Conversion of waste thermoplastics into porous carbons has attracted wide attention due to the requirement of recycling of large quantities of municipal solid waste. This work reports the preparation of porous carbon sheets on magnesium oxide from mixed thermoplastics including polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate in a closed autoclave at 500 °C. The influence of the weight ratio of magnesium oxide to mixed plastics on the yield and textural properties of the carbon was examined. The morphology and structure of the porous carbon were also characterized. The maximum BET surface area was 713 m² g⁻¹ at a weight ratio of MgO/polymer of 4 and the maximum pore volume was 5.27 cm³ g⁻¹ at a weight ratio of MgO/polymer of 6. The reaction mechanism was explored by analyzing the product distribution and composition of gas and liquid at different reaction times. Aromatics were the main source for the growth of carbon. Model experiments of carbonization of different aromatics were conducted to evaluate the carbonization reactivity of aromatics. Polycyclic aromatic hydrocarbons, especially acenes, produced more carbon.

Conversion of waste polymer on a metal-free catalyst is a promising method for the preparation of nanocarbons. Herein, we synthesized porous carbon sheets and hollow carbon shells through the carbonization of polystyrene on magnesium oxide with different morphologies at 700 °C using a one-pot method. The morphologies, microstructure, phase structure, surface element composition, thermal stability, and textural properties of the obtained nanocarbons were analyzed by SEM, TEM, XRD, TGA, and Raman. The yield of the nanocarbons increased as the weight ratio of magnesium oxide to polystyrene increased. Magnesium oxide acted as a template for the shape-controlled growth of the carbon nanostructure. The surface area of the porous carbon sheets and hollow carbon shells reached 854 and 523 m² g⁻¹ without any activation, respectively. The porous carbon sheets were used as adsorbents to remove methylene blue from water and showed an adsorption capacity of 358.8 mg g⁻¹. Product composition for the pyrolysis of polystyrene in the presence of magnesium oxide was analyzed using GC and GC-MS to elucidate the reaction mechanism. The yield of styrene in the liquid products reached 50% by the catalysis of polygonal magnesium oxide. This strategy provides a cheap and sustainable catalyst for converting polymer into high-value nanocarbons and useful chemicals.

Recently, there has been intense interest in the conversion of plastics into high value-added carbon nanomaterials (CNMs), however, the effect of catalyst diameter on the formation of CNMs is still ambiguous. Herein, uniform NiO catalysts with different diameter (18–227 nm) were firstly prepared by a sol–gel combustion synthesis method and calcination at different temperatures. Subsequently, the combined organically-modified montmorillonite (OMMT)/NiO catalyst was used to catalyze carbonization of polypropylene (PP, selected as an example of plastics) into CNMs at 700 °C. The effect of NiO catalyst diameter on the yield, morphology, microstructure, phase structure, thermal stability and texture properties of CNMs including sponge-like cup-stacked carbon nanotubes (CS-CNTs) and carbon fibers were investigated by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy, thermal gravimetric analysis and N₂ sorption. Besides, the effects of NiO catalyst diameter on the coalescence and reconstruction of NiO particles were explored. It was demonstrated that NiO catalysts with small diameter were more susceptible to coalescence and reconstruction into rhombic shape, which facilitated the growth of long, straight CS-CNTs. Finally, the obtained sponge-like CS-CNTs were found to show high performance in the adsorption of diesel, vegetable oil, kerosene and mineral oil with good recycling performance. It is believed that this work will contribute to the conversion of waste plastics into high value-added CNMs.

Six new coordination compounds Ni(cppca)(H₂O)₄·2H₂O (1), Co(cppca)(H₂O)₄·2H₂O (2), {Cd₂(cppca)₂(H₂O)₅}_n (3), {[Cd₃(cppca)₂(H₂P₂O₇)(H₂O)₆]·2H₂O}_n (4), {Cu(Hcppca)₂}_n (5) and {[Mn₇(cppca)₆(Hcppca)₂(H₂O)₁₀]·2H₂O}_n (6) have been obtained by reactions of the corresponding metal salts and the rigid ligand 5-(3-carboxy-phenyl)-pyridine-2-carboxylic acid (H₂cppca) under solvothermal conditions. All the compounds were fully characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, thermal analysis and powder X-ray diffraction. The single-crystal X-ray analyses showed that compounds 1–6 have rich structural chemistry ranging from mononuclear (1 and 2), one-dimensional (3 and 4), two-dimensional (5) to three-dimensional (6) structures. Moreover, the framework of compound 6 may be simplified into a 3-nodal net with Schlafli symbol {4²·6}{4²·8²·10²}{4³·6²·8·10⁴}₂, which shows an unprecedented (3,4,5)-connected topology net. The fluorescent properties of compounds 3 and 4 were investigated in the solid state and in various solvent emulsions, which indicated that compounds 3 and 4 are both highly sensitive fluorescent probes for the acetone molecules. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic interactions between metal centers in compounds 1, 2, 5 and 6.