Search

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]

The article discusses a study which examined the degradation and flame retardancy of polypropylene/organically modified montmorillonite (PP/OMMT) nanocomposite. The study found that the catalysis of hydrogen proton composed of montmorillonite (H-MMT) affects the carbonization behavior of PP. It also discovered the influence of Brønsted acid sites on the H-MMT catalyze degradation reaction of PP.

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]

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 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]