Allegretto Juan A, Dostalek Jakub, Rafti Matías, Menges Bernhard, Azzaroni Omar, Knoll Wolfgang
Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas , Universidad Nacional de La Plata, CONICET , Calle 64 y Diag. 113 , 1900 La Plata , Argentina.
Universidad Nacional de San Martin (UNSAM) , San Martín , Argentina.
J Phys Chem A. 2019 Feb 7;123(5):1100-1109. doi: 10.1021/acs.jpca.8b09610. Epub 2018 Dec 17.
Metal-organic framework (MOF) thin films are promising materials for multiple technological applications, such as chemical sensing. However, one potential limitation for their widespread use in different settings is their stability in aqueous environments. In the case of ZIF-8 (zeolitic imidazolate framework) thin films, their stability in aqueous media is currently a matter of debate. Here, we show that optical waveguide spectroscopy (OWS), in combination with surface plasmon resonance (SPR) spectroscopy, offers a convenient way for answering intriguing questions related to the stability of MOF thin films in aqueous solutions and, eventually provide a tool for assessing changes in MOF layers under different environmental conditions. Our experiments relied on the use of ZIF-8 thin films grown on surface-modified gold substrates, as optical waveguides. We have found a linear thickness increase after each growing cycle and observed that the growing characteristics are strongly influenced by the nature of the primer layer. One of our findings is that substrate surface modification with a 3-mercapto-1-propanesulfonate (MPSA) primer layer is critical to achieve ZIF-8 layers that can effectively act as optical waveguides. We observed that ZIF-8 films are structurally stable upon exposure to pure water and 50 mM NaCl solutions but they exhibit a slight swelling and an increase in porosity probably due to the permeation of the solvent in the intergrain mesoporous cavities. However, OWS revealed that exposure of ZIF-8 thin films to phosphate-buffered saline solutions (pH 8) promotes significant film degradation. This poses an important question as to the prospective use of ZIF-8 materials in biologically relevant applications. In addition, it was demonstrated that postsynthetic polyelectrolyte modification of ZIF-8 films has no detrimental effects on the structural stability of the films.
金属有机框架（MOF）薄膜是多种技术应用的理想材料，如化学传感。然而，它们在不同环境中广泛应用的一个潜在限制是其在水环境中的稳定性。就沸石咪唑酯骨架（ZIF-8）薄膜而言，其在水介质中的稳定性目前仍存在争议。在此，我们表明，光波导光谱（OWS）与表面等离子体共振（SPR）光谱相结合，为回答与MOF薄膜在水溶液中的稳定性相关的有趣问题提供了一种便捷方法，并最终提供了一种评估不同环境条件下MOF层变化的工具。我们的实验依赖于使用生长在表面改性金基底上的ZIF-8薄膜作为光波导。我们发现每个生长周期后薄膜厚度呈线性增加，并观察到生长特性受底漆层性质的强烈影响。我们的发现之一是用3-巯基-1-丙烷磺酸盐（MPSA）底漆层对基底表面进行改性对于获得能够有效充当光波导的ZIF-8层至关重要。我们观察到，ZIF-8薄膜在暴露于纯水和50 mM NaCl溶液时结构稳定，但它们可能由于溶剂渗透到晶粒间介孔腔中而出现轻微膨胀和孔隙率增加。然而，OWS显示ZIF-8薄膜暴露于磷酸盐缓冲盐水溶液（pH 8）会导致薄膜显著降解。这对于ZIF-8材料在生物相关应用中的潜在用途提出了一个重要问题。此外，已证明对ZIF-8薄膜进行合成后聚电解质改性对薄膜的结构稳定性没有不利影响。
