Research On The Adsorption And Degradation Mechanisms Of Quinolone Antibiotics In Wastewater By Functionalized Biochar

Antibiotics are a group of emerging environmental contaminants that are very difficult to deal with.A large number of antibiotics discharged into the environment can cause serious harm to the ecological environment and human health.Therefore,the removal of antibiotics from water is the focus of researchers.Among many antibiotic removal methods in water,adsorption and photocatalytic method have attracted much attention because of their high removal rate and no secondary pollution.Biochar is a carbonaceous material with strong adsorption capacity for pollutants in water.Its large specific surface area and porous structure are conducive to the loading of photocatalysts.Therefore,the preparation of functionalized biochar by loading photocatalyst on biochar has great application potential for the adsorption and degradation of antibiotics in water.However,as far as we know,the adsorption and degradation mechanism of functional biochar for antibiotics in water is still not clear.Therefore,in this study,distillers grains,sawdust,and grapefruit peel were used as raw materials to prepare magnetic biochar by one-step co-pyrolysis with hematite to adsorb ciprofloxacin（CIP）and norfloxacin（NOR）in water.The influencing factors and adsorption mechanism of magnetic biochar in the process of adsorbing CIP and NOR were studied through physicochemical characterization and site energy analysis.On this basis,magnetic biochar was used as the carrier of photocatalyst to load Ti O₂to prepare Fe/Ti biochar.The adsorption and degradation performance and mechanism of CIP and NOR in water were studied,and the degradation paths of CIP and NOR were analyzed.Finally,the practical application potential of magnetic biochar and Fe/Ti biochar was evaluated.The main conclusions are as follows:（1）The analysis of the physicochemical properties of biochar showed that the pore size of biochar decreased with the increase of pyrolysis temperature,and the maximum adsorption pore size gradually decreased.After loading Fe and Ti O₂,there were flake Fe oxides and cluster Ti O₂ particles on the surface of Fe/Ti biochar.Most of Fe and Ti could combine with O element on the surface of biochar,and some Fe and Ti could also combine with C element.（2）Magnetic biochar and Fe/Ti biochar were prepared by the one-step pyrolysis method.They had good adsorption capacity and photocatalytic performance.The maximum adsorption capacity of magnetic biochar for CIP and NOR could reach18.08 and 11.90 mg/g.In 40 mg/L CIP and NOR solution,the degradation efficiency of Fe/Ti biochar for CIP and NOR could reach 88.4%and 88.0%.（3）The results of adsorption kinetics and adsorption isotherms showed that the adsorption of CIP and NOR on magnetic biochar was electrostatically adsorbed to the surface,and then could produce adsorption such as cation exchange interaction,π-πinteraction,hydrophobic and hydrogen bonding,etc.Theπ-πinteraction and the polar interaction are the dominant mechanisms in the adsorption process of CIP and NOR by magnetic biochar.（4）The results of free radical quenching experiments and degradation pathways showed that when the heterogeneous system of CIP,NOR,and Fe/Ti biochar was irradiated with visible light higher than the band gap energy.Fe/Ti biochar was excited to produce e^-and h⁺in the conduction band and valence band respectively.Then a series of reactions can take place on the surface of Fe/Ti biochar to generate·O^2-,·OH,and other active substances to oxidatively degrade CIP and NOR.In addition,h⁺can directly oxidize CIP and NOR molecules to form degradation products.