Micro-meso porous biocarbons derived from a typical biopolymer with superior adsorption capacity for methylene blue dye and high-performance supercapacitors

Three micro-mesopores carbons (SAs) are successfully prepared by a facile route via the activation of sodium alginate with a green activator of calcium chloride. These samples are used for efficient adsorption of methylene blue (MB) and high-performance supercapacitors (SCs). The specific surface areas, pore size feature, and surface functional groups and their effect on the adsorption of MB dye and SCs are systematically investigated. Impressively, it is found that the micropore volume percentage (VMicro/VT) and oxygen-containing species of prepared SAs had a positive effect on adsorption ability toward MB. In detail, the adsorption capacities of SA-1 (662.7 mg g-1) and SA-2 (718.4 mg g-1) toward MB are significantly larger than that of SA-3 (198.2 mg g-1). Further, SA-2 has a slightly higher adsorption capacity than that of SA-1, relating to its abundant micropore region and much more oxygenated functionality. Furthermore, the adsorption kinetics data suggest that the adsorption process of MB onto three SAs is mostly prone to chemical adsorption, with an effect of hydrogen bonding/electrostatic interactions between SA adsorbents with negative charge surface originated from oxygen-containing functional groups and MB molecules. Electrochemical tests reveal the SC assembled with SA-1 shows the best comprehensive performances due to its more rational pore size distribution and higher SSA proportion originated from meso- and macropores, with a high specific capacitance of 222.6 F g-1 at 1.0 A/g in alkaline and excellent cycling stability. These results demonstrate that the prepared biocarbon with a suitable hierarchical porous nature would be beneficial for the adsorption of MB dye and SCs.