The effects of pH, ionic strength, and natural organics on the transport properties of carbon nanotubes in saturated porous medium

Carbon Nanotubes (CNTs) are widely utilized, and their inadvertent release into the soil and ground water systems may have detrimental environmental implications. Therefore, it is critical to comprehend the effect of several environmental conditions on the fate and transport of CNTs in porous media. In previous studies, a narrow range of pH, ionic strength, and collector grain size have only been considered while evaluating the transport and retention of functionalized multiwalled carbon nanotubes (f-MWCNTs). None have highlighted the effect of environmentally relevant concentrations of natural organic matter and particle concentrations on the mobility of f-MWCNTs in porous medium. The current study aims to fill the knowledge gap by evaluating the fate and transport of f-MWCNTs at different, environmentally relevant physicochemical conditions of pH (5, 7, and 9), ionic strengths (10, 50, and 100 mM), humic acid as representative of natural organic matter (0.1, 1, and 10 mg/L) and particle concentrations (10, 25, and 50 mg/L) through saturated porous medium (quartz sand). It was noted that a wide range of pH and humic acid imparted an overall negative charge on the particles, enhancing their mobility (C/C0 > 0.8). However, transport of the f-MWCNTs was hindered in the presence of high ionic strength and particle concentrations (C/C0 < 0.1). The transport profile was mathematically simulated using a one-dimensional advection-dispersion equation (ADE) and colloidal filtration theory (CFT). Additionally, interaction energy profiles based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory were estimated to gain a better understanding of the mechanism of f-MWCNT deposition. In light of the potential environmental consequences, the impact of real-world water systems (tap, river, lake, and ground water) on the transport behaviour of f-MWCNTs was also investigated. The study considerably advances our understanding of the various physicochemical and environmental factors that can critically impact the transport of f-MWCNT in porous media, which could prove beneficial for environmental applications and risk management.