Emine Ülker

Tuning the Electronic Properties of Prussian Blue Analogues for Efficient Water Oxidation Electrocatalysis: Experimental and Computational Studies

Although several Prussian Blue analogues (PBAs) have been investigated as water oxidation catalysts, the field lacks a comprehensive study that focuses on the design of the ideal PBA for this purpose. Here, members of a series of PBAs with different cyanide precursors have been investigated to study the effect of hexacyanometal groups on their electrocatalytic water oxidation activities. Cyclic voltammetric, chronoamperometric, and chronopotentiometric measurements have revealed a close relationship between the electron density of electroactive cobalt sites and electrocatalytic activity, which has also been confirmed by infrared and XPS studies. Furthermore, pH-dependent cyclic voltammetry and computational studies have been performed to gain insight into the catalytic mechanism and electronic structure of cyanide-based systems to identify possible intermediates and to assign the rate-determining step of the target process.

A Novel Polyaniline–Poly(3-Methylthiophene)–Poly(3,3′-Diaminobenzidine) Electrode for the Determination of Dopamine in Human Serum

A polyaniline–poly(3-methylthiophene)–poly(3,3′-diaminobenzidine) film was deposited on a platinum disc electrode in dichloromethane containing tetrabuthylammonium perchlorate supporting electrolyte and used for the amperometric determination of dopamine. At a pH of 2.0, this electrode allowed successful determination at a lower potential than the oxidation potential of dopamine. The limit of detection, limit of quantification, and the linear dynamic range were determined to be 1.63 × 10−5 mM, 5.43 × 10−5 mM and 5.43 × 10−5 to 100.0 mM (R2 = 0.997), respectively. The reproducibility was investigated by using three different films and good analytical results were obtained. In addition, the modified electrode was successfully employed to determine dopamine in human serum with good recoveries.

Water Oxidation Electrocatalysis with a Cobalt-Borate-Based Hybrid System under Neutral Conditions

The development of new water oxidation electrocatalysts that are both stable and efficient, particularly in neutral conditions, holds great promise for overall water splitting. In this study, the electrocatalytic water oxidation performance of a new cobalt-based catalyst, Co3 (BO3 )2 , with a Kotoite-type crystal structure is investigated under neutral conditions. The catalyst is also hybridized with CNTs to enhance its electrocatalytic properties. A remarkable increase in catalytic current along with a significant shift in the onset overpotential is observed in Co3 (BO3 )2 @CNT. Additionally, CNT addition also greatly influences the surface concentration of the catalyst: 12.7 nmol cm-2 for Co3 (BO3 )2 @CNT compared with 3.9 nmol cm-2 for Co3 (BO3 )2 . Co3 (BO3 )2 @CNT demands overpotentials of 303 and 487 mV to attain current densities of 1 and 10 mA cm-2 , respectively, at pH 7. Electrochemical and characterization studies performed over varying pH conditions reveal that the catalyst retains its stability over a pH range of 3-14. Multi-reference quantum chemical calculations are performed to study the nature of the active cobalt sites and the effect of boron atoms on the activity of the cobalt ions.

Non-Enzymatic phenol determination in river water over modified electrode with poly(3-methylthiophene)

This paper describes non-enzymatic phenol determination using poly(3-methylthiophene) coated Pt electrode. Modified electrode was prepared on Pt disc surface in dichloromethane medium containing 500 mM 3-methylthiophene (3MT) and 100 mM tetrabuthylammonium perchlorate (TBAP). This electrode was used for amperometric determination of phenol in NaHSO4 / Na2SO4 (SBS) solution at pH 2.0. For this purpose, 0.70, 0.80 and 0.90 V potentials were applied and results were compared. Limit of detection and linear range were found as 4.22x10-5 and 1.41x10-4 – 4.00 mM (with R2=0.9932) at 0.90 V working potential, respectively. Repeatability of method was tested by using at least three modified electrode for 0.5, 1.0 and 2.0 mM phenol concentrations and relative standard deviation (RSD were found as 2.49%, 1.92% and 2.75%, respectively. To test the accuracy of method and matrix effect, phenol determination was carried out for 1.0 and 2.0 mM phenol concentrations in artificially contaminated river water samples at optimum condition and recovery values were found as 96.44% and 99.60%, respectively. Proposed method was found as simple, rapid and economic for phenol determination. Keywords: Phenol; Poly(3-methylthiophene); Amperometric determination; Non-enzymatic DOI: 10.17350/HJSE19030000030 Full Text:

Electroanalysis of Pyrocatechol in River Water Over Pt Electrode Modified with Polyaniline-Poly(3-Methylthiophene)-Poly(3,3 -Diaminobenzidine) Film

NaHSO/NaSO (SBS) (pH 2.0) çözeltisi içerisinde amperometrik I-t yöntemi kullanılarak polianilin-poli(3metiltiyofen)-poli(3,3’-diaminobenzidin) (PANI P3MT PDAB) kaplı Pt disk elektrot üzerinden pirokatekol tayini başarılı bir şekilde gerçekleştirildi. 0,45 V–0,65 V aralığında potansiyel değerleri uygulandı ve 0.50 V optimum potansiyel olarak belirlendi. Analitik parametreler (gözlenebilme sınırı, alt tayin sınırı ve doğrusal çalışma aralığı) sırasıyla 7.37×10-5, 2.47×10-4 ve 2.47×10-4-25.0 mmol.L-1 olarak bulundu. Ayrıca, matriks girişimini ve geliştirilen yöntemin doğruluğunu test etmek için, pirokatekol derişimi 5.0 ve 10.0 mmol.L-1 olacak şekilde yapay olarak kirletilmiş nehir sularında pirokatakol tayini gerçekleştirildi. Geri kazanım değerleri sırasıyla % 101.1 ve % 101.2, olarak elde edildi. Pirokatekolün yükseltgenme potansiyelinden (0.62 V) daha düşük potansiyelde (0.50 V) matriks etkisi olmaksızın pirokatakol tayini gerçekleştirildi.

Synthesis of Poly(Vinylferrocene) Perchlorate/Poly(3,3’-Diaminobenzidine) Modified Electrode in Dichloromethane for Electroanalysis of Hydroquinone

Poly(vinylferrocenium) perchlorate-poly(3,3’-diaminobenzidine) (PVF+ClO4–-PDAB) composite film was synthesized electrochemically for the first time on Pt disc electrode in a dichloromethane solution containing poly(vinylferrocene) (PVF) polymer, 3,3’-diaminobenzidine (DAB) monomer and tetrabutylammonium perchlorate as supporting electrolyte. This modified electrode was characterized using cyclic voltammetry, Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometry, atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) methods and it was used for amperometric determination of hydroquinone (HQ) at potential ranges of 0.40 and 0.60 V. The best analytical results for HQ was obtained at 0.45 V in NaHSO4/Na2SO4 solution (pH 2.0) and limit of detection, limit of quantification and linear response range were found as 7.469 × 10-5, 2.489 × 10-4 and 2.489 × 10-4-65.0 mmol L-1 (R2 = 0.996), respectively. These results were compared to poly(3,3’-diaminobenzidine) (PDAB) coated and uncoated Pt electrodes. The best analytical results were obtained with composite film because of behavior as electron transfer mediator of PVF.