FeS₂-mediated Plasma And Photo-fenton Catalyzed Removal Of Typical Antibiotics From Water And Its Mechanism

Antibiotics are discharged into water bodies during production and after use,posing a serious threat to ecological safety and human health.Therefore,effective removal of antibiotics from water has become a key issue in the field of environmental protection.In comparison to common methods like biodegradation and physical adsorption,advanced oxidation technologies,such as glow discharge plasma（GDP）and Fenton technology,have shown promising applications for the removal of organic pollutants from water.However,GDP has low energy utilization efficiency,and homogeneous Fenton systems have limitations such as a narrow operating p H range,generation of large amounts of iron sludge,and difficulties in recovery.FeS₂,a narrow bandgap（0.95 e V）semiconductor,possesses advantages such as broad light response range and ease of preparation.It can also act as a Fenton catalyst,overcoming the limitations of GDP and homogeneous Fenton technologies.Additionally,the morphology of a material can influent its properties,and different morphologies of FeS₂ may exhibit varying catalytic activities.Therefore,this study investigated the degradation of two commonly used and difficult-to-degrade antibiotics,tylosin（TYL）and sulfadiazine（SDZ）,using FeS₂-mediated GDP and photocatalytic Fenton technologies.The degradation performance of GDP and photocatalytic Fenton technologies for antibiotics was examined,and the catalytic mechanisms of the two technologies were discussed,along with the proposed degradation processes for TYL and SDZ.Furthermore,three different morphologies of FeS₂ were prepared to degrade SDZ,and the catalytic performance and crystal properties of the three FeS₂ morphologies were compared to analyze the inherent relationship between FeS₂ morphology and catalytic performance.The main research findings are as follows:（1）FeS₂ improved the energy utilization efficiency of GDP.GDP/FeS₂ exhibited superior degradation and mineralization performance compared to the standalone GDP system,with a 17.5%increase in TYL removal rate.FeS₂ facilitated the generation of both free radicals（·OH,·O₂^-）and non-radicals（h⁺,e^-）through high-energy electrons,photocatalysis,heterogeneous Fenton,and O₃ catalysis in the GDP system.The sulfur ions on the surface of FeS₂ accelerated the conversion of Fe（III）to Fe（II）,promoting free radical generation.Additionally,the acidic solution generated from FeS₂ oxidation self-regulated the heterogeneous Fenton reaction,enhancing the oxidative potential of·OH and the adsorption of positively charged TYL.The active species in the system attacked TYL,causing its chain scission to form cyclic intermediates,which were further oxidized into small organic acids and ultimately mineralized into H₂O and CO₂.（2）The removal efficiency of SDZ by FeS₂ photocatalytic Fenton technology varied under different initial p H conditions.Moreover,FeS₂ exhibited good reproducibility and total organic carbon removal efficiency during the photocatalytic Fenton process.FeS₂photocatalytic Fenton system involved homogeneous Fenton,heterogeneous Fenton,and photocatalytic reactions,utilizing the generated free radicals（·OH,·O₂^-,and h⁺）and a small amount of·SO₄^-to degrade SDZ.In this process,FeS₂ and light promoted the conversion of Fe（III）to Fe（II）,facilitating free radical generation.Furthermore,the S vacancies on the surface of FeS₂ improved the charge separation and surface reactions,further enhancing the catalytic activity of FeS₂.Two possible degradation pathways for SDZ were proposed based on the observed degradation intermediates.（3）Three different morphologies of FeS₂,namely,cubic,octahedral,and spherical,were synthesized using hydrothermal and solvothermal methods.The three FeS₂morphologies had similar particle sizes but differed in surface roughness.The catalytic performance for SDZ degradation varied significantly among the three FeS₂ morphologies,with removal rates of 24.5%,93.4%,and 38.1%for cubic,octahedral,and spherical FeS₂,respectively.The octahedral FeS₂ exhibited the best catalytic performance.All three FeS₂samples exhibited type IV isotherms,with the octahedral FeS₂ sample having the highest specific surface area and pore volume,consuming more hydrogen peroxide and generating more hydroxyl radicals.The octahedral FeS₂ had a smaller bandgap,shorter average carrier lifetime,higher exposure of active crystal facets,and a higher concentration of sulfur vacancies.The differences in catalytic performance among the three FeS₂ morphologies were attributed to variations in crystal facet exposure and surface defects,which were influenced by different growth conditions,resulting in changes in electronic structure and surface state.The differences in crystal facets affected the physicochemical properties and photoelectric performance of the catalyst,while surface defects further influenced the catalytic activity.The synergistic effect of exposed crystal facets and surface sulfur vacancies promoted the generation of catalytic active species in FeS₂,accelerating the degradation of SDZ.The findings of this study are expected to provide a solution to the drawbacks of plasma and Fenton technologies in the treatment of antibiotics in water.These findings will also serve as a reference for the practical application of FeS₂-assisted advanced oxidation technologies for the degradation of antibiotics in water.The study further analyzed the inherent relationship between the microstructure of FeS₂ and its catalytic performance,thereby enriching the theoretical foundation of FeS₂ catalysis.