Fabrication of N, O dual-doped ultra-microporous carbon from microalgae for efficient CO2 capture via deep eutectic solvent-assisted hydrothermal carbonization

Abstract

A novel approach for porous carbon fabrication from microalgae is presented for efficient CO2 capture. Microalgae-derived hydrochar is produced through deep eutectic solvent-assisted hydrothermal carbonization (DES-HTC), followed by chemical activation to obtain N, O dual-doped ultra-microporous carbon. The finalized carbon exhibited high nitrogen content (3.92%), oxygen content (21.46%), and ultra-micropore volume (0.25 cm3/g). Subsequently, it exhibited excellent CO2 adsorption capacity (4.37 mmol/g) and CO2/N2 selectivity (32) at 25 °C and 1 bar. Equilibrium and in-situ FTIR spectra of CO2 adsorption substantiated that the synergy between the abundant oxygen and nitrogen functional groups and the ample ultra-micropores significantly enhanced the capacity. Characterization of hydrochar indicated that the addition of DES during HTC effectively accelerated the Maillard reaction, facilitating the insertion of nitrogen and oxygen atoms into the carbon matrix and reducing their loss in subsequent chemical activation. Furthermore, DES was found to increase thermally unstable oxygen functional groups during HTC, promoting in ultra-micropore formation during activation. These findings provide a framework for advancing microalgae-based carbon materials in CO2 capture applications.