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Polyethylene terephthalate (PET) plastic has been extensively used in our social life, but its poor biodegradability has led to serious environmental pollution and aroused worldwide concern. Up to now, various strategies have been proposed to address the issue, yet such strategies remain seriously impeded by many obstacles. Herein, waste PET plastic was selectively carbonized into three-dimensional (3D) porous carbon nanosheets (PCS) with high yield of 36.4 wt%, to be further hybridized with MnO2 nanoflakes to form PCS-MnO2 composites. Due to the introduction of an appropriate amount of MnO2 nanoflakes, the resulting PCS-MnO2 composite exhibited a specific capacitance of 210.5 F g−1 as well as a high areal capacitance of 0.33 F m−2. Furthermore, the PCS-MnO2 composite also showed excellent cycle stability (90.1% capacitance retention over 5000 cycles under a current density of 10 A g−1). The present study paved an avenue for the highly efficient recycling of PET waste into high value-added products (PCSs) for electrochemical energy storage. [ABSTRACT FROM AUTHOR]

Catalyzing carbonization of polymer itself to form a protective carbonaceous layer has been proven to be an effective way to improve polymer's flame retardancy, but there is still a great challenge to achieve synchronous enhancement in traditional test standards (such as LOI and UL-94 testing). In this study, a stiffener skeleton strategy combined with catalyzing carbonization was proposed to improve the flame retardancy of polycarbonate (PC). The synergistic effect of nanosized carbon black (CB)/Ni 2 O 3 on carbon yield and combustion properties of PC were investigated. An improvement with 31.4% in LOI, V0 in UL-94, and 50% reduction for PHRR in cone calorimeter test was achieved. According to char morphology and structure analysis, the flame retardancy mechanism was attributed to the enhanced barrier effect of carbon layer with interconnected structure and self-supporting capacity, which was promoted by the formation of carbon skeleton framework from PC and the catalytic carbonization from combined catalysts. [ABSTRACT FROM AUTHOR]

Highlights: [•] Catalytic carbonization of PP into cup-stacked carbon nanotubes (CS-CNTs). [•] Yield and morphology of CS-CNTs were modulated by halogenated compound content. [•] Halogenated compound significantly influenced the degradation products of PP. [•] Coalescence and reconstruction of NiO were affected by PP degradation products. [•] Acid-treated CS-CNT showed high performances in adsorption of metallic ions and dyes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Catalytic carbonization of mixed plastics (including PP, PE and PS) into HCSs. [•] The diameter of mesoporous HCSs was modulated by the addition of OMMT. [•] The yield of uniform HCSs was increased by adding more Co3O4 catalyst. [•] OMMT promoted the dispersion of Co3O4 and the degradation of mixed plastics. [•] This method offers a potential way to effectively convert waste plastics into HCSs. [Copyright &y& Elsevier]

Highlights: [•] Catalytic carbonization of PE into cup-stacked carbon nanotubes (CS-CNTs). [•] Yield and morphology of CS-CNTs were modulated by the chain structure of PE. [•] The chain structure of PE significantly influenced the degradation products of PE. [•] The degradation products of PE determined the growth of CS-CNTs. [•] This one-pot approach offers a potential way to convert waste plastics into CS-CNTs. [Copyright &y& Elsevier]

[Display omitted] • A green and high-yield route to recycle waste masks into CNTs/Ni hybrids. • The yield of carbon as high as 64.4 g/100 g waste masks. • The Ni(OH) 2 /NiCl 2 as universal catalysts to catalytic carbonization waste masks form different environments. • Superior microwave absorption performances with reflection loss of -56.3 dB and absorption bandwidth of 4.3 GHz. With the worldwide pandemic of COVID-19, a tremendous amount of face masks have been consumed and discarded, resulting in serious environment pollution and infectious hazards. Herein a green and high-yield route has been developed to recycle waste masks (WMs) into CNTs/Ni hybrids via catalytic carbonization. Our results exhibited that the yield of carbon was as high as 64.4 g/100 g WMs. Furthermore, the as-fabricated CNTs/Ni hybrids were applied for microwave absorption, which displayed superior performances, including a strong reflection loss of -56.3 dB and an absorption bandwidth of 4.3 GHz with absorber thickness of only 2.0 mm. The mechanism was mainly ascribed to the favorable synergistic effects of CNTs and Ni on conduction and magnetic losses, dipolar polarization, interfacial polarization and impedance matching. Thus, this work provides an environmentally friendly, scalable and cost-effective strategy for recycling waste masks into high-valuable carbon nanomaterials, and exploits their potential application for microwave absorption. [ABSTRACT FROM AUTHOR]

Highlights: [•] Catalytic carbonization of polypropylene (PP) into cup-stacked carbon nanotubes (CS-CNTs). [•] The yield and morphology of CS-CNTs were modulated by organically-modified montmorillonite (OMMT) content. [•] OMMT influenced the degradation products of PP and the coalescence and reconstruction of NiO nanoparticles. [Copyright &y& Elsevier]

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]

Abstract: A one-pot approach to prepare Cu–Ni/C heterogeneous composites by carbonization of polypropylene (PP) using combined catalysts of Ni2O3 and CuCl was proposed. TEM, SEM, TGA and Raman measurements were performed to investigate the effects of Cl/Ni molar ratios on the yield and morphology of the resultant carbon materials. The yield of carbon materials in Cu–Ni/C first increased and then decreased as the Cl/Ni molar ratio increased, and the maximum yield was achieved at Cl/Ni molar ratio of 0.125. Longer and thinner carbon nanotubes (CNTs) were obtained at low Cl/Ni ratios while shorter carbon fibers were formed at high Cl/Ni ratios. The effect of Cl/Ni molar ratio on the active sites for the growth of carbon materials and degraded products of PP were investigated by XRD, GC and GC–MS. Interestingly, the resultant Cu–Ni/C showed the catalysis to “Click” reaction. As a result, the initial catalytic substances (Ni2O3 and CuCl) could be effectively used twice as catalysts in the carbonization of PP and in the later application of the resultant Cu–Ni/C composites. More importantly, this approach is a new potential method to transform waste polymer materials into valuable metal/carbon heterogeneous composites. [Copyright &y& Elsevier]