Fast fabrication, gas sense characteristics and kinetics of cubic Ti-BIPA-TC-MOF film composite optical waveguides

A cubic Ti-metal-organic framework (MOF) ([Ti₂–(TpA)₂–H₂BIPA]), constructed from a titanium metal centre and a benzo-imidephenanthroline tetracarboxylic acid (H₄BIPA–TC) ligand was photo-inductively grown on the surface of a titanium dioxide (TiO₂) composite optical waveguide (COWG) substrate and the influence of photo-inductive growth period on the [Ti₂–(TpA)₂–H₂BIPA] film surface morphology, optical properties and gas adsorption/sensing characteristics was investigated. The results showed that [Ti₂–(TpA)₂–H₂BIPA] formed a cubic structure after grew for only 5 min. As an ideal gas adsorbent, it exhibits a specific response to ethylenediamine (EDA) among various benzene, amine and acid gases, due to the intrinsic electron deficiency, rich COOH active sites of the Ti–BIPA–TC–MOF–5 frame and the higher molar refractive indexes or dipoles of EDA than other gases. In the EDA concentration range from 10 ppt to 100 ppm, the Ti–BIPA–TC–MOF–5 film COWG exhibited a rapid, repeatable response. Moreover, the Ti–BIPA–TC–MOF–5 film COWG was relatively stable, within 17 d of EDA detection, the response intensity was almost constant and slightly decreased within 40 d. In a static gas adsorption stage at 283–313 K, the EDA gas adsorption behaviour of the Ti–BIPA–TC–MOF–5 film is consistent with the pseudo-second-order kinetic model.