Nitrogen self-doped chitosan carbon aerogel integrating with CoAl-LDH for ultra-efficient sulfamethoxazole degradation based on PS-AOPs: From batch to continuous process

Nitrogen self-doped chitosan carbon aerogel (NCCA) integrating with CoAl layered double hydroxide (CoAl-LDH) was successfully fabricated and utilized for the ultra-efficient activation of peroxymonosulfate (PMS) toward sulfamethoxazole (SMX) degradation. And the NCCA/CoAl-LDH-2 catalyst possessed the highest catalytic activity with 97.5% of SMX degradation efficiency in 5 min and 74.8% of total organic carbon (TOC) removal efficiency in 30 min, may being on account of the synergistic interaction between NCCA and CoAl-LDH. Additionally, the NCCA/CoAl-LDH-2 catalyst not only had good reusability and stability, but also could realize continuous degradation of SMX solutions via a fixed-bed reactor. Furthermore, the results of quenching tests, electrochemical measurements as well as electron paramagnetic resonance (EPR) analysis demonstrated that both non-radical and radical processes participated in the SMX degradation, in which the latter played a predominant role. X-ray photoelectron spectroscopy (XPS) corroborated that the main active sites were the CO groups and graphitic N of NCCA, and the Co3+/Co2+ redox cycle of CoAl-LDH. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis and density functional theory (DFT) calculation containing the laplacian bond order (LBO) and Fukui index were carried out to deeply explore the reasonable SMX degradation pathways. This current study provided a theoretical basis to design an efficient PMS activation system toward continuous antibiotics degradation.