Hüseyin Çelikkan

An efficient way to reduce graphene oxide by water elimination using phosphoric acid

This study concerns the synthesis of high-quality graphene by the water elimination reaction in the presence of phosphoric and sulfuric acid (H3PO4–G and H2SO4–G). Graphene was synthesized via a single-step efficient reduction method which is not yet found in the literature. This new method is called the acidic method and offers significant advantages, such as absence of toxic products, ease of purification and a high-quality graphene yield. Graphene formation from graphene oxide (GO) was verified by the use of Fourier transform infrared spectroscopy (FT-IR), raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermal properties and the surface morphology of the graphene obtained were elucidated by the use of thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). H3PO4–G prepared by this method was observed to have a very high conductivity value of 3860 S m−1 and a low capacitance value of 114 F g−1 cm2. The capacitance and conductivity values of graphene samples obtained with the conventional method by the use of sodium borohydride (NaBH4–G) as a reducing agent were compared with those obtained with the acidic reduction method. It was seen that the acidic reduction method showed promising features for the production of high-quality graphene and its applications.

Cellulosic tent fabric coated with boron nitride nanosheets

This study concerns with the preparation of flame retardant and hydrophobic cellulosic fabric by using hexagonal boron nitride nanosheets (h-BNNs). h-BNNs were prepared from hexagonal boron nitride (h-BN) using two different exfoliation methods. These methods include direct sonication (aq-BNNs) and sonication after pretreatment with Hummers method (Hum-BNNs) in aqueous medium. The characterization of h-BNNs was carried out by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), limited oxygen index (LOI), and water contact angle (WCA) analysis. The surface morphologies of h-BNNs were investigated via atomic force microscope (AFM). The coating with the h-BNNs was proved by scanning electron microscopy (SEM). Hummers method is considered to be more effective reaction by gained functionality to h-BN structure. In this way, it will easily provide physical or chemical interaction between the functionalized h-BN and cellulosic structure. A nanometric-sized large layers and slightly functionalized h-BNNs were obtained using Hummers method. Hum-BNNs dispersions were sprayed onto the surface of cellulosic tent fabric to show flame retardance properties. However, it was observed that the flame retardant effect of nanolayered h-BNNs prepared by both methods were insufficient. In addition, ultrahydrophobic surfaces were almost obtained using aq-BNNs and Hum-BNNs. It was conclusively proposed that a few amounts of Hum-BNNs can be used as hydrophobic coating for cellulosic fabric surface with this way.

A novel and highly sensitive electrochemical sensor based on a high-quality modified graphene electrode for the determination of hydrochlorothiazide in pharmaceutical formulations and human plasma

This study is concerned with the development of a practical, efficient and highly sensitive electrochemical sensor for the determination of hydrochlorothiazide (HCT) in pharmaceutical dosage forms or clinical samples using a high-quality modified graphene electrode (H-GRE) which has recently emerged as a very promising material for sensor applications. High-quality graphene (H-GR) was synthesized efficiently by a single-step reduction method from graphene oxide (GO). It was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and transmission electron spectroscopy (TEM). The electrochemical behavior of HCT was investigated using adsorptive stripping differential pulse voltammetry on the H-GRE. The H-GRE showed excellent electrochemical activity for the oxidation of HCT. Under the optimized experimental conditions, the linear response range of HCT was found to be 0.1–48.0 μM with a detection limit (based on S/N = 3) of 19 nM. This improved electrode may provide a promising alternative sensor for the determination of HCT in pharmaceutical formulations and clinical samples.

An ultra-sensitive 2D electrochemical sensor based on a PtNPs@graphene/Nafion nanocomposite for determination of α1-AR antagonist silodosin in human plasma

This paper reports a platinum nanoparticles/graphene/Nafion nanocomposite (PtNPs@GRP/NFN) as a novel and highly sensitive two-dimensional (2D) sensing nanoplatform for the electrochemical determination of silodosin (SLN). The electrochemical behavior of SLN was investigated at the proposed sensor (PtNPs@GRP/NFN/GCE) using adsorptive stripping differential pulse voltammetry (AdsDPV). The PtNPs@GRP nanocomposite was synthesized effectively from graphene oxide (GO) and Pt salt by a single-step chemical reduction method. The morphology and structure of the PtNPs@GRP nanocomposite were characterized using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Electrochemical characterization was also performed by cyclic voltammetry (CV) at the PtNPs@GRP/NFN/GCE. The sensor exhibited extraordinary electrochemical activity towards the SLN at nanomolar levels. Under optimal conditions, a sufficiently linear calibration curve in the range of 1.8–290.0 nM with an extremely low detection limit of 0.55 nM (S/N = 3) was obtained at the PtNPs@GRP/NFN/GCE. This sensor was successfully applied to determine the content of SLN in human plasma with satisfactory results.

