The samples CDC-50 and CDC-80 (Figure 1b,c) show similar microscopic morphology to the pristine CDC, suggesting the microporous nature of all the three samples. These results coincide with the pore size data shown
in Table 1. Figure 1 TEM images of CDCs: (a) CDC, (b) CDC-50, and (c) CDC-80, and (d) micropore size distribution of CDCs. CO2 capture performances of the CDCs According to classical gas adsorption theories, gas adsorption on porous carbons usually relies on the highly developed microporous structure and large specific surface area. Recent studies also demonstrated that micropores (<1 nm) are beneficial to CO2 adsorption for porous materials [18, 35–38]. In this work, CDC-50 shows lower specific area and micropore volume (Table 1
and selleck screening library Figure 1d) than the pristine CDC and CDC-50-HR. However, as shown in Figure 2a, CDC-50 (3.87 mmol g−1 under 1 atm) possesses an apparently higher CO2 uptake than the pristine CDC (3.66 mmol g−1 under 1 atm) and CDC-50-HR (2.63 mmol g−1 under 1 atm). Likewise, CDC-80 has a lower specific surface area PD0332991 order and the same micropore volume than/as its reduced product CDC-80-HR. However, the former (2.71 mmol g−1 under 1 atm) possesses an obviously higher CO2 uptake than the latter (1.63 mmol g−1 under 1 atm). As for CDCs, their CO2 uptakes do not have a linear correlation with their micropore volume, as is shown in Figure 2b inset. So, the CO2 adsorption results for the CDCs cannot be explained by classical adsorption theories. Nevertheless, it is very instructive to find that the
CO2 uptakes per unit surface area of the carbons are positively related to the oxygen content of the carbons (Figure 2b), indicating that the CO2 adsorption capacity of the carbons was greatly facilitated by the introduction of oxygen-containing groups to the carbon. This result agrees well with the work of Liu . Figure 2 CO 2 adsorption isotherms for the CDCs (a) and a plot of CO 2 uptake vs. oxygen content (b). The inset is a plot of CO2 uptake vs. micropore volume. In order to check details reveal the effect of oxygen-containing groups on CO2 adsorption for the carbons, a theoretical carbon surface model (OCSM) containing six different typical O-containing functional groups was developed in light of Niwa’s model . A pure carbon model without oxygen atoms 4��8C (CSM) was also devised for comparison, as is shown in Figure 3. Density functional theory B3LYP was employed to study the interactions between these models and CO2, and all the configurations were optimized with the 6-31 + G* basis set for all atoms using the Gaussian-03 suite package . Figure 3 Theoretical carbon models and hydrogen bond energies. Theoretical models for (a) oxygen-containing carbon surface and (b) pure carbon surface (red ball: oxygen atom; grey ball: carbon atom; small grey ball: hydrogen atom). (c) Hydrogen bond energies at different adsorption sites.