Electrochemical characterization and sensor behaviours of carbazole based copolymers

Karbazol içerikli kopolimerlerin elektrokimyasal karakterizasyonu ve sensör davranışları

Abstract

The electropolymerization of carbazole (Cz), Nvinylcarbazole (NVCz), and copolymer of carbazole and p-Tolylsulfonyl pyrrole, P(Cz-co-pTsp) were studied onto carbon fiber microelectrodes (CFMEs) in different solution media. The detailed characterization of the resulting electrocoated homo and copolymers were studied by various techniques, i.e. cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Fourier transform infrared reflectance spectrophotometry (FTIR-ATR), ultraviolet visible spectrophotometry (UV-vis), scanning electron microscopy (SEM), and energy dispersive electron microscopy (EDX) analysis. CFMEs have variety practical advantageous and applications; one of them could be to obtain flexible micron sized polymeric films. The micron and nano sized polymeric films were obtained by CV, chronoamperometric and chronopotentiometric methods. These results indicated that the thickness of the film can be controlled by the optimum conditions. The oxidative characterization of poly-carbazole,-N-vinylcarbazole, and P(Cz-co-pTsp) were carried in different solutions in 0.1 M (i.e. sodium perchlorate (NaClO4) / propylene carbonate (PC), NaClO4 / acetonitrile (ACN), potassium perchlorate (KClO4) / PC, lithium perchlorate (LiClO4) /ACN, LiClO4 /PC and 0.05 M tetraethyl ammonium perchlorate (TEAP) / dichloromethane (CH2Cl2)).The highest electro activity and rate of polymerization were obtained for P(Cz-co-pTsp) (oxidation peak current density, 0.49 $mu A$ $cm^{-2}$) compare to PCz (0.15 $mu A$ $cm^{-2}$) and P(NVCz) (0.17 $mu A$ $cm^{-2}$). The electrocoated copolymer corresponding to an initial feed ratio of $[pTsp]_0/[Cz]_0=5$ was observed as polaron that means electron moving through the constituent atoms of a solid material, causing the neighbouring positive changes shift toward it and the neighbouring negative charges to shift away and bipolaron on indium tin oxide (ITO), its electrochromic behaviour can be monitored clearly. Ultraviolet-visible (UV-vis) of PCz and P(Cz-co-pTsp) indicate that the polymers have two charge carriers, one is polaron, the other bipolaron. Finally, random polymerization of Cz and Cz-co-pTsp were studied. In-situ UV-vis spectroscopic study show that the band gap of P(Cz-copTsp) is 2.25 eV and ~3.05±0.05 eV for PCz, which is closer to the previous findings (3.25 eV). This difference in the band gap values may come from the incorporation of the carbazole into the resulting polymer. In this study, electrochemical impedance spectroscopic (EIS) behaviour of electrocoated CFMEs was also studied for PCz, P(NVCz), and P(Cz-copTsp). Comparison of their specific capacitance (Csp) and double layer capacitance (Cdl) values (Cz-co-pTsp) for the initial feed ratio of $[pTsp]_0/[Cz]_0=200$ has shown the highest specific capacitance ($C_{sp}$=15.6 mF $cm^{-2}$) and double layer capacitance ($C_{dl}$=18.5 mF $cm^{-2}$), which corresponds the highest surface area for the polymer. The solution effect was also investigated in this study. PCz showed the highest electroactivity in 0.1 M LiClO4/ACN (at 6.5 $mu A$ $cm^{-2}$, 9th cycle was taken) compared to 0.1 M NaClO4 / PC (0.5 $mu A$ $cm^{-2}$) and 0.1 M LiClO4 /PC (0.4 $mu A$ $cm^{-2}$) during the electrogrowth of polymeric film (9th cycle was taken, at a scan rate of 100 mV $s^{-1}$). This result is in parallel line with the result of capacitive values, the highest specific capacitance ($C_{sp}$=6.80 mF $cm^{-2}$) and double layer capacitance ($C_{dl}$=160 mF $cm^{-2}$) were obtained for PCz in 0.1 M LiClO4 /ACN. PCz and P(Cz-co-pTsp) films were electrochemically deposited as well as in a needle-type carbon fiber microelectrodes (diameter ~7 $mu m$) in 0.1 M LiClO4 / ACN. The response of the sensors was tested towards different dopamine concentrations. The influence of the presence of ascorbic acid on the dopamine signal was analyzed by differential pulse voltammetry (DPV). Sensors displaying a good amperometric response to different dopamine concentrations with a detection limit of 0.27 $mu M$ (3S/N) for PCz and 0.50 $mu M$ (3S/N) for P(Cz-co-pTsp) in dopamine and an efficient protection against ascorbic acid interference at physiology concentration values (500 $mu M$) were obtained. DPV experiments show that P(Cz-co-pTsp) has the highest current (69.30 nA) compare to PCz (65.00 nA) and P(NVCz) (22.00 nA) in 0.1 M NaClO4 /ACN on carbon button microelectrode. These results are in parallel line with the result of needle-type carbon fiber microelectrode in 0.1 M LiClO4/ACN for PCz (44.60 nA) and for P(Czco- pTsp) (71.50 nA).

