Preparation of Carbon Micro- and Nanomaterials through Plasmochemical Treatment of Wastewater Contaminated with Acid Violet 7

The plasma-chemical decomposition of Acid Violet 7 dye and simultaneous production of carbon micro- and nanomaterials were investigated. For the purification of wastewater contaminated with the dye, we used a plasma electrochemical setup with modified electrodes. The experiments were conducted in a galvanostatic mode with current intensities of 45 and 80 A and voltages ranging from 21 to 24 V. Two types of carbon-containing degradation products were formed. One type comprised fine-dispersed hydrophobic material, which, due to its low specific weight, hydrophobicity, and inclusion of gas bubbles, floated and concentrated at the interface between the solution and air phases. This material predominantly consisted of particles ranging in size from 1 to 5 µm, with some particles in the order of hundreds of nanometers present as well. Another type consisted of hydrophilic particles larger than 50 µm, which were deposited at the bottom of the cell. Plasma-chemical treatment leads to rapid degradation of the Acid Violet 7 molecule. Intensive discoloration of the dye solution occurs within the first 5–7 min. Exposure for 20 min resulted in an 8.4-fold decrease in chemical oxygen demand (COD).