Sorption of diclofenac by polystyrene microplastics: Kinetics, isotherms and particle size effects

Diclofenac (DCF) is a common pharmaceutical that widely distributed in natural waters, and has been received an increasing attention because of its potential toxicity. Additionally, microplastics are also ubiquitous pollutants in natural waters, but little information is available on their interactions. In this study, the sorption of DCF on polystyrene microplastics (PS MPs) with different particle sizes was investigated, and the influence of environmental factors was also explored. Results indicated that the pseudo-second-order kinetic model was suitable to describe the sorption process. The sorption capacity increased with the increase in particle size. The isotherms data for the sorption of DCF on 0.5 and 1 mu m PS MPs were best fitted with the Dubinine-Radushkevich model, but the Freundlich and Langmuir models could best describe the sorption of DCF 5 and 20 mu m PS MPs, respectively. It is suggested that the sorption was a chemisorption, which is also verified by Fourier transform infrared spectroscopy (FTIR) results. Furthermore, the sorption capacity decreased as pH increased, and increased as ionic strength increased. These findings give a new perspective that the microplastics with larger sizes hold promise for the treatment of DCF-contaminated water.

Automated summary

This study investigated the sorption of diclofenac (DCF) on different particle sizes of polystyrene microplastics (PS MPs) and explored the influence of environmental factors. The results showed that the sorption capacity increased with the increase in particle size and followed the pseudo-second-order kinetic model. The most suitable sorption models varied with different particle sizes of microplastics. Additionally, pH and ionic strength had an impact on the sorption capacity.