Catalytic Dechlorination Of Trichloroethylene Using Bimetallic Ni-Fe Nanoparticles

Treatment of chlorinated aliphatic hydrocarbons (CAHs) withnanoiron particles represents the most recent significant innovativetechnology for environmental remediation, e.g., groundwater remediation.Rates of reductive dechlorination of CAHs have been further enhanced byinclusion of other metals such as Pd, Ni, etc. to form bimetallicnanoparticles. The Fe in the bimetallic nanoparticles acts as the reductantgenerating hydrogen from water, while the second metal acts as a catalyst.In the presence of the second catalytic metal, CAHs are preferentiallydechlorinated by hydrogenolysis or hydrogenation mechanisms involvingthe reaction of adsorbed or absorbed atomic hydrogen, which can greatlyincrease the reaction rate.In this study, borohydride aqueous phase co-reduction of ferrous saltand nickelous salt was conducted to prepare the bimetallic Ni-Fenanoparticles. The products of the catalytic dechlorination oftrichloroethylene (TCE) were identified by GC/MS and GC retentiontime qualification. The influence of reaction temperature, pH value and occurrence of common groundwater ions on the dechlorination efficiencyof trichloroethylene was investigated. The composition and morphologychange of the bimetallic Ni-Fe nanoparticles during the reaction wasdetermined by scanning electron microscopy-energy dispersivespectroscopy (SEM-EDS) and transmission electron microscopy (TEM).The results are as following:1. The removal ratio of trichloroethylene and the yield of ethanewere9.9%and zero respectively in8hours over nanoiron, while theremoval ratio of trichloroethylene and the yield of ethane were93.9%and58.7mol%respectively over bimetallic Ni-Fe nanoparticles under theconditions of C_TCE=23.8mg/L, C_Ni-Fe=3.22g/L, pH=8.5and V_g: V_l of thereactor=29:21.2. The predominant product is ethane, and ethylene, methane,n-butene, n-butane and trans-2-butene are produced during the catalyticdechlorination of trichloroethylene.3. The higher temperature or lower pH value are beneficial to thecatalytic dechlorination of trichloroethylene within the temperature rangeof10-25℃or pH range of6.5-7.5. The occurrence of commongroundwater ions is unfavorable to the reaction. The removal ratio of nearsaturated trichloroethylene (1100mg/L) in6hours was97.2%, and theyield of ethane was13.4mol%in8hours.4. The nickel content of the fresh bimetallic Ni-Fe nanoparticles was 20.4wt%, and it increased to26.4wt%and29.9wt%after8hours and24hours of reaction. The diameter of the bimetallic Ni-Fe nanoparticles was10-20nm. Small amount of hollow particles appeared after8hours and24hours of reaction.