Gümüş nanoparçacıklar içeren fonksiyonel çok duvarlı karbon nanotüp ile modifiye edilmiş elektrotlar ile diklofenak'ın voltametrik tayini
Voltammetric determination of diclofenac with electrodes modified with functional multiwalled carbon nanotubes containing silver nanoparticles
- Tez No: 995244
- Danışmanlar: DOÇ. DR. SEVGİ GÜNEY
- Tez Türü: Yüksek Lisans
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2026
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Lisansüstü Eğitim Enstitüsü
- Ana Bilim Dalı: Kimya Ana Bilim Dalı
- Bilim Dalı: Kimya Bilim Dalı
- Sayfa Sayısı: Belirtilmemiş.
Özet
Diklofenak ([2-[(2,6-Diklorofenil)amino]fenil]asetik asit) (DCF), ticari olarak erişilebilir bir non-steroidal antiinflamatuar ilaç olup, zatürre veya iltihap gibi çeşitli hastalıkların tedavisinde dünya genelinde kullanılmaktadır. DCF'nin standart seviyeleri insanlar için güvenli olsa da aşırı doz alımı (günde 150 mg'ın üzerinde) aplastik anemi gibi çeşitli yan etkilere yol açabilir. Ayrıca, çevrede 1 μg/L'nin altında bulunsa bile DCF'nin varlığı bazı hayvan türleri üzerinde önemli derecede olumsuz etki yaratabilir. Çeşitli hastalıkların tedavisinde en yaygın kullanılan farmasötiklerden biri olan DCF, atık suyun uygunsuz şekilde işlenmesi veya tüketiciler tarafından ilaçların hatalı kullanımı sonucunda çevreyi ciddi şekilde kirletebilir. İlaç endüstrisinde diklofenak talebinin yüksek olması nedeniyle, kantifikasyonu için yüksek performanslı sıvı kromatografisi, gaz kromatografisi, kapiler elektroforez, spektrofotometri, spektroflorometri ve ince tabaka kromatografisi gibi farklı analitik yöntem kullanılsa da bu yöntemlerin numune ön işlemi (ekstraksiyonlar veya kimyasal reaksiyonlar), ön türevlendirme, zaman alıcı analiz, ihtiyaç duyulan teknisyenler ve ekipmanın bakımı nedeniyle yüksek analiz maliyeti gibi bazı dezavantajları vardır. DCF'nin karakterizasyonu ve miktar tayini için elektrokimyasal teknikler, daha kısa analiz süreleri, daha düşük maliyet, iyi hassasiyet ve seçicilik, bazı durumlarda numunenin ön işlem gerektirmemesi gibi birçok avantaj nedeniyle öne çıkmaktadır. Elektrokimyasal tekniklerde, analitik parametreler elektrodun tepkisine bağlı olduğundan, çalışma elektrodu önemli bir rol oynar. Bu nedenle çeşitli malzeme ve tekniklerin kullanılmasıyla Kimyasal Olarak Modifiye Edilmiş Elektrotlar (KME) hazırlanarak elektrotların analizdeki verimlilikleri artırılabilir. Çünkü, KME'ler analitlerin çalışma elektrodu yüzeyinde gerçekleşen reaksiyonlarını katalizleyerek indirgenme veya yükseltgenme pik potansiyellerini azaltır ve analizin duyarlılığının ve seçiciliğinin gelişmesini sağlarlar. Bu çalışmada, gümüş nanoparçacıklar (AgNPs) içeren karboksil fonksiyonel-çok duvarlı karbon nanotüp (MWCNT-COOH) ve hidroksil fonksiyonel-çok duvarlı karbon nanotüp (MWCNT-OH) kompozit malzemeler sentezlenmiştir. Sentezlenen kompozit malzemeler taramalı elektron mikroskobu (SEM), geçirimli elektron mikroskobu (TEM) ve enerji dağılımlı X-ışını spektroskopisi (EDX) yöntemleri kullanılarak karakterize edilmiştir. İlave olarak, sentezlenen kompozit malzemeler camsı karbon elektrotların (GCE) modifikasyonunda kullanılarak MWCNT-COOH@AgNPs/GCE ve MWCNT-OH@AgNPs/GCE sensör sistemleri geliştirilmiş ve literatürde ilk defa DCF'nin elektrokimyasal tespitinde kullanılmışlardır. DCF'nin, hazırlanan modifiye elektrotlar üzerindeki elektrokimyasal yükseltgenmesine ait tarama hızı, pH, girişim etkisi gibi analitik parametreler, döngülü voltametri (CV) ve diferansiyel puls voltametrisi (DPV) yöntemleri kullanılarak incelenmiş ve DCF'nin tespiti için en uygun deneysel koşullar belirlenmiştir. DCF'nin geliştirilen modifiye elektrot sistemleri üzerindeki elektrokimyasal yükseltgenmesine ait reaksiyon kinetiği ve reaksiyon mekanizması aydınlatılarak belirlenen en uygun analiz koşullarında DCF'nin gerçek ilaç örneğinde analizi gerçekleştirilmiştir. Geliştirilen sensörlerin morfoloji ve yüzey