Facile sol–gel fabrication of MnOx/Graphite nanostructured electrodes for sustainable produced water treatment

In this study, manganese oxide films were successfully deposited on Graphite sheets using a sol-gel dip-coating method. The films were subsequently employed as anode electrodes for the electrochemical oxidation of produced water (PW) in the polishing stage of the treatment. Electrodes were fabricated by optimizing key parameters affecting the synthesis of manganese oxide colloids, including precursor concentration, withdrawal speed, and calcination temperature, through a dip-coating process on Graphite sheets followed by thermal treatment and calcination. The electrochemical performance of the electrodes was evaluated through cyclic voltammetry (CV) and their chemical oxygen demand (COD) removal efficiency during the electrochemical oxidation of PW. A comparison of the electrochemical efficiencies of fabricated electrodes under different fabrication conditions in the treatment process showed that the optimal conditions included an initial manganese acetate concentration of 0.3 M, five coating layers, a withdrawal speed of 5.5 mm/min, and calcination at 300 °C for 60 min, which led to the formation of a crystal structure of Mn₂O₃. The results showed the specific capacity of 92.161 mF/cm², 86.96% COD removal at 30 mA/cm² after 120 min and an estimated lifetime of 500 h. The structural and morphological characterization of the optimized electrode using X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the uniform deposition of Mn₂O₃ nanoparticles on the Graphite substrate. The findings indicate that the proposed MnO_x electrode exhibits both high efficiency and stability, making it a promising candidate for the electrochemical oxidation of produced water as well as for applications in electrochemical supercapacitors.