Organic acid promoting the degradation of nonylphenol by persistent free radicals in biochar

The environmental and health impacts of nonylphenol (NP) have led to increased efforts in developing green and efficient treatment methods. This study prepared biochar (BC) from pine leaves and sludge at 300 °C and 400 °C, and added organic acid to regulate persistent free radicals (PFRs) for continuous reactive oxygen species (ROS) production to degrade NP. Low-temperature biochar contained more oxygen containing functional groups, enhancing redox reactions. Organic acid effectively regulated pH and provided electrons, promoting high-redox-potential ROS generation in the organic acid-biochar (OA-BC) PFRs system, significantly increasing NP degradation. Notably, 85.71 % of NP was removed using 0.2 g/L 300 °C sludge-derived biochar and 20 mM citric acid. Quenching experiments confirmed that hydroxyl radicals ( OH) played the most significant role in NP degradation. Electrochemical tests and DFT calculations showed that biochar-PFRs can mediate electron transfer from organic acid, maintaining stable ROS generation. This research offers valuable insights into ROS generation and a novel approach for NP degradation.