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Potentiometric Sensors for Iodide and Bromide Based on Pt(II)-Porphyrin

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      Abstract

      Pt(II) 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin (PtTMeOPP) was used in the construction of new ion-selective sensors. The potentiometric response characteristics (slope and selectivity) of iodide and bromide-selective electrodes based on (PtTMeOPP) metalloporphyrin in o-nitrophenyloctylether (NPOE), dioctylphtalate (DOP) and dioctylsebacate (DOS) plasticized poly(vinyl chloride) membranes are compared. The best results were obtained for the membranes plasticized with DOP and NPOE. The sensors have linear responses with near-Nernstian slopes toward bromide and iodide ions and good selectivity. The membrane plasticized with NPOE was electrochemically characterized using the EIS method to determine its water absorption and the diffusion coefficient into the membrane.

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      Visible-light-induced water splitting based on two-step photoexcitation between dye-sensitized layered niobate and tungsten oxide photocatalysts in the presence of a triiodide/iodide shuttle redox mediator.

      Water splitting into H2 and O2 under visible light was achieved using simple organic dyes such as coumarin and carbazole as photosensitizers on an n-type semiconductor for H2 evolution, a tungsten(VI) oxide (WO3) photocatalyst for O2 evolution, and a triiodide/iodide (I3(-)/I(-)) redox couple as a shuttle electron mediator between them. The results on electrochemical measurements revealed that the oxidized states of the dye molecules having an oligothiophene moiety (two or more thiophene rings) in their structures are relatively stable even in water and possess sufficiently long lifetimes to exhibit reversible oxidation-reduction cycles, while the carbazole system required more thiophene rings than the coumarin one to be substantially stabilized. The long lifetimes of the oxidized states enabled these dye molecules to be regenerated to the original states by accepting an electron from the I(-) electron donor even in an aqueous solution, achieving sustained H2 and I3(-) production from an aqueous KI solution under visible light irradiation when they were combined with an appropriate n-type semiconductor, ion-exchangeable layered niobate H4Nb6O17. The use of H4Nb6O17 loaded with Pt cocatalyst inside the interlayer allowed the water reduction to proceed preferentially with a steady rate even in the presence of a considerable amount of I3(-) in the solution, due to the inhibited access of I3(-) to the reduction site, Pt particles inside, by the electrostatic repulsion between the I3(-) anions and the negatively charged (Nb6O17)(4-) layers. It was also revealed that the WO3 particles coloaded with Pt and IrO2 catalysts exhibited higher rates of O2 evolution than the WO3 particles loaded only with Pt in aqueous solutions containing a considerable amount of I(-), which competitively consumes the holes and lowers the rate of O2 evolution on WO3 photocatalysts. The enhanced O2 evolution is certainly due to the improved selectivity of holes toward water oxidation on IrO2 cocatalyst, instead of undesirable oxidation of I(-). Simultaneous evolution of H2 and O2 under visible light was then achieved by combining the Pt/H4Nb6O17 semiconductor sensitized with the dye molecules having an oligothiophene moiety, which can stably generate H2 and I3(-) from an aqueous KI solution, with the IrO2-Pt-loaded WO3 photocatalyst that can reduce the I3(-) back to I(-) and oxidize water to O2.
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        Porphyrinoids for Chemical Sensor Applications.

        Porphyrins and related macrocycles have been intensively exploited as sensing materials in chemical sensors, since in these devices they mimic most of their biological functions, such as reversible binding, catalytic activation, and optical changes. Such a magnificent bouquet of properties allows applying porphyrin derivatives to different transducers, ranging from nanogravimetric to optical devices, also enabling the realization of multifunctional chemical sensors, in which multiple transduction mechanisms are applied to the same sensing layer. Potential applications are further expanded through sensor arrays, where cross-selective sensing layers can be applied for the analysis of complex chemical matrices. The possibility of finely tuning the macrocycle properties by synthetic modification of the different components of the porphyrin ring, such as peripheral substituents, molecular skeleton, coordinated metal, allows creating a vast library of porphyrinoid-based sensing layers. From among these, one can select optimal arrays for a particular application. This feature is particularly suitable for sensor array applications, where cross-selective receptors are required. This Review briefly describes chemical sensor principles. The main part of the Review is divided into two sections, describing the porphyrin-based devices devoted to the detection of gaseous or liquid samples, according to the corresponding transduction mechanism. Although most devices are based on porphyrin derivatives, seminal examples of the application of corroles or other porphyrin analogues are evidenced in dedicated sections.
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          Potentiometric ion sensors.

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            Author and article information

            Affiliations
            [1 ]Faculty of Chemistry, Biology, Geography, West University of Timisoara, 4 V. Parvan Ave, Timisoara 300223, Romania; danavlascici@ 123456yahoo.com
            [2 ]Institute of Chemistry Timişoara of Romanian Academy, 24 M. Viteazul Ave, Timisoara 300223, Romania; plesu_nicole@ 123456yahoo.com (N.P.); ancalascu@ 123456yahoo.com (A.L.); mihaelapetric@ 123456yahoo.com (M.P.); mdorosencu@ 123456yahoo.com (M.C.); anca_palade@ 123456yahoo.com (A.B.)
            [3 ]Faculty of Industrial Chemistry and Environmental Engineering, Politehnica University Timisoara, Pta Victoriei 2, Timisoara 300006, Romania; gfagadar@ 123456yahoo.com
            Author notes
            [* ]Correspondence: efagadar@ 123456yahoo.com ; Tel.: +40-256-491-818
            Journal
            Sensors (Basel)
            Sensors (Basel)
            sensors
            Sensors (Basel, Switzerland)
            MDPI
            1424-8220
            16 July 2018
            July 2018
            : 18
            : 7
            30012951
            6068665
            10.3390/s18072297
            sensors-18-02297
            © 2018 by the authors.

            Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

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