Sustainable N, P co-doped hierarchical porous carbon via coupling phytic acid-melamine assisted hydrothermal carbonization with high temperature activation

Developing sustainable carbon materials with both dye adsorption and electrochemical properties offers a promising strategy for carbon neutrality. Herein, a coupled carbonization strategy was employed to prepare porous carbon with high-level heteroatom doping and hierarchical pores, involving the co-hydrothermal treatment of wood flour with phytic acid and melamine, followed by K₂CO₃ activation. Phytic acid and melamine act as P/N sources and structural builders, promoting hydrochar formation via phosphate coordination and condensation reactions, resulting in a stable cross-linked network rich in N, P, and O. The resulting N, P co-doped hierarchical porous carbon (NP-PC) exhibits an ultrahigh surface area (2792 m² g^-1, a 344 % increase compared to pure wood flour-derived carbon), suitable mesoporosity (36 %), and tailored surface chemistry (19.86 at% heteroatom content). At room temperature, NP-PC demonstrates an exceptionally high adsorption capacity for methylene blue (3028 mg g^-1 after 6 h contact) and rapid adsorption kinetics (90 % removal within 5 min), outperforming most reported carbon-based adsorbents. NP-PC retains an adsorption capacity above 2500 mg g^-1 even after five regeneration cycles. As a supercapacitor working electrode, NP-PC electrode also shows excellent electrochemical performance, delivering a specific capacitance of 380 F g^-1 at 0.5 A g^-1 and retaining 273 F g^-1 at 25 A g^-1. This study achieves the conversion of low-value biomass into high-performance functional carbons, providing a sustainable solution for integrated environmental and energy applications.