Electrochemical Investigation of Zinc(II)-Furdap Amide Complex in DMSO Medium

The electrochemical behavior of Zinc(II)-furdap amide complex has been investigated by the use of several electrochemical methods in DMSO on platinum electrode. Both the ligand and the complex gave one electron transfer re- duction. Although there was no oxidation peak observed corresponding to the reduction of ligand, there was a correspond- ing oxidation peak appeared for the complex. The number of electrons transferred was calculated as 1 by the use of bulk electrolysis, rotating disc electrodes employing Kouteck� -Levich equation. The reversibility tests revealed that the reac- tion followed a quasi reversible mechanism. The mechanism was also confirmed by simulation studies. ks and  values were found to be 1.0 10 -7 cm s -1 and 0.4, respectively. The diffusion coefficient (D) was found as 6.93  10 -5 cm 2 s -1 by the use of Cottrell slope obtained from chronoamperometry experiments and ultra micro disc steady state current (iss).

Reduced graphene oxide/platinum nanoparticles/nafion nanocomposite as a novel 2D electrochemical sensor for voltammetric determination of aliskiren

This study describes the fabrication of a sensitive and selective graphene-based electrochemical nanosensor for the detection of aliskiren (ALS). It is the first research study where the electrochemical oxidation and determination of ALS were investigated by cyclic voltammetry (CV) and adsorptive stripping differential pulse voltammetry (AdsDPV) using a 2D nanocomposite electrode modified with reduced graphene oxide/platinum nanoparticles/nafion (rGO/PtNPs/NFN/GCE). An rGO/PtNP nanocomposite was synthesized directly from graphene oxide (GO) and platinum salt using a single-step chemical reduction method. The synthesized rGO/PtNPs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The developed sensor exhibited excellent electrocatalytic activity (i.e. shifting the potential from 1225 to 1059 mV) towards the oxidation of ALS. The voltammetric responses of ALS presented a good linearity with an increase in concentration within two concentration ranges of 0.045–0.45 μM and 0.45–2.70 μM with a low detection limit of 8.2 nM. The analytical applicability of the proposed sensor was demonstrated by determining ALS with the recovery result of 97.0% in human blood plasma. The results strongly suggested that the proposed sensor could be promising as an alternative analytical approach for routine analysis of ALS in clinical samples.

ASKORBİK ASİTİN MoS2 ESASLI ELEKTROTLA ELEKTROKİMYASAL TAYİNİ

OZET Bu calismada, grafen, grafen oksit ve MoS 2 iki boyutlu nanotabakalarina ayrilmak suretiyle hazirlanan 10 farkli kaplama suspansiyonu kullanilarak, damlatarak-kaplama yontemiyle elektrot modifikasyonu gerceklestirilmistir. Farkli kompozisyonlarda hazirlanan 20 farkli modifiye elektrot ile askorbik asit (AA) tayini icin elektrokatalitik duyarlik incelenmistir. Olcumler diferansiyel puls voltametrisi (DPV) teknigi ile gerceklestirilmistir. Elektrodun modifikasyonu yapilarak 2,8 kata kadar duyarlikta artis saglanmistir. MoS 2 ’un AA’e karsilik bir katalitik etkinliginin goruldugu bu calismada, AA’e karsi duyarlik 7,26 µA.mM -1 , dogrusal calisma araligi 20 µM - 1100 µM araliginda ve gozlenebilme siniri da 7,7 µM olarak bulunmustur. Modifiye elektrotla gerceklestirilen gercek numune analizinde ortalama % 5,05 hatayla AA tayini gerceklestirilmistir. Hazirlanan MoS 2 ’un tabaka kalinligi atomik guc mikroskobu (AFM) cihaziyla olculmus ve modifiye elektrot yuzeyi taramali elektron mikroskobu (SEM) ile goruntulenmistir.