Reductive Dechlorination Of Trichloroethylene By Spinel-Type NiFe₂O₄ With Oxygen Vacancy Defects And Bimetallic Copper-Iron Supported On Copper-Iron Complex Oxides

Spinel-type complex oxides have been demonstrated to be able to degrade chlorinated organic compounds at temperature of 250℃, which has also been confirmed by our group. Since in most cases groundwater remediation at ambient temperature is crucial, in this research, spinel-type NiFe2O4 and copper-iron complex oxides were partly reduced to produce spinel-type NiFe2O4 with oxygen vacancy defects and bimetallic copper-iron supported on copper-iron complex oxides in order to give them reductive dechlorination activity at room temperature.Spinel-type NiFe2O4 and copper-iron complex oxides prepared by sol-gel method were reduced by sodium borohydride in aqueous solution to produce spinel-type NiFe2O4 with oxygen vacancy defects and bimetallic copper-iron supported on copper-iron complex oxides. The morphological variation was evidenced by XRD and XPS. The influence of amount of sodium borohydride and calcination temperature of the complex oxides on degradation and reductive dechlorination of trichloroethylene, a common groundwater pollutant, were evaluated. The variation of morphological and chemical composition of the two materials mentioned above caused by reaction with aqueous trichloroethylene was determined. And thus the mechanism of reductive dechlorination was established.Trichloroethylene is converted predominantly into ethane upon spinel-type NiFe2O4 with oxygen vacancy defects. And ethane and ethylene are mainly generated upon bimetallic copper-iron supported on copper-iron complex oxides.The degradation of trichloroethylene increases with the increase of the amount of sodium borohydride, while corresponding continuous increase of ethane production does not occur for spinel-type NiFe2O4 with oxygen vacancy defects. It indicates that in this set up the oxygen vacancy defects cannot be enhanced indefinitely. Lower calcinations temperature is beneficial to the degradation of trichloroethylene over spinel-type NiFe2O4 with oxygen vacancy defects. In comparison, ethane production dramatically decreases for the sample calcinated at 800℃.In aqueous solution, trichloroethylene molecules accept electrons at the oxygen vacancy defects. Meanwhile, hydroxyl anions adsorbed on the defects and protons adsorbed on the spinel-type oxygen anions act as hydrogen donors. As a result, hydrogenolysis of trichloroethylene takes place.Maximum trichloroethylene degradation and ethane production are achieved for bimetallic copper-iron supported on copper-iron complex oxides calcinated at 600℃. Bimetallic copper-iron plays a role in reductive dechlorination of trichloroethylene. And extraordinarily positive effect of the host hematite on degradation and reductive dechlorination of trichloroethylene should be noted.Spinel-type NiFe2O4 with oxygen vacancy defects and bimetallic copper-iron supported on copper-iron complex oxides are believed to be prospective materials for degradation of chlorinated organic contaminants present in environmental water.