Nanoscale Titanium Dioxide (nTiO₂) Transport in Natural Sediments: Importance of Soil Organic Matter and Fe/Al Oxyhydroxides

Abstract

Many engineered nanoparticle (ENP) transport experiments use quartz sand as the transport media; however, sediments are complex in nature, with heterogeneous compositions that may influence transport. Nanoscale titanium dioxide (nTiO) transport in water-saturated columns of quartz sand and variations of a natural sediment was studied, with the objective of understanding the influence of soil organic matter (SOM) and Fe/Al-oxyhydroxides and identifying the underlying mechanisms. Results indicated nTiO transport was strongly influenced by pH and sediment composition. When influent pH was 5, nTiO transport was low because positively charged nTiO was attracted to negatively charged minerals and SOM. nTiO transport was slightly enhanced in sediments with sufficient SOM concentrations due to leached dissolved organic matter (DOM), which adsorbed onto the nTiO surface, reversing the zeta potential to negative. When influent pH was 9, nTiO transport was generally high because negatively charged medium repelled negatively charged nTiO. However, in sediments with SOM or amorphous Fe/Al oxyhydroxides depleted, transport was low due to pH buffering by the sediments, causing attraction between nTiO and crystalline Fe oxyhydroxides. This was counteracted by DOM adsorbing to nTiO, stabilizing it in suspension. Our research demonstrates the importance of SOM and Fe/Al oxyhydroxides in governing ENP transport in natural sediments.

Effects of Freeze-Thaw Cycles on Phosphorus from Sediments in the Middle Reaches of the Yarlung Zangbo River

“…The increase in Al, Fe and Si atoms in the sediment particles means that these elements are released from the organic matter under the freeze-thaw action, and the increase in oxygen consumption during the release process leads to a decrease in the O atom content. This result confirms the hypothesis presented by Leanne et al [33] that freeze-thaw cycles change the organic matter morphology of soil, and among the present elements, Fe and Al mineral elements react most intensely during the freeze-thaw process; these reactions may consume oxygen and release carbon dioxide.…”

Combined Effects of Fe/Al Oxyhydroxide Coating and pH on Polystyrene Nanoplastic Transport in Saturated Sand Media

“…2), consistent with previous findings (Lyu et al, 2020;Wang et al, 2012). This is likely due to the great disparity in pH PZC (point of zero charge), which followed the order of Al oxyhydroxide (9.9; Figure S3) > Fe oxyhydroxide (7.2; Figure S3) > quartz sand (2-3) (Fisher-Power & Cheng, 2018). Furthermore, an increase in pH led to more negatively charged surface for both Fe/Al oxyhydroxide-coated and uncoated sand.…”

Cotransport and Deposition of Iron Oxides with Different-Sized Plastic Particles in Saturated Quartz Sand

“…Iron oxides (i.e., goethite and hematite) with concentrations from a few μg/L to several hundred mg/L are ubiquitously present in natural environment such as in soil and sediment . Since they can interact with different substances, iron oxides have been demonstrated to play important roles on the fate, transport, and cycling of nutrients or contaminants in soil and subsurface environments. − For instance, many previous studies found that iron oxides could serve as mobile carrier for a wide of range of colloids such as dissolved organic matter, nanoscale titanium dioxide, bacteria, , and viruses, heavy metals such as lead, arsenic, and copper, , radioactive substances such as strontium and plutonium, and nutrients such as phosphorus , and sulfur . Hence, the fate and transport of iron oxides in porous media has drawn great attentions in past decades.…”