Preparation and Optical Study of Zn(II) Metal Organic Framework Thin Film for Xylene Gas Sensing Application

An optically transparent metal‐organic framework thin film, [Zn2(bdc)2(dpNDI)]n, is grown on the tin‐diffused glass substrate using layer‐by‐layer liquid phase epitaxial (LPE) growth method at room temperature (20 °C). The influence of growth cycle on morphology, optical properties, and gas sensibility of [Zn2(bdc)2(dpNDI)]n thin film is studied for the first time. The [Zn2(bdc)2(dpNDI)]n thin film displays a honeycomb framework with a large pore size, uniform surface morphology, and higher absorbance after 11 cycles of growth. The optical gas sensing performance of [Zn2(bdc)2(dpNDI)]n thin films is then monitored using the planar optical waveguide (POWG) gas detection system under UV light (395 nm) irradiation. As a result, the [Zn2(bdc)2(dpNDI)]n thin film POWGs exhibit a greater adsorption response to xylene gas, due to the larger refractive index and absorbance changes upon various volatile organic compounds (VOCs). The thin film POWG sensor shows fast, reversible response to xylene gas, in the concentration range of 1–1000 ppm. Furthermore, the xylene gas adsorption kinetics at different temperature is also investigated, in which the xylene gas adsorption behaviors of [Zn2(bdc)2(dpNDI)]n thin film follow a pseudo‐second order (PSO) model; at room temperature, the adsorption capacity on the unit surface is 7.92 μg cm−2. The [Zn2(bdc)2(dpNDI)]n thin films are grown on the surface of optical waveguide glass slides by controlling the growth cycle at room temperature. The influences of growth cycle on gas sensibility are studied subsequently. Under UV light irradiation, the thin film exhibits greater adsorption response to xylene gas. The gas adsorption kinetics follows pseudo‐second‐order model.