Synthesis of some functional conducting polymers, characterization, Mott-Schottky analysis and sensor applications

Until the late 1970's, polymeric materials were associated with low conductivity. In fact, this low conductivity has been used to advantage in applying polymeric materials as insulators. This concept has changed with discovery of conducting polyacetylene and declaration of poly-p-phenylene, polypyrrole, polythiophene, polyaniline, polycarbazole, and polyindole among other polymers. These polymers are called as conducting polymers (CPs). CPs, thus, have attracted strong interest in materials science because they are utilized for advanced technologies due to their interesting and unique electrical conductivity and electroactivity. They are mostly used in promissing technological applications such as biosensor, biomedical science, electrochromic, photovoltaic devices, batteries, light-emitting diodes, supercapacitors, and actuators. Electrochemical impedance spectroscopy (EIS) is the most widely used one of electroanalytical techniques. EIS is a non destructive methode and useful in research of electrode / electrolyte interface providing sensitive information about the surface. The biggest advantage of this technique is that it provides the distinction in the different processes which are simultaneously taken place on the surface of electrode. Several electronic characteristics of a semicocnducting film can be obtained from the semiconductor/liquid interface behavior when a bias voltage is applied to modulate the width of the space-charge capacitance, and thus the value of the capacitance.The most common and established method for the capacitance determination is impedance spectroscopy technique. Mott-Schottky analysis can be performed by using EIS technique to obtain semicocnducting parameter of semiconducting film where capacitance voltage measurement is carried out, and thus the carrier density, the flat-band potential of semiconductor materials can be easly found. Important process can take place in the semicoductor modifed electrode when immersed in electrolyte such as ions adsorption, double layer, charge transfer between the electrode and electrolyte, during this process, a charge separation will occur because of electron transfer across the interface. and mass transfer. The study of interface of semiconductor/electrolyte is important issue due to both basic and practical aspect of science. Conducting polymers as the electrode material have been mostly used the aferomentioned potential applications. It has been observed that the interphase properties of the electrode and the electrolyte affect processability of these materials. The electrical conductivity of organic semiconductors depends on the carrier density (electron or hole) and carrier mobility. Carrier density is affected by the some factors which are morphology of the solid film, the nature of the organic semiconductors and electroylte. Polypyrrole is a widely used conducting polymer in terms of electrical conductivity and environmental stability. Pyrrole-1-propionic acid (PPA), pyrrole derivative, has emerged as a novel material with biosensor construction and reported in a few papers. Poly(pyrrole-1-propionic acid) (Poly(PPA)) film in biosensor construction enables rapid diffusion, fast response and high response signal due to its low conductivity and self-limiting growth. Huge amount of research dedicated to the electropolymerization of pyrrole and its derivatives in the last two decades. However, substituted pyrrole on the 3-position have received much less attention compared to corresponding thiophenes due to the limited availability of 3-substituted pyrroles, their chemical synthesis being quite complex. On the other hand, substitution in the 3-position of the pyrrole ring gives the possibility of introducing specific functional groups on the polypyrrole chain. Pyrrole-3-carboxylic acid (PCA) is 3-substituted pyrrole derivative which can be polymerized the 2-5 position offers the possibility of attaching biomaterial. Electrochemically synthesized poly(pyrrole-3-carboxylic acid) (PPCA) were used in ion exchange, pH measurements, and sensor. Polycarbazole (PCz) and its derivatives have been widely studied in the literature. PCz is a high thermal stability, mechanical strength conducting polymer causing the diffuclty in workability. However, PCz has drew interest with developments in synthetic methodology. Electroactive PCz has found applications in electrochromic devices, transistors, in electrochemical sensors. Carbazole-9-acetic acid (CzA) is important derivative of carbazole because carboxylic acid group is of the active functional group, and it plays an important role in further modificiation. In the first part of thesis, PPA was electrochemically polymerized on a glassy carbon electrode (GCE) in various electrolytes (NaClO4, Et4NBF4, Bu4NClO4,and Bu4NPF6) using cyclic voltammetry (CV). The structure and morphology of the modified electrode was characterized by fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The morphological characterizations of the poly(PPA) films synthesized in the various supporting electrolyte solutions were demonstrated by SEM and AFM. Electrochemical impedance spectroscopy (EIS) and Mott–Schottky (M–S) analysis were performed to collect information about the semiconducting properties of