Covalent grafting of aminated compounds on Vulcan XC72R by melamine in situ diazotization

The immobilization of 2,4-diamino-1,3,5-triazine on carbon Vulcan XC72R surface was achieved through the in situ diazotization of melamine. The resulting grafted species represent 2.3 wt.% of the modified material and are thermally stable up to 265 °C. Nitrogen adsorption isotherms show that the carbon microporosity decreased after modification translating in a 25% decrease of the BET surface area. X-ray photoelectron spectroscopy data suggest the presence of 2,4-diamino-1,3,5-triazine groups at the surface by bonding through a carbon–carbon bond and/or by an azo bridge. These materials were evaluated as CO2 sorbents by thermal swing adsorption in a thermogravimetric analyzer. At 40 °C, the modified powders displayed a maximal adsorption capacity of 0.23 mmol/g that is smaller than the initial unmodified material. Nonetheless adsorption capacity of the grafting groups helps to improve the selectivity of the materials although physisorption seems to be the main mechanism for CO2 capture.