One-step carbonization/activation synthesis of chitosan-based porous sheet-like carbon and studies of adsorptive removal for Rhodamine B

In this work, new N, O-codoped chitosan-derived carbon adsorbents (CKC-x, x refer to the calcination temperature) were synthesized over a simple process of chitosan-KOH aerogel production and simultaneous carbonization/activation of the aerogel. CKC-700 was characterized by sheet-like morphology (even containing a portion of carbon nano-sheet of 3 nm thickness), high porosity and specific surface area (1702.1 m2/g), and pyridinic/pyrrolic/graphitic N groups. The simultaneous carbonization/activation of chitosan-KOH aerogel prepared by top-down coagulation of chitosan aqueous solution by KOH aqueous solution rendered these beneficial characteristics. CKC-700 exhibited a superior adsorption capacity for Rhodamine B (RhB) to other chitosan-derived carbon adsorbents, and the maximum adsorption capacity for RhB of 594 mg/g was achieved at 55 °C. CKC-700 also possessed reasonable reusability for the removal of RhB, and the removal efficiency was still above 95 % in the fifth cycle. The effects of adsorption temperature and time, adsorbent dose, organic dye concentration, and solution pH on the adsorption capacity of CKC-700 were studied. Moreover, the adsorption isotherm, kinetics, thermodynamics, and the adsorption mechanism of RhB on CKC-700 were discussed. In addition, CKC-700 also showed favorable adsorption performance for methylene blue (441 mg/g), methyl orange (457 mg/g), and congo red (500 mg/g) at around 25 °C.