(259e) Nitrogen-Functionalized Graphene Oxide By Supercritical Ammonia for Carbon Dioxide Adsorption

Nitrogen-functionalized graphene oxide (N-FGO) was developed by reacting graphene oxide (GO) with supercritical ammonia (scNH₃). Functionalization was done by combining as-prepared GO with NH₃aq (28%) in an Inconel batch reactor for 1 hour by subjecting it to supercritical conditions with reaction temperature of 250⁰C and operating pressure of 30mPa. At this condition, H₂O content of the NH₃aq, will still be in subcritical condition. To investigate the effect of H₂O content two methods were used. Assessment were based on the nitrogen content for each method after functionalization. In the first method, the system was in water-rich phase (denoted by N-FGO-1), GO was directly combined with NH₃aq, enabling H₂O to react with GO during functionalization. On the other hand, the second method was in ammonia-rich phase (denoted by N-FGO-2), where GO was placed in a holder to limit the reaction with H₂O. The successful functionalization was proven by characterizing GO properties before and after functionalization using Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), X-ray diffraction spectroscopy (XRD). Higher N content was achieved in N-FGO-2, however, both method were effective in the functionalization. Reaction mechanisms that describes the functionalization process were proposed based from characterization results. In this study, it was assumed that only replacement of terminal carbon occurred during the functionalization process which was due to the nucleophilic substitution reaction aided by the supercritical conditions. At supercritical condition, NH₃ forms radicals, such as -NH₂, -NH and â??N. These radicals may react with C atoms forming new functionalities such as pyrrolic N, amino N (amine, imides and amides), and pyridinic N. Functionalization with carboxylic group involves subsequent reactions with scNH₃, dehydration and decarboxylation process. Reactions with epoxy group involves ring opening and hydroxyl group undergo dehydration forming aromatic amine.

Furthermore, carbon dioxide (CO₂) adsorptive properties were evaluated using thermal gravimetric (TG) apparatus. From results, N-FGO-2 resulted to the highest CO₂ adsorption capacity around 0.5 mmol CO₂/g adsorbent. While, N-FGO-1 can adsorbed around 0.45 mmol CO₂/g adsorbent and GO can adsorbed around 0.3 mmol CO₂/g adsorbent. Results indicate that the higher the N content of the adsorbent the higher the adsorptive capacity.

The study has presented promising results which can make notable contributions in the fields of carbon and graphene chemistry. The proposed novel process of graphene oxide functionalization with N groups can be applied to various types of materials and other carbon-based materials which in turn can be potentially useful for relevant applications such as electronics, energy conversion, storage devices, catalytic support and carbon capture.