Dense non-aqueous phase liquids, such as trichloroethylene (TCE) and carbon tetrachloride (CCl4), are widespread groundwater and soil contaminants which cause long-term environmental pollution. Extensive efforts have been carried out to develop the optimal remediation strategy. Here, we will introduce a composite with natural occurring halloysite nanotubes (HNTs) serving as the supports and embedded nanoscale zero valent iron (NZVI) being the reactive agent to treat TCE and dechlorinate it to non-toxic products. This HNT-Fe composite unites the current prominent method of using NZVI with the nanoscale tubular structure of halloysite, which has shown a superior transport characteristic compared with isometric spherical particles. Besides, anionic polyelectrolytes such as carboxymethyl cellulose (CMC) or anionic surfactants such as dioctyl sodium sulfosuccinate (AOT) can be loaded into the lumen of halloysite since the internal surface of halloysite is positively charged. Dosing halloysite with surfactants or polyelectrolytes can enhance its suspension stability in groundwater and the entrapping ability of the hydrophobic compound. The hydrophobic modification of halloysite enables the composites to target organic contaminants and facilitates the dehalogenation reaction by increasing the local concentration of TCE in the vicinity of iron particles through rapid TCE adsorption.
This composite has been proven to be effective and has several conspicuous advantages: (a) the synthesize process is a simple incipient wetness impregnation method (b) the NZVI particles are well dispersed on the halloysite nanotubes, preventing them from aggregation, which eliminates the major challenge of using NZVI (c) the composite particles are of the optimal size for transport through sediments.
The presentation will focus on the detailed materials synthesizing and characterization, and the significant aspects of transport and reaction of this composite in remediation of groundwater contaminants will be discussed.
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