Carbon spheres synthesized from KHCO3 activation of glucose derived hydrochar with excellent CO2 capture capabilities at both low and high pressures

In the current work, we reported a facile synthesis method for carbon spheres utilizing KHCO3 activation. Glucose was hydrothermally reacted at 200 °C to produce spherical hydrochar at high yield, and cetyltrimethylammonium bromide (CTAB) was added to mediate the morphology. The hydrochar was then activated with KHCO3 in the presence of urea. The obtained carbon spheres exhibited ultrahigh specific surface area of 3576 m2/g. It was also found that urea effectively promoted pore formation during activation. Superior CO2 capture performances were achieved at both 1 and 20 bar. At 25 °C and 1 bar, the carbon spheres showed high CO2 uptake of 4.26 mmol/g. While at 20 bar, impressively high uptakes of 35.57 mmol/g (0 °C) and 23.04 mmol/g (25 °C) were achieved, which were the highest among the reported results for porous carbons at 20 bar. At 1 bar, ultramicropore (<0.7 nm) was the most important factor in deciding CO2 uptake, while nitrogen doping significantly enhanced adsorption heat and selectivity. At 20 bar, the uptake showed clear dependence on surface area. The carbon spheres in our work showed great potential in pre-combustion CO2 capture.