Surface modification of polyethylene microplastic particles during the aqueous-phase ozonation process

Microplastics coexist with the chemical reactive oxygen species in natural waters, however, there is still a lack to elucidate the effect of these radicals on the microplastic surficial oxidation. In this study, the ozonation of polyethylene microplastics was carried out under varying ozone dosages ranging from 4 to 7 mg/min for 60, 120 and 180 min, where its ozone uptake was iodometrically compared and surficial modification was spectroscopically analyzed using FTIR and XPS. For that, the lowest ozone uptake was 16% at 4 mg/min ozone supplied for 60 min whereas the highest was observed of 44% at 7 mg/min ozone added for 180 min. Moreover, in the FTIR analysis, carbonyl (1,600-1,800 cm(-1)) and hydroxyl (3,200-3,600 cm(-1)) indices were improved more than 20% and 13% when they were ozonized at 7 mg/min for 180 min compared to 4 mg/min for 60 min, respectively. XPS also revealed that 7 mg/min of ozone supplied for 180 min provided the highest of oxygen functionalities, but while there was no significant change in C-C bond. It can be concluded that the surficial modification of PE including formation of oxygen functionalities could be more preferably influenced by the reaction time than ozone dosages.

Automated summary

This study investigated the effect of ozonation on polyethylene microplastics, revealing that the formation of oxygen functionalities on the surface is more influenced by reaction time rather than ozone dosages. Specifically, higher ozone dosages and longer reaction times led to increased presence of carbonyl and hydroxyl indices, as well as oxygen functionalities on the surface of the microplastics. This suggests that the surficial modification of polyethylene is more significantly affected by the duration of the reaction.