Study on the Removal of Methylene Blue by a Low-Voltage Submerged Arc Generated by the Graphite Electrodes

Plasma generated by a submerged arc has great potential in wastewater treatment. Carbon is widespread in nature. It is easily acquired and biocompatible. In this article, a low-voltage submerged arc generated by contact-separate of two electrodes is proposed to decompose methylene blue (MB). The process achieved a removal efficiency of 92.9% after 15 min treatment. The emission spectrum of the submerged arc indicated that active particles such as $\cdot $ OH radicals, oxygen atoms, and hydrogen peroxide (H2O2) have been produced. Additionally, in the process of arc treatment, the wavelength of the absorption peak of MB solution shifted toward ultraviolet region. It indicated the demethylation of the MB molecules. The eroded particles from the graphite electrodes were also examined, and the carbon quantum dots were observed. Furthermore, micro-scale fibrous entangled particles and layered particles with abundant pore structures were observed. These results demonstrate that the eroded particles own an absorption ability for MB, continuing decolorization of the treated solution without additional active particles generated by the submerged arc plasma.