Enhanced removal of methylene blue from water by mesopore-dominant biochar from kelp: Kinetic, equilibrium and thermodynamic studies

Algae is increasingly used to produce biochar by pyrolysis, while the process often makes biochar with micropore-dominant and limited porosity, showing limited removal capacity of dyes. Herein, kelp biochar with hierarchical pores and superior methlyene blue (MB) removal performance is obtained by a mild KOH activation after pyrolysis to consolidate intrinsic pores, constituting to be a critical step for mesopores introduction. The as-made AKC-800 has high-surface-area and average pores of 2392 m2/g and 2.25 nm, enabling it to have amazing MB uptake of 964.5 mg/g, much larger than that of commercial activated carbons with close surface areas. The importance of mesopores in kelp biochar is clearly confirmed towards the diffusion of MB molecules. Adsorption kinetics and isotherms are well-fitted by pseudo-second-order and Langmuir model with a spontaneous endothermic behavior, and the superior removal performance is mainly owned to an increase in surface areas and decrease in ion-transport resistance by mesopores. This strategy is promising to convert kelp into efficient adsorbents for dyes removal and also cost-effective process for environmental protection on an industrial scale.