Exfoliation Of Graphite Rods Research Articles

Detection of 8-Hydroxy-2'-Deoxyguanosine Biomarker with a Screen-Printed Electrode Modified with Graphene.

In this work we present the preparation of graphene material by exfoliation of graphite rods via pulses of current in electrolyte, containing a mixture of boric acid (0.05 M) and sodium chloride (0.05 M). The material was morphologically and structurally characterized by SEM/TEM/HR-TEM, XRD and FTIR techniques. TEM investigation of graphene flakes deposited onto carbon-coated grids allowed the visualization of thin and transparent regions, attributed to few-layer graphene (FLG), as well as thick and dark regions attributed to multi-layer graphene (MLG). The mixed composition of the material was additionally confirmed by XRD, which further indicated that the amount of FLG within the sample was around 83%, while MLG was around 17%. The performance of a screen-printed electrode (SPE) modified with graphene (SPE-Gr) was tested for 8-hydroxy-2′-deoxyguanosine detection. The graphene-modified electrode had a higher sensitivity in comparison with that of SPE, both in standard laboratory solutions (phosphate buffered saline—PBS) and in human saliva.

Graphene-based materials produced by graphite electrochemical exfoliation in acidic solutions: Application to Sunset Yellow voltammetric detection

Two graphene-based materials were prepared by exfoliation of graphite rod with pulses of current. The first material (denoted EGr-1) was exfoliated in a mixture of sulphuric and nitric acid (3:1 ratio; 0.5 M each; pH 1) giving a material composed of graphene (40% few-layer; 32% multi-layer) and graphene oxide (28%). The second material (denoted EGr-2) was prepared by exfoliation of the graphite rod in 0.05 M boric acid (pH 5.1) in which 0.05 M NaCl was added to increase the electrolyte conductivity. After preparation, the materials were used for the modification of two glassy carbon (GC) electrodes, denoted GC/EGr-1 and GC/EGr-2, respectively. The performances of each electrode toward Sunset Yellow (SY) detection were tested in laboratory solutions (pH 6 PBS) containing increasing concentrations of SY (3 × 10−7–1 × 10−4 M). It is important to emphasize that the sensitivities, linear ranges and the limits of detection of the two electrodes were different. Hence, in the case of the electrode covered with graphene prepared in strong acidic solution (GC/EGr-1) the sensitivity was 0.017 A·M−1, the linear range between 6 × 10−6 and 1 × 10−4 M, the LOD was 1.8 × 10−6 M. In contrast, the electrode covered with the material prepared in weak acidic solution (GC/EGr-2) has higher sensitivity (0.021 A·M−1) wider linear range (1 × 10−6–1 × 10−4 M) and lower LOD (3 × 10−7 M).

Exfoliation of graphite rods via pulses of current for graphene synthesis: Sensitive detection of 8-hydroxy-2′-deoxyguanosine

In this paper we present for the first time a novel method for graphene-based materials synthesis, by exfoliation of graphite rods via pulses of current (pulse duration of 2.5 s; pause between two pulses of 0.8 s). The method has several advantages over the classical one (d.c. current exfoliation) such as the prevention of the electrolyte over-heating, the generation of less amount of graphitic material into the final sample, the increase of the synthesis yield, and the excellent reproducibility in sample quality when the synthesis parameters are preserved. The first material (EGr-A) was obtained in strong acidic solution made by a mixture of H2SO4 and HNO3 (3:1 ratio; 1 M each; pH 1). The second material (EGr-S) was prepared in a salt solution of 0.2 M ammonium sulphate (pH 5). Both materials were morphologically and structurally characterized by SEM, XRD and XPS. The XRD investigation proved that the EGr-A sample contains graphene oxide (GO- 39%) along with few-layer graphene (FLG- 44%) and multi-layer graphene (MLG- 17%). In contrast, the EGr-S sample consists of two-layer graphene (89%) and multi-layer graphene (11%). The performances of two glassy carbon (GC) electrodes modified with the graphene based materials (GC/EGr-A and GC/EGr-S) were investigated towards 8-Hydroxy-2′-deoxyguanosine (8-OHdG) detection and compared with those of bare GC. As expected, the graphene-modified electrodes have a high sensitivity (0.67 A M−1 cm−2 for GC/EGr-S and 0.53 A M−1 cm−2 for GC/EGr-A), a wide linear range (3 × 10−7–10−4 M) and low detection limit (LOD = 9.09 × 10−8 M). In contrast, the bare electrode has higher detection limit (LOD = 3 × 10−7 M) and considerably lower sensitivity towards 8-OHdG (0.22 A M−1 cm−2).

Preparation of Metal-Free Nitrogen-Doped Graphene Via Direct Electrochemical Exfoliation of Graphite in Ammonium Nitrate

Nitrogen-doped graphene (N-graphene) nanosheets have been synthesized via electrochemical intercalation and exfoliation of graphite rods in ammonium nitrate aqueous solutions. This method produces N-graphene free from possible metal contaminations that can be utilized as efficient electrocatalysts towards oxygen reduction reactions.