New insights on aging mechanism of microplastics using PARAFAC analysis: Impact on 4-nitrophenol removal via Statistical Physics Interpretation

The aging effects of Polyethylene terephthalate (PET) microplastics were studied under Fenton process and Seawater. This research work mainly focuses on the aging mechanism of PET microplastics under two different conditions and their effect of aging on the adsorption of organic contaminants. The results of optical microscopic images, Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman Spectroscopy, carbonyl, carboxyl index, X-ray powder diffraction (XRD) and dissolved organic carbon (DOC) help to understand the aging mechanism of PET microplastics. Parallel factor analysis (PARAFAC) and two-dimensional correlation spectroscopy (2D-COS) were performed using 3D Excitation-Emission Matrix (3D-EEM) to understand the possible dissolved organic matter released during the Fenton process and seawater. The release of protein/phenol like components was observed in seawater whereas humic acid-like component was noted in the Fenton process. Later, the aged PET microplastics were tested for their adsorption capacity towards 4-nitrophenol at three different temperatures (15, 30 and 45 °C). The adsorption capacity of aged microplastics was found to be higher than the normal PET microplastics for all three different temperatures. Hydrogen bonding, n-pi interaction performed a significant role than pi-pi and hydrophobic interaction in the adsorption mechanism. A double layer with double energy model was found to be the best fit in the adsorption processes. The calculated adsorption energies (ΔE1, ΔE2) from the statistical physics modeling also confirms the physisorption mechanism. The above experimental results help to understand the behavior of microplastics at different aging period and how it acts as a carrier for pollutant in the marine environment.