Sorption potential of microplastics for azo- and phthalocyanine printing dyes

Abstract

Synthetic printing dyes and microplastics (MPs) are ubiquitous pollutants in wastewater. This study aims to reveal the interactions between these contaminants when they interact in the natural environment. Five types of MPs (powdered polyethylene, granulated polyethylene, polyvinyl chloride, polyethylene terephthalate, and polypropylene) in combination with one phthalocyanine (Cyan) and one azo dye (Magenta) were subjected to adsorption tests in a synthetic aqueous matrix. The experimental parameters were dye concentration (1–200 mg/L), adsorbent mass (30 mg), experimental time (0–312 h), pH (7.3 ± 0.1) and temperature (25 °C). Both dyes are very well adsorbed on the studied polymers (qe = 273–581 mg/g) with polyvinil chloride showing the highest sorption capacity (581 mg/g for Cyan and 550 mg/g for Magenta). The experiment data fitted the Elovich kinetic model and Langmuir isotherm well, indicating monolayer chemisorption. Equilibrium was reached after 72–192 h. Electrostatic attraction, hydrogen bonds, π-π interactions, halogen bonding and van der Waals interactions, are an integral part of adsorption mechanisms of printing dyes on MPs. A model developed by the authors accurately predicted the sorption rate and capacity, implying a possible application to other printing dyes. The results of this research can serve as a basis for further research, such as wastewater treatment technologies for dye and microplastic removal and ecotoxicological studies.