Surficial Modification of Polyethylene Microplastic Particles during the Aqueous-phase Ozonation Process

초록

Microplastic contamination has gained an attention in the recent decades, due to their small size (Von Moos, Burkhardt-Holm and Ko?hler, 2012; Masura et al., 2015), large distribution (Browne et al., 2011; Eerkes-Medrano, Thompson and Aldridge, 2015; Gewert, Plassmann and Macleod, 2015) and ecological toxic effects in all trophic levels including microorganisms (Nomura et al., 2016; Sun et al., 2018), plants (Bhattacharya et al., 2010), animals (Fossi et al., 2012; Martinez-Gomez et al., 2017; Zikova et al., 2017), and even human being (Karami et al., 2017). In response to, various advanced oxidation processes have been reported to either ascertain their chemical weathering behaviour or develop the more feasible plastic treatment process (Liu et al., 2019; Tofa et al., 2019). This study aims to investigate any surficial modification of polyethylene (PE) microplastics under varying ozone dosages of 4, 5, 6 and 7 mg/min for 60,120 and 180 min where their extent of ozone uptake was iodometrically compared. From this, the lowest ozone uptake was as of 16 % at 4 mg/min ozone supplied for 60 min whereas the highest was observed at 44% of 7 mg/min ozone added for 180 min. Their surficial changes were found that vinyl, carbonyl, and hydroxyl indices were each ranged of 900-1000 cm-1, 1600-1800 cm-1 and 3200-3600 cm-1, respectively. In this regard, the extents of carbonyl (e.g., the highest ketones peak at 1720 cm-1) and hydroxyl groups were enhanced at the highest of 20% and 13%, ozonized at 7 mg/min for 180 min over 4 mg/min for 60 min, respectively. However, there was no meaningful modification on vinyl groups. At 4 different dosages for 180 min, XPS also revealed that 7 mg/min of ozone supplied gave the highest of oxygen functionalities formed, but there was no significant change in C-C bond. It can conclude that the modification and the formation of oxygen functionalities could be more preferably influenced by the reaction time rather than that of dosages.