Study On Biochar-supported Zero-valent Iron(nZVI) Bimetallic Activation Of PMS For Degradation Of Norfloxacin

Norfloxacin（NOR）has the characteristics of broad antibacterial spectrum,strong tissue penetration,low adverse reactions and low price,which is widely used in the field of pharmaceutical culture.NOR enters the environment through wastewater,aquaculture discharge and improperly treated medical waste,leading to water pollution,which is difficult to be effectively removed by traditional sewage treatment technology.The advanced oxidation process of persulfate is a method of degradation of pollutants by sulfate radical（SO₄^-·）as oxide.Compared with the traditional advanced oxidation process,SO₄^-·has higher REDOX potential,more activation modes and lower storage and transportation costs,and has attracted wide attention.Bimetallic modified nZVI activated peroxy monosate（PMS）can improve the production efficiency of sulfate radical,and biochar loading can further improve the production efficiency of radical,which can be used for efficient degradation of NOR in water environment.In this paper,nZVI/Mn,nZVI/Ag,nZVI/Cu and nZVI/Co were doped and modified by several transition metals（Mn,Ag,Co and Cu）to prepare nZVI/Mn,nZVI/Ag,nZVI/Cu and NZVI/Co,and their ability to activate PMS to degrade NOR in water was explored,from which nZVI/Cu and NZVI/Co were selected.The NOR degradation rates of materials with different metal ratios were studied.Using reed as raw material,biochar（BC）was fired,and nZVI/Cu and nZVI/Co were supported on biochar by liquid phase reduction method to produce biochar supported zero-valent nano-iron copper（BC@nZVI/Cu）and biochar supported zero-valent nano-iron cobalt（BC@nZVI/Co）.The effects of different materials dosage,biochar content,initial PMS concentration,initial NOR concentration and p H on the degradation of NOR by material activated PMS were investigated,the reaction kinetics and the change of iron ion concentration during the degradation process were explored,and the leading free radical of the reaction was studied to speculate the reaction mechanism.The main conclusions are as follows:（1）By comparing several zero-valent nano-iron bimetals and materials with different metal doping ratios,it was found that the activation PMS had the best degradation effect when the doping amount of Cu and Co was 5wt%,which were 68.6%and 84.4%,respectively.（2）BC@nZVI/Cu and BC@nZVI/Co were analyzed by X-ray diffraction（XRD）,X-ray energy spectrum（EDS）,scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）.XRD patterns can confirm the existence of zero-valent iron in the composites,SEM shows that the bimetallic dispersion of the two composites is better than that before composite,improving the agglomeration of nZVI/Cu and nZVI/Co,EDS and XPS characterizations indicate the presence of Cu and Co in the two composites.FT-IR indicated that the composite materials retained the active groups on the surface of biochar,and the above characterization results indicated that both kinds of composite materials were successfully prepared.（3）The effects of different reaction conditions and biochar content on the degradation of NOR by material activated PMS were studied.The results showed that the iron-carbon ratio was 1:When the material dosage was 0.1 g/L,the initial PMS concentration was 0.2 mmol/L and the initial NOR concentration was 20 mg/L,the removal rate of BC@nZVI/Cu and BC@nZVI/Co were 87.3%and 93.1%respectively.In addition,p H also has an effect on the removal rate of materials.Under alkaline conditions,NOR removal rate decreases significantly,but has little effect on BC@nZVI/Co.Under weakly alkaline conditions,the removal rate of NOR activated by BC@nZVI/Co can still reach 80.2%.（4）The kinetics of the reaction showed that the process of BC@nZVI/Cu and BC@nZVI/Co activated PMS to degrade NOR was more consistent with the pseudo-second-order kinetic model.The dominant free radical of the reaction was confirmed.It was found that the dominant free radical of the system was sulfate radical under acidic and neutral conditions.The proportion of hydroxyl radical also increased.The concentration of iron ion in the reaction process was monitored,and it was found that most Fe⁰was transformed into free iron in the reaction process.With the progress of the reaction,Fe²⁺was transformed into Fe³⁺by reacting with PMS,and Fe³⁺reacted with Fe⁰to form Fe²⁺to form metal ion cycle.The addition of Cu and Co accelerated the corrosion of Fe⁰in the above cycle.Under alkaline conditions,the production of Fe²⁺is limited,and the content of SO₄^-·generated in reaction with PMS decreases,leading to the reduction of NOR removal rate.