Pyrolytic temperature dependent conversion of sewage sludge to carbon catalyst and their performance in persulfate degradation of 2-Naphthol

The evolution of oxygen-functioning groups in sewage sludge based carbon is influenced by minerals presented in the raw sludge. In this study, the FeCl3 and polyacrylamide conditioned sludge in real wastewater treatment plant and demineralized sludge were carbonized in the temperature range of 300 °C–800 °C to investigate the roles of temperature and ash components on the interactions between surface groups conversion and crystalline structure evolution. The temperature-dependent ash effect on the conversion of oxygen containing groups was found by using XPS, Boehm titration, XRD and TPR characterization. The phase transfer of hematite to magnetite promoted the formation of hydrophilic organic groups at 600 °C, which may play a significant role on carbon’s adsorptive and catalytic behavior. To gain an in-depth knowledge and understanding, the as-prepared carbon was used as heterogeneous catalyst in persulfate degradation of a model pollutant 2-Naphthol. The use of carbon obtained at 600 °C (MC600) can achieve 88.7% and 47% of 2-Naphthol and TOC removal respectively at neutral pH, far higher than that of MC prepared at 300 and 800 °C. Further research revealed a strong correlation between adsorptive and catalytic efficiency of MC and its mineral structure, surface functional groups as well as operating pH. The formed hydrophilic oxygen-containing groups at higher temperature of MC600 are responsible for 2-Naphthol retention and the hydrogen bonds in siloxane bridges can easily adsorb persulfate. The pH effect on degradation in the presence of persulfate verified the broad pH operation, which is apparently superior than conducting with traditional heterogeneous Fenton process. The quenching experiments and EPR spectrum were further used to detect the oxidative species SO4- and HO, and confirmed the catalytic role of MC.