Upcycling waste plastics into high value-added carbon nanomaterials has been a hot topic due to everincreasing generation of waste plastics, however, little attention has been paid to valuable hollow carbon spheres (HCSs). Herein, uniform mesoporous HCSs with controllable diameter and high surface area were efficiently prepared through the carbonization of mixed plastics consisting of polypropylene, polyethylene and polystyrene under the combined catalysis of organically-modified montmorillonite (OMMT)/Co3O4 at 700 degrees C. The morphology, microstructure, phase structure, textural property, surface element composition and thermal stability of HCSs were investigated by Scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy, N-2 sorption, X-ray photoelectron spectroscopy and thermal gravimetric analysis. The effects of OMMT on the dispersion of Co3O4 in the mixed plastics and the degradation of mixed plastics were studied. It was found that OMMT not only promoted the dispersion of Co3O4 in the mixed plastics, which favored to control the diameter of HCSs, but also promoted the degradation of mixed plastics into light hydrocarbons and aromatics, which facilitated the growth of HCSs. Finally, a possible mechanism was proposed to explain the growth of uniform HCSs with controllable diameter. This facile method provides a novel potential way to convert waste plastics into valuable HCSs, which can be used as catalyst support, adsorbent, storage medium and template for the synthesis of other useful hollow materials, etc. (C) 2014 Elsevier B.V. All rights reserved.