Enhanced degradation of tetracycline with zinc-based adenine-derived P, N co-doped carbon via peroxydisulfate activation

In this study, a P, N co-doped carbon with excellent adsorption and peroxydisulfate (PDS) catalytic activity based on zinc-based adenine complex (Zn-Ade) derived has been designed and fabricated via a facile two-step pyrolysis strategy. Under the optimized conditions, the synthesized phosphorus and nitrogen co-doped carbon (PNC-4, 4 is the mass ratio of KH2PO4 to pristine nitrogen-doped carbon) has a high graphitic N and pyrrolic N and exhibited excellent catalytic activity in PDS activation. A small amount of PNC-4 (0.05 g/L) could remove about 92.44 % of TC within 80 min when the initial tetracycline (TC) concentration was 20 mg/L (PDS = 0.1 g/L; initial pH = 5.71), which could be attributed to the accelerated electron transfer and large adsorption capacity of PNC-4. The adsorption of TC on PNC-4 was chemisorption and the maximum theoretical capacity of adsorption (qmax) was 500.577 mg/g. The results of reactive oxygen species (ROS) capture experiments and electrochemical characterization confirmed that TC was oxidized mainly through electron transfer mechanism. Furthermore, the reaction rate constant (k) was significantly positively correlated with the graphitic N and pyrrolic N contents and weakly positively correlated with the defects, respectively. These findings demonstrated that graphitic N and pyrrolic N enhanced PDS activation and oxidized TC via the electron transfer pathway. Finally, the results of toxicity assessment showed that the toxicity of the intermediates were significantly reduced after TC degradation. This study not only propelled the mechanistic understanding of the collaborative contribution of active sites to PDS activation, but also offered a new strategy for the design of bifunctional carbon materials for adsorption and catalysis.