Synthesis and Application of MnO2/Exfoliated Graphite Electrodes for Enhanced Photoelectrochemical Degradation of Methylene Blue and Congo Red Dyes in Water

Exfoliated graphite (EG), manganese dioxide (MnO 2 ), and EG/MnO 2 -based electrodes were used in this work for the degradation of organic pollutants in wastewater under visible light irradiation. Methylene blue and Congo red dyes were used for the degradation. The synthesis of the nanocomposite electrodes was carried out through the co-precipitation technique. The electrodes were engaged for degradation of the dyes under electrochemical oxidation, photolysis, and photoelectrochemical methods. The characterization techniques utilized encompass transmission electron microscopy (TEM), ultraviolet-visible (UV) analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Fourier transformed infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and X-ray diffraction (XRD). The EG/MnO 2 photoanode was applied in the photoelectrochemical degradation of 0.1 × 10–4 M methylene blue and Congo red dyes in 0.1 M Na 2 SO 4 under visible light irradiation. The XRD analysis revealed that the MnO 2 exist as α-MnO 2 . SEM morphologies showed a satisfying dispersion of MnO 2 on EG. The EG/MnO 2 composite absorbed a noticeable amount of light in the visible light region compared with the pure EG and MnO 2 . The photoelectrochemical degradation process resulted in enhanced degradation efficiency of Congo red (97.6%) and methylene blue (98.7%) within 60 min and was observed to be higher than those of photolysis and electrochemical oxidation processes. Graphical Abstract