Synthesis of Halloysite/MnFe2O4 Heterogeneous Fenton Catalyst for Efficiently Degradation of Organic Pollutants

To address the limitations associated with the conventional Fenton process, which often exhibits a restricted pH range and presents challenges in terms of catalyst recovery and second pollutant, an improved magnetic heterogeneous catalyst of halloysite/MnFe2O4 (HNT/MnFe2O4) was optimally synthesized. It showed that HNT/MnFe2O4 catalysts could achieve 90% removal efficiency to 50 mg/L of methylene blue (MB) at pH 4–10 with high utilization of hydrogen peroxide (H2O2), and the used HNT/MnFe2O4 catalysts could be easily separated from solution via magnetic separation. The presence of anions (NO3-, Cl-, SO42-, CO32- and HCO3-) and HA scarcely affected the degradation of MB by HNT/MnFe2O4 catalysts and the removal efficiency of MB only decreased by less than 10% in the 5th cycle compared to the fresh catalyst. Furthermore, HNT/MnFe2O4 catalysts demonstrated their capability to effectively degrade various organic pollutants such as benzohydroxamic acid, xanthate, and eosin Y. The excellent catalytic performance of HNT/MnFe2O4 catalysts was attributed to the synergistic effects between HNT and MnFe2O4. The EPR spectra and quenching experiments indicated that the main reactive oxygen species (ROS) that participated in the degradation process were ·OH and ·O2-. ·OH directly attacks MB molecular and ·O2- accelerates the reduction of metal ions. Therefore, HNT/MnFe2O4 catalysts demonstrated a good potential for organic pollutant degradation. This study provides valuable insights into the synthesis of novel catalysts and their practical applications in organic wastewater purification.