Colloidally dispersible activated carbons and yarn-like colloidal assemblies of hydrochar

Abstract

It was hypothesized that activated carbons (ACs) prepared from hydrochar could be dispersed in solvents under certain conditions. The crude hydrochar formed by the hydrothermal carbonization (HTC) of glucose and was purified by dialysis. Dried dispersions of hydrochar were chemically activated with potassium bicarbonate (KHCO₃) at temperatures of 750–800 ​°C in N₂. The AC prepared from a freeze-dried dispersion of hydrochar could be dispersed in ethanol as 500 nm-sized colloids. It was noted that on regular drying of the hydrochar dispersions, macroscopically large, long, curved, and thin rods of hydrochar formed in the vials. The rods comprised colloidally-packed spherical particles. The rods may have formed from cracked and fractured colloidal coatings and detached from the wall of the vials. This conclusion was supported by analysing the structural features of the rods. The macroscopic shapes were retained on the chemical activation when the hydrochar precursor had been pyrolyzed in N₂ before activation. The ACs had specific surface areas of up to 1800 ​m²/g, and CO₂ uptake levels of up to 7.1 ​mmol/g at 0 ​°C and 101 ​kPa.