Degradation And Mechanism Of Typical Chlorinated Hydrocarbons Under Ultraviolet Irradiation

As the important raw materials and solvents,chlorinated hydrocarbons are widely used in industry.Due to their great adverse effect on human health,efficient technologies for chlorinated hydrocarbons removal are urgent.In the present study,firstly,the photocatalytic degradation of C₂HCl₃ was carried out.Then photochemical reduction technology was utilized to decompose CCl₄ and CHCl₃,which possess strong recalcitrance to oxidation.C₂HCl₃,CCl₄ and CHCl₃ were degraded well and the main results are as follows.?1?Due to the higher migration ability of h⁺and e^-,BiOCl-0.6 showed better photocatalytic performance than BiOCl-6.0 for C₂HCl₃ degradation under the irradiation of medium-pressure UV mercury lamp?UV?.The degradation rate descended with increasing pH and C₂HCl₃ concentration.Impurities such as SO₄^2-,NO₃^-and NOM exerted adverse effects on C₂HCl₃ degradation except Cl^-.The generation of·OH and O₂^·-in UV-BiOCl system was detected by ESR.Both·OH,O₂^·-and h⁺contributed to the degradation and C₂HCl₃?30 mg/L?was almost completely decomposed and dechlorinated in 120 minutes.?2?UV-BiOCl system was unable to decompose CCl₄,however,CCl₄?5 mg/L?was rapidly degraded with a removal efficiency of around 98.0%in 40 minutes when CH₃CH₂OH or HCOONa was added.The degradation of CCl₄ was inhibited in aqueous solution with elevated pH and groundwater.BothCH₃ C HOH and O₂^·-were involved in the degradation of CCl₄ in UV-BiOCl-CH₃CH₂OH system and the lag phase was caused by the quenching effect of O₂ toCH₃ C HOH.CO₂^·-was the main specie that caused CCl₄ degradation in UV-BiOCl-HCOONa system.The main product was CHCl₃ with dechlorination efficiency of about 40.0%.?3?In UV254?the low-pressure UV mercury lamp with a maximum emission at254 nm?-Na₂SO₃ system,the elevated Na₂SO₃ concentration and pH accelerated the degradation of CCl₄,while O₂ and impurities inhibited the reaction.The removal efficiency of CCl₄ was 31.7%in groundwater with other condition constant.The quenching experiment indicated that e^-_aq induced the degradation of CCl_4.CCl₄?10mg/L?was almost completely degraded and dechlorinated within 60 minutes with the generation of CHCl₃,C₂Cl₄ and C₂HCl₃ during degradation process.Additionally,the removal efficiencies of 5 mg/L CHCl₃ and CH₂Cl₂ in UV254-Na₂SO₃ system achieved 97.9%in 30 minutes.?4?The degradation rate of CHCl₃ in UV254-Na₂S system enhanced with increasing Na₂S concentration and then slowed down.The high rate was observed at elevated initial pH and the removal efficiency of CHCl₃ in groundwater was around1/3 folds that in deionized water.The degradation of CHCl₃ was mainly caused by e^-_aq.The rate constant between e^-_aq and CHCl₃ was determined to be 6.5×10⁹ L/?mol·s?by competition kinetics.CHCl₃?10 mg/L?was almost completely decomposed and dechlorinated within 60 minutes.The main intermediates were CH₂Cl₂ and cis-1,2-C₂H₂Cl₂.