Tailored Carbon Nanocomposites for Efficient CO2 Capture

Abstract

CO₂ capture by adsorption on proper solid materials appears to be a promising approach, due to its low energy requirements and ease of implementation. This study aimed to prepare efficient materials for CO₂ capture based on composites of nanocarbon and reduced graphene oxide, using graphite, L-ascorbic acid, and glycine as precursors. The materials were characterized by XRD, low-temperature N₂ adsorption, FTIR, Raman, and XPS spectroscopies, along with SEM and TEM. The CO₂ adsorption capacities, heats of adsorption, and selectivity were determined. A hierarchical porous structure was found for NC-LAA, NC/RGO-LAA, and NC/RGO-Gly. At 273 K and 100 kPa, the adsorption capacities for NC-LAA and NC-Gly reached 2.6 mmol/g and 2.5 mmol/g, respectively, while for the composites, the capacities were 1.7 mmol/g for NC/RGO-Gly and 3.5 mmol/g for NC/RGO-LAA. The adsorption ability of the glycine-derived materials is related to the presence of nitrogen-containing functional groups. The heats of adsorption for NC-LAA, NC-Gly, and NC/RGO-Gly reveal chemisorption with CO₂. Except for chemisorption, the NC/RGO-LAA material shows a sustained physical adsorption up to higher CO₂ coverage. The best adsorption of CO₂, observed for NC/RGO-LAA, is connected with the synergy between carbon dots and RGO. This composition ensures both sufficient oxygen surface functionalization and a proper hierarchical porous structure.

Keywords: CO2 adsorption; carbon dots; nanocarbon; nanocomposite; reduced graphene oxide.

Figure 1

PXRD patterns of NC-LAA, NC-Gly, NC/RGO-LAA, NC/RGO-Gly, and referent RGO.

Figure 2

Nitrogen adsorption–desorption isotherms (a,c) and pore size distribution (b,d) of NC-LAA (red), NC-Gly (blue), NC/RGO-LAA (magenta), and NC/RGO-Gly (olive). The insets in (b,d) present the micropore size distribution of the respective samples. The shaded part of the insets represents the pores below 0.8 nm.

Figure 3

SEM (SEI) images of NC-LAA (a), NC/RGO-LAA (b), NC-Gly (c), NC/RGO-Gly (d) and RGO (e).

Figure 4

Bright-field TEM micrographs of NC-LAA (a), NC/RGO-LAA (b), NC-Gly (c), NC/RGO-Gly (d), and RGO (e), and HRTEM image of NC/RGO-LAA (f).

Figure 5

FTIR (A) and Raman spectra (B) of (a) NC-Gly (blue), (b) NC-LAA (red), (c) NC/RGO-Gly (olive), (d) NC/RGO-LAA (magenta), and (e) bare RGO (dark yellow).

Figure 6

XPS C1s, O1s, and survey spectra of NC-LAA, NC/RGO-LAA, NC-Gly, and NC/RGO-Gly, and N1s spectra of NC-Gly and NC/RGO-Gly.

Figure 7

XPS C1s, O1s, and survey spectra of NC/RGO-LAA, NC/RGO-Gly, and RGO, and N1s of NC/RGO-Gly.

Figure 8

Adsorption isotherms of CO₂ at 273 K for NC-LAA (left, red), NC-Gly (left, blue), NC/RGO-LAA (right, magenta), NC/RGO-Gly (right, olive), and bare RGO (right, dark yellow).

Figure 9

Heats of CO₂ adsorption for NC-LAA (red), NC-Gly (blue), NC/RGO-LAA (magenta), and NC/RGO-Gly (olive).

Figure 10

Predictive CO₂/N₂ selectivity of NC/RGO-LAA at 273 K, depending on pressure.