Influencing Factors Of Photodegradation And Phototransformation Of Phenol In Salty Water

Photodegradation and phototransformation processes are important environmental photochemical pathways for pollutants in water.Phenol is one of the important industrial raw materials and it is also a typical representative of organic pollutants in water.The phenol photochemical reactions experiences are one of the main environmental processes in water body after phenol is discharged into the natural water environment with the factory wastewater.High light intensity in arid region environment and high salinity in rivers of arid region highlight the importance of photodegradation and phototransformation reactions of pollutants.However,the influence of factors in water environment on the photodegradation and phototransformation of phenol is not yet clear,especially for the effect on phototransformation process.In this dissertation,the processes of photodegradation and phototransformation of phenol in salty water were studied under simulated light.The effect of different basic factors(pH,chloride,ferric ion,carboxylic acid,etc.)on phenol degradation rate and the formation of chlorophenols,four products of phenol(catechol,hydroquinone,resorcinol and p-benzoquinone)and the amounts of OH were investigated.The following conclusions were drawn:(1)The degradation rate of phenol was the highest at pH=1.0.Different Cl-concentrations had no significant effect on the degradation rate of phenol.Phenol degradation rate increased with increasing Fe3+concentration and then decreased.Adding carboxylic acids would reduce phenol photodegradation rate(2)The amounts of four phenol degradation products showed the order of p-benzoquinone>catechol>hydroquinone>resorcinol and catechol>hydroquinone>p-benzoquinone>resorcinol after carboxylic acid was added.Catechol,hydroquinone and resorcinol reached the largest amount at pH=3.0,while benzoquinone at pH=1.0.The four degradation products increase firstly and then decreased with the increased of Cl-and Fe3+concentrations.The maximum amounts of the four degradation products were observed when Cl-concentration was 0.1 mol/L and Fe3+ concentration was 1×10-3 mol/L.After the system was added to a low concentration of carboxylic acid,the generation of catechol and hydroquinone were inhibited.And when high concentration carboxylic acid was added,the generation of catechol and hydroquinone increased.The addition of carboxylic acid(high concentration or low concentration)reduced the production of resorcinol and p-benzoquinone(3)Chlorophenols generation obeyed the similar rule in distilled water and simulated water media.It was shown that phenol phototransformation revealed the same mechanism in both medium.The amounts of chlorophenols in different mediums showed the order of natural water>simulated water>distilled water The higher initial phenol concentration,the higher chlorophenols production.The acid condition was beneficial to chlorophenols formation,and the highest pH was 3.0.As the concentration of Fe3+and Cl-increased,the amounts of chlorophenols produced increased firstly and then decreased.Chlorophenols concentrations reduced by adding oxalic acid,citric acid and tartaric acid to the system.The addition of tartaric acid had few effect on the generation of chlorophenols(4)The investigation of the mechanism was shown that:under different influencing factors,there were similarities and differences between OH generation rule and the degradation rate of phenol,the formation of four-degradation products from phenol,indicating that OH was one of the active substances affecting the photodegradation process of phenol.Under different influencing factors,there were similarities between·OH generation rule and the formation of chlorophenols.It was shown that·OH influenced the production of chlorophenols indirectly by affecting the production of Cl·.The amounts of OH were all inhibited after NO3-,HCO3-,NO3-+ carboxylic acid and HCO3-+carboxylic acid were added to Fe3+/Cl-system,respectively.The inhibitory effect of NO3-was stronger than that of HCO3-Through this research,we could further understand the changes in the amounts of each products and the rule for the generation of OH during the photodegradation and phototransformation of phenol.In Fe3+/Cl-system,OH was the main active material in the photodegradation reaction of phenol.The amounts of catechol and hydroquinone increased after carboxylic acid was added,while the amounts of OH decreased,indicating that the presence of other active substances in the system affected the phototransformation reaction of phenol along with the adding of carboxylic acid.In Fe3+/Cl-system,there was an indirect relation between OH and chlorophenols during the phototransformation reaction of phenol.OH formation promoted the generate of Cl·and induced the amounts of chlorophenols increased.When Fe3+/Cl-system coexisting with NO3-or HCO3-,there might be other pathways to influence the amounts of chlorophenols.The results of this study would help to further understand the photodegradation and phototransformation behavior of phenolic organics in water and provide reference for the evaluation of ecological risk of phenol in natural water.