5,10,15,20-Tetraphenylporphyrin (TPP) was synthesized, and a glass optical waveguide (OWG) was coated with a gas-phase protonated TPP thin film to develop a sensor for NH3 gas detection.
The detection of hydrogen sulfide (H2S) and ethanediamine, toxic gases that are emitted from industrial processes, is important for health and safety. An optical sensor, based on the absorption spectrum of tetrakis(4-nitrophenyl)porphyrin (TNPP) immobilized in a Nafion membrane (Nf) and deposited onto an optical waveguide glass slide, has been developed for the detection of these gases. Responses to analytes were compared for sensors modified with TNPP and Nf-TNPP composites. Among them, Nf-TNPP exhibited significant responses to H2S and ethanediamine. The analytical performance characteristics of the Nf-TNPP-modified sensor were investigated and the response mechanism is discussed in detail. The sensor exhibited excellent reproducibilities, reversibilities, and selectivities, with detection limits for H2S and ethanediamine of 1 and 10 ppb, respectively, and it is a promising candidate for use in industrial sensing applications.
A simply designed sensor was able to measure trimethylamine (TMA) gas down to a concentration of 0.1 ppb at room temperature, and its response and recovery times were 1.4 s and 5.6 s, respectively.
The sensing behavior of a thin film composed of metal-free 5, 10, 15, 20-tetrakis (p-hydroxy phenyl) porphyrin and zinc phthalocyanine complex towards m-xylene, styrene, and HCl vapors in a homemade planar optical waveguide (POWG), was studied at room temperature. The thin film was deposited on the surface of potassium ion-exchanged glass substrate, using vacuum spin-coating method, and a semiconductor laser light (532 nm) as the guiding light. Opto-chemical changes of the film exposing with hydrochloric gas, m-xylene, and styrene vapor, were analyzed firstly with UV-Vis spectroscopy. The fabricated POWG shows good correlation between gas exposure response and absorbance change within the gas concentration range 10–1500 ppm. The limit of detection calculated from the logarithmic calibration curve was proved to be 11.47, 21.08, and 14.07 ppm, for HCl gas, m-xylene, and styrene vapors, respectively. It is interesting to find that the film can be recovered to the initial state with trimethylamine vapors after m-xylene, styrene exposures as well as HCl exposure. The gas-film interaction mechanism was discussed considering protonation and π-π stacking with planar aromatic analyte molecules.
The sensitive detection of trimethylamine has been accomplished by using a homogeneous optical waveguide sensor system. Also the sensor can be easily fabricated by using tetraphenylporphyrin manganese (MnTPP) as sensitive materials to detect different volatile organic compounds (VOC). NMR (H-NMR), field-emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS), infrared (IR), and ultraviolet-visible (UV-vis) instrumental means were used to characterize its structure. Gas-sensing measurements indicated that the sensing element has shown good selectivity, high sensitivity and a low detection limit level of 0.1 ppm to trimethylamine (TMA) with the presence of interference gases at room temperature. For a range of trimethylamine concentrations from 0.1 to 1000 ppm, the sensor has shown a short response time. Also the response time and recovery time are 1.5 and 50 s, respectively. Simulation experiments (dichloromethane, chloroform and carbon tetrachloride were selected as interference gases) showed little interference with its gas sensing. That may provide an ideal candidate for detecting the freshness of fish and seafood.
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