the poly(PPA) films. From the Mott–Schottky analysis, the carrier densities (ND) of the poly(PPA) films obtained were 3.25×1016,1.59×1016, 1.17×1016, and 0.52×1016 cm-3,and the flat-band potentials (EFB) were 0.41, 0.32, 0.37, and 0.36 V for the poly(PPA) films in NaClO4, Et4NBF4, Bu4NClO4, Bu4NPF6 , respectively. The resulting Mott–Schottky plots of the poly(PPA) films indicate that the films are p-type semiconductors. EIS analysis were performed to determine the capacitive behaviors by variation of electrolyte types in a monomer-free solution. An equivalent-circuit model of R(W(CR)(QR))(CR) was used to fit the theoretical and experimental data to interpret the polymer electrode/electrolyte interface properties and to provide information about equivalent circuit parameters with variation of electroltye nature. In the second part of thesis, we describes that the fabrication of Indium Tin Oxide /gold nanoparticles/nickel oxide/poly(Pyrrole-N-propionic acid) (ITO/GNPs/NiO/poly(PPA)) multilayered film, and modification with Tyrosinase (Ty).The ITO/GNPs/NiO/poly(PPA) electrode was fabricated by sequential electrochemical assembly onto ITO substrate which electrochemical deposition provides a facile, inexpensive technique for synthesis of multilayered film within the adherent morphology with controllable film thickness. CV, FTIR-ATR, SEM, and AFM were used to characterize the film assembly processes. The properties of a semiconductor/electrolyte interface were investigated based on the Mott–Schottky approach for the modified electrodes, with the flat band potential according to the potential intercept and the carrier density according to the linear slopes. The ND and EFB of ITO/GNPs/NiO/poly(PPA) were obtained as 2.48x1021 cm-3 and 0.26 V, respectively. Tyrosinase was immobilized using carbodiimide coupling reaction. The bioelectrode was characterized by FTIR-ATR, SEM, AFM, electrochemical impedance spectroscopy (EIS). A Randles equivalent circuit was introduced for modeling the performance of impedimetric biosensing for the detection of the dopamine (DP) and the interface of bioelectrode/electrolyte. The EIS of the ITO/GNPs/NiO/poly(PPA)-Ty exhibited significant changes in the charge transfer resistance (RCT) value toward the detection of dopamine over a linear range of 80 µM to 0.2 mM with a limit of detection (LOD) of 5.46 µM. In the third part of thesis, pyrrole-3-carboxylic acid (PCA) was electropolymerized on a GCE. The Electropolymerization process was performed in 0.1 M NaClO4/ACN, Et4NBF4/ACN using cyclic voltammetry. Urease (Urs) was immobilized onto poly(pyrrole-3-carboxylic acid) (PPCA) modified GCE via covalent binding, exploiting EDC/NHS chemistry. Electrochemical impedance spectroscopy was used to investigate the interfacial behavior of urease immobilized PPCA surfaces at open circuit potential (OCP). The impedance spectra were fitted before and after immobilization of Urs using equivalent circuits of R(C(R(Q(RW)))), which describe changes due to the Urs immobilization process. After immobilization of urease onto the PPCA matrix, the RCT increased for electrodes, which RCT of urease immobilized PPCA-NaClO4 matrixes were lower than that of the urease immobilized PPCA-Et4NBF4 matrixes indicating higher charge transfer ability. A decrease in double layer capacitance (Cdl) values when Urs was immobilized at the PPCA-NaClO4 electrode surface was observed, whereas an increase in Cdl values at the PPCA-Et4NBF4 electrode surface was observed. The Mott-Schottky approach was performed to investigate interface properties of the protein modified polymer matrix. It was possible to observe that the processes occurred by the immobilization of enzyme on the polymer matrix with changes in the semiconducting properties of the PPCA films. The electrodes with immobilization of urease resulted in a n-type semiconducting behavior revealing a positive slope. An increase in acceptor concentration of the electrodes, and a shift of the EFB to more positive values with increasing amount of urease was observed as well. The Urs based electrode (PPCA-NaClO4-Urs) was used for detection of urea, which was detected in range of 0.9 to 14 mM with a detection limit (LOD) of 8.28 µM. In the fourth part of thesis, the electrochemical polymerization of 9-carbazole acetic acid (CzA) monomer was performed in various feed ratios of room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) in acetonitrile (ACN) to investigate the effect of RTIL on morphology, impedance, capacitance, and semiconducting properties. It was observed that the low amounts of the RTIL (10 and 20 %) in the mixture improve the electrochemical polymerization process compared to the RTIL-free electrolyte. Indeed, after a certain amount % BMIMBF4 which was threshold (40%), the process turned strongly unfavored. SEM was used to understand the influence of the feed ratio of BMIMBF4 to ACN on the surface structure of obtained polymer films. The surface morphology of poly(9-carbazole acetic acid) (PCzA) revealed dependence on the feed ratio of BMIMBF4. Electrochemical impedance spectroscopic experiments were performed in a pure BMIMBF4 (100 %) indicated that as the feed ratio of BMIMBF4 increased, the capacitive behavior of the polymer decreased. From the Mott–Schottky analysis, the highest flat band potential (EFB=2.87 V) was obtained for the 40% PCzA-BMIMBF4 film.