In this study, we used a continuous flow device to simulate actual water treatment works and explored the impact of the coagulant dosage and shear rate combination on kaolin floc properties. The results indicated that an increase in coagulant dosage contributed to larger floc size and more compact floc structure. As coagulant dosage further increased, both floc size and fractal dimension were reduced. For different shear rate combinations, the floc size during the transitional phase increased with the decrease of fractal dimension, followed by the reduction of floc size and increase of floc density in the steady state because of the breakage and restructure of flocs. Considering that the actual coagulation process aims to generate large flocs without breakage, this indicates that the time to reach a steady state for floc size is the optimal coagulation time. Thus, the optimal shear rate combination (59–48–17 s⁻¹) is the one which reached steady state for floc size at the end of the coagulation process. In contrast to constant shear rate, decreasing shear rate enhances the floc growth, leading to similar floc properties for different shear rate combinations. This is the first time temporal evolution of floc size and structure in a continuous flow reactor has been reported.

Modification of catalysts by multi-heteroatom doping (S, P, B) is an effective way to improve the peroxomonosulfate activation performance of catalysts. In recent years, highly toxic and persistent trace organic contaminants have been frequently detected in water. Consequently, we proposed the advanced oxidation processes of peroxomonosulfate activated by multi-heteroatom doped Fe@CN (X-Fe@CN) to eliminate trace organic contaminants. The physical phases of X-Fe@CN and its precursors were characterized by X-ray diffraction and scanning electron microscopy. In evaluating the catalytic properties and iron ion leaching of X-Fe@CN-activated PMS for the removal of dicamba and atenolol, B-Fe@CN and PB-Fe@CN were selected and optimized. The active sites of the catalysts were characterized by X-ray photoelectron spectroscopy and Raman. The pathways of PMS activation by B-Fe@CN and PB-Fe@CN were identified in combination with electron paramagnetic resonance and electrochemical experiments. Defects, O-B-O and pyrrolic nitrogen on the surface of B-Fe@CN could adsorb and activate PMS to produce SO₄^•−, ·OH and ¹O₂. Further doping with P enhanced the electron transfer on the catalyst surface, thus accelerating the activation of peroxomonosulfate. This study compared the effects of multi-heteroatom modifications and further demonstrated the synergistic effect between P and B, which can provide a theoretical basis for the selection of multi-heteroatom doped catalysts in water treatment.