Performance And Mechanism Of Ru-PDAP-Activated Periodate/Hydrogen Peroxide Degradation Of Sulfapyridine In Water

Sulfapyridine（SPD）is one of the widely used sulfonamide antibiotics,but it has the disadvantage of being biotoxic and causing endocrine disruption.Periodate（IO₄^-,PI）is an advanced oxidant with good redox potential.Recent studies have confirmed that PI/H₂O₂system can generate reactive radicals,such as·OH,¹O₂,IO₃^·-,O₂^·-,and HO₂^·,etc.However,the research on PI/H₂O₂is still at the basic stage and has certain gaps,which need to be studied in depth to improve its mechanism of action.Ruthenium（Ru）is one of the platinum-based metals and has good redox catalytic properties with obvious charge transfer between ligands,which needs further study.Based on this,this study mainly explored the performance and mechanism of the PI/H₂O₂/Ru-PDAP system for the degradation of SPD.First,system comparison experiments were performed and the reaction conditions and mechanism of action of PI/H₂O₂on SPD were optimized.The oxidation capacities of different advanced oxidation processes were:PI/H₂O₂/Ru-PDAP>PI/H₂O₂>PDS/H₂O₂>PDS/H₂O₂/Ru-PDAP>PDS>PI>Ru-PDAP,proving the superior ability of PI/H₂O₂/Ru-PDAP.The preferred efficiency of degradation of SPD in the PI/H₂O₂system was:PI/H₂O₂=2 m M/2 m M,pH=3（96.64%of SPD degradation）.At an initial concentration of 50 mg/L of SPD,the degradation rate was greater than 70%.The quasi-second-order kinetic fit was more consistent with the process of degradation of SPD by PI/H₂O₂with the preferred condition k=0.0251 M^-1·min^-1（R²=0.9971）.pH 3was dominated by·OH,¹O₂and IO₄^·-,IO₃^·-,and also O₂^·-at pH 5.pH 7 and11 were dominated by the action of ¹O₂.The·OH sources included two main pathways:₄^-+₂^·-+₂→₃^-+·+₂+^-and H₂O₂+O₂^·-→·OH+OH^-+¹O₂.Secondly,the preparation of Ru-PDAP was carried out and the better conditions for the degradation of SPD by PI/H₂O₂/Ru-PDAP were explored by single factor and response surface method.The successful preparation of Ru-PDAP was demonstrated using BET,SEM,TEM,XRD,XPS,FTIR,Raman,oxygen vacancy,and zero charge point characterization.Ru in Ru-PDAP was uniformly distributed on PDAP;Ru-PDAP had an obvious hexagonal crystal structure,abundant functional groups,and oxygen vacancy structure;the pHZPC of Ru-PDAP was 4.63,and the Ru solubility was only 0.70%.In addition,the five times reuse of Ru-PDAP was effective.SPD degradation rate increased with rising Ru addition ratio,Ru-PDAP addition,and decreasing pH,and did not change with temperature.When the SPD concentration increased to 50 mg/L,the SPD degradation rate exceeded90%.Preferred was pH 3,Ru-PDAP（100:200）addition of 100 mg/L,PI:H₂O₂=2 m M:2 m M.The minimum degradation rate of SPD was increased by 2.57 times compared to PI/H₂O₂.The selected optimal reaction system k=1.8811 M^-1·min^-1（R²=1.0000）.Response surface method results for the pH range 5-9 indicated that the order of the effect of each factor on the degradation rate of SPD was:initial pH>Ru-PDAP addition>Ru:PDAP.The model predicted the degradation rate of SPD to be 94.43%at an initial pH of 9.00 and Ru-PDAP（100:200）addition of 136.7 mg/L.The validation result was 90.35%,and the model fit was valid.Third,uniform Ru loading and hole structures were still observed for the reacted Ru-PDAP.In addition to providing oxygen holes,promoting electron transfer diffusion,and adsorption of organic matter to form nano-reaction-limited domains,the interconversion of multiple valence states of Ru in Ru-PDAP could provide more electrons.pH 3 conditions the main acting substances were·OH,IO₄^·-,IO₃^·-and ¹O₂.Compared with the PI/H₂O₂system,the decrease of SPD degradation rate in the PI/H₂O₂/Ru-PDAP system at pH 5 was attributed to the disappearance of·OH,which correlated with the pHZPC of Ru-PDAP of 4.63.In addition,the significant increase in SPD degradation rate at pH 7 and pH 11 compared to PI/H₂O₂was mainly due to the effect of ¹O₂,IO₄^·-and IO₃^·-.At pH 3,IO₄^-+O₂^·-+H₂O→IO₃^-+·OH+O₂+OH^-was used as the main pathway for·OH production in the PI/H₂O₂/Ru-PDAP system.The SPD degradation pathways were mainly hydroxylation,oxidation,bond opening,and methyl substitution,and IO₄^-completely reacted to IO₃^-without iodinated compounds.Finally,the effectiveness and toxicity of PI/H₂O₂/Ru-PDAP were evaluated for practical applications.The SPD degradation rates of materials activated PI/H₂O₂were ranked as Ru-PDAP>Fe/Ce@BC>Cu/Ce@BC.The SPD degradation rates were 99.01%and 99.03%under the inlet and outlet conditions of the wastewater plant at pH 3,respectively.pH 7 was more favorable for SPD degradation under high COD or effluent conditions.When various anions or humic acids were present,the degradation of SPD by PI/H₂O₂/Ru-PDAP was not affected or even promoted,especially the addition of Na₂CO₃increased the degradation of SPD by 99.60%.PI/H₂O₂/Ru-PDAP could achieve>80%degradation of sulfadiazine,methylparaben,and tetrabromobisphenol A within 30 min,proving the universality of the PI/H₂O₂/Ru-PDAP system.The degradation of SPD was complete at pH 7,with almost no residual intermediates.The ECOSAR software predicted that the three products were harmful in terms of chronic toxicity;the acute toxicity of all degradation products was in the non-hazardous category.Algal toxicity tests demonstrated that the PI/H₂O₂/Ru-PDAP degraded SPD system could promote algal growth.