Degradation of Pentachlorophenol by CTAB-Modified Ni/Fe Bimetallic Nanoparticles in the Soil Solution

Pentachlorophenol (PCP) has been widely used as a wood preservative, fungicide, insecticide, and general biocide. This study evaluated the feasibility of applying Ni/Fe nanoparticles (NPs) modified with a surfactant, cetyltrimethylammonium bromide (CTAB), to remediate a PCP-contaminated soil solution at a contaminated site in southern Taiwan. The removal mechanisms of PCP with CTAB-modified Ni/Fe NPs (Ni/Fe-CTAB) were elucidated by examining PCP removal kinetics, adsorption ratios, dechlorination efficiencies, and identification of intermediates. Using Ni/Fe-CTAB with 2 wt % Ni at one critical micelle concentration (CMC) of CTAB, nearly 100% removal of PCP was observed within 5 min and dechlorination was completed after 24 h. The enhanced PCP reduction by Ni/Fe-CTAB was mainly caused by the rapid adsorption of PCP by CTAB and subsequent dechlorination at the Ni/Fe surface. The increase in PCP adsorption was attributed to the electrostatic attraction between electronegative phenolate groups of PCP and positively charged Ni/Fe-CTAB resulting from the cationic CTAB coating. Dechlorination of PCP led to the production of phenol and lesser chlorinated phenols, which were less toxic and more biodegradable than PCP. This study demonstrated the potential of using bimetallic nanoparticles in tandem with surfactants for remediating highly halogenated contaminants in soil solution.