Attachment of various-shaped polystyrene microplastics to silica surfaces: Experimental validation of the equivalent Cassini oval extended DLVO model

Allan Gomez-Flores; Suheyon Jin; Hyojeong Nam; Li Cai; Shaoxian Song; Hyunjung Kim

doi:10.1016/j.jhazmat.2024.134146

Attachment of various-shaped polystyrene microplastics to silica surfaces: Experimental validation of the equivalent Cassini oval extended DLVO model

J Hazard Mater. 2024 May 15:470:134146. doi: 10.1016/j.jhazmat.2024.134146. Epub 2024 Mar 27.

Authors

Allan Gomez-Flores¹, Suheyon Jin¹, Hyojeong Nam¹, Li Cai², Shaoxian Song³, Hyunjung Kim⁴

Affiliations

¹ Department of Earth Resources and Environmental Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea.
² College of Environmental Science and Engineering, Donghua University, Shanghai 201620, China.
³ School of Resources and Environmental Engineering, Wuhan University of Technology, Wenzhi Street 34, Wuhan, Hubei 430070, China.
⁴ Department of Earth Resources and Environmental Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Republic of Korea. Electronic address: kshjkim@hanyang.ac.kr.

PMID: 38583206
DOI: 10.1016/j.jhazmat.2024.134146

Abstract

Microplastics (MPs) vary in shape and surface characteristics in the environment. The attachment of MPs to surfaces can be studied using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, this theory does not account for the shape MPs. Therefore, we investigated the attachment of spherical, pear-shaped, and peanut-shaped polystyrene MPs to quartz sand in NaCl and CaCl₂ solutions using batch tests. The attachment of MPs to quartz sand was quantified using the attachment efficiency (alpha). Subsequently, alpha behaviors were interpreted using energy barriers (EBs) and interaction minima obtained from extended DLVO calculations, which were performed using an equivalent sphere model (ESM) and a newly developed equivalent Cassini model (ECM) to account for the shape of the MPs. The ESM failed to interpret the alpha behavior of the three MP shapes because it predicted high EBs and shallow minima. The alpha values for spherical MPs (0.62-1.00 in NaCl and 0.48-0.96 in CaCl₂) were higher than those for pear- and peanut-shaped MPs (0.01-0.63 in NaCl and 0.02-0.46 in CaCl₂, and 0.01-0.59 in NaCl and 0.02-0.40 in CaCl₂, respectively). Conversely, the ECM could interpret the alpha behavior of pear- and peanut-shaped MPs either by changes in EBs or interaction minima as a function of orientation angles and electrolyte ionic strength. Therefore, the particle shape must be considered to improve the attachment analyses.

Keywords: Attachment efficiency; Cassini oval; Microplastic; Shape; XDLVO.