Victorian brown coal (VBC) is an abundant and cheap precursor to carbon materials. Its important properties include an abundance of acidic functional groups, large inherent porosity, a colloidal gel-like nature consisting of macromolecules suspended in an aqueous solution (typically > 60 wt% water) and exceptionally low inorganic content. Prior work on the preparation of carbons (chars) from VBC, have often led to ultramicroporous products, as evidenced by low BET surface areas (< 15 m²g^-1) from N₂ adsorption-desorption, yet simultaneously high DR surface areas (~ 800 m² g^-1) measured by CO₂ adsorption.We have sought to more carefully control the textural characteristics, surface composition and extent of graphitisation, of carbons prepared from VBC. These morphological/ chemical characteristics are important since they influence the wettability, electrical conductivity, adsorptive properties, and other physical/ chemical properties that are important for its utilisation in various applications, e.g., adsorption, supercapacitors, catalyst supports. In this work we have employed a variety of techniques, including freeze-drying, salt-templating (with various salts), templating with waste materials (e.g., waste tyre). These methods have previously not been explored to prepare carbons from VBC. The char prepared from freeze-dried VBC had a far higher BET surface area of >1000 m²g^-1 and contained micro- and mesopores detectable by N₂ adsorption-desorption. We found that the creation of a hierarchical pore structure could be facilitated by a combination of (1) ice-templating, (2) salt-templating, and (3) chemical activation by the salt templates. In particular, when ZnCl₂was applied in our synthesis method, the carbon had a mesopore volume of ~1 cm³ g^-1and a BET surface area of ~1870 m² g^-1, considerably higher than reported from other lignite-derived carbons. These carbons can also be produced in ‘honeycomb monolithic’ form, following a patented method developed in our group. Using VBC as the binder, we have converted mixtures of waste tyre and VBC into hierarchical structured micro-mesoporous monolithic carbons.

Daniel Italia-Prasad

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