(215y) Hydrothermal Pre-Treatment for Mesoporous Carbon Synthesis: Enhancement of Chemical Activation

A hydrothermal pre-treatment process is used to enhance activation of biomass during the production of mesoporous activated carbon. ZnCl₂ as the activating agent was incorporated into the biomass (coconut shells) during a hydrothermal pre-treatment step.  The pre-treatment was followed by pyrolysis accompanied by physical activation. The resultant mesoporous activated carbons possessed higher total surface area and a greater degree of mesoporosity compared to the biomass that was pyrolysed without hydrothermal treatment.  The cause of higher mesoporosity is inferred to be the more conducive environment for accessibility of ZnCl₂ to the biomass provided by the hydrothermal treatment due to reduced diffusion resistance.  In addition, the hydrothermal environment facilitated generation of oxygen-containing functional groups that contributed to enhanced activity of ZnCl₂.  Up to 67% increase in the mesoporous surface area has been achieved with the inclusion of the pre-treatment step.  Analogously, the amount of ZnCl₂ required to deliver the same performance in the absence of the pretreatment step is an additional 50%. The effect of hydrothermal treatment with and without ZnCl₂ along with sequence of ZnCl₂ addition has been investigated in order to differentiate between the hydrothermal effect and incorporation of ZnCl₂ during hydrothermal treatment. The mesoporous activated carbons were tested for adsorption of textile dyes and possessed high adsorption capacities of up to 526 mg/g and 630 mg/g for methylene blue and erythrosine red, respectively.   The incorporation of the hydrothermal pre-treatment is an important step in developing processes that make efficient and effective use of activating agents.