Synergistic Mechanism Of Norfloxacin Degradation By Peroxymonosulfate Activated By Cobalt-nickel Bimetallic Catalyst

Antibiotics play an important role in the prevention or treatment of bacterial infections in humans and animals.However,it can enter natural water environmental along with medical waste,pharmaceutical wastewater,and animal waste,causing serious threats to ecosystems and human health.As a typical quinolone antibiotic,the concentration of norfloxacin（NOR）in the environment can reach"ng～mg"level.It is difficult to remove NOR by traditional wastewater treatment processes,due to the inhibitory effect of NOR on microorganisms,which brings great challenges to water pollution prevention and Control.Therefore,how to effectively treat wastewater containing antibiotics is an important issue that needs to be solved urgently in the water environment.At present,among the commonly used antibiotic wastewater treatment technologies,advanced oxidation process（AOP）has been proved to be an effective technology to degrade such refractory pollutants by using highly active and strong oxidizing active species.Compared with hydroxyl radical（^·OH）,sulfate radical(SO₄^·-)based on peroxymonosulfate（PMS）has many advantages,such as high oxidation potential（2.5-3.1 V）,high utilization efficiency,long service life（4 s）and little influence on water environment background,etc.,and shows more excellent performance in the field of pollutant degradation.Among them,magnetic transition metal-based catalysts,such as cobalt-,iron-and nickel-based catalysts,have been proved to be effective PMS activators with the advantages of high activation efficiency,low dosage and good recovery performance.Compared with single metal catalysts,double metal catalysts can significantly improve the activation performance of PMS and further improve the degradation ability of pollutants through the synergistic effect between metals,but the specific mechanism involved is not clear.Therefore,two kinds of cobalt-nickel bimetallic catalysts,NiCo₂O₄NS and NiCo₂N,were prepared in this paper,and the synergistic mechanism of activating PMS to degrade NOR was deeply studied.The main research contents are as follows:1.NiCo₂O₄NS promotes peroxymonosulfate activation for efficient norfloxacin degradation and mechanism.Firstly,we synthesized a kind of ultrathin NiCo₂O₄nanosheets（NiCo₂O₄NS,～1 nm）with high activity exposed crystal facet（311）,and used it to activate PMS to degrade NOR.The synergistic effects between Niand Co were the dominant activation mechanism.Compared with Co₃O₄,NiCo₂O₄NS adsorb PMS through a unique“bridge”mode,where both Co and adjacent Niinteract with the same O atom in PMS,increasing the number of electron transfer for enhanced breakage of O-O bond.NiCo2O4NS/PMS system shows excellent NOR degradation efficiency in a wide pH range.NiCo₂O₄NS with high cycling stability,could reach 100%degradation of other typical pollutants,and showed higher degradation performance in actual wastewater.2.NiCo₂N promotes peroxymonosulfate activation for efficient norfloxacin degradation and mechanism.Based on the synergistic effect of Co and Niin the above research,we successfully synthesized cobalt and nickel nitride（NiCo₂N）by calcining Ni_1/2Co_2/3（OH）₂in ammonia atmosphere,and applied NiCo₂N to activate PMS to degrade pollutants for the first time.Different nitrogen species（such as pyridine nitrogen and pyrrole nitrogen）coordinate with Ni/Co to form Ni-N/Co-N bond and act as the main catalytic active sites for PMS activation.¹O₂ and SO₄^·-are the main active species.Compared with NiCo₂O₄NS,NiCo₂N can achieve 100%degradation in 10 min,showing excellent catalytic activity.The synergistic effect of Ni-Co-N is the key to activate PMS.It is also widely applicable to other typical pollutants,with 100%degradation efficiency of bisphenol A,rhodamine B,tetracycline,sulfamethoxazole,etc.NiCo₂NSPMS system showed excellent NOR degradation efficiency in a wide p H range.It shows high degradation performance in actual wastewater due to the existence of Cl^-,H₂PO₄^-and NO₃^-.Meanwhile,it has excellent recyclability.Therefore,NiCo₂N shows a good practical application prospect in actual wastewater treatment.This paper first reveals that the synergistic mechanism between cobalt and nickel on NiCo₂O₄NS nanosheets promoting activation of peroxymonosulfate to effectively degrade norfloxacin;Based on the synergistic mechanism of bimetals,the bimetallic nitride NiCo₂N was applied to the field of PMS activation and degradation of pollutants for the first time,which broadened its catalytic application range;This study provides important enlightenment for understanding the activation mechanism of PMS and designing PMS catalysts with bimetallic active sites.