Impact of different soil solutions on the stability and photocatalytic activity of commercial zinc oxide nanoparticles

Abstract

Zinc oxide (ZnO) nanoparticles are extensively utilized across various industries due to their versatile applications. However, the widespread use of these nanoparticles raises concerns regarding their potential release into soil environments, and also into the soil solution. Therefore, this study aims to delve into the interplay between different soil solution properties and the stability as well as photocatalytic activity of commercially available ZnO nanoparticles. It is observed that these interactions precipitate a reduction in the primary crystallite sizes of ZnO, primarily attributed to the release of Zn²⁺ ions under acidic conditions, and the formation of zinc complexes or hydroxides in alkaline environments. In acidic media, there is a concomitant decrease in the hydrodynamic diameter of ZnO, serving as further confirmation of Zn²⁺ release, which is corroborated by analytical measurements. Conversely, in alkaline media, the hydrodynamic diameter remains unaltered, suggesting the formation of an amorphous layer on the nanoparticle surface in such conditions. Further analyses into the surface chemistry of ZnO nanoparticles reveal the adsorption of various organic substances onto their surfaces. These organic compounds potentially function as electron traps or occupy active sites, however, after the interaction with soil solutions, the material was still able to degrade the model pollutant. So, the interaction with soil solutions reduced the activity, but the catalyst retained its efficiency. In essence, this study underscores the importance of comprehensively understanding the behavior of ZnO nanoparticles in soil environments. Such insights are pivotal for informed decision-making regarding the sustainable utilization of ZnO nanoparticles across various industrial domains.