Adsorption behavior of methylene blue on diverse microplastics

Microplastics might be prone to accumulate dye pollutants in the aquatic environment, increasing their potential environmental risks. However, there were rare studies on the interaction between microplastics and dye pollutants. In this study, the interaction between methylene blue (MB) and microplastics (polystyrene (PS), polyvinyl chloride (PVC), and polymethyl methacrylate (PMMA)) were thoroughly investigated, and the effects of pH, salinity, humic acid, particle size, temperature, and natural aquatic environment were considered. The adsorption capacity of MB on microplastics followed the order PMMA > PVC > PS. The sorption process for microplastics to MB could be well described by the pseudo-second-order model and Langmuir model, revealing that the adsorption was monolayer chemisorption. Electrostatic interaction and CH/pi interaction could promote the adsorption of MB on microplastics. PMMA and PVC could combine with MB through polar interaction. The adsorption of PVC to MB was affected by halogen bonding, and there was a pi-pi interaction between PS and MB. The specific surface area and functional groups of microplastics were the main factors affecting the adsorption performance of MB on microplastics. The sorption process exhibited a pronounced pH dependency due to the effect of pH on the surface charge of the microplastics. The presence of NaCl and humic acid could compete with MB for adsorption sites on the surface of microplastics. High temperature promoted the adsorption of MB on PVC and PMMA but inhibited that of PS. Moreover, the adsorption capacities of MB on microplastics were significantly reduced in the natural aquatic environment (Xiang River).

Automated summary

This study investigated the interaction between microplastics and dye pollutants, focusing on the adsorption of methylene blue (MB) on different types of microplastics. The adsorption capacity of MB on microplastics was influenced by factors such as pH, salinity, humic acid, temperature, and particle size, with different types of microplastics showing varied adsorption capabilities. The adsorption process was found to be monolayer chemisorption, influenced by electrostatic interaction, CH/pi interaction, polar interaction, halogen bonding, and pi-pi interaction. The presence of NaCl and humic acid competed with MB for adsorption sites, and high temperature promoted adsorption on PVC and PMMA but inhibited adsorption on PS. In the natural aquatic environment (Xiang River), the adsorption capacities of MB on microplastics were significantly reduced.