Effect of surfactants and implementation strategies for the pentachlorophenol degradation with Ni/Fe bimetallic nanoparticles in soil

Pentachlorophenol (PCP) removal was found to be dependent on many factors including soil surface charge, Ni/ Fe nanoparticle (NP) dosage, pH, and types of surfactants. Desorption efficiencies of PCP from the contaminated soil treated with DI water, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Triton X-100 (TX-100) were 88.2%, 1.35%, 103%, and 80.9%, respectively. PCP desorption was significantly enhanced by anionic SDS but reduced by cationic CTAB. PCP desorption efficiency was governed by van der Waals attraction and electrostatic interaction among surfactants, soil particles, and Ni/Fe nanoparticles. For SDSmodified Ni/Fe NPs, SDS bilayers form on the positively charged Ni/Fe surface to sterically and electrostatically stabilize Ni/Fe and enhance the PCP removal efficiency of Ni/Fe in soil. However, an opposite effect was observed in the CTAB-modified Ni/Fe. In the soil slurry, CTAB was readily detached from Ni/Fe and subsequently form a CTAB bilayer on the soil surface to adsorb PCP at the soil surface that significantly reduce PCP degradation by blocking PCP from accessing the Ni/Fe reactive sites although the Ni/Fe-CTAB exhibited extremely high reactivity for PCP in soil solutions. Based on the results, remediation strategies using a combination of surfactants and Ni/Fe bimetallic nanoparticles for ex-situ soil remediation were proposed.