Degradation Of Nitrogen-Containing Heterocycle Compounds By Sulfate Radical Based Advanced Oxidation

Sulfate radicals(SO4·-)have received notable attention as an alternative of ·OH in wastewater treatment,due to a comparable oxidation potential as-OH;a longer half-life time in aqueous solution(30-40 ?s);and a wider operational pH range(2-8).Nitrogen-containing heterocyclic compounds are widely used in pesticides and pharmaceuticals because of their good biological activity,however,its pollution can not be ignored in environment.Technologies of nitrogen-containing heterocyclic compounds removal by SR-AOPs need to be explored,and the degradation mechanisms of various nitrogen-containing heterocyclic compounds should be investigated to reference to the degradation of other nitrogen-containing heterocyclic compounds.The degradation of three nitrogen-containing heterocyclic compounds in different sulfate radical based advanced oxidation systems was studied.Degradation of sulfamethazine(SMZ),a pyrimidine heterocyclic compound containing nitrogen,by heat-activated persulfate(PS)oxidation was investigated in aqueous solution.Experimental results demonstrated that SMZ degradation followed pseudo-first-order reaction kinetics,andthe pseudo-first-order rate constant(kobs)was increased markedly with increasing concentration of PS and temperature.Radical scavenging tests revealed that the predominant oxidizing species was SO4·-.Aniline moiety in SMZ molecule was confirmed to be the reactive site for SO4·-attack by comparison with substructural analogs.Non-target natural water constituents affected SMZ removal significantly,e.g.,Cl-and HCO3-improved the degradation while fulvic acid reduced it.6 products derived from sulfonamide S-N bond cleavage,aniline moiety oxidation and Smiles-type rearrangement were identified,and transformation pathways of SMZ oxidation were proposed.Results reveal that heat-activated PS oxidation could be an efficient approach for remediation of water contaminated by SMZ and related nitrogen-containing heterocyclic compounds.As a nitrogen-containing heterocyclic compound containing the sulfonamide group like SMZ,sulfachloropyridazine(SCP)was selected as the target compound to compare the catalytic activity of schwertmannite and jarosite in heterogeneously activated PS oxidation processes,finding that the schwertmannite/PS system was more effective for SCP degradation than jarosite/PS system at the same pH or PMS concentrations conditions.Both schwertmannite and jarosite exhibit higher activity at pH 3.High PS concentration was beneficial for SCP degradation in the two systems.The concentration of iron leaching of schwertmannite was increased with the reaction time increase,however,it maintained a low level in jarosite/PS system even after reaction for 540 min.Six intermediate products of SCP were detected in two systems;S-N bond cleavage,hydroxylation and Smiles-type rearrangement were the main pathways of SCP degradation.Atrazine(ATZ)is a triazine heterocyclic compound containing nitrogen which is different from the two mentioned above.Degradation of ATZ in heterogeneously Co3O4 activated PMS oxidation process was studied.It was found that high PMS concentrations and near neutral pH(pH 6)were beneficial for optimal ATZ degradation.Minimal cobalt leaching was found to occur during reaction,shown by a maximum dissolved Co concentration(0.06 mg/L)found at pH 3 and decreasing with increasing pH.During the reaction,Co3O4 showed high potential for reusability.Structural properties of the pristine and used Co3O4 catalysts were characterized,with no changes observed post-reaction.A total of 7 intermediate products of ATZ were detected,and quantifications of intermediate products were operated.Transformation pathways were proposed,including dealkylation,dechlorination-hydroxylation and alkylic-oxidation are for catalytic decomposition of ATZ in the Co3O4/PMS system.The results indicated that Co3O4/PMS system was an efficient approach for organic pollutants removal,and the tiny amount of cobalt dissolution makes it possible for practical applications.In summary,the nitrogen-containing heterocyclic compounds can be effectively degradated in the investigated SR-AOPs through differences degradation pathways.