Changes in physical and chemical properties of microplastics by ozonation

Abstract

This study evaluated the altered properties of microplastics during the ozonation process in water matrices. The selected polymers include low-density polyethylene, high-density polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinyl chloride. The morphology, contact angle, and chemical composition of the pristine and altered microplastics were characterized using field-emission scanning electron microscopy-energy dispersive spectrometry, contact angle analysis, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS). Microplastic oxidation can lead to surface abrasion, cracking, and fragmentation. XPS analysis indicated that a C=O double bond (carbonyl group) and carboxylic acid/ester bond (O−C=O) were generated in the ozone process. In addition, all the carbonyl index values increased, implying that the number of oxygen functional groups on the surface of the microplastics increased. The contact angle also decreased, indicating that the hydrophilic portion of the microplastics increased due to oxidation. Microplastics, whose surfaces are roughened owing to oxidation or reduced in size owing to fragmentation, pose a fatal threat to aquatic life. In addition, microplastics with increased oxygen functional groups and hydrophilicity due to oxidation treatment have different adsorption properties. Relatively hydrophilic microplastics adsorb heavy metal cations that can adversely affect ecosystems by acting as heavy metal transport mediators.