Influence of surfactant on CO2 capture using mesoporous MgO

https://doi.org/10.3390/catal7040116

“With the introduction of surfactants as templates, the synthesized MgO nanomaterials exhibited a specific morphology and a high specific surface area. In order to evaluate the effect of the surfactant types, different MgO samples were synthesized using a variety of surfactants, including poly (ethylene glycol)-poly (propylene glycol)-poly(ethylene glycol) triblock copolymer (P-123), polyvinylpyrrolidone (PVP), cetyl trimethyl ammonium bromide (CTAB), and sodium dodecyl sulfate (SDS). Meanwhile, the CO₂ adsorption capacity of non-assisted MgO, MgO attained through thermal decomposition of commercial Mg(OH)₂ (coded as MgO-TD) as well as light MgO were studied simultaneously and compared as the control. Table 1 summarizes the synthetic conditions, texture parameters, and CO₂ adsorption capacities of different types of surfactant-assisted MgO. The adoption of a hydrothermal synthesis method with the introduction of various surfactants led to a marked enhancement in the CO₂ uptake of the MgO materials. Except for the sample of light MgO, all other freshly prepared MgO compounds showed a much higher BET specific surface area (>194.3 