In this work we describe a soft-lithographic approach to fabricate sub-micrometer MOFbased 2D photonic structures. Nanometric Zeolitic Imidazole Framework material ZIF-8 (zinc) was chosen as the sensible MOF material because of its chemical stability and its vapor selective adsorption properties. Two different systems were fabricated: nanopatterned colloidal ZIF-8 homo-and ZIF-8/TiO 2 hetero-structures. Several features (stripes, squares, etc.) with dimension as small as 200 nm, were replicated on different substrates such as silicon, flexible plastics and even on aluminum cans, over relatively large surfaces (up to 1 cm 2). In addition, we demonstrate here that these photonic MOF-heterostructures can be used as very low-cost sensing platforms compatible with smart-phone technology. This method relies on the evaluation of the change in diffraction efficiency of the photonic MOF-patterns, induced by the MOF refractive index variation, which is simply detected by a CCD camera, as those integrated in simple smart-phones, without need of complex optical instrumentations for transduction data processing. Performances of the sensors were first evaluated using isopropanol adsorption/desorption cycling as a model case. In addition, a "real" environmental issue was tackled. Selective detection of styrene in presence of interfering water was demonstrated at concentration below the human permissible exposure limit. In-situ ellispometric analyses were also carried out in order to confirm the sensor performances and to propose a mechanism for styrene uptake into the nanoMOFs.
A straightforward crack‐patterning method is reported allowing the direct formation of periodic cracks in metal–organic framework (MOF) nanoparticle films during dip‐coating deposition. The crack propagation and periodicity can be easily tailored by controlling the evaporation front and the withdrawal speed. Several MOF‐patterned films can be fabricated on large surfaces and on several substrates (flat, curved or flexible) including the inner surface of a tube, not achievable by other lithographic techniques. We demonstrate that the periodic cracked arrays diffract light and, due to the MOF sorption properties, photonic vapor sensors are fabricated. A new concept of “in‐tube”, MOF‐based diffraction grating sensors is proposed with outstanding sensitivity that can be easily tuned “on‐demand” as function of the desired detection range.
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