Removal of 2,4-dichlorophenol by stabilized nano-scale zero valent iron

Nano-scale zero valent iron (nZVI) in-situ remediation technology has been widely studied in the past decades (Shih et al., 2011, Arvaniti et al., 2015). A lot of contaminants can be removed by nZVI, including nitrate, heavy metals, halogenated organics (Yu et al., 2014). However, nZVI has some disadvantages: first, nZVI nanoparticles easily trend to aggregate with each other due to the magnetic force and van der waals force, forming micro-scale or even larger particles; second, the nZVI surface will be covered by the iron (hydr)oxides generated during the reaction, which will overlap the active sites and passivate the nZVI; third, nZVI nanoparticles are difficult to recycle due to the extremely size, and secondary pollution may be produced. These defects will restrict the nZVI application for the remediation of contaminated sites. Some special materials have been used to stabilize the nZVI nanoparticles and inhibit the aggregation and passivation, such as activated carbon, organobentonite, resin, and carboxymethylcellulose (He and Zhao, 2007, Chang et al., 2011). Magnetic composites, polyacrylamide modification and other preparation methods have applied to enhance the separation of nZVI from aqueous phase (Wang et al., 2015). In our study, an environmentally friendly and novel material, multi-walled carbon nanotubes (MWCNTs) was used to support the palladium-doped nZVI (Pd/Fe) nanoparticles and adsorb 2,4-dichlorophenol (2,4-DCP). In addition, nano-scale Fe₃O₄ was introduced to stabilize Pd/Fe nanoparticles and improve the retrievability via a magnetic separation. (author)