Incorporating Fe₃C Into B,N Co-doped CNTs:Non-radical-dominated Peroxymonosulfate Catalytic Activation Mechanism

In recent decades,with the rise of industrialization and urbanization,the problem of water pollution is becoming increasingly serious.And the discharge of organic wastewater has increased sharply,among which antibiotic wastewater has become a research hotspot in the field of wastewater purification worldwide.As a kind of refractory organic pollutants,antibiotics will cause irreparable damage to human health and natural environment if they remain in water environment.Among the existing wastewater treatment technologies,the advanced oxidation processes technology based on sulfate radical(SO₄^·-)has a huge application space in the treatment of antibiotic wastewater due to its strong oxidation capacity,fast reaction rate,wide range of use,easy operation condition control and satisfactory catalyst stability.Nowadays,the research on high-efficiency catalysts for advanced oxidation processes method has developed rapidly,among which nano-carbon has been widely used as the substrate material for catalytic reaction because of its excellent biocompatibility,stabilized structure and chemical properties and no secondary pollution.In this study,B and N co-doped carbon nanotubes（CNTs）contain iron carbide（Fe₃C@BN-C）were prepared using melamine,iron trichloride hexahydrate and boric acid as precursors.The mechanism of activation of doxycycline hydrochloride（DOX-H）was studied by using Fe₃C@BN-C/PMS mixed system.The research contents are shown as follows:（1）Fe₃C@BN-C catalyst was prepared by one-step pyrolysis and calcined at 700℃,800℃and 900℃,respectively.Then,the crystalline structure,chemical constitute,morphosis,specific surface area（SSA）,surface functional groups and other properties were studied by XRD,XPS,SEM,HRTEM,FT-IR and BET.The results of XRD,XPS,SEM and HRTEM showed that B and N co-doped carbon nanotube composites incorporated Fe₃C nanoparticles were successfully synthesized.The characteristic peak corresponding to C-O（N/B）bond was observed at 1090-1370 cm^-1 by FT-IR spectrum analysis,which further illustrates the B and N atoms doping on the carbon skeleton and combine with carbon atom.BET results indicate that the catalytic material has greater specific surface area and ample defect sites,this is a strong correlation with adsorption capacity and catalytic property of catalysts.（2）The Fe₃C@BN-C/PMS system was established,DOX-H was taken as the main target pollutant,and a suite of degradation experiments were used to estimate the catalytic activity of DOX-H and the decompositon performance of DOX-H by controlling the physical and chemical factors.Degradation of the experimental results show that in the presence of PMS,Fe₃C@BN-C-8 in three different pyrolytic temperature in the preparation of catalyst showed the most excellent catalytic performance and its within 120 min of DOX-H degradation rate could reach 91.9%.The degradation experiment of controlling p H showed that Fe₃C@BN-C/PMS system exhibited the most high-efficiency degradability at p H=7,and had a wide adaptability to the p H of water quality（3-11）.The results of the cycle experiment showed that the material had good stability and reusability.（3）Further studies showed that Fe₃C nanoparticles with oxygen-containing functional groups such as pyridinic N,pyrrolic N,graphite N,boron and nitrogen dopants played a crucial role in improving the activity of the catalyst.In addition,quenching tests and electron paramagnetic resonance（EPR）studies manifested that the degradation of DOX-H by Fe₃C@BN-C catalyzed activation of PMS was a non-radical oxidation reaction following singlet oxygen（¹O₂）as the main active oxygen species.Based on LC-MS results,14 possible intermediates in DOX-H degradation process were proposed.This study not only provided a novel and valuable catalyst for the treatment of pharmaceutical wastewater,but also provided a new perspective for the study of active PMS,which is mainly based on non-free radical pathway.