One-pot synthesis of core/shell Co@C spheres by catalytic carbonization of mixed plastics and their application in the photo-degradation of Congo red

Abstract

Much attention has been paid to the synthesis of core/shell metal@carbon composites, but many of the proposed methods are limited by sophisticated procedure and expensive precursors. Herein, a facile one-pot approach is established to prepare magnetic core/shell Co@C spheres through catalytic carbonization of mixed plastics (consisting of polypropylene, polyethylene and polystyrene) by Co₃O₄ at 700 °C. The yield, composition, morphology, phase structure, textural property, surface element composition, thermal stability and magnetic property of core/shell Co@C spheres are investigated. The core/shell Co@C spheres have a distinct ordered and curved graphitic structure, and their main diameters are in the range of 110–130 nm. Besides, they show a ferromagnetic behavior with high saturation magnetization (85.6–101.6 emu g⁻¹). Furthermore, it was observed that Co₃O₄ was uniformly distributed in mixed plastics and formed a network structure, which provided a precondition for the carbonization of mixed plastics into core/shell Co@C spheres with uniform sizes. Finally, the core/shell Co@C spheres were found to show high performance in photo-degradation of Congo red (CR) with good recyclablity, reusability and long-term stability. It was demonstrated that the outer carbon shell promoted the degradation of CR and served as a protective layer for cobalt core to improve acid resistance, while the inner cobalt core accelerated the decomposition of H₂O₂ into radicals, which catalyzed the degradation of CR. More importantly, this simple approach offers a potential way to prepare magnetic core/shell metal@carbon composites from cheap waste plastics.