Study On The Modification Of Carbon Nitride And The Photocatalytic Mechanism Of Fluoroquinolone Antibiotics

Currently,antibiotics have been produced and used in large scale.These antibiotics can enter the environment with wastewater as the as they cannot be completely removed by conventional sewage treatment processes.It has been demonstrated that antibiotic in the environment could break ecological balance and pose a threat to public health.Therefore,it is of great practical significance to develop economic,efficient,and environmentally friendly treatment technologies for the removal of antibiotics.Photocatalytic technology,as a kind of advanced oxidation process,has been used for the removal of antibiotic wastewater.Carbon nitride is a new type of photocatalyst.Unfortunately,the photocatalytic efficiency of bulk g-C₃N₄ is still far from satisfactory,which is mainly due to the low specific surface area?<10 m²/g?,high recombination rates of photogenerated electron-hole pairs,and narrow visible-light absorbance.Therefore,in this study,g-C₃N₄ based composite was prepared via a facile method and applied to the degrdation of antibiotics.The main contents are as follows:First,the photocatalytic degradation kinetics and mechanism of norfloxacin?NOR?was investigated in a sunlight-driven photocatalyst mesoporous g-C₃N₄?mpg-C₃N₄?.The morphology and structure of mpg-C₃N₄ were studied by transmission electron microscope?TEM?,X-ray diffraction?XRD?,and nitrogen adsorption-desorption isotherms?BET?.The results showed that mpg-C₃N₄ exhibited the mesoporous structure with the pore size of ca.12 nm,which could provide more active site for photoreaction.The degradation of NOR followed the Langmuir-Hinshelwood?L-H?kinetics model,and the adsorption of NOR followed the second order kinetics,indicating that surface reactions and chemisorptions played the important roles during the photocatalysis process.Further study of reactive species?RSs?by RSs scavenging experiment showed that superoxide anion radical(O₂^?-)and photohole?h⁺?were responsible for the major degradation of NOR.In the second place,we synthesized the mpg-C₃N₄/CQDs,and applied for the removal of fluoroquinolones antibiotics?FQs?through the synergistic adsorption and photocatalysis.The mesoporous structure of the mpg-C₃N₄/CQDs offers a larger population of adsorption sites,which can enhance the capacity for the adsorption of FQs.Under visible light irradiation,mpg-C₃N₄/CQDs demonstrated a higher photocatalytic activity for FQs degradation than did bulk g-C₃N₄ or mpg-C₃N₄.This enhancement might have been ascribed to the high surface area of the mpg-C₃N₄,unique up-converted photoluminescence?PL?properties,and the efficient charge separation of the CQDs.The eradication of FQs followed the Langmuir-Hinshelwood kinetic degradation model and absorption pseudo-second-order kinetic model,indicating that surface reactions and chemical sorption played significant roles during the photocatalysis process.The results of electron spin resonance?ESR?technology and reactive species?RSs?scavenging experiments revealed that the superoxide anion radical(O₂^?-)and photo-hole?h⁺?were the primarily active species that initiated the degradation of FQs.Based on the identification of intermediates and the prediction of reactive sites,the degradation pathways of ofloxacin?OFX?were proposed.A residual antibiotic activity experiment revealed that mpg-C₃N₄/CQDs provided very desirable performance for the reduction of antibiotic activity.Results indicated that applying mpg-C₃N₄/CQDs absorption-photocatalysis system for remediation of FQs contaminated water matrix is technically possible.