A novel TiO2-modified THPP-BCP composite optical waveguide sensor for the determination of ethylenediamine at ppb level.

Composite thin films OWG sensors show higher sensitivity than single film-based OWG sensors, making them particularly useful in the detection of trace gases. In this work, we developed a new tetra hydroxyphenyl porphyrin (THPP)-bromocresol purple (BCP)/TiO2 gel composite film-based OWG (THPP-BCP/TiO2-OWG) sensor for identifying ethylenediamine (EDA) gas. The fabricated sensor was characterized using ultraviolet and infrared spectroscopy and atomic force microscopy. The test result shows that the response of the THPP-BCP/TiO2-OWG composite film sensor to analytes was 3-4 times higher than that of the single film THPP-OWG sensor. The THPP-BCP/TiO2-OWG sensor exhibited excellent selectivity and remarkable response to EDA gas at a concentration of < 1 ppb at room temperature, with fast response (1 s) and recovery (3 s) times. The high refractive index TiO2 film contributes to OWG's sensitivity, while the THPP and BCP's sensitivity to bases further increased the sensor's response to EDA gas. The combination of THPP-BCP thin film and TiO2 gel film provides a powerful platform for OWG sensors that are highly sensitive, specific, and stable in the detection of trace gases.

Fabrication and characterization of photo-responsive metal-organic framework membrane for gas sensing using planar optical waveguide sensor.

A facile, novel fabrication approach using UV light irradiation was proposed to fabricate a photo-responsive metal-organic framework (PR-MOF-1, [Zn2-(bdc)2-(dpNDI)]n, where bdc = benzene-1,4-dicarboxylic acid; dpNDI = N,N'-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxy diimide) membrane. The morphology of the PR-MOF-1 framework evolved from a honeycomb porous structure to a densified ladder-layered structure after 60 min of UV-light illumination. The as-grown film was optically transparent and exhibited a greater sensing response to ethylenediamine (EDA) gas in the presence of interfering substances such as ammonia and dimethylamine as well as benzene, toluene, xylene, and styrene gases, as measured using an asymmetric planar optical waveguide gas sensor. When the EDA gas molecule was adsorbed on the surface of the membrane, charge transfer between them preferably occurred, leading to a change in the membrane surface conformation. As an ideal sensing material for EDA gas detection, the PR-MOF-1 membrane showed a relatively high surface sensitivity (11,000 times cm-1) after 60 min of growth, and it could quickly (in less than 2 s) detect 1 ppb of EDA gas with a significant response (S/N = 3.45). During the static gas adsorption process, the EDA gas adsorption kinetics fit well with pseudo-second-order (PSO) model, and the adsorption capacity (qe) on a unit surface showed a high value of 33.91 µg cm-2 at 283 K. The high selectivity and sensitivity of the PR-MOF-1 membrane for EDA gas indicate the effectiveness of the light irradiation method for alteration of the metal- organic framework membrane structure and control of the gas sensing properties.

Substituent Effect on Porphyrin Film-Gas Interaction by Optical Waveguide: Spectrum Analysis and Molecular Dynamic Simulation.

Substituent effect on optical gas sensing performance in porphyrin-based optical waveguide detection system was studied by molecular dynamics simulation (MDS), absorption/emission spectrum analysis, and optical waveguide (OWG) detection. The affinities of porphyrin with seven types of substituents (-H, -OH, -tBu, -COOH, -NH2, -OCH3, -SO3-) on para position of meso-phenyl porphyrin toward gas molecules in adsorption process were studied in different size of boxes with the same pressure and concentration. Analyte gases (CO2, H2S, HCl, NO2) were exposed to porphyrin film in absorption spectrophotometer, and in OWG with evanescent field excited by a guiding laser light with 670 nm wavelength. The extent of interaction between host molecule and the guest analytes was analyzed by the number of gas molecules in vicinity of 0.3 nm around substituents of porphyrin molecules. Optical waveguide results reveal that sulfonate porphyrin is mostly responsive to hydrochloride, hydrosulfide gas and nitrogen dioxide gases with strong response intensity. Molecular dynamics and spectral analysis provide objective information about the molecular state and sensing properties. Molecular rearrangements induced by gas exposure was studied by spectral analysis and surface morphology before and after gas exposure taking hydrosulfide gas as an example. Film-gas interaction mechanism was discussed in terms of each gas and substituent group characters.