Different Advanced Oxidation Techniques For Degradation Of Ephedrine In Water

Ephedrine is not only the main component of cold medicine,but also a precursor of methamphetamine.Due to drug abuse and drug abuse,ephedrine as a psychoactive substance has been frequently detected in water environments around the world,and it may have potential environmental risks.Therefore,more attention should be paid to ephedrine in the water environment.The degradation effect of ephedrine in the traditional sewage treatment process is not good,so this article uses two different oxidation techniques of ultraviolet persulfate and sodium hypochlorite to treat ephedrine in water.The process of oxidative degradation of ephedrine was explored,mainly divided into three aspects:kinetics,influencing factors and degradation pathways.First,UV-254 nm activated persulfate?PS?advanced oxidation technology was used to remove ephedrine in water.It was found that UV irradiation alone or persulfate alone had little effect on the removal of ephedrine?the degradation rate was less than 3%in 10 minutes?,and the combination of ultraviolet persulfate had a strong synergistic effect,and the degradation rate exceeded 97%in 10 minutes.When the initial concentration of PS is 500?mol·L^-1,the higher the initial concentration of ephedrine,the slower the degradation reaction rate,and the oxidative degradation reaction conforms to the second-order kinetic equation.Then explored the influence of different factors including pH,water matrix?HCO₃^-,NO₃^-,Cl^-,HA?on the degradation effect.As a result,it was found that acidic and alkaline conditions significantly inhibited the degradation reaction,and under the condition of pH 7,the degradation reaction rate was the fastest.HCO₃^-,NO₃^-,Cl^-and HA all have different degrees of inhibition on the degradation of ephedrine.At the same concentration,the degree of inhibition is HA>Cl^->NO₃^->HCO₃^-.Finally,UPLC-MS/MS was used to identify five kinds of ephedrine degradation intermediates,and the degradation mechanism and conversion pathway were proposed.The degradation mechanism may include electrophilic substitution and elimination reactions.Sodium hypochlorite has low use cost and simple operation.Therefore,this article further studied the degradation effect of sodium hypochlorite on ephedrine,and found that the degradation rate of ephedrine under different conditions of UV/Cl,sunlight/Cl and darkness/Cl in 40 min were It was 96.0%,94.7%and 94.3%,indicating that different light sources had little effect on the reaction rate of sodium hypochlorite oxidative degradation of ephedrine,so subsequent experiments used sodium hypochlorite alone as an oxidant to remove ephedrine in water.When the initial concentration of sodium hypochlorite is 1000?mol·L^-1,the higher the initial concentration of ephedrine,the slower the degradation reaction rate,and the oxidative degradation reaction conforms to the second order kinetic equation,k=7.42×10²(mol·L^-1)^-1·min^-1.Then explore the influence of different factors such as pH,water matrix(Fe³⁺,HCO₃^-,NO₃^-,HA,etc.)on the degradation effect.It was found that acidic conditions inhibited the degradation reaction and alkaline conditions promoted the degradation reaction.When the pH was 11,the degradation reaction rate reached the fastest.Cu²⁺,Fe³⁺,HCO₃^-ions have significant inhibitory effects on the degradation reaction;Ca²⁺,Mg²⁺,NO₃^-,SO₄^2-,HA ions have different degrees of inhibitory effects;Br^-and I^-(the initial concentration is greater than 0.1 mmol·L^-1)Promote the degradation reaction.Finally,UPLC-MS/MS identified 10 kinds of ephedrine degradation intermediates,the degradation mechanism may include electrophilic substitution,dehydration and elimination reactions.The comparison shows that the two oxidation methods of ultraviolet persulfate system and sodium hypochlorite have good degradation effect on ephedrine.Among them,the ultraviolet persulfate system has a better effect on the removal of ephedrine.The degradation rate exceeds10%in 10 minutes,but its cost is higher.It is more suitable for water treatment plants with UV disinfection system installed;The degradation rate in min exceeds 94%,its cost is low,the operation is simple and convenient,and it is more suitable for industrial production.