Relationship between self-seeded and epitaxial crystallization from polymer solutions: A potentially new method for molecular weight separation and a new decoration method for alkali halides

Catalytic Strategies for the Upcycling of Polyolefin Plastic Waste

Chemical upgrading of waste plastics is currently one of the most important methods for addressing plastic pollution. In comparison to the current methods of incineration or landfill, chemical upgrading enables the utilization of carbon and hydrogen elements in waste plastics as resources. This process strongly relies on efficient catalysts and reaction systems. Through catalyst design, waste plastics can be converted into fuels or chemicals under the optimized reaction conditions, extending their life cycles. In this review, we systematically discuss various chemical conversion methods for polyolefin waste plastics, which account for a large proportion of waste plastics. We further explore the remaining challenges and future development trends in this field, including improving product value through product engineering and shifting research perspectives to exploring the tolerance of catalysts toward impurities in practical waste plastic waste rather than using pure plastic feedstock.

Sustainably Recycling and Upcycling of Single-Use Plastic Wastes through Heterogeneous Catalysis

The huge amount of plastic waste has caused a series of environmental and economic problems. Depolymerization of these wastes and their conversion into desired chemicals have been regarded as a promising route for dealing with these issues, which strongly relies on catalysis for C-C and C-O bond cleavage and selective transformation. Here, we reviewed recent developments in catalysis systems for dealing with single-use plastics, such as polyethylene, polypropylene, and polyethylene glycol terephthalate. The recycling processes of depolymerization into original monomers and conversion into other economic-incentive chemicals were systemically discussed. Rational designs of catalysts for efficient conversion were particularly highlighted. Overall, improving the tolerance of catalysts to impurities in practical plastics, reducing the economic cost during the catalytic depolymerization process, and trying to obtain gaseous hydrogen from plastic wastes are suggested as the developing trends in this field.

Upcycling Single-Use Polyethylene into High-Quality Liquid Products

Our civilization relies on synthetic polymers for all aspects of modern life; yet, inefficient recycling and extremely slow environmental degradation of plastics are causing increasing concern about their widespread use. After a single use, many of these materials are currently treated as waste, underutilizing their inherent chemical and energy value. In this study, energy-rich polyethylene (PE) macromolecules are catalytically transformed into value-added products by hydrogenolysis using well-dispersed Pt nanoparticles (NPs) supported on SrTiO₃ perovskite nanocuboids by atomic layer deposition. Pt/SrTiO₃ completely converts PE (M _n = 8000-158,000 Da) or a single-use plastic bag (M _n = 31,000 Da) into high-quality liquid products, such as lubricants and waxes, characterized by a narrow distribution of oligomeric chains, at 170 psi H₂ and 300 °C under solvent-free conditions for reaction durations up to 96 h. The binding of PE onto the catalyst surface contributes to the number averaged molecular weight (M _n) and the narrow polydispersity (Đ) of the final liquid product. Solid-state nuclear magnetic resonance of ¹³C-enriched PE adsorption studies and density functional theory computations suggest that PE adsorption is more favorable on Pt sites than that on the SrTiO₃ support. Smaller Pt NPs with higher concentrations of undercoordinated Pt sites over-hydrogenolyzed PE to undesired light hydrocarbons.