Effects of different pretreatment strategies during porous carbonaceous materials fabrication on their peroxydisulfate activation for organic pollutant degradation: Focus on mechanism

Metal-free porous carbonaceous materials (PCM) are compelling for peroxydisulfate (PDS) activation. However, pore-creating processes are multifarious and their influences on PDS activation performance for organic degradation have not been elucidated. Herein, several PCM were synthesized via different pretreatment strategies, including manual grinding (MG), impregnation (IP) and ball milling (BM), to probe their influence on PDS activation efficiency. Therein, the PCM fabricated via BM for 60 min (BM60) was superior to all other varieties. The quantitative structure–activity relationship (QSAR) unveiled that BM accelerated the vertical expansion of turbostratic domains on PCM. The rate constant (kobs) of sulfadiazine (SDZ) degradation in PCM/PDS system positively correlated to the defective degree over PCM and CO content, indicating that the abundant defective structures over PCM contributed to enhance the PDS activation capacity by exposing more CO active sites. The CO groups can efficiently donate electrons to S2O82− inducing the breakage of peroxy bond because of the brilliant electron donating capacities of BM60, which resulted in the generation of radicals. Robust mechanism studies by multiple electrochemical methods and in situ Raman technology suggested metastable intermediates (BM60/PDS*) with a higher redox potential was the predominant oxidant which can extract electrons from SDZ via a one-electron-transfer regime, while radicals were the secondary oxidants. This finding for the first time explicitly illuminated the electron transfer direction in the nonradical pathways of PDS activation for organics degradation by PCM and deepened the fundamental understanding on the electron-transfer pathway.