Systematic evaluation of activated carbon-Fe3O4 composites for removing and degrading emerging organic pollutants

Abstract

In this study, a comparative activity assessment of several activated carbon (AC) and AC-Fe3O4 composites was performed to evaluate their efficiency and versatility as Fenton-like catalysts. Although many studies have demonstrated the advantages of AC-based materials as Fenton-like catalysts, most have been developed using only one oxidant and/or one pollutant. Here, untreated (AC0) and acid-treated AC (ACA) iron-oxide composites were synthesized, characterized, and compared in terms of activity to bare AC using several oxidants and pollutants, the activation efficiency of hydrogen peroxide (H2O2) and ammonium persulfate ((NH4)2S2O8), and the subsequent oxidation extent and kinetics of bisphenol-A, atrazine, and carbamazepine by the AC-based materials were studied in depth. The persulfate-based systems showed considerably higher pollutant removal in the presence of the catalysts, despite lower persulfate decomposition rates: atrazine and carbamazepine were partially degraded, mainly through a radical-dependent pathway; the highest removal of atrazine was achieved with the ACA-iron composite, whereas carbamazepine was best removed by the AC0-iron composite. In contrast, bisphenol A was completely mineralized, probably via a non-radical pathway, in the presence of all AC-based composites, even at very low persulfate concentrations. Furthermore, bisphenol A removal remained high for several consecutive cycles, with the most efficient removal and stability observed in the presence of ACA. These findings reveal the high complexity of AC-based systems, with multiple binding sites and degradation pathways unique to each combination of pollutants, catalysts, and oxidants. In general, the composition of the waste stream governs the applicability of these materials. Thus, the structure-function correlations and degradation mechanisms revealed here are crucial for improving sorbent-catalyst design and accelerating the implementation of low-cost remediation and in situ regeneration technologies.