Conversion of polystyrene into porous carbon sheets and hollow carbon shells over different magnesium oxide templates for efficient removal of methylene blue

Abstract

Conversion of waste polymer on a metal-free catalyst is a promising method for the preparation of nanocarbons. Herein, we synthesized porous carbon sheets and hollow carbon shells through the carbonization of polystyrene on magnesium oxide with different morphologies at 700 °C using a one-pot method. The morphologies, microstructure, phase structure, surface element composition, thermal stability, and textural properties of the obtained nanocarbons were analyzed by SEM, TEM, XRD, TGA, and Raman. The yield of the nanocarbons increased as the weight ratio of magnesium oxide to polystyrene increased. Magnesium oxide acted as a template for the shape-controlled growth of the carbon nanostructure. The surface area of the porous carbon sheets and hollow carbon shells reached 854 and 523 m² g⁻¹ without any activation, respectively. The porous carbon sheets were used as adsorbents to remove methylene blue from water and showed an adsorption capacity of 358.8 mg g⁻¹. Product composition for the pyrolysis of polystyrene in the presence of magnesium oxide was analyzed using GC and GC-MS to elucidate the reaction mechanism. The yield of styrene in the liquid products reached 50% by the catalysis of polygonal magnesium oxide. This strategy provides a cheap and sustainable catalyst for converting polymer into high-value nanocarbons and useful chemicals.