Microwave-assisted catalytic hydrothermal carbonization of Laminaria japonica for hydrochars catalyzed and activated by potassium compounds

There are limited investigations describing preparation and application of alga-based hydrochars via microwave–assisted catalytic hydrothermal carbonization (MA-CHTC). Therefore, hydrochars were successfully prepared from macroalgae biomass Laminaria japonica impregnated with KH₂PO₄, KCl, K₂CO₃, and KOH as acidic, neutral salt, and alkaline catalysts, respectively, via the MA-CHTC. Comprehensive characterization of physicochemical properties of the hydrochars, including yields, elemental and phase composition, specific surface areas, functional groups, and morphology, confirmed different catalytic effects of these catalysts on hydrochar formation. Adsorption kinetics and isotherms of Pb(II) revealed significant improvement of adsorption capacities for Pb(II) due to synergetic chemical activation of the spiked catalysts. Therefore, the synergetic catalytic effects and chemical activation is benefic for tailored design of engineered hydrochars with different properties for special application through selection of catalysts during the MA-CHTC process.