Transport Of Surfactant Dispersed Multi-Walled Carbon Nanotubes In Porous Media

Multi-Walled Carbon Nanotubes(MWCNTs) are a kind of nanomaterials with wide applications. They may be reaeased into the environment in the processs of production, transportation and utilizeation, water and soil environment are the ultimate sinks of MWCNTs in environment. MWCNTs are difficult to be degredated, and are deterious to human cells and microbes in some conditiions. MWCNTs have strong adsorption for lots of organic pollutants and some hevy metal ions, and may change the environmental behaviors of these pollutants by adsorption.The suspension and transport in water and porous media of MWCNTs are key factors affecting the environmental risks of MWCNTs.In this research, three types of surfactants, i.e., dodecylbenzenesulfonic acid, sodium salt (SDBS), cetyltrimethylammonium bromide (CTAB), and octyl-phenol-ethoxylate (TX100) were used to prepare stable MWCNT suspensions. Two clay minerals (kaolinite and montmorillonite) were used for adsorption of the three types of surfactants to determine their effect on surfactant facilitated MWCNT suspensions. These MWCNT suspensions were also transport to several kinds of porous media, i.e., pure quartz sand, quartz sand mixed with clay minerals, quartz sand coated by humic acid, natural sand and natural silt clay. The transport ability and mechanism were analysed, and a series of important conclusions were drawn according to these analysis:1. Stable MWCNT suspensions can be made in low SDBS, CATAB or TX100 concentrations (40ppm);2. Clay minerals can affect the surfactant facilitated MWCNT suspendsions by several mechanics:(1) release ions into the suspensions; (2) change the pH of suspendsions; (3) adsorb surfactants from suspensions; (4) adsorb MWCNTs directly and form a clay mineral-surfactant-MWCNTs mixture, this kind of phenomenon only occurred when kaolinite was added into CTAB facilitated MWCNT suspension.3. CTAB facilitated MWCNT suspension is difficult to transport in soil or aquifer.4. Dispersed MWCNTs are difficult to transport through clay layers.5. Clay minerals can inhibit the transport of MWCNTs in sandy aquifer drastically.6. The presence of di-valent ions could decrease the migration ability of MWCNTs evidently.7. The transport of MWCNTs could increase when humic acid was deposited on the surface of porous media.8. In the presence of 0.6 mM CaCl2, SDBS or TX100 facilitated MWCNT suspensions can transport 3 m in quartz sand, but this distance will be decreased by the add in of clay minerals. The transport distance of SDBS or TX100 facilitated MWCNT suspensions can transport to farer distance in humic acid coated quartz sand compare to that in pure quartz sand. The transport distances of MWCNTs in natural sand are shorter than that in pure quartz sand.