Study On The Adsorption Performances Of Norfloxacin And Ciprofloxacin Onto Nitrogen-doped Activated Carbon

Antibiotics were widely used in the treatment of infectious diseases of humans and animals.In the production and use of antibiotics,a large amount of antibiotic wastewater was produced,which had caused serious harm to the natural environment and human health.Therefore,it was urgent to find a high-efficiency treatment method for antibiotic wastewater.Adsorption method was one of the effective methods for removing antibiotics from the environment.Shaddock peel,as an agricultural waste,had a wide source and it was rich in C element,which was an ideal raw material for preparing activated carbon.In this paper,high-performance nitrogen-doped activated carbon was prepared by hydrothermal carbonization and KOH activation using shaddock peel as the raw material,to explore its adsorption performance for norfloxacin(NFX)and ciprofloxacin(CIP),aiming to lay a theoretical foundation for quinolone antibiotic wastewater treatment.Nitrogen-doped activated carbon was prepared from shaddock peel using urea as the nitrogen source and KOH as the activator.The Box-Behnken(BBD)central composite design model in response surface methodology was used to optimize the activation conditions of nitrogen-doped activated carbon.The optimal conditions for the preparation of nitrogen-doped activated carbon(NAC)were as follows:activation temperature 833℃,activation time 2.4 h,and the ratio of KOH to hydrochar 2.34:1.The specific surface area of NAC was 2481.81 m~2/g.The adsorption performances of NAC for NFX were studied.The BBD model was used to optimize the adsorption conditions of NFX on NAC.The results showed that the optimal adsorption conditions were adsorption time of 227 min,p H6.8,and initial NFX concentration of 200 mg/L.Adsorption thermodynamics studies indicated that the adsorption experimental data were fitted well with the Langmuir and Koble-Corrigan(K-C)isothermal models.At 298 K,the maximum monolayer adsorption of NFX was 746.29 mg/g.The thermodynamic parameters indicated that the adsorption of NFX by NAC was a spontaneous endothermic process.The adsorption capacity of NFX by NAC was increased by increasing the temperature.The kinetic datas were fitted well with the pseudo-second-order kinetic model.The intragranular diffusion model indicated that the adsorption process was controlled by the combination of intragranular diffusion and boundary layer diffusion.The adsorption performances of NAC for CIP were studied.The adsorption conditions of CIP on NAC were optimized by response surface methodology.The optimal adsorption conditions were obtained as follows:adsorption time 254 min,p H6.7,and initial CIP concentration 200 mg/L.The thermodynamic studies showed that the Langmuir and K-C isothermal models could describe the adsorption process well of CIP onto NAC.At 298 K,the maximum monolayer adsorption capacity of CIP was752.05 mg/g.The adsorption process of CIP on NAC was an endothermic process,and high temperature was conducive to the adsorption.The adsorption of CIP by NAC was in accordance with the pseudo-second-order kinetic model.The adsorption process was affected by not only intragranular diffusion but also boundary layer diffusion.NAC was characterized by FTIR,X-ray photoelectron spectroscopy,specific surface aperture analyzer and scanning electron microscope,and its adsorption mechanisms were discussed.The adsorption of NFX and CIP by NAC was affected by hydrogen bond,π–πinteraction,hydrophobic interaction,Lewis acid-base interaction and electrostatic interaction.In addition,nitrogen doping can enhance the hydrophobic effect and Lewis acid-base effect,thus increasing the adsorption capacity of NFX and CIP.NAC has ultra-high adsorption capacity for NFX and CIP,and it is a very promising adsorbent for the treatment of antibiotic wastewater,providing a new way for the treatment of antibiotic wastewater.