Converting polyesters into carbon materials for energy and environmental applications provides a promising way to recycle urban and industrial waste plastics. However, previous strategies could not precisely control the crosslinking reaction of polyester. Herein, poly(ethylene terephthalate) (PET) is transformed into O,S-doped hierarchically porous carbon (OSHPC) using sodium lignosulfonate (SLS) and ZnO at 550 oC. SLS/ZnO show a synergistic effect on the PET carbonization. Firstly, a crosslinking structure is generated through esterification of carboxylic acid in PET degradation products with hydroxyl group in SLS. Subsequently, ZnO promotes de-carbonylation of crosslinking structure into vinyl-terminated chains and radical species to form carbon framework with rich micropores. Upon ZnO removal, numerous mesopores/macropores are introduced. OSHPC thereby bears micro-/meso-/macropores with rich chemical groups, which favor for water transportation. Meanwhile, the bead-like particles in OSHPC improve sunlight absorption. The combined advantages endue OSHPC with high performance in solar vapor generation to produce freshwater from wastewater/seawater. The evaporation rate under 1 kW/m2 is 1.51 kg/m2/h, and the metallic ion removal efficiency is >99.9%. This work reutilizes waste polyesters to fabricate functional carbon and contributes to environmental remediation and solar energy exploitation.