Özet

Bu çalışmada Karbazol (Cz), N-vinilkarbazol (NVCz) ve Karbazol ile p-Toluilsulfonil pirol kopolimeri P(Cz-ko-pTsp) farklı çözelti ortamlarında karbon fiber mikroelektrot üzerine kaplandı. Elektro- kaplama ile elde edilen homo ve kopolimerlerin detaylı karakterizasyonu çeşitli yöntemlerle incelendi: (Döngülü Voltamogram (DV), FTIR-ATR spektrofotometri, Ultraviyole spektrofotometri (UV-vis),Taramalı Elektron Mikroskopu (TEM), enerji dağılımlı X-ışınları analizi ve Elektrokimyasal Empedans Spektroskopisi (EES). Elde edilen sonuçlar elektro-polimerizasyonun elektrot tipine, tarama hızına, uygulanan potansiyele, çözelti çeşidine ve uygulanan metoda oldukça bağlı olduğunu gösterdi. Döngülü voltamogram sonuçlarına göre, kopolimer P(Cz-ko-pTsp) oluşumu içerisinde maksimum anodik akım yoğunluğu, başlangıç monomer konsantrasyon oranı $[pTsp]_0/[Cz]_0=5$ değeri için 0.49 $mu A$ $cm^{-2}$ olarak elde edildi. Bu değer polikarbazolün (PCz:0.15 $mu A$ $cm^{-2}$) anodik akım yoğunluğundan yaklaşık 3 kat daha yüksektir. In-situ UV-vis spektroskopik inceleme, P(Cz-ko-pTsp) bant aralığı 2.25 eV, PCz için ise 3.05±0.05 eV, olduğunu göstermiştir (Literatür degeri 3.25 eV, PCz). Bant aralığındaki bu küçük değişme, ürün kopolimere Cz’nin katılmasından kaynaklanıyor olabilir. Polimer elektrotların kapasitör davranışı olduğu farklı konsantrasyon ve metotlarla (DV, kronoamperometri ve kronopotansiyometri) gözlendi ve bu sonuçlar elektrotların elektrokimyasal kapasitör olarak kullanılabileceğini gösterdi. Polikarbazol (PCz) ve P(Cz-ko-pTsp) filmleri aynı zamanda mikrokapiler sistemle hazırlanan tek karbon fiber mikroelektrot üzerine 0.1 M LiClO4/ACN ortamında elektrokimyasal (Diferansiyel Pulse Voltametre (DVP)) yöntemle kaplandı. Sensor davranışı farklı dopamin konsantrasyonlarına karşı test edildi. Askorbik asidin dopamin varlığında bulunma etkisi DPV ile analiz edildi ve sonuçlar geliştirilen mikrobuton elektrotlar ile teyit edildi.