Removal Of Typical Chlorinated Hydrocarbons In Water By Heterogeneous Catalyst Activated Peroxymonosulfate

Chlorinated hydrocarbons were extremely biotoxic and difficult to be degraded naturally.Therefore,the remediation of chlorinated hydrocarbon pollution has always been the key concerns in the field of environmental engineering.In this study,three kinds of heterogeneous cobalt catalysts were prepared:nano CoFe₂O₄,carbon nanotube supported CoFe₂O₄（CNTs-CoFe₂O₄）and nitrogen sulfur co-doped graphene supported CoFe₂O₄（ns/GO-CoFe₂O₄）.The degradation of trichloroethylene by three kinds of catalysts activated peroxymonosulfate（PMS）was compared;for carbon tetrachloride was difficult to be oxidized,a reduction system was built based on activated PMS with HCOONa as electron donor added.The main conclusions were as follows:（1）The results of catalyst characterization showed that the obvious agglomerations occurred among CoFe₂O₄ nanoparticles,the particle size was between150-200 nm,and the specific surface area was 12.83 m²/g.CNTs-CoFe₂O₄ and ns/GO-CoFe₂O₄ could inhibit the agglomeration of particles,reduce the particle size（50-150 nm）and increase the specific surface area（45.68 and 60.12 m²/g）;All of e three materials showed typical spinel characteristics,and the proportions of all elements in the material were similar to the preset value.（2）The highest removal efficiency of trichloroethylene was achieved at initial pH of 11 in activated PMS system while strong acid（pH≤3）and strong alkali（pH≥13）would inhibit the reaction;the degradation of trichloroethylene was promoted by the increase of temperature,catalyst dosage and PMS concentration to a certain extent,but the exceed catalyst dosage and PMS concentration would have a negative impact on the whole reaction system;The degradation process of trichloroethylene could be fitted by pseudo first order kinetics.（3）With the increase of catalyst reuse times,the degradation efficiency of trichloroethylene in activated PMS system decreased;Under neutral conditions,the dissolution of cobalt ions in CoFe₂O₄ was about 0.32 mg/L,the lower dissolutions of cobalt ions appeared in CNTs-CoFe₂O₄ and ns/GO-CoFe₂O₄（0.21 and 0.023 mg/L）;The acidic conditions（pH=3）slightly increased the dissolution of metals.（4）·OH and SO₄·^-were the main active substances in the degradation of trichloroethylene by activated PMS system,of which·OH played a more vital role.During the dechlorination process of trichloroethylene,few intermediate products were produced,and the final products were CO₂,H₂O and Cl^-.（5）The removal efficiency of carbon tetrachloride（1 mg/L）was 87.7%within360 min by ns/GO-CoFe₂O₄ activated PMS in the presence of HCOONa,and the degradation efficiency of carbon tetrachloride increased with the temperature,catalyst dosage and PMS concentration;the increase of HCOONa concentration could promote carbon tetrachloride degradation in a certain range,However excessive HCOONa would inhibit the degradation of carbon tetrachloride;the optimal pH range for carbon tetrachloride degradation is 5-9,and CO₂·^-was the main active substance to degrade carbon tetrachloride in this system.