Organic framework engineering in mesoporous Nb2O5 thin films used as an active medium for organic vapors sensing

Abstract

In the current study triblock copolymers (Pluronics) consisting of central poly(propylene oxide) (PPO) block flanked by two poly(ethylene oxide) (PEO) chains are used as organic templates for generating mesoporosity in thin Nb2O5 films. In order to optimize the polymer framework within the Nb2O5 films, two copolymers with different chemical compositions and properties are used, namely Pluronic PE 6200 and PE 9400. The copolymers’ micelle formation is studied by Dynamic Light Scattering (DLS) measurements of the copolymer aqueous solutions at different temperatures and concentrations and by Transmission Electron Microscopy (TEM). Thin films of mesoporous Nb2O5 films are deposited by sol-gel and spin-coating methods and characterized by TEM, UV-VIS reflectance spectroscopy and non-linear fitting for optical properties determination. The porosity of the films is calculated using effective medium approach on the basis of dispersion curves of the calculated refractive indices. The development of porosity in the films is studied as a function of the duration of the annealing. Besides, the sensing properties of mesostructured films are tested with vapors of acetone as a probe molecule of VOC’s (Volatile Organic Compounds) by reflectance measurements prior to and after exposure to vapors. The films optical response is demonstrated and possible application as optical indicator for VOC’s is discussed.