Facile synthesis of hierarchical N-doped hollow porous carbon whiskers with ultrahigh surface area <i>via</i> synergistic inner–outer activation for casein hydrolysate adsorption

Abstract

N-doped hollow porous carbon materials have attracted significant scientific interest in the field of peptide adsorption, drug delivery and catalysis. However, their facile synthesis is still a challenge due to the lack of an ideal template and effective route for high specific surface area (SSA). In this work, we report a facile approach for preparing N-doped hollow porous carbon whiskers (HPCWs) by using CaCO₃ whiskers as a green template and double inner-activating agent. Two inner activators, CO₂ and Ca(OH)₂, are generated from the CaCO₃ whisker template during the carbonization process. Among them, Ca(OH)₂ was formed by H₂O vapors reacting with the remaining template CaO. Attributed to the drastic synergistic effect of inner-activation (CO₂ or Ca(OH)₂) and outer-activation (KOH), the synthesized HPCWs exhibit ultrahigh SSA (3007 m² g^-1), the largest pore volume (2.63 cm³ g^-1) and a controllable proportion of micropores (S_m/S_t, 60-86%). These intriguing pore structure characteristics of HPCWs endow with them rich target-oriented applications, as exemplified by their outstanding adsorption for casein hydrolysate (10 080 mg g^-1), which is two orders of magnitude (10²) higher than that of common porous materials. This facile and green synthesis strategy may pave a new way to prepare hollow porous carbon materials with the desired pore structure and high surface area for numerous applications.