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Due to the ever-increasing plastic waste causing serious environmental problems, it is highly desirable to recycle it into high-value-added products, such as carbon nanomaterials. However, the traditional catalytic carbonization of hydrocarbon polymers is severely prohibited by the complexity of real-world plastic waste due to the existence of halogen-containing polymers. In this study, through a universal combined template based on magnesium oxide and iron(III) acetylacetonate (Fe(acac)3), a three-dimensional hollow carbon sphere/porous carbon flake hybrid nanostructure is prepared from carbonization of plastic waste with high yields (>70 wt%). This approach is not only suitable for hydrocarbon polymers, but also for halogen-containing polymers. Interestingly, the obtained advanced carbon framework exhibits excellent performance in lithium-ion batteries (802 mA h g−1 after 500 cycles at 0.5 A g−1). The present research paves a new avenue to upcycle plastic waste into a high value-added product. [ABSTRACT FROM AUTHOR]

The controlled carbonization of polymers is one of the most important polymer reactions. It represents the conversion process of polymeric precursors into carbonaceous materials in a "controlled" manner. In this review, we summarize the research progress on the controlled carbonization of (waste) polymers in preparing functional carbon materials with well-defined microstructures, fabricating advanced polymer composites with enhanced flame retardancy, and converting waste polymers into high value-added nanocarbon materials. The carbonization mechanisms of polymers with different compositions and chain structures are highlighted. How to match the degradation reaction of polymers with the carbonization reaction of the degradation products is addressed to improve the carbonization efficiency and optimize the growth of carbon materials. The applications of (waste) polymer-derived carbon materials in electrochemical energy storage and environmental remediation are reviewed. Current existing limitations and future perspectives are also given. [ABSTRACT FROM AUTHOR]

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]

• Carbon nanosheets (CNSs) was prepared from "real-world" mixed waste plastics. • Organically-modified montmorillonite was selected as the catalytic template. • Porous carbon nanosheets (PCNSs) was fabricated by KOH activation of CNSs. • PCNSs were featured on hierarchically micro-/mesoporous structures. • PCNSs showed high capacitance and excellent rate capability for supercapacitors. Recently, sustainable development and serious energy crisis called for appropriate managements for the large number of municipal and industrial waste plastics as well as the development of low-cost, advanced materials for energy storage. However, the complexity of waste plastics significantly hampers the application of ever used methods, and little attention is paid to the utilization of waste plastics-derived carbon in energy storage. Herein, porous carbon nanosheets (PCNSs) was produced by catalytic carbonization of "real-world" mixed waste plastics on organically-modified montmorillonite (OMMT) and the subsequent KOH activation. PCNSs was featured on hierarchically micro-/mesoporous structures with the pore size distribution centered on 0.57, 1.42 and 3.63 nm and partially exfoliated graphitic layers, and showed a high specific surface area of 2198 m2 g−1 and a large pore volume of 3.026 cm3 g−1. Benefiting from these extraordinary properties, PCNSs displayed a superior performance for supercapacitors with high specific capacitances approaching 207 and 120 F g−1 at a current density of 0.2 A g−1 in aqueous and organic electrolytes, respectively. Importantly, when the current density increased to 10 A g−1, the specific capacitances remained at 150 F g−1 (72.5%) and 95 F g−1 (79.2%) in aqueous and organic electrolytes, respectively. The outstanding rate capability of PCNSs was in sharp contrast to the performance of traditional activated carbons. This work not only provides a potential way to recycle mixed waste plastics, but also puts forward a facile sustainable approach for the large-scale production of PCNSs as a promising candidate for supercapacitors. [ABSTRACT FROM AUTHOR]

Undoped, N-doped, and S-doped porous carbons were prepared via the hard-template method by direct carbonization of aromatic precursors on MgO at 500 °C and autogenic pressure. The influence of aromatic precursors on the yield, morphology, structure, surface composition, and textural properties of the carbons was investigated. The side-chain and number of the benzene ring promoted the yield of carbon. Acenes produced more carbon among the polycyclic aromatic hydrocarbons. The highest yield of carbon was 52.9 wt% using pyrrole as precursor on a commercial sheet MgO. The size of micropores and macropores as well as nitrogen content was also dependent on the aromatics. Three types of MgO were compared using pyrrole as precursor. Morphology of MgO played a key role on the yield of porous carbon. The yield of carbon reached 50.5 wt% and the surface area of carbon was 671 m 2  g −1 on a home-made MgO. After KOH activation, the surface area of the porous carbon increased dramatically to 2788 m 2  g −1 and exhibited a high adsorption capacity up to 980.4 mg g −1 for methylene blue. [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]

