Hydrochars of mixed marine biomass and plastic wastes: Carbonization scenarios and the performance as ketoprofen adsorbents

Abstract

The hydrothermal (HT) conversion of mixed biomass and plastic waste to hydrochar adsorbents has attracted significant attention; however, factors controlling the structure and adsorption properties of hydrochar remain still poorly understood. Herein, HT treatment of the marine biomass waste (crab shells (CR) and fishery waste-derived chitin (CT) and chitosan (CS)) mixed with plastic waste (polyethylene (PE) and polyethylene terephthalate (PET)) at temperatures of 200–250 °C and residence times of 4–12 h was conducted to prepare hydrochars for screening their adsorption characteristics towards ketoprofen, a pharmaceutical pollutant. PET underwent efficient degradation when processed with marine biomass, particularly in mixtures with CS, which facilitated PET depolymerization through an aminolysis reaction. Hydrochars derived from PET mixed with CS demonstrated adsorption capacities for ketoprofen of ca. 25 mg/g due to the presence of the amine, amido, and aromatic groups providing sites for electrostatic interactions, hydrogen bonding, and π-π interactions with ketoprofen. The ketoprofen adsorption was best described by the pseudo-second-order kinetic model and Freundlich-type isotherm. On the other hand, no significant decomposition of PE was observed during the HT treatment of PE and biomass mixtures even in the presence of H₂O₂ oxidizer. However, the hydrochars of CS and CR prepared in the presence of PE exhibited markedly improved ketoprofen adsorption capacity compared to hydrochars of CR and CS. The results of this study demonstrate the benefits of combining plastic and biomass in the waste streams to control waste degradation along with the structure and adsorption properties of the hydrochars.