Electrochemical Removal of Organic and Inorganic Pollutants Using Robust Laser-Induced Graphene Membranes

The removal of emerging environmental pollutants in water and wastewater is essential for high drinking water quality or for discharge to the environment. Electrochemical treatment is a promising technology shown to degrade undesirable organic compounds or metals via oxidation and reduction, and carbon-based electrodes have been reported. Here, we fabricated a robust, porous laser-induced graphene (LIG) electrode on a commercial water treatment membrane using the multilasing technique and demonstrated the electrochemical removal of iohexol, an iodine contrast compound, and chromium(VI), a highly toxic heavy metal ion. Multiple lasing resulted in a more ordered graphitic lattice, a more physically robust carbon layer, and a 3-4-fold higher electrical conductivity. These properties ultimately led to a more efficient electrochemical process, and the optimized LIG electrodes showed a higher hydrogen peroxide (H₂O₂) generation. At 3 V, 90% of Cr(VI) was removed after 6 h and reached >95% removal after 8 h at pH 2. Cr(VI) was mainly reduced to Cr(III), with small amounts of Cr(I) and Cr(0), which were partially deposited on the electrode membrane surface, confirmed with X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy analysis. Under the same conditions, 50% of iohexol was degraded after 6 h and the transformation products (TPs) were identified using ultra-performance liquid chromatography coupled with mass spectroscopy. A total of seven main intermediates were identified including deiodinated TPs (m/z = 695, 570, and 443), probably occurring via three transformation pathways including oxidative deiodination, amide hydrolysis, and deacetylation. The electrical energy costs calculated for the removal of 2 mg L^-1 Cr(VI) was ∼$0.08/m³ in this system. Taken together, the porous LIG electrodes might be utilized for electrochemical removal of emerging contaminants in multiple applications because they can be rapidly formed on flexible polymer substrates at low cost.