Novel nanostructured carbons derived from epoxy resin and their adsorption characteristics for CO2 capture

Abstract

In this work, a nanocasting technique has been used to synthesize oxygen enriched carbon adsorbents with epoxy resin as the precursor and mesoporous zeolite as a template. Carbonization and physical activation with CO₂ was carried out to prepare different carbon adsorbents. Characterization of the synthesized adsorbents was done using N₂ sorption, XRD, SEM, TEM, TGA, FTIR spectroscopy, CHN analysis, and XPS. The surface area and pore volume of the synthesized adsorbent prepared at 600 °C were found to be a maximum of 686.37 m² g⁻¹ and 0.60 cm³ g⁻¹, respectively, but showed a lower adsorption capacity due to lesser oxygen content as compared to the sample prepared at 700 °C. The sample prepared at 700 °C exhibited the highest CO₂ uptake, approximately 0.65 mmol g⁻¹, at 30 °C due to the high oxygen content, which was estimated to be about 53.98% determined using CHN analysis and also due to high surface basicity confirmed by XPS. The sample prepared by direct carbonization of the polymeric precursor shows a completely non-porous and highly acidic material having the least adsorption capacity. It was found that an increase in concentration of CO₂ increases adsorption capacity and an increase in adsorption temperature decreases adsorption capacity. CO₂ adsorption kinetics were performed by using three kinetic models and from the correlation coefficient, adsorption kinetics were found to obey fractional order with error% within the range of 4.24%. For checking the regenerability, four adsorption–desorption cycles were examined. It was found that the adsorbents exhibit easy regenerability, stable adsorption capacity and good selectivity for CO₂–N₂ separation. The experimental data are well fitted with the Freundlich isotherm, showing a heterogeneous adsorbent surface. The isosteric heat Q_st of CO₂ is 9.09 kJ mol⁻¹, which indicates the presence of the physisorption process. The negative value of Gibbs free energy suggests the spontaneous nature of the process. The values of ΔH° and ΔS° were found to be −2.562 kJ mol⁻¹ and 0.033 kJ mol⁻¹ K⁻¹, respectively. The negative value of ΔH° suggests the exothermic nature of the adsorption process.