Methylene Blue with Rotatable Bonds Driven Self‐Assembly of Cellulosic Biomass Synthesis of Bifunctional N/O/S‐Rich Carbon Foams for Dye Adsorption and Supercapacitors

Abstract Effective development of bifunctional carbon materials with simultaneous dye adsorption and electrochemical performance is highly desirable for achieving carbon neutrality but challenging. Herein, the highly active methylene blue (MB) is pioneeringly employed to reinforce self‐assembly of cellulose chains, achieving the controllable fabrication of carbon foams with high‐level heteroatom doping and interconnected porous structure. Specifically, the sunflower pith as a cellulose precursor is impregnated with MB solution and then subjected to pyrolysis, where MB, as both N/S source and structural builder, can form stable 3D cross‐linked networks with cellulose chains via dynamic hydrogen bonding from its thiazine ring and rotatable tertiary‐amine groups, enabling the carbon foams with high N/S content and hierarchical porous structure. The resultant carbon foams (NSPC‐700) are employed as a reasonable model‐like system to more deeply scrutinize the synergistic effect of interconnected porous structure and N/S‐doping engineering for carbons in MB adsorption and SCs. Consequently, the NSPC‐700 demonstrates high MB‐adsorption capacity (302.2 mg g −1 ), and the MB‐adsorbed NSPC‐700 achieves high gravimetric capacitance (408 F g −1 ) and volumetric capacitance (494 F cm −3 ) at 0.5 A g −1 , the assembled aqueous supercapacitor and organic supercapacitor deliver remarkable capacitance retention (76.28%, 100 A g −1 ) and high energy density (88.01 Wh kg −1 ), respectively.