kimyası; özellikle oksijen fonksiyonel gruplarının türü ve dağılımının, sensörlerin DCF analizinde sergiledikleri elektrokimyasal performansları üzerindeki etkisini dikkate alarak değerlendirilmiştir. Elde edilen sonuçlara dayanarak, MWCNT-OH@AgNPs/GCE sensör ile DCF analizinde, MWCNT-COOH@AgNPs/GCE'ye kıyasla daha düşük bir tayin sınırı (LOD) elde edilmiştir. Ayrıca, önerilen MWCNT-OH@AgNPs/GCE sensörün iyi geri kazanımları, ticari ilaç örneği test edilerek doğrulanmıştır. Elde edilen sonuçlar, MWCNT-OH@AgNP' lerin çeşitli örneklerde az miktardaki analitleri tespit etmek için sensörlerin geliştirilmesinde önemli bir adımı temsil etmektedir.
Özet (Çeviri)
Diclofenac ([2-[(2,6-dichlorophenyl)amino]phenyl]acetic acid) (DCF) is a commercially available non-steroidal antiinflammatory drug widely used around the world for the treatment of various diseases, including pneumonia and inflammatory conditions. Although standard therapeutic levels of DCF are considered safe for humans, excessive intake (above 150 mg per day) may lead to several adverse effects, such as aplastic anemia. Furthermore, even at concentrations below 1 μg/L in the environment, DCF can exert significant negative effects on various animal species. As one of the most commonly used pharmaceuticals in medical treatments, DCF poses a considerable risk to environmental systems when wastewater is improperly treated or when medications are inappropriately disposed of by consumers. Due to the high demand for diclofenac in the pharmaceutical industry, various analytical methods—such as high-performance liquid chromatography, gas chromatography, capillary electrophoresis, spectrophotometry, spectrofluorometry, and thin-layer chromatography—are employed for its quantification. However, these techniques have several disadvantages, including sample pretreatment requirements (extractions or chemical reactions), derivatization steps, time-consuming analyses, the need for specialized technicians, and high analytical costs associated with equipment maintenance. Electrochemical techniques have emerged as attractive alternatives for the characterization and quantification of DCF due to their shorter analysis times, lower cost, good sensitivity and selectivity, and, in some cases, the elimination of sample pretreatment. Because analytical parameters in electrochemical analyses depend on the electrode response, the choice of working electrode is of critical importance. Chemical Modified Electrodes (CMEs) can be prepared using various materials and fabrication strategies to enhance electrode performance. By catalyzing the redox reactions of analytes occurring on the electrode surface, CMEs reduce oxidation or reduction peak potentials and thereby improve the sensitivity and selectivity of the analysis. In this study, composite materials consisting of silver nanoparticles (AgNPs) combined with carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) and hydroxyl-functionalized multi-walled carbon nanotubes (MWCNT-OH) were synthesized. These composites were used to modify glassy carbon electrodes (GCE), resulting in the development of MWCNT-COOH@AgNPs/GCE and MWCNT-OH@AgNPs/GCE sensor systems, which were employed for the first time in the literature for the electrochemical detection of DCF. Analytical parameters related to the electrochemical oxidation of DCF-such as scan rate, pH, and potential interference effects-were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV), and the optimal experimental conditions for DCF determination were established. The reaction kinetics and mechanism of DCF oxidation on the modified electrodes were elucidated, and under these optimized conditions, DCF was successfully quantified in a commercial pharmaceutical sample. Functionalization of multi-walled carbon nanotubes with silver nanoparticles provided a synergistic effect that enhanced both the electroactive surface area and