Study On Photodegradation Of Flumequine And Sulfamethoxypyridazine In Aqueous Environment

Antibiotics are constantly injected into the environment due to their extensive use and have become a new type of pollutants in the environment.Advanced oxidation technology（AOP）is widely used in the degradation of organic pollutants because of its high efficiency,simplicity and less secondary pollution.In this study,flumequine（FLU）and sulfamethoxypyrazine（SMP）antibiotics were selected as the research objects,and their photocatalytic degradation and photooxidative degradation were studied.The research have carried out from the following three aspects:（1）Three kinds of nitrogen-doped TiO₂photocatalysts were synthesized by solid phase thermal decomposition.Using flumequine（FLU）as the target contaminant,the photocatalytic performance of these catalysts was evaluated.The obtained photocatalysts were characterized using scanning electron microscopy（SEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman spectrum and UV-Vis diffuse reflection spectra（UV-Vis-DRS）.The NH₄NO₃-doped catalyst（TiO₂/AN）sample exhibited higher photocatalytic performance than other N-doped catalysts under simulated sunlight irradiation,and 100%removal efficiency of FLU was achieved after 4 hours of illumination.The photogenerated holes（h⁺）and hydroxyl radicals（HO^·）are main reactive species involved in the photocatalytic degradation of FLU.Eight intermediates for photocatalytic degradation of FLU were detected.（2）N doped and B/N codoped TiO₂photocatalysts were synthesized by thermal decomposition method.The prepared catalysts were characterized using various techniques including XRD,BET,FT-IR,UV-vis DRS,XPS,SEM and Raman spectroscopy.BET results showed that 300B-N/TiO₂sample has higher BET surface area than undoped TiO₂and N-TiO₂samples.XPS analysis indicated that the B atoms mainly occupy the interstitial position of the TiO₂.The photocatalytic performance of prepared undoped and doped TiO₂catalysts was evaluated under simulated sunlight irradiation by employing FLU as a target compound.The photocatalytic performance of TiO₂catalyst can be obviously enhanced by B/N codoping.In addition,B/N codoped TiO₂catalysts exhibit excellent cycling stability.The photocatalytic activity remained 90.1%for300B-N/TiO₂after four repeated runs.The scavenger study shows that the main reactive species in the photocatalytic degradation process of FLU were superoxide radical(O₂^·￣)and photogenerated electrons（e^-）.In addition,sixteen degradation intermediates were identified by LC/MS/MS technique,which suggested three possible degradation pathways for FLU.（3）The degradation kinetics,influencing factors and degradation mechanism of SMP in aqueous solution were studied by UV/CO（Ⅱ）/peroxymonosulfate（PMS）homogeneous system.The results on direct photodegradation of 11 sulfonamide antibiotics under simulated sunlight indicated that the direct photolysis of SMP is the slowest among these SAs.Then the oxidation degradation of SMP in UV/Co（Ⅱ）/PMS system was systematically explored.Up to 95.2%removal of 0.071 m M SMP was observed after 20 minutes of reaction under the optimal condition with a molar ratio of 1:150:5 between SMP,PMS and Co（Ⅱ）.The effects of some coexisting anions on degradation of SMP were investigated.Radical scavenger experiments indicated that hydroxyl radicals（HO^·）are prevailing active species responsible for SMP removal in UV/Co（Ⅱ）/PMS system.Eight intermediates for SMP degradation were identified.The degradation of SMP in UV/Co（Ⅱ）/PMS system was accomplished mainly by hydroxylation of the aromatic ring,extrusion of SO₂,oxidation of NH₂group and N-S bond cleavage.