Mechanochemical synthesis of sulfidated microscale zerovalent iron/graphene composite for enhanced degradation of tetracycline

This study introduces a novel ternary composite comprising sulfur (S), reduced graphene oxide (rGO), and microscale iron (mZVI) powder through a straightforward ball milling process. The composite was employed as an activator for H2O2 in the degradation of tetracycline (TC). Impressively, the S-mZVI/rGO composite exhibits significantly enhanced TC removal efficiency in the presence of H2O2 compared to bare mZVI and S-mZVI alone. In the S-mZVI/rGO/H2O2 system, 97.2 % of the TC can be removed within 60 min, with an apparent rate constant (kobs) of 0.054 min−1, which is 49.18 and 2.14 times than that in the mZVI/H2O2 (0.001 min−1) and S-mZVI/H2O2 system (0.025 min−1), respectively. Furthermore, the S-mZVI/rGO composite exhibits outstanding TC removal efficiency across a broad pH range (3 ∼ 9), consistently exceeding 90 % under optimal conditions. The much superior activity of S-mZVI/rGO/H2O2 process is attributed to both radical (OH) and non-radical pathways (1O2 and electron transfer), with the latter contributing more. The catalyst's performance is also affected by the defective sites on the surface and the rapid cycle of Fe2+/Fe3+. Moreover, the degradation pathways of TC are proposed according to the intermediate products detected by HPLC-MS. Finally, the S-mZVI/rGO/H2O2 demonstrates high resistance to inorganic anions and natural organic matter in aquatic environments. Overall, S-mZVI/rGO is expected to be a cost-effective and highly efficient heterogeneous Fenton-like catalyst for the removal of organic contaminants from wastewater.