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The wide application of carbon nanosheets (CNS) is still restricted by low production. Meanwhile, the accumulation of waste plastic generates serious environmental pollution. Nowadays, the conversion of waste plastic into two-dimensional CNS is regarded as a promising way to address these issues due to the high carbon content of waste plastic. However, this conversion process is still impeded by low-efficient catalysts so far. Herein, the highly efficient carbonization of waste polypropylene (PP) into CNS is achieved using a combined catalyst of ferrocene and sulfur. The carbonization process in sealed space ensures an ultrahigh carbon yield (62.8%) and a thin thickness (4–4.5 nm) of as-prepared CNS, even though little catalyst is used. After activation, the activated carbon nanosheets (ACNS) show a well-defined hierarchical porous structure with a large specific surface area (3200 m2 g−1) and a big pore volume (3.71 cm3 g−1). The ACNS based electrode delivers a high specific capacitance of 349 F g−1 at 0.5 A g−1. The fabricated symmetric supercapacitor manifests a high energy density of 23 Wh kg−1 at 225 W kg−1. These findings provide a reference for the efficient conversion of waste plastic into energy storage materials. Image 1 • Waste PP is converted into thin carbon nanosheets (4–4.5 nm) using combined catalyst. • Vapor-phase reaction endows the prepared CNS with a high carbon yield (62.8%). • Activated carbon nanosheets show a large specific surface area and a big pore volume. • A high specific capacitance with superior cycling stability is proved. • This work reports an efficient conversion of waste plastic into electrode material. [ABSTRACT FROM AUTHOR]

Abstract: A one-pot approach was established to prepare carbon nanotubes (CNTs) through the carbonization of polypropylene (PP) by the combined catalysts of activated carbon (AC) with Ni2O3. The combination of AC with Ni2O3 showed a synergistic catalysis on the catalytic conversion of PP to form CNTs. The effects of the content of AC and carbonization temperature on the yield of CNTs were studied. The morphology, phase structure and thermal stability of the obtained CNTs were analyzed by means of SEM, TEM, XRD, TGA and Raman. In this synergistic catalysis, the surface functional groups (especially carboxylic groups) of AC were proved to be the key factor. AC not only promoted the cracking of PP fragment radicals into light hydrocarbons and the dehydrogenation and aromatization of the resultant light hydrocarbons into aromatic compounds, but also promoted the formation of the intermediate aromatic compounds or polycyclic aromatic hydrocarbons (PAHs) from the reaction of light hydrocarbon products and aromatic compounds. Additionally, AC assisted in situ Ni catalyst (originated from the reduction of Ni2O3) catalyzing the dehydrogenation and aromatization of intermediate aromatic compounds or PAHs products to form CNTs. At last, a layer-by-layer assembled mechanism based on benzene rings for the growth of CNTs using PP as carbon source and combined AC/Ni2O3 as catalysts was proposed. This mechanism will help to understand the growth mechanism of CNTs using virgin or waste plastics as carbon sources. More importantly, this approach offers a new potential way for large-scale production of CNTs from waste plastics using cheap AC as a cocatalyst. [Copyright &y& Elsevier]