Electrochemical degradation of emerging pollutants via laser-induced graphene electrodes

Abstract

Emerging pollutants of concern (e.g., pharmaceuticals) are challenging to remove by conventional methods, persistent in the aquatic system, and can be toxic to mankind and the environment. Carbamazepine (CBZ) is a widely used pharmaceutical for neuropathic diseases and detected in water systems around the world. Similarly, methylene blue (MB), used in pharmaceutical, laboratory and textile industries poses a threat to the environment. Electrochemical water treatment is a promising technology shown to remove emerging pollutants and organic pharmaceuticals through oxidation and reduction pathways. Recently, laser-induced graphene (LIG) electrodes were fabricated on top of polymer materials and showed antifouling properties and effective oxidizing species generation (i.e., H2O2) at 2–3 V. Here we show that LIG-derived electrodes can remove and degrade organic pollutants from water with an applied voltage via reactive oxygen species generation. The surface area of the LIG electrodes, applied voltage, and the concentration of H2O2 were studied to optimize CBZ and MB degradation. We observed that the LIG electrodes could degrade 64% of CBZ after 6 h at 2.5 V and, together with adsorption to the electrode, 82% was removed from solution after 24 h. Partially degraded CBZ accounted for only 3% of total removal and degradation products were identified by ultra-performance liquid chromatography and mass spectrometry. Similarly, a complete color removal of MB could be obtained in 6 h at 2.5 V corresponding to an 80% dye transformation, which was most likely due to chemical oxidation. Since these LIG electrodes can be rapidly formed on flexible polymer substrates at low cost, this technology might lead to novel water treatment devices and strategies presented herein might potentially lead to solutions for removing emerging contaminants in wastewater.