Optical gas sensing and kinetics of azobenzene modified niobium metal-organic framework film composite optical waveguides

Abstract

A niobium metal-organic framework (Nb-MOF) film with graphene-like structure fabricated on lithium niobate (LiNbO3) film composite optical waveguides1 (COWG) substrate, then modified by embedding azobenzene2 (AZB) using UV-light irradiation approach. The characteristics, including structure, morphology, gas sensitivity and kinetics were studied. After modifying, film morphology evolves to an ant-nest structure, which resulted in a flatter surface, smaller pores, higher optical density and refractive index. In dynamic gas sensing test (at 298 K, 0.92 atm), [email protected] film COWG uniquely responded to H2S coexisting with the same concentration (10 ppm) of benzenes and amines. The proton transfer and Lewis acid-base interactions were dominant during H2S gas adsorption. A spatial hindrance to proton transfer results a lower sensitivity of [email protected] film COWG than that of Nb-MOF film COWGs. H2S gas adsorption kinetics followed the pseudo-second order (PSO)3 model, the adsorption capacity (qe) on per unit surface exhibits a medium value of 77.34 ng·cm−2 at 298 K.