Green Approach to Produce a Graphene Thin Film on a Conductive LCD Matrix for the Oxidative Transformation of Ciprofloxacin

This study demonstrates the use of disposed liquid crystal display (LCD) glass as a supporting matrix for the fabrication of a binder/linker free thin film graphene electrode. Graphene oxide (GO) was drop casted onto the LCD matrix and electrochemically reduced to form an ErGO-LCD electrode which was subsequently employed for the electro-Fenton oxidation of ciprofloxacin. Fourier transform infrared spectroscopy confirms the presence of (i) functional groups such as C=O, N-H, C≡N, and C-N on the LCD matrix, (ii) attachment of GO onto the LCD, and (iii) reduction of oxygen functionalities at the surface of the ErGO-LCD electrode. Raman and X-ray photoelectron spectroscopy were performed to examine the nature and chemical composition of the GO-LCD and ErGO-LCD electrodes. Cyclic voltammetry and electrochemical impedance spectroscopic studies revealed the enhancement of the oxidation-reduction properties and reduction of charge transfer resistance (Rct 17 ω) in the presence of [Fe(CN)6]3-/4- redox species. Electro-Fenton results revealed that a high concentration of H2O2 (45 mg L-1) was produced at acidic pH as compared to neutral (20 mg L-1) or alkaline (15 mg L-1) conditions. Furthermore, a higher current efficiency for the production of H2O2 was found at -1.0 V (63%) as compared to -1.5 V (59%) and -2.0 V (51%). Degradation studies showed >99% removal of ciprofloxacin was observed at pH 3.5 as compared to pH 7.0 (92%) or pH 9.0 (77%) at -1.5 V. The reuse experiments suggested that the electrode is stable and reusable for more than 7 cycles of experiments. The average pseudo-first-order kinetic rate constant for seven cycles of reuse was found to be 0.017 min-1.