Carbon-rich colloids are of great fundamental and technological interest and in this thesis, I tested a range of hypotheses and studied aspects of small hydrochar-based colloids and their colloidal and material chemistry. Crude hydrochar dispersions were synthesized by hydrothermal carbonization of glucose and purified by dialysis. After the purification, stable and monodisperse dispersions of colloidal hydrochar particles in water were obtained. Evaporation of water from the colloidal hydrochar dispersion led to that the hydrochar particles deposited into repeated strip patterns on glass substrates, or underwent directed assembly into macroscopic rods or yarn-shaped objects at the glass-water-air interface.

In one study, we studied the strip patterns that comprised dense assemblies of hydrochar particles formed through directed assembly on the substrates during evaporation of water as a function of the sodium dodecylsulfate (SDS) addition, pH of the dispersion, geometry of the substrates, and concentration of the colloidal particle. The mechanisms were presented. In the published paper included in the thesis, the formation of the macroscopically large and assembled rods was studied during evaporation of water from the colloidal hydrochar dispersions. This assembly was studied along with the electrostatic stability of the dispersions at various pH and ion strengths and the redispersability of the assembled rods into the constituting colloidal particles. For matters of applications of the rod assemblies, pyrolysis and templating silicon carbide -tricopper silicide ((SiC-Cu₃Si) by reactive infiltration with a copper silicon alloy by reaction infiltration were introduced.

In two manuscripts, aspects of the dispersions of hydrochar particles were studied with means of KHCO₃ activation into activated carbons (ACs). In one study, hydrochar particles were activated, and then the ACs were dispersed in a solvent after physical grinding. The morphology, porosity, and CO₂ sorption properties, etc. of the activated carbons prepared by chemical activation were studied for freeze-dried hydrochar particles and the long bent yarn assemblies pretreated under different conditions. ACs of electrospun nanofibers of polyvinylpyrrolidone (PVP) and colloidal hydrochar were oxidized and chemically activated with KHCO₃ or K₂CO₃ and studied for the adsorption of CO₂.