Fast fabrication and gas-sensing characteristics of petal-like Co-MOF membrane optical waveguide

In this work, metal organic frameworks (MOFs) were chosen as sensing materials for the development of a planar optical waveguide (POWG) gas sensor with improved selectivity. Petal-like Co-MOFs ([Co(TpA)dpNDI], where TpA = terephthalic acid and dpNDI = dipyridyl-naphthalenediimide) membranes were fabricated via UV light irradiation of the surface of an Sn-diffused glass optical waveguide slide as the substrate. The obtained film exhibited a high refractive index (1.873–1.875) and optimum thickness to support a strong single-mode (TE0) guided light signal, fulfilling the essential requirements of a POWG sensor. The [Co(TpA)dpNDI] membrane POWGs uniquely responded to ethylenediamine (EDA) coexisting with interfering gases such as methylamine, dimethylamine, and BTXs (benzene, toluene, xylene, and styrene). When the membrane was exposed to EDA gas, host–guest charge transfer and refractive index modulation were induced. The [Co(TpA)dpNDI] membrane POWG exhibited a fast and remarkable response to EDA (S/N = 3.15) even at low concentration (1 ppb), which suggests the capability of this membrane POWG for EDA sensing. The sensor also showed response repeatability in the detection range of 1000 ppm to 1 ppb, and a high adsorption capacity at ambient temperature (17.46 μg cm−2).