Surface modified Ti-MOF/TiO2 membrane and its gas sensing characteristics

A titanium metal organic framework/Titanium dioxide (Ti-MOF/TiO2) composed membrane was fabricated by light inductive growth of Ti-MOF ([Ti2-(TpA)2-NDI]n, TpA=terephthalic acid, NDI=1,8,4,5-naphthalene-tetracarboxdiimide) on a TiO2 film composite optical waveguide (COWG) substrate. Ti-MOF/TiO2 membrane conforms a mesoporous structure with 24 nm of pore size and 108 nm of thick via continuous growth for 40 min under 340 nm UV-light illumination. Under ambient condition, in terms of COWG sensors, Ti-MOF/TiO2 exhibited the greatest response to ethylenediamine (EDA), followed by NO2, methylamine, trimethylamine, when exposed to 15 types of benzenes, amines, and acidic gases. In order to improve response selectivity, Ti-MOF/TiO2 film was modified with 1,3,3-trimethylindolinonaphthospirooxazine (SP) forming SP@Ti-MOF/TiO2 COWG. This modified COWG showed improved selectivity response by showing robust response to EDA and a negligible response to others. When the EDA gas molecule was adsorbed on the surface of the membrane, charge transfer between them preferentially occurred, leading to a change in the optical parameter. The surface-modified SP@Ti-MOF/TiO2 COWG showed a fast (3 s) and reversible response with a wide detection range (0.1-1000 ppb) to EDA gas without the interference of BTXs, acidic gases, and other amines.