Low temperature modified sludge-derived carbon catalysts for efficient catalytic wet peroxide oxidation of m-cresol

Abstract

A method for recycling sewage sludge was investigated to prepare catalysts with a desired shape for use in the catalytic wet peroxide oxidation (CWPO) reaction. Sludge-derived carbon (SC) was first modified with HNO₃ solutions under different conditions; only the SCs modified at or below 0 °C retained their columnar shape instead of corroding into a powder. The prepared samples were tested in the CWPO reaction using m-cresol as the target pollutant. The highest degradation rate of 97.6% after 30 min was found for the sample modified at 0 °C with 6 mol L⁻¹ HNO₃ for 24 h (SC-T0) with the stoichiometric dose of hydrogen peroxide required for the complete mineralization of m-cresol. The sample modified at the commonly used temperature of 60 °C converted only 17.7% of the m-cresol after reaction. The physical and chemical properties of the SCs were fully characterized. All the modified samples benefited from the pore expansion effect of HNO₃ and had a larger specific surface area than the original SC. For SC samples with abundant surface oxygen groups and iron species, treatment with HNO₃ at 0 °C allowed the sample to retain abundant basic surface oxygen groups and iron species in addition to removing large amounts of negatively charged species, thus achieving the effective utilization of H₂O₂ and improving the catalytic activity. The oxidation route for m-cresol in the presence of SC-T0 was also studied with the assistance of density functional theory. The ability to regenerate SC-T0 without any loss of performance was demonstrated over three runs.