Citation:

Virkutyte, J., S. R. Al-Abed, H. Choi, AND C. Bennett-Stamper. Distinct Structural Behavior and Transport of TiO₂ Nano- and Nanostructured Particles in Sand. M. Adler, F. Grieser, J.B. Li, and D. Prieve (ed.), Colloids and Surfaces A: Physicochemical and Engineering Aspects. Elsevier B.V., Amsterdam, Netherlands, 443:188-194, (2014).

Impact/Purpose:

The main objective of this study is to provide scientific evidence that commercially available nano-TiO₂ particles have different nanostructures (NPs and NSPs) and these differences highly affect their behavior and transport in porous medium. Furthermore, we are proposing that the term "NPs" to be more strictly used to describe certain nanoparticles and to differentiate those from "NSPs", therefore avoiding any confusion in discussing their mobility and potential impacts in the environment. Furthermore, we carefully selected four commercially available well-known TiO₂ particles based on their unique physical structure and one home-synthesized TiO₂ particles, and tested the transport of TiO₂ NPs and NSPs through a porous medium under various reaction environments changing solution pH, ionic strength in the presence and absence of encapsulating agent CMC.

Description:

Environmental impact of TiO₂ particles along with other widely-used nanomaterials as a new class of contaminants has recently emerged. Due to the lack of detailed information and proper understanding of their properties as a result of synthesis (nanoparticles vs nanostructured particles), there is a disagreement in interpreting their behavior and transport in the environment. In this study, we discuss the characteristic retention and breakthrough of commercially available TiO₂ particles with unique nanoscale structure, i.e. well-defined nanoparticles (NPs) and nanostructured particles (NSPs), through sand under various reaction environments. NPs such as P-25 (30 nm) were completely different in terms of their physicochemical structure from NSPs, which may be more proper to be considered as micro or bulk TiO₂ particles. Such observation undoubtedly evidenced an important finding that encapsulating NPs with stabilizers such as carboxymethyl cellulose abundant in the environment and changing their surface chemistry with pH and ionic strength greatly affected their dispersion in the aqueous phase and mobility through a clean quartz medium, while those strategies were not so effective for NSPs. Therefore, it is apparent that the terms NPs and NSPs should be more strictly differentiated in their use in order to avoid any confusion in assessing their mobility in the environment.

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