huge open porosity and thus a remarkably capacity to store and uptake different gases [2, 3]. Recently, increasing efforts are devoted toward finding synthetic routes that enable downsizing MOF crystals to the nanoscale. Achieving control over the size and shape of nanoMOFs and finding ways to assemble them is essential for their exploitation in integrated devices such as sensors, gas separation membranes or photoelectrodes.

In this study we explore the conversion of free-standing arrays Cu nanowires with controlled diameter and length synthesized by electrodeposition in etched ion-track membranes into HKUST-1. In a first process step, free-standing Cu wires are produced by dissolving the ion-track polymer template. In a second step, the wires are converted into HKUST-1 structures by electrochemical oxidation. Applying 2.5 V versus a Cu counter electrode, the Cu nanowires are oxidatively dissolved and the MOF is built up as the as-formed Cu²⁺ ions bind to the BTC³⁻ ligands in the electrolyte solution. The morphology and crystallinity of the samples at different transformation stages is investigated by scanning electron microscopy (Fig. 1) and transmission electron microscopy, respectively. X-ray diffraction spectra measured at different conversion times reveal the appearance of the characteristic reflections of HKUST-1. These results will be compared with previous studies of the transformation of Cu nanowires to HKUST-1 nanowires inside the polymer membrane [4].

Figure 1: SEM images of cylindrical Cu nanowires (a) before and (b) during the electrochemical conversion process, and (c) of a representative octahedral particle after complete conversion to HKUST-1.

References

[1] Freund R, Canossa S, Cohen SM, Yan W, Deng et al. Angewandte Chemie International Edition. (2021) 2: 23946-23974

[2] Chui SS-Y, Lo SM-F, Charmant JP, Orpen AG, Williams ID. Science. (1999) 283:1148-50.

[3] Li H, Li L, Lin R-B, Zhou W, Zhang Z, Xiang S, et al. EnergyChem. (2019) 1:100006.

[4] Caddeo F, Vogt R, Weil D, Sigle W, Toimil-Molares ME, Maijenburg AW. ACS applied materials & interfaces . (2019)11:25378-87.