A novel oxidized hierarchical porous carbon with vesicule-like ultrathin graphitic walls for efficient removal of anionic and cationic dyes

This work developed a novel oxidized hierarchical porous carbon (OHPC) with vesicule-like ultrathin graphitic walls via a method of air oxidation and used as an efficient adsorbent for Congo red (CR) and Malachite green (MG) removal. Results show that the OHPC2 oxidized at 400 °C possesses three-dimensional hierarchical pores with vesicule-like ultrathin graphitic walls. The prepared OHPC2 not only has a large specific surface area of 1020 m² g^-1 with a high pore volume, but also has abundant oxygen-containing functional groups. These unique structural features endow the OHPC2 with high adsorption capacities for CR (2729.5 mg g^-1) and MG (1697.3 mg g^-1) removal. The adsorption processes of CR and MG are in accordance with the Langmuir isotherm and Quasi-second-order kinetic models. The thermodynamic studies illustrate that the adsorption processes were thermodynamically feasible and spontaneous. Various characterization analysis explained that the adsorption mechanism may involve pore-filling effect, π-π conjugation, hydrogen bonding, and electrostatic attraction. Moreover, the OHPC2 exhibits good cycling stability and is identified as a desirable adsorbent for actual wastewater treatment.