Theoretical Study On The Degradation Mechanism And Degradation Efficiency Of Typical Nitrogenous PPCPs In UV/H₂O₂ And UV/PDS

Pharmaceuticals and personal care products(PPCPs)have pseudo-persistent,refractory properties as an emerging contaminant.Nitrogenous compounds have high biological activity which are widely used in production and life,are frequently detected in the environment.The addition of N increases its solubility and biological toxicity in water.Nitrogenous PPCPs have non-negligible harm to ecology and human health,and have gradually attracted people’s attention and research.Advanced oxidation processes(AOPs)provide good removal of these contaminants due to their ability to produce free radicals with high oxidizing capacity.Six typical nitrogenous PPCPs were selected as study subjects,including N,N-diethyl-3-methylbenzamide(DEET)whose N located on the branched chain,1-β-D-ribofurasyl-1,2,4-triazole-3-carboxamide(ribavirin)containing N in the ring,benzotriazole(BTA),benzimidazole(BMZ),indazole(IDZ),indole(IDO)in different amounts and locations of N in the ring.Its degradation behavior and degradation efficiency in UV/H2O2 and UV/PDS processes were studied by quantum chemical calculation,and the toxicity of the products was predicted.The main conclusions are as follows:1.The degradation of DEET in UV/H2O2This part reveals the degradation behavior of DEET from two aspects of thermodynamics and kinetics,and simulates the influence of environmental factors on degradation efficiency.The results show that H-abstraction(HAA)reaction dominates the DEET initiated reaction with HO·.The branch chain of DEET is more susceptible to attack by HO·,and the benzene ring is relatively stable and difficult to undergo ringopening reaction.At 298 K,the reaction rate constant between DEET and HO’ is 2.04× 109 M-1 s-1.A certain range of higher oxidant concentration,lower pollutant concentration,and acidic condition favor the degradation of DEET.Natural organic matter(NOM)in water acts as free radical scavengers and inhibits DEET degradation.The products are mainly hydroxylated homologues of DEET,which are still harmful or toxic to aquatic organisms and have developmental toxicity.2.The degradation of BTA,BMZ,IDZ,IDO in UV/PDSIn this section,four nitrogenous heterocyclic pollutants,BTA,BMZ,IDO and IDZ were selected as research objects to reveal the difference of nitrogen dependence on the degradation behavior and degradation efficiency of pollutants.The results showed that the higher the nitrogen content in the nitrogenous heterocycle,the lower the reaction rate of pollutants with HO· and SO4·-.Nitrogenous heterocycles are more susceptible to attack by HO·.When two nitrogen atoms are present in the heterocycl,the rate constant of reaction of the ant-nitrogen-containing pollutant is greater than that of the metanitrogen.At different pH values,the degradation efficiency of different pollutants varies differently.The degradation efficiency of BTA and BMZ is proportional to pH,and IDZ is inversely proportional to pH.Within the scope of the study,the degradation efficiency of IDO was less affected by pH.pH affects degradation efficiency by changing the concentration of HO· and SO4·-and the presence of contaminants.The ring-opening products are more toxic.3.Comparative study of ribavirin degradation in UV/H2O2 and UV/PDSThis section compares the degradation differences of ribavirin in UV/H2O2 and UV/PDS.The results showed that the main initial reaction type of ribavirin with HO·and SO4·-was HAA reaction.The nitrogenous heterocycle is very stable and difficult to open the ring to degrade.Ribavirin is more likely to react with HO’ than SO4·-.Compared to UV/H2O2,UV/PDS can more effectively degrade ribavirin.UV/H2O2 has the best degradation efficiency under acidic conditions.The UV/PDS process is insensitive to pH and can be used over a wide range.The ring-opening products of ribavirin are harmful to aquatic organisms,developmentally toxic and mutagenic.