Physical and Chemical treatments to produce graphene and their related applications

Abstract

In this work Few Layers Graphene (FLG) and Graphene Oxide (GO) were produced by using physical and chemical treatments, and two types of applications were tested with GO. The first application concerns the Drug delivery in the field of nano-medical treatments, while the second regards environmental remediation for removal of pollutants from water. Few Layers Graphene (FLG) was produced from natural graphite by two methods: i) Sonication in a mixture of solvents, and ii) With the aid of an external agent (zeolite crystals) in the exfoliation process. In the first stage, the mixture was made with two types of solvents: N-methyl-2 pyrrolidone and Dimethylsulfoxide in different ratios. The exfoliation was carried out in that mixtures, then the centrifugation was applied in order to remove unexfoliated graphite. The supernatant suspensions were characterized using Ultraviolet - visible spectroscopy (UV-vis), and Raman Spectroscopy. The Uv-visible analysis and the Raman spectroscopy showed of existence of Few layers Graphene (FLG). In the second stage, the zeolite 4A (Z4A) was selected. The experiments were carried out to improve the exfoliation of graphite, after the exfoliation and centrifugation; the stability was achieved in those that were added the zeolite 4A. Supernatant solutions were characterized by Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), Electron Diffration, and Raman Spectroscopy. The 3_BS suspension and the 7_F suspension showed the best results; these reached the greatest amount of days in suspension. The Electrical Characterization (EC) was carried out using 3_BS and 7_F suspensions. The drop-casting technique was used over Al2O3 substrates with gold (Au) InterDigitated Electrodes (IDE). The Current–Voltage (I-V) characterization was performed, and the results were averaged for each sample and computed; in order to obtain the 2D resistivity (ρ2D). Finally, an annealing treatment was applied on the Al2O3/Au substrates; afterwards, the resistivity improves, for 3_BS ink by a factor of 1.75 and for the 7_F ink by a factor of 1.3. Graphene Oxide was produced from natural graphite flakes. A chemical treatment was applied in order to produce graphene oxide through the Hummer’s method and Improved Hummer’s method. At the end of the process, the graphene oxide was recovered under form of colloidal suspensions. The characterization was made by Field Emission Scanning Electron Microscopy (FESEM), Ultraviolet–visible (UV-vis) spectroscopy, Fourier Transform Infrared spectroscopy (FTIR), Energy Dispersive Spectroscopy (EDS), and Raman Spectroscopy. The results showed a good level of oxidation in the material and small flakes of graphene oxide. Concerning to the adsorption process for drug delivery, a cancer drug was used. Doxorubicin (DOX) hydrochloride was placed in contact with GO to evaluate the capacity of adsorption of the material using the depletion method. The study was carried out by using different initial concentrations of DOX and different pH values. All experiments were placed under agitation in dark conditions at room temperature and different incubation times. Once the results of final concentrations was completed, the quantity loaded onto GO were calculated. Finally, the kinetic adsorption showed a percentage of 95% at pH 3 in only 24 hours of interaction. The GO presented excellent characteristics to be used in nano-medical applications. Regarding environmental applications, an adsorption study was conducted using commercial Acridine Orange dye (AO). The adsorption process was proved using the depletion method. AO was prepared in aqueous solution at different concentrations, and these were placed under agitation and dark conditions at different contact times to evaluate the kinetic adsorption. The GO was analyzed at different weight using the highest concentration of AO. On the other hand, the temperature and the incubation time were varied, to find out the best conditions for the adsorption process. The kinetic of adsorption showed a percentage of adsorption among 75% to 95% in the first 20 min for higher concentrations and GO showed a better adsorption process to higher temperatures