H₂O₂ Activation And Norfloxacin Degradation Catalyzed By Coprecipitates Of Dissolved Organic Matter And Iron Oxides

Norfloxacin is a typical quinolone antibiotic that has been widely used in medical treatment and animal husbandry.In recent years,the treatment of antibiotic pollution has attracted wide attention.Fenton-like process is a typical advanced oxidation technology,in which hydrogen peroxide?H₂O₂?is activated to generate hydroxyl radicals to degrade antibiotics and other recalcitrant pollutants.The development of a more efficient and low-cost Fenton-like reaction catalyst with a simple preparation method is highly needed.It has been shown that coprecipitates of organic matter and iron oxide have stronger redox activity than iron oxide itself.Dissolved black carbon?DBC?and humic acid?HA?are two representative types of dissolved organic matter,which contain a large number of redox-active quinone and phenolic groups,and can act as electron carriers to participate in the redox transformation of pollutants.The coprecipitates of DBC/HA and iron oxides were prepared and characterized,and then used to activate H₂O₂ to generate hydroxyl radical?·OH?for the degradation of norfloxacin.Black carbon was prepared by the pyrolysis of wheat straw at a constant temperature of400°C for 3 hours.The dissolved black carbon samples were extracted from a black carbon suspension?60 g/L?by filtration and freeze-drying.Dissolved black carbon or HA were added into Fe²⁺-containing buffer system with specific molar ratios of C/Fe=0.2,C/Fe=1.6 and C/Fe=3.0,respectively,to prepare coprecipitates of iron oxide and DBC(DBC-FeO_?C/Fe=0.2?,DBC-FeO?C/Fe=0.2?and DBC-FeO?C/Fe=0.2?)or HA(HA-FeO?C/Fe=0.2?,HA-FeO?C/Fe=1.6?and HA-FeO_?C/Fe=3.0?).FTIR and X-ray photoelectron spectroscopy analyses were conducted to characterize the existence of carboxyl,quinone and other redox active groups in DBC-FeO and HA-FeO.The activation of H₂O₂ by different coprecipitates to generate·OH was investigated.When 0.25 g/L coprecipitates and 2 mM H₂O₂ were added,the accumulated·OH concentration in the system of DBC-FeO_?C/Fe=0.2?,DBC-FeO_?C/Fe=0.2?and DBC-FeO_?C/Fe=0.2?in 3 h was 109,199and 341?M,respectively,while that in the system of HA-FeO_?C/Fe=0.2?,HA-FeO_?C/Fe=0.2?and HA-FeO_?C/Fe=0.2?was 98?M,156?M and 281?M,respectively.I n addition,·OH production increased with the increase of concentrations of coprecipitate?0.1-0.75 g/L?and H₂O₂?2-4 mM?.Norfloxacin degradation in Fenton-like reactions catalyzed by these two types of coprecipitates was investigated.The maximum degradation efficiency of the DBC-FeO and HA-FeO systems for norfloxacin after 3 h could reach 90.9%and 74.7%when 0.1g/L coprecipitate and 1 mM H₂O₂ were used.Meanwhile,the norfloxacind egradation rate increased with the increase of the C/Fe ratio?0-3?and the coprecipitate concentration?0.05-0.15g/L?.Electron paramagnetic resonance analysis and quenching experiments showed that hydroxyl radical played a major role in the degradation of norfloxacin.The consecutive degradation experiment showed that the norfloxacin degradation rates of DBC-FeO and HA-FeO mediated systems could still reach 76.2%and 73.9%after 5 runs of operation.The degradation of norfloxacin by these two kinds of coprecipitates was stable and could be reused in the treatment of norfloxacin.