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