Impact of pyrolysis temperature and solution pH on singlet oxygen dominated dye degradation in biochar activated...

Activation of peroxymonosulfate by various agents to produce sulfate radical in water medium is an efficient route for the degradation of several recalcitrant organic pollutants. Biochar is found to be an effective catalyst for the activation of peroxymonosulfate. The impact of pyrolysis temperature on dye removal by biochar activated peroxymonosulfate process at various pH conditions was investigated in this study. Biochar produced from coir pith at 350 °C, 500 °C, and 650 °C was used for the degradation of Rhodamine B at pH 3, 6, and 9. Complete removal of Rhodamine B was observed in all the pH conditions and within 60 min of reactions. The surface charge of biochar was not an activator of peroxymonosulfate. Singlet oxygen was found to be the predominant oxidant generated by the activation of peroxymonosulfate by biochar via the electron acceptor pathway. Peroxymonosulfate was activated mainly by C = O groups and persistent free radicals of biochar. Even though the dye removal efficiency was similar for biochar produced at different pyrolysis temperatures and solution pH, singlet oxygen generation was higher at pH 9 and with biochar produced at 500 °C. Singlet oxygen contributed 59% of dye degradation and was predominant at all the pH conditions considered. Hence, the non-radical pathway degradation by biochar activated peroxymonosulfate is a promising solution for reducing the environmental impact of dye pollution.