Synthesis And Gas Sensing Properties Of Tetrakis (4-nitrophenyl) Porphyrin,tetraphenylporphyrin,and Its Zinc And Copper Compound

The amount of pollutants are becoming more and more along with the development of national economy,among them,toxic or harmful gases are the main cause that accrue pollution in human living area.Therefore,it is indispensible to develop low-cost chemical sensors to accurately detect toxic substance with low concentration.This paper mainly concentrates on the development of chemical sensors based on porphyrin and it’s metal complexes;the electronic transition behavior and gas sensitivity of free-base porphyrins and it`s derivatives;interaction of free-base porphyrin with acidic gases;development of optical and electrochemical sensors based on free-base porphyrin and it`s derivatives;comparison of two gas detection methods at room temperature.The semiconductor-type of porphyrins and it`s derivatives were discussed by response signals of electrochemical sensors when exposed to analyte gases.The more details are as follows:（1）Tetraphenylporphyrin（TPP）,zinc tetraphenylporphyrin（ZnTPP）,copper tetraphenylporphyrin（CuTPP）and Meso-tetrakis（4-nitrophenyl）porphyrin（TNPP）were synthesized by Alder and Lindsey method.UV-vis spectra,Fourier infrared（FT-IR）spectroscopy,nuclear magnetic resonance（¹H NMR）were applied to study thier spectral charactersitics;besides X-ray phtoelectron spectroscopy（XPS）was utilized to characterize valence state of Cu ions in CuTPP powders The results indicated that,Soret-peak of metalloporphyrins were blue shifted camparing to that of free-base porphyrin（blue-shift degreee of ZnTPP and CuTPP was different）,while the Soret-peak of TNPP is red-shifted,xhich is related to the electronic transition of the-NO₂ and porphyrin ring.The disappearance of the N-H bond and appearance of the metal-H bond in the FT-IR spectrum indicated formation of the metal porphyrin.Due to electron-withdrawing groups in TNPP,the density of electron clouds at the periphery of the porphyrin molecule is reduced,resulting in the displacement of hydrogen atoms to low magnetic fields.The XPS data of CuTPP showed that the valence of Cu ions in the complex was 2.（2）A glass optical waveguide was coated with a gas-phase protonated TPP thin film to develop a sensor for the detection of NH₃ gas.The results showed that the TPP thin film agglomerate to H-based J-type aggregates after treatment of TPP sensing element with H₂S gas.The protonated TPP molecules in the OWG sensing element acted as NH₃ receptors because of the gas-phase protonated TPP film morphologically changed from J-type aggregates to free base monomers when it was deprotonated by exposure to NH₃.In this case,H₂S gas could be used to increase the relative amount of J-type aggregation in the TPP film and restore the sensor response.The reversible surface morphology of the TPP film was analyzed by ¹H NMR spectroscopy,atomic force microscopy（AFM）,and UV-vis spectroscopy.In addition,TPP electrochemical sensors revealed certain response to H₂S,NO₂ gases at room temperature.（3）ZnTPP was used as sensing material to fabricate optical waveguide thin film for the detection of NO₂ gas.The surface morphology of the ZnTPP film was analyzed by AFM and SEM microscopies.Spectral changes of the gas-sensitive element before and after exposure to NO₂ gas were investigated by FT-IR,UV-vis and XRD,then gas-sensing mechansim was discussed.Experimental data indicated that,the gas-sensing mechanism of ZnTPP undergoes two-step reactions;first step reflected in the change of FT-IR,the second step chages the color of gas-sensing element.Furthermore,ZnTPP as a sensitive material,the electrochemical sensing element was developed and its gas sensitivity to NO₂ was monitored.The result depicted,detection limit was found to be much higher than the lowest concentration detected by the optical waveguide method.（4）The CuTPP was fixed on the surface of the optical waveguide to form thin films,and an electrochemical gas sensor was fabricated by coating CuTPP on the surface of the ceramic tube,then gas-sensitivity of the two sensitive elements to various gases was monitored.AFM and SEM microscopies were used to charatereised the surface morphologies of the sensitive element.The gas-sensing properties of CuTPP were the same with thoes of the ZnTPP film/K⁺-exchanged optical waveguide gas sensor,but the gas sensitivity to NO₂ gas was poorer than that of the ZnTPP gas sensor.Meanwhile,the gas-sensing mechansim of CuTPP sensitive element to NO₂gas was simular with that discribed in Zn TPP.（5）The detection of hydrogen sulfide（H₂S）and ethanediamine（EDA）,toxic gases emitted from industrial processes,is important for health and safety.An optical sensor,based on the absorption spectrum of 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 EDA.The analytical performance characteristics of the Nf-TNPP-modified sensor were investigated and the response mechanism was discussed in detail.The sensor exhibited excellent reproducibilities,reversibilities,and selectivities,with detection limits for H₂S and EDA of 70 ppt and10 ppb,respectively,and is a promising candidate for use in industrial sensing applications.In addition,the response of TNPP electrochemical sensors to various gases showed that semiconductor-type of the TNPP was simular with that of TPP.