Session: Applications & Implications of Nanomaterials in the Environment:

The surface fouling of photocatalytic nanoparticles, such as titanium dioxide (TiO₂) nanoparticles, can influence their reactivity in water treatment processes or natural environments. Here, we explore how the chemistry and structure of adsorbed natural organic matter (NOM) and protein coatings changes the nanoparticle reactivity, including the generation of reactive oxygen species (ROS) such as hydroxyl radicals, holes, superoxide anion and singlet oxygen that can degrade recalcitrant pollutants. For NOM, the coating characteristics and subsequent ROS generation by the NOM-coated TiO₂nanoparticles was found to be distinct depending on the water chemistry in which the NOM adsorbed. For example, the NOM adsorbed mass in moderately hard water (MHW) was higher with a wide range of low to high molecular weight species, whereas adsorption from deionized water (DIW) resulted in lower adsorbed mass of predominantly mid - molecular weight fractions. Degradation experiments with phenol indicated that the generation of hydroxyl radical was not affected by the different NOM coatings. However, the degradation of one of the byproducts, catechol, was dissimilar: NOM coating in DIW enhanced the degradation, whereas the coating from MHW suppressed the degradation relative to bare TiO₂. At least two mechanisms were identified that were required to explain these surprisingly divergent behaviors. First, hole formation was much higher in the case of NOM coatings in DIW, which favors the degradation of catechol by a hole-mediated pathway. Secondly, the suppression of catechol degradation can be explained by lower catechol adsorption for NOM coatings in MHW, likely attributable to a more complete surface coverage or thicker/denser adsorbed layer. This study hence emphasizes the importance of the adsorbed layer properties on surface reactivity. Subsequently, the effect of heterogeneous coatings of NOM and protein on the degradation of phenol, byproduct formation, and ROS generation will be studied to further explore the role of surface chemistry and adsorbed layer structure on the photoreactivity of the nanoparticles.

Stacey M. Louie

Assistant Professor, University of Houston

Appearances