Adsorption behaviors of microplastics from packaging materials subjected to ultraviolet irradiation and microbial colonization

Microplastics (MPs) in nature inevitably undergo various aging processes and may exhibit varied interfacial interactions with the coexisted contaminants. Here several discarded disposable polyethylene and polypropylene plastic packaging materials were collected and employed as the raw materials of MPs, and the effects of stimulated UV irradiation and microbial colonization on the variations of surface physicochemical characteristics, including biofilm content, oxygen-containing functional groups, oxygen/carbon ratio, hydrophilicity and surface charge properties were explored. Simultaneously, the adsorption behavior of each MPs on the representative cationic dye crystal violet (CV), as well as the influences of salinity and pH of CV solution, was investigated. The fitting results of kinetic and isotherm models indicated that the adsorption process was mainly multilayer on heterogeneous surfaces, involving hydrogen bonding, electrostatic attraction and hydrophobic interactions, which were further confirmed by FTIR spectra, pH and salinity experiments, respectively. This study elucidated the variation of surface physicochemical characteristics of MPs during natural aging processes and the possible interfacial interactions with CV, which provided theoretical information on MPs as the potential pollutant carriers.