Degradation of γ-Hexachlorocyclohexane Using Carboxymethylcellulose-Stabilized Fe/Ni Nanoparticles

Carboxymethylcellulose (CMC)-stabilized and Ni-doped nanoscale zero valent iron (nZVI) particles (CMC-Fe/Ni) were synthesized to remove γ-hexachlorocyclohexane (γ-HCH) in aqueous solution. Fourier transform infrared spectroscopy results suggested that the CMC molecules were adsorbed onto iron primarily through carboxylate groups by monodentate complexation, and hydroxyl groups were also involved in the interactions between CMC and iron. The adsorbed CMC made the zeta potential of Fe/Ni nanoparticles more negative. At reaction pH of 8.3, the absolute value of zeta potential of the CMC-Fe/Ni was almost twice that of the bare one. The stability of colloidal nanoparticles was greatly enhanced as initial CMC concentration increased from 0 to 0.1 % (w/w) and did not increase further with higher CMC doses. Batch studies showed that 99.9 % of 10 mg/L γ-HCH was removed after 4 h at a mono nZVI loading level of 0.1 g/L, while the γ-HCH could be completely removed in 5 min using CMC-Fe/Ni, which exhibited a 13 times greater kobs as compared to that using bare Fe/Ni. Within 20 h, 60 mg/L γ-HCH was totally removed through 6 cycles of consecutive treatment using CMC-Fe/Ni. GC-MS analysis showed that 3,4,5,6-tetrachlorocyclohexene was the main intermediate and chlorobenzene was the final product when using mono nZVI. When treating by Fe/Ni nanoparticles, 1,2,3,4,5-pentachlorocyclohexene, 3,4,5,6-tetrachlorocyclohexene, and 1,4-dichlorobenzene were formed as intermediates and benzene and chlorobenzene as the final products. Possible degradation pathways were proposed based on the identified intermediates, and dehydrochlorination, dichloroelimination, and hydrogenolysis were involved in dechlorination.