Comparison of adsorption capacity of 4-Nonylphenol on conventional and biodegradable microplastics aged under natural water

This study investigated the adsorption of 4-Nonylphenol (4-NP) on aged microplastics (MPs) composed of polyethylene terephthalate (PET) and poly(butylene-adipate-co-terephthalate)/polylactic acid (PBAT/PLA). Morphological analysis revealed wear, wrinkles, and increased surface roughness in both aged MPs, with X-ray diffraction showing slight increases in crystallinity. Infrared spectroscopy showed an increase in the carbonyl index from 2.78 to 4.37 for PBAT/PLA and 0.51 to 2.32 for PET after aging. The natural water from the San Pedro River in Chile Atacama region (5.91 mS·cm^-1 conductivity, 3.25 PSU salinity, 2955 mg·L^-1 total dissolved solids, 435 mg·L^-1 CaCO₃ hardness) was used as the environmental medium and compared with a 0.01 mol·L^-1 CaCl₂ as a model solution. Kinetic modeling showed a decrease in 4-NP percentage removal from 90.0 % (2277 μg∙g^-1 adsorption capacity) to 50.2 % (1268 μg∙g^-1) for PET and from 86.8 % (2087 μg∙g^-1) to 70.3 % (1955 μg∙g^-1) for PBAT/PLA when comparing the model solution to natural water, with 30 and 84 h equilibrium times, respectively. Isotherm data showed that 4-NP/PET fits BET n-layer and Temkin models, while 4-NP-PBAT/PLA fits the Toth and Hill models The ionic composition of natural water induces cation attraction to polarized MPs surfaces, intensifying competition for adsorption sites. This involves ion and molecular cooperation, 4-NP reorientation, external diffusion effects, and surface oxidation variations, which are attributed to explaining the bilayer (PET) and monolayer (PBAT/PLA) formation. This work contributes to understanding MP pollution and the importance of considering the bioplastics life cycle, since their waste presents significant potential to resist external factors for transporting contaminants.