Removal of Cr6+ from wastewater via adsorption with high-specific-surface-area nitrogen-doped hierarchical porous carbon derived from silkworm cocoon

The development of highly efficient adsorbents is an effective way to remove Cr6+ from wastewater for environment protection. Herein, a high-specific-surface-area nitrogen-doped hierarchical porous carbon (NHPC) derived from silkworm cocoon was synthesized and applied as an efficient adsorbent for the removal of Cr6+ from wastewater. The resultant NHPC possesses a specific surface area as high as 3134 m2 g−1 and a unique hierarchical porous structure with a large number of small mesopores (2-4 nm) and micropores (0.8-2 nm) embedded in the sidewall of bowl-like macropores (200-300 nm), in which sufficient exposure of adsorption sites and high-flow transfer of Cr6+ ions can be achieved. As a result, the NHPC exhibits a remarkable adsorption performance with a larger adsorption capacity (366.3 mg g−1), a higher adsorption rate (4 × 10−2 g mg−1 min−1) and a superior recyclability in comparison with the commercial adsorbent (Norit CGP). Thermodynamic and kinetic analyses indicate that the adsorption process is spontaneous and endothermic, which fits well with the pseudo-second-order kinetic model and Langmuir isotherm model. This biomass-based porous carbon with well-defined hierarchical porous structure can be applied as a promising adsorbent for the removal of Cr6+ from wastewater.