Study On The Degradation Of 4-nitrophenol In Water By A Heterogeneous Electro-fenton Oxidation Procecc

Fenton oxidation has many advantages such as high oxidation efficiency,high reaction speed.However,it also has various shortcomings.For example,the catalyst can`t be recycled,the reaction needs low pH and it can easily produce secondary pollution.The heterogeneous electro-Fenton oxidation process can overcome the shortcomings,so it has a high value of practical application.The phenols can cause great harm to our environment,damage the ecosystems,and cause the animals and plants disease.So the research was carried out to degradade the phenols in water used by heterogeneous electro-Fenton oxidation process.This research has three parts:（i）Preparing heterogeneous catalyst,the catalytic performance and stability of the catalyst;（ii）On the basic of preparing catalyst,forming a heterogeneous electro-Fenton system,the impact of pH,catalyst dosage,the initial concentration of 4-nitrophenol and other factors on 4-nitrophenol removal rate was investigated;（iii）Get the component analysis of the samples after reaction through GCMS,study the possible degradation pathways of 4-nitrophenol.The following conclusions were achieved:（1）The ferrous ions was loaded onto activated carbon by ordinary immersion method.The activated carbon with ferrous ions was coated with agar.The catalyst still showed good catalytic performance.Under the conditions of the hydrogen peroxide concentration of 100 mg/L,pH 3.0,the agar concentration of 0.3%,25 g/L iron catalyst,when the reaction time was reached 180 min,decomposition rate of H₂O₂ was 80%.The concentration of ferrous ions in water was only 1 mg/L.（2）The quality of activated carbon was 5 g,adsorbed nitrobenzene reaching saturation,added 100 mg/L H₂O₂,the concentration of nitrobenzene was changed from 45.0 mg/L to 3.9 mg/L,and the removal rate was 91.33%;the concentration of ferrous ions in water was only 0.9 mg/L after the reaction.So it can be concluded that most Fenton oxidation was occurred on the surface of activated carbon,heterogeneous Fenton-like reaction was exist.（3）Fe³⁺ was loaded on zeolite and the catalytic performance of catalyst was studied.Under the conditions of initial H₂O₂ concentration of 100 mg/L,12 g zeolite addition,pH 3.0,when the reaction time was reached 120 min,decomposition rate of H₂O₂ was 84.6%,hence the catalyst showed good catalytic performance;when the pH was 5 or 7,decomposition rate of H₂O₂ was still high,so it can be also concluded that heterogeneous Fenton reaction could expand the range of pH.（4）The degradation of 4-nitrophenol by the heterogeneous electro-Fenton reaction,under the conditions of pH 2.2,4-nitrophenol of 100 mg/L,12 g zeolite,the removal rate of 4-nitrophenol was 96.51% by the treatment of 60 min.The degradation effect was obvious.After the catalyst was used four times,the removal rate of 4-nitrophenol almost remain 89.02%,the concentration of ferrous ions in water was only 0.83 mg/L after the reaction,most of ferrous ions still presented on zeolite,so it can be determined that the catalyst had good stability.The concentration of TOC changed from 51.75% to 16.22%,the removal rate was 68.66%,most degradation products of 4-nitrophenol in the form of inorganic carbon in water.（5）The degradation products was analysed through GC-MS.The results showed that the degradation pathways of 4-nitrophenol was like this:-NO2 of 4-nitrophenol felled off the ring and added hydroxyl,4-nitrophenol transform to hydroquinone,H+ fell off the hydroxyl transform to p-benzoquinone,p-benzoquinone was oxidized and formed small molecules and mineralization at last;when Cl-was added to the system,the system had produced many substances which had chlorine element,typical substances such as chlorinated phenols and chlorinated nitrophenol.