Manipulating the morphology of self-assembly broccoli-like cobalt nickel spinel for enhancing the peroxydisulfate activation towards highly-effective ciprofloxacin degradation: Radical and non-radical pathways, mechanism and toxicity evaluation

[Display omitted] •MCo2O4 was synthesized via a one-pot hydrothermal method.•The N element was in favor of broccoli-like NiCo2O4 generation.•DFT was used to reveal the reason for the quick CIP degradation performance.•Direct electron transfer was verified to be one of the non-radical pathways.•A possible CIP degradation pathway was proposed via LC-MS/MS. Self-assembly broccoli-like cobalt nickel spinel via a one-pot hydrothermal method, and built NiCo2O4/PDS (NiCo2O4/PDS) system for highly effective ciprofloxacin (CIP) degradation within a wide pH range (3–10). Note that quick CIP removal (98.5 % removal in 15 min with 0.2 g/L NiCo2O4 and 1.00 g/L PDS dosage) was observed without pH adjustment (pH = 6.2) in the system with the highest reaction rate of 0.2677 min−1, which was 35.22, 2.47, and 3.36 times over that of MgCo2O4 (0.0076 min−1), Co3O4 (0.1085 min−1), CuCo2O4 (0.0797 min−1), respectively. DFT calculations found that the lowest PDS adsorption energy (−4.91 eV) of NiCo2O4 among MCo2O4 (M = Ni, Mg, Co, and Cu) was the major reason for the great catalytic performance. Quenching experiments implied that OH and SO4− were identified to be the dominant ROS for CIP degradation, while amperometric i-t experiments revealed that direct electron transfer between PDS and CIP also contributed to the CIP degradation via a non-radical pathway. The proposed degradation pathway of CIP was deduced according to the determined nine intermediates of CIP. This work provides a new perspective for designing highly efficient heterogeneous catalysts with broccoli-like structures and renders environmental remediation with cobalt nickel spinel possible.