Study On The Removal And Mechanism Of Tetracycline By Nano Zero Valent Manganese Loaded Pomelo Peel Biochar

Tetracycline（TC）is widely used as an inexpensive and effective antibiotic.However,due to its abuse and unreasonable discharge,it has been frequently detected in various water bodies,and the environmental pollution problems caused by TC and its wastewater have seriously affected the surrounding ecological environment and human health.The traditional removal approach is costly and prone to secondary pollution,etc.and the result is not satisfactory.Therefore,searching for a new effective method to control tetracycline wastewater pollution has become a hot spot of great concern.Adsorption method has been gradually favored by scholars for antibiotic wastewater treatment because of its advantages of easy access,low cost,high removal efficiency,simple operation,and no by-products.In recent years,zero-valent manganese has shown a large potential for pollutant control,however,problems such as easy oxidation and poor stability which limited its application in the treatment of wastewater.The surface of biochar contains a large number of oxygen-containing functional groups and large specific surface area and stable structure,which may play a synergistic role in the removal of pollutants with zero-valent manganese after loading,and is an ideal Nano-zero-valent manganese carrier material that is being increasingly applied in the removal of pollutants.In this study,Nano-zero-valent manganese（n ZVMn）and Nano-zero-valent manganese pomelo peel biochar composite（n ZVMn/BC）were successfully prepared by liquid-phase reduction method to investigate their adsorption performance toward TC in water.The materials were characterized using SEM-EDS,BET,FTIR,XRD,XPS and Zeta potential analysis technology.The removal performance of TC by the two materials under different environmental factors was systematically investigated,and their isothermal adsorption models and kinetic models were also explored.Combining characterization techniques to reveal the mechanism of TC adsorption by zero-valent manganese nanoparticles and their zero-valent manganese biochar material.The main findings can be concluded as following:（1）nZVMn was synthesized by liquid-phase reduction.The adsorption performance of n ZVMn on TC under various conditions was systematically investigated.The specific surface area of n ZVMn was 54.44 m²/g,pore volume was0.52 cm³/g,and pore size was 37.76 nm.The material was partially oxidized during synthesis and storage,forming a core-shell structure with n ZVMn as the core and manganese oxide as the shell.The manganese oxide mainly existed in the form of tetravalent manganese.The results indicated when the material dosage was 0.4 g/L,the removal rate of TC can exceed 80%in a wide initial pH range（pH=5-11）after reaction for 2 h,and the optimal pH was 9.The inhibition effect of cations on adsorption capacity was Mg²⁺>Ca²⁺>Na⁺.Through the analysis of adsorption kinetics and adsorption isotherm of n ZVMn.The adsorption isotherms of obtained n ZVMn were well described by Langmuir isotherm,and their adsorption kinetics were well estimated via pseudo-second-order model,indicating that the adsorption of TC on n ZVMn was mainly due to monolayer molecular adsorption.The theoretical maximum adsorption capacity was 426.63 mg/g.（2）Based on the nZVMn,the removal of TC by n ZVMn/BC was investigated,and the influences of n ZVMn/BC dosage,solution pH and ionic strength on its removal were discussed.The results revealed the maximum TC removal（86.4%）and adsorption（350.13 mg/g）by n ZVMn/BC composite at mass ratio of biochar to zero-valent manganese 2:1,optimum pH range 5-9.The pseudo-second-order kinetic model and Freundlich isotherm model provided the better correlation for the experiment data.indicating that the composite was a multi-layer chemisorption.The BET results showed that the specific surface area,pore volume and pore size of the zero-valent manganese were 73.48 m²/g,0.32 cm³/g,and 25.99 nm,respectively.Compared with the single zero-valent manganese,the decrease in pore volume and pore size was caused by the fact that n ZVMn was embedded in the pore size of biochar.Four adsorption-desorption recycling experiments on n ZVMn/BC revealed that the removal efficiency can still reach 73.12%,which has high recyclability.The composite material still maintained superior TC adsorption（above 150 mg/g）in actual water despite the interference of various factors such as organic matter,anions,and cations.（3）In this paper,TC was taken as the target pollutant,SEM-EDS、BET、FTIR、XRD、XPS and Zeta potential analyzer were used to characterize and analyze the as-prepared materials.The results showed that the adsorption of n ZVMn and n ZVMn/BC on TC includes electrostatic adsorption,hydrogen bonding,π-πinteraction and other forces,in addition,there may be complexation between manganese and tetracycline.The loose porous structure provideed larger specific surface area and more active sites.In conclusion,the use of zero-valent manganese biochar as an economical,efficient and environmentally-friendly material can effectively remove TC from wastewater.The development of the experiment can provide theoretical basis and practical platform for the removal of antibiotic wastewater.