2022 Volume 1 Issue 4 Pages 206-213
A suspension of microalgae (Spirulina or Chlorella) biomass powder, a terephthalaldehyde condensation accelerator, and Mg pre-templates (MgCl2, Mg(OAc)2, Mg(OH)2, or mixtures with MgO) in water was hydrothermally reacted at 220 °C for 14 h in an autoclave. The MgCl2 additive changed the reaction solution pH to acidic, reducing the yield of the insoluble hydrothermal product. In contrast, Mg(OAc)2, Mg(OH)2, and the MgO mixture retained the pH of the solution as neutral to weakly alkaline, producing a large amount of non-porous hydrothermal carbon. After or before removal of the Mg template by acid washing, the particulate hydrothermal carbons were carbonized by heating from room temperature around 25 °C to 900 °C under an Ar atmosphere. The resulting Mg-free algal carbonized materials were N-containing porous carbons with specific surface areas ranging from 200–1500 m2/g, mesopore/total pore volume ratios ranging from 0.6 to 0.9, and electrochemical capacitances in the range of 150–320 F/g at 0.1 A/g in 1M H2SO4.
