Removal of polystyrene microplastic from aqueous solutions with London Plane bark biochar: Pyrolysis temperature, performance and mechanism

Abstract

The seasonally shed bark of London Plane tree is an ideal source for biochar due to its high lignin content. Microplastics derived from plastic wastes has become a hot topic due to its potential threats to ecosystems. The aim of this work is to convert the shed bark into efficient London Plane bark biochar (LBC) adsorbents and investigate its application in microplastics adsorption. The effects of pyrolysis temperature on LBC structure, surface properties and microplastic adsorption were investigated and the best adsorption performance of 60.05 mg/L was found at the 550 °C-pyrolyzed LBC. The wet sieve-weighing method was applied to assess the adsorption effect of LBC and verified with thermogravimetric analysis. The adsorption of polystyrene (PS) particles on LBC was in accordance with the Sips isothermal model and the second-order-kinetics model. The robustness of LBCs and the adsorption mechanism were investigated. With the analysis from pore size distribution, SEM images, FTIR and XPS spectra, physical trapping, surface complexation, hydrogen bonding and π-π interaction all play key roles in the adsorption of PS onto the LBC surface. This study not only provides a new approach for the removal of microplastics, but also offers a broad perspective on the treatment of biomass waste.