Abstract
The liquid phase epitaxy (LPE) of the metal-organic framework (MOF) HKUST-1 has been studied for three different COOH-terminated templating organic surfaces prepared by the adsorption of self-assembled monolayers (SAMs) on gold substrates. Three different SAMs were used, mercaptohexadecanoic acid (MHDA), 4’-carboxyterphenyl-4-methanethiol (TPMTA) and 9-carboxy-10-(mercaptomethyl)triptycene (CMMT). The XRD data demonstrate that highly oriented HKUST-1 SURMOFs with an orientation along the (100) direction was obtained on MHDA-SAMs. In the case of the TPMTA-SAM, the quality of the deposited SURMOF films was found to be substantially inferior. Surprisingly, for the CMMT-SAMs, a different growth direction was obtained; XRD data reveal the deposition of highly oriented HKUST-1 SURMOFs grown along the (111) direction.
Highlights
Metal-organic frameworks (MOFs) [1,2,3,4] are highly crystalline porous coordination polymers (PCPs) consisting of two essential building components: metal or metal/oxo coupling units and functional organic linkers
The X-ray Diffraction (XRD) data demonstrates the presence of thin films of HKUST-1 on the different types of COOH-self-assembled monolayers (SAMs)
The results for the SURMOF grown on the mercaptohexadecanoic acid (MHDA)-SAM are consistent with previous findings, which reported a preferred growth along the (100)
Summary
Metal-organic frameworks (MOFs) [1,2,3,4] are highly crystalline porous coordination polymers (PCPs) consisting of two essential building components: metal or metal/oxo coupling units and functional organic linkers. It has been reported that HKUST-1 ([Cu3BTC2·xH2O]n, btc = benzene-1,3,5-tricarboxylate) grows along the (100) direction on a carboxylic acid-terminated MHDA (16-mercaptohexadecanoic acid) SAM, whereas on a hydroxyl-terminated MUD (16-mercaptoundecan-1-ol) SAM or pyridine-terminated PPMT ((4-(4-pyridyl)phenyl)methanethiol) SAM, a different growth direction, (111), is obtained [29,31,34,36] In this contribution, we report a systematic study on the influence of the packing density of the carboxylic acid group on the orientation and quality of MOF thin films grown using the liquid phase epitaxy method [31,32]. Somewhat unexpectedly, the packing density of COOH-groups controls the quality of the MOF films but that there is an area density threshold above which a switch of the growth direction of the SURMOF is observed This observation provides important information about the growth mechanism of MOFs in the context of the LPE method
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