The Flows of Engineered Nanomaterials from Production, Use, and Disposal to the Environment

Surface Adsorption of Suwannee River Humic Acid on TiO2 Nanoparticles: A Study of pH and Particle Size

TiO₂ nanoparticles are some of the most widely used metal oxide nanomaterials mainly because of their diverse industrial applications. Increasing usage of these nanoparticles raises concerns about the potential adverse effects on the environment. Humic acid is a ubiquitous component of the natural organic matter in the environment that is known to get adsorbed onto nanoparticle surfaces. In this study, adsorption of humic acid on TiO₂ nanoparticles of two different sizes (5 and 22 nm) is studied at different environmentally relevant pH values using attenuated total reflectance Fourier transformation infrared spectroscopy. These vibrational spectra provide insights into the nature of the adsorption process (extent of adsorption and reversibility) as a function of pH as well as information about the bonding to the surface. Additionally, the impact of humic acid adsorption on surface charge and agglomeration has been investigated. Interestingly, the results show that the humic acid adsorption is strongly pH-dependent and that adsorption of humic acid on TiO₂ nanoparticles alters the extent of agglomeration and modifies the zeta potential and surface charges depending on the pH, thus potentially increasing the bioavailability of TiO₂ nanoparticles in the environment.

How reliably can a material be classified as a nanomaterial? Available particle-sizing techniques at work

ABSTRACT

Currently established and projected regulatory frameworks require the classification of materials (whether nano or non-nano) as specified by respective definitions, most of which are based on the size of the constituent particles. This brings up the question if currently available techniques for particle size determination are capable of reliably classifying materials that potentially fall under these definitions. In this study, a wide variety of characterisation techniques, including counting, fractionating, and spectroscopic techniques, has been applied to the same set of materials under harmonised conditions. The selected materials comprised well-defined quality control materials (spherical, monodisperse) as well as industrial materials of complex shapes and considerable polydispersity. As a result, each technique could be evaluated with respect to the determination of the number-weighted median size. Recommendations on the most appropriate and efficient use of techniques for different types of material are given.