Highly-ordered Porous Coordination Polymer Nanofilms Grown by Layer-by-Layer Deposition Technique
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Highly-ordered Porous Coordination Polymer Nanofilms Grown by Layer-by-Layer Deposition Technique Rie Makiura1,2 and Hiroshi Kitagawa2,3 1 Nanoscience and Nanotechnology Research Center, Osaka Prefecture University, Osaka 5998570, Japan 2 CREST, Japan Science and Technology Agency, Tokyo 102-0075, Japan 3 Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
ABSTRACT The facile bottom-up fabrication of a perfect preferentially-oriented MOF nanofilm, NAFS-1 on a solid surface, which is endowed with highly crystalline order both in the out-of-plane and in-plane orientations to the substrate, as determined by synchrotron X-ray surface crystallography, was achieved by the unique combination of a layer-by-layer growth technique coupled with the Langmuir-Blodgett (LB) method. INTRODUCTION The assembly of molecular building blocks with metal ions and organic linkers, ranging from so-called metal-organic frameworks (MOFs) to extended organic-inorganic hybrids, has been attracting intense interest [1-2]. MOFs are highly ordered crystalline coordination polymers with well-defined porous networks. Because of their potential applications associated with the presence of pores and cavities, such materials have been examined for storage, separations, sensors, size- and shape-selective catalysis, molecular recognition, and nanoscale reactors. However, the assembly of MOF films whose size and growth direction are completely controlled has proven an extremely challenging task [3,4]. Although there have been experimental reports that showed promising results in obtaining partially ordered system, the structural details, especially an in-plane direction have remained completely unknown [3,4]. Here, we present how the layer-by-layer growth and the LB methods can be integrated to allow fabrication of a perfectly crystalline MOF thin film on a solid surface comprising metalloporphyrin building units and metal ion joints.
EXPERIMENTS 5,10,15,20-tetrakis-(4-carboxyphenyl)-porphyrin-Co-(II) (CoTCPP) was purchased from Porphyrin Systems. Silicon single crystal, Si(100) were used as a substrate in XRD measurements. Amorphous quartz was used as a substrate for UV-vis absorption spectroscopic
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measurements. Before the film fabrication, the substrates were immersed successively into ultrasonic baths of chloroform, acetone, and ethanol, each for 30 minutes.
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CoTCPP and pyridine (py) were dissolved together into mixed chloroform/methanol solvent (3:1, v/v, 0.2 mM for CoTCPP). 0.1 M of CuCl2ǜ2H2O aqueous solution was prepared as a subphase and poured carefully into a Langmuir trough. CoTCPP/pyridine solution was spread onto the CuCl2 subphase. The surface was compressed by two barriers and the formation of the ordered array on the surface was followed by measuring surface pressure (S) with KSV minitrough system and the molecular area in the array was evaluated. The CoTCPP-py-Cu array formed at the surface was transferred onto the substrate at room temperature. The substrate with the CoTCPP-py-Cu a
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