Catalytic conversion of waste plastics into high value-added carbon nanomaterials (CNMs) has attracted increasing attention; however, the role of lattice oxygen in the carbonization of plastics still remains ambiguous. In this work, firstly, a nickel catalyst with different content of lattice oxygen was prepared by the sol–gel combustion synthesis method. Subsequently, the effect of lattice oxygen in the nickel catalyst on the catalytic carbonization of polypropylene (PP, an example of plastics) into CNMs was investigated. It was found that the yield of CNMs increased dramatically with the increasing content of lattice oxygen. Large and short platelet-like carbon fibers were obtained when the content of lattice oxygen was low. With the increasing content of lattice oxygen, small, winding and short carbon nanofibers were produced. When the content of lattice oxygen further increased, long, small and straight cup-stacked carbon nanotubes were formed. Besides, it was demonstrated that lattice oxygen not only prevented the coalescence of nickel catalyst nanoparticles into large particles and promoted their reconstruction into rhombic shape, but also facilitated the catalytic carbonization of PP degradation products. This work provides new insights into the carbonization mechanism of plastics and puts forward a novel chemical method to prepare CNMs with diverse morphologies by controlling the content of lattice oxygen in the catalyst. [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]

Recently,upcycling waste plastics into high-value-added carbonnanomaterials has attracted much attention; however, few studies havefocused on the conversion of waste plastics into graphene with highyield. Herein, we report a simple novel method to synthesize grapheneflakes (GFs) with high yield through catalytic carbonization of wastepolypropylene (PP) using organically modified montmorillonite (OMMT)as degradation catalyst and template at 700 °C. The yield, morphology,microstructure, phase structure, thermal stability, and surface elementcomposition of GFs were investigated. In addition, it was found thatOMMT not only promoted the degradation of waste PP into light hydrocarbonsand aromatics but also acted as template and catalyzed carbonizationof the light hydrocarbons and aromatics into GFs. At last, a possiblemechanism for the formation of GFs was put forward. This simple approachprovides a novel way to effectively prepare high-value-added GFs usingwaste plastics as carbon sources. [ABSTRACT FROM AUTHOR]

A one-potapproach was established to effectively convert polypropylene(PP) and linear low density polyethylene (LLDPE) into carbon nanomaterials(CNMs) including cup-stacked carbon nanotubes and carbon nanofibersunder the combined catalysis of HZSM-5/NiO or HZSM-5/Ni2O3at 700 °C. The effects of HZSM-5 content, a nickelcatalyst, and the carbon precursor on the morphology, microstructure,phase structure, and thermal stability of CNMs were investigated withscanning electron microscopy, transmission electron microscopy (TEM),high-resolution TEM, X-ray diffraction, Raman spectroscopy, and thermalgravimetric analysis. The effect of HZSM-5 content on the degradationproducts of PP and LLDPE was analyzed by gas chromatography and gaschromatography–mass spectrometry. With increasing HZSM-5 content,the yields of light hydrocarbons and aromatics increased due to protonacid sites on the surface of HZSM-5 catalyzing cracking of PP or LLDPEdegradation products. This one-pot approach provides a novel potentialway to largely transform mixed waste polyolefin into high value-addedCNMs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Catalytic carbonization of polystyrene into mesoporous hollow carbon nanospheres (HCNs). [•] Organically-modified montmorillonite (OMMT) improved the yield and morphology of HCNs. [•] OMMT affected the cobalt catalyst dispersion and the polystyrene degradation products. [•] The growth mechanism of mesoporous HCNs was studied. [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]

Abstract: The effect of combination between a trace of halogenated compounds (such as ferric chloride and ammonium bromide) and Ni2O3 particles on the carbonization of polypropylene (PP) was investigated during combustion. The results showed a synergistic catalysis of combined halogenated compounds with Ni2O3 in promoting the formation of the residual char during combustion. The investigation on the promotion mechanism showed that halide radical releasing from halogen-containing additives worked as a catalyst to accelerate dehydrogenation–aromatization of degradation products of PP, which promote the degradation products to form the residual char catalyzed by nickel catalyst. The results of GC and GC/MS confirmed that halogenated compounds could accelerate dehydrogenization and aromatization of degradation products of PP. The morphological observation showed that longer fiber-like structure was formed in the residual char of PP/halogenated compound/Ni2O3 composites comparing with PP/Ni2O3 composite. As a result, the presence of a trace amount of halogenated compounds could significantly improve the flame retardancy of PP/Ni2O3 composites, which is proved by cone calorimeter tests. [Copyright &y& Elsevier]

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]