electron-transfer capabilities. This resulted in a significantly improved current response and a lower detection limit. To characterize the nanostructure and performance of the sensor, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) were employed, and the results were compared with those obtained using a multi-walled carbon nanotube–modified glassy carbon electrode and an unmodified glassy carbon electrode. In the first part of the study, the electrochemical behavior of DCF on the glassy carbon electrode surface was investigated using the CV method. In the DCF voltammograms obtained in acidic medium, an oxidation peak was observed during the forward scan. The irreversibility of the oxidation reaction was demonstrated by the absence of a reduction peak in the reverse scan. Scan-rate analysis showed that two electrons are transferred during the electrochemical oxidation of DCF, and pH studies revealed that protons also participate in the reaction process. DCF is primarily oxidized on the aromatic rings and at the nitrogen atom. Hydroxyl radicals attack these regions, leading to the formation of hydroxylated intermediates and dechlorinated products. The addition of hydroxyl radicals to the aromatic rings results in hydroxylated products, and depending on radical concentration and reaction conditions, multiple hydroxylation sites may form. Due to the adsorption of the oxidation product of DCF on the electrode surface, the peak current gradually decreased in potential scans following the first cycle. By examining the relationship between peak current and the square root of the scan rate obtained from cyclic voltammograms recorded at different scan rates in a [Fe(CN)6]3−/4− solution, the specific surface area of the GCE was calculated as 0.0642 cm². In the second part of the study, glassy carbon electrodes modified with different concentrations of MWCNT-COOH were prepared, and the electrochemical behavior of DCF was examined using CV. As the concentration of MWCNT-COOH on the electrode surface increased from 0.2 mg/mL to 1.0 mg/mL, the oxidation peak current of DCF also increased; however, at 1.0 mg/mL, the current decreased. Therefore, the optimal MWCNT-COOH concentration for GCE surface modification was determined to be 0.8 mg/mL. Comparing the cyclic voltammogram of MWCNT-COOH/GCE with that of the bare GCE under the same conditions, the increase in peak intensity and the shift of the oxidation peak toward more negative potentials indicated that MWCNT-COOH/GCE exhibited significant electrocatalytic activity toward the oxidation of DCF. From the dependence of peak current on the square root of scan rate in [Fe(CN)6]3−/4− solution, the specific surface area of MWCNT-COOH/GCE was determined to be 0.1096 cm². The fact that the active surface area of the MWCNT-COOH-modified electrode increased by approximately 70.7% compared with the unmodified GCE confirmed the catalytic effect of the increased surface area on DCF oxidation. Scan-rate studies in DCF solution indicated that the electrochemical oxidation of DCF on MWCNT-COOH/GCE is adsorption-controlled and involves the transfer of two electrons. The pH studies showed that equal numbers of electrons and protons participate in the electrochemical oxidation of DCF on MWCNT-COOH/GCE. In the third part of the study, a carboxyl-functionalized multi-walled carbon nanotube composite containing AgNPs (MWCNT-COOH@AgNPs) was synthesized. The characterization of the nanostructure of the composite material was done by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The GCE modified with this composite material was prepared, and its electrochemical characterization was performed by CV in acidic and basic media. The reduction and oxidation peaks observed in the voltammogram confirmed the presence of AgNPs on the electrode surface. It was also determined that DCF undergoes an irreversible electrochemical oxidation reaction on MWCNT-COOH@AgNPs/GCE. These results were compared with those obtained using MWCNT-COOH-modified GCE without AgNPs. Due to the enhanced electron transfer between the silver nanoparticles and the DCF molecules, and the resulting increase in catalytic activity, the MWCNT-COOH@AgNPs/GCE exhibited higher current intensity and a more negative peak potential than MWCNT-COOH/GCE. The optimal amount of MWCNT-COOH@AgNPs on the electrode surface was determined to be 1.6 mg/mL. From the dependence of peak current on the square root of scan rate in K3[Fe(CN)6]/K4[Fe(CN)6] solution, the specific surface area of MWCNT-COOH@AgNPs was found to be 0.192 cm², and compared with MWCNTCOOH/GCE, the specific surface area of MWCNT-COOH@AgNPs/GCE increased by 75.2%. The pH studies indicated that equal numbers of electrons and protons participate in the electrochemical oxidation of DCF on MWCNT-COOH@AgNPs/GCE, and the optimum pH for DCF analysis was determined to be 5.0. Cyclic voltammograms of DCF at different scan rates demonstrated that the oxidation reaction occurring on the MWCNT-COOH@AgNPs/GCE surface is diffusion-controlled and involves two electrons and two protons. Under optimized experimental conditions, DCF showed linearity in the ranges 1.0×10⁻⁷–1.0×10⁻⁶ M and 1.0×10⁻⁶–5.0×10⁻⁵ M, and the limit of detection (LOD) was found to be 6,23×10⁻⁸ M. The practical applicability of the modified electrode was demonstrated by determining the concentration of DCF in a pharmaceutical sample. The results confirmed that MWCNT-COOH@AgNPs/GCE can be successfully used for real-sample DCF analysis. In the fourth part of the study, the electrochemical behavior of DCF on MWCNT-OH/GCE was first investigated by CV in 0.1 M HClO4 solution, and an irreversible and distinct anodic peak at 0.88 V corresponding to DCF oxidation was observed in the voltammogram. Comparing the behavior of MWCNT-OH/GCE with that of bare GCE under identical conditions, the increase in peak current and the negative shift in peak potential showed that MWCNT-OH/GCE exhibited significant electrocatalytic activity toward DCF oxidation. In the second and subsequent potential scans, a considerable decrease in the oxidation peak current at 0.88 V was observed due to the adsorption of DCF oxidation products on the electrode surface. Glassy carbon electrodes modified with different concentrations of MWCNT-OH were prepared, and DCF's electrochemical behavior was examined by CV. As the concentration of MWCNT-OH increased from 0.2 mg/mL to 0.6 mg/mL, the oxidation peak current increased, but at higher concentrations, the current decreased. Therefore, the optimal MWCNT-OH concentration for GCE modification was determined to be 0.6 mg/mL. From the scan-rate studies in [Fe(CN)6]3−/4− solution, the specific surface area of MWCNT-OH/GCE was calculated as 0.1064 cm². The approximately 65.7% increase in active surface area compared with the bare GCE confirmed the catalytic enhancement of DCF oxidation on MWCNT-OH/GCE. Scan-rate data in the DCF solution indicated that the electrochemical oxidation of DCF on MWCNT-OH/GCE is adsorption-controlled and involves two electrons. The pH studies revealed that equal numbers of electrons and protons are involved in the electrochemical oxidation of DCF on MWCNT-OH/GCE. In the fifth part of the study, a hydroxyl-functionalized multi-walled carbon nanotube composite containing AgNPs (MWCNT-OH@AgNPs) was synthesized. Glassy carbon electrodes modified with this material were prepared, and their electrochemical characterization was conducted using CV. The appearance of reduction and oxidation peaks in the voltammogram confirmed the presence of AgNPs on the electrode surface. It was also determined that DCF undergoes an irreversible electrochemical oxidation reaction on MWCNT-OH@AgNPs/GCE. These results were compared with those obtained using MWCNT-OH/GCE without AgNPs. Due to the enhanced electron transfer between silver nanoparticles and DCF molecules, and the resulting increase in catalytic activity, MWCNT-OH@AgNPs/GCE exhibited higher current intensity and a more negative peak potential than MWCNT-OH/GCE. The optimal amount of MWCNT-OH@AgNPs on the electrode surface was determined to be 0.8 mg/mL. From the dependence of peak current on the square root of scan rate in K3[Fe(CN)6]/K4[Fe(CN)6] solution, the specific surface area of MWCNT-OH@AgNPs was found to be 0.2394 cm², and compared with MWCNT-OH/GCE, the specific surface area of MWCNT-OH@AgNPs/GCE increased by 125%. The pH studies displayed that equal numbers of electrons and protons are involved in the electrochemical oxidation of DCF on MWCNT-OH@AgNPs/GCE, and the optimum pH for DCF analysis was determined to be 5.0. Cyclic voltammograms of DCF recorded at different scan rates revealed that the oxidation reaction on the MWCNT-OH@AgNPs/GCE surface is diffusion-controlled and involves two protons and two electrons. Under optimized experimental conditions, two linear regions were identified for DCF analysis: 5.0×10⁻9-1.0×10⁻⁷ M with the linear equation Ip (µA) = 3.96833 + 1.02167×10⁸ CDCF (M) (R²=0.98945), and 1.0×10⁻⁷-1.0×10⁻⁶ M with the linear equation Ip (µA) = 12.66369 + 1.18659×10⁷ CDCF (M) (R² = 0.99633). The limit of detection (LOD) was calculated as 3.4×10⁻9 M. The practical applicability of the modified electrode was demonstrated by determining the concentration of DCF in a pharmaceutical sample. The recovery values obtained indicated that MWCNT OH@AgNPs/GCE can be successfully used for real-sample DCF analysis. The effects of potential interfering molecules such as ascorbic acid (AA) and uric acid (UA), which may be present in the analysis environment, were investigated using DPV. Even when AA and UA were present at concentrations 50 times higher than DCF, the change in the DCF peak current remained within the ±5% tolerance limit. This result demonstrated that DCF can be reliably analyzed in the presence of AA and UA. The repeatability of DCF analysis using MWCNT-OH@AgNPs/GCE was evaluated, and the relative standard deviation (RSD) for three measurements was found to be 4.89%, indicating acceptable repeatability. The stability of MWCNT-OH@AgNPs/GCE was assessed, and the peak current obtained two weeks after electrode preparation remained nearly unchanged compared with the initial value, demonstrating that the electrode exhibited acceptable stability for DCF analysis. In addition, the proposed MWCNT-OH@AgNPs/GCE sensor showed a wider linear range and a lower detection limit compared with many reports in the literature. These results indicate that the developed sensor can be integrated into a portable platform to enable real-time, on-site analysis. These features provide a low-cost, scalable, and high-performance sensor for DCF monitoring in practical settings, filling significant gaps in the current literature. Evaluation of the data obtained from SEM, TEM, and EDX analyses revealed that MWCNT-OH@Ag exhibits more pronounced aggregation compared to the MWCNTCOOH@Ag nanocomposite. Comparison of the nanotube morphologies revealed that the hydroxyl-functionalized nanotubes have a larger cross-sectional diameter than their carboxyl-functionalized counterparts. Consistent with the EDX results, the Ag nanoparticle percentage appears higher in the hydroxyl-functionalized structure. Based on functional group interactions, it was normally expected that the carboxyl functionalized nanotubes adsorb more Ag ions and consequently contain a greater amount of reduced Ag nanoparticles. The deviation from this expected trend may be attributed to the larger diameter of the hydroxyl-functionalized nanotubes, which likely enables greater adsorption of silver ions on their surface, ultimately resulting in the formation of a higher number of Ag nanoparticles.
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