3D-printed gyroid carbon monoliths as multifunctional electrodes for electrocatalytic H2O2 production and electro-Fenton applications

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Abstract
3D carbon monoliths with gyroid architecture were fabricated by digital light processing (DLP) 3D printing followed by oxidative stabilization, pyrolysis and steam activation (ACG) to develop multifunctional electrodes for electrogeneration of H2O2, adsorption and heterogeneous electro-Fenton applications. Iron oxide nanoparticles were added into the polymer precursor to produce Fe-containing monoliths with iron active sites (Fe-ACG). Carbonaceous materials revealed well developed porous structure, with Smicro values of 1192 and 885 m2/g for ACG and Fe-ACG, respectively. Steam activation also improved the electrogeneration of H2O2 with ACG through the 2 e– oxygen reduction reaction (4.0·10-4 mol/g of H2O2). However, salicylic acid scavenging experiments indicated 2.4 times higher hydroxyl radicals formation with Fe-ACG due to the efficient activation of H2O2 via heterogeneous Fenton-like mechanism. A kinetic model was developed to describe the H2O2 generation and consumption, confirming the catalytic role of the immobilized iron species. The adsorption, catalysis, electrocatalysis and intensified (external addition combined with electrogeneration of H2O2) electrocatalysis degradation of hydroxybenzene (1 g/L) were evaluated. ACG and Fe-ACG materials initially retained 70% of hydroxybenzene by adsorption; the subsequent catalytic and electrocatalytic reactions further oxidized this pollutant, with Fe-ACG achieving overall hydroxybenzene and TOC conversions of 79 and 55% by electro-Fenton, respectively. Intensified electro-Fenton resulted in the highest performance, achieving 94.6 and 68.7% of removal and mineralization, respectively. In addition, Fe-ACG cathode maintained high activity using a tertiary treated wastewater and after four consecutive reuse cycles. These results demonstrate that gyroid carbon monoliths are robust and effective multifunctional electrodes for wastewater treatment processes.

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