Converting poly(ethylene terephthalate) waste into N-doped porous carbon as CO₂ adsorbent and solar steam generator

Sustainable conversion of waste plastics into valuable carbon materials for diverse applications provides a promising strategy to dispose the municipal and industrial waste plastics. However, it remains a challenge to precisely control the crosslinking reaction for transforming waste polyesters into N-doped porous carbon (NPC) with well-defined microstructures. Herein, we put forwards a strategy of stepwise crosslinking using melamine and ZnCl₂/NaCl eutectic salts to convert poly (ethylene terephthalate) (PET) into NPC at 550 °C. We prove that firstly melamine reacts with PET degradation products to form a crosslinking structure, and subsequently ZnCl₂/NaCl promote the dehydration and decarboxylation of the crosslinking structure to generate a more thermally stable crosslinking structure. The coordination of two tandem crosslinking reactions is critical to control the microstructure of NPC. Without activations, NPC shows large specific surface area of 1173 m² g⁻¹, abundant N dopants, and rich oxygen-containing groups. These combined features endure NPC with excellent performance in CO₂ capture and solar steam generation, e.g., high CO₂ adsorption capacity of 6.47 mmol g⁻¹ and evaporation rate of 1.62 kg m⁻² h⁻¹. More importantly, NPC is compared to or prevails over previous carbon-based CO₂ adsorbents or photothermal materials. This work will advance the research on “green” reutilization of low-cost polyester wastes to prepare sustainable carbon for solar energy conversion, environmental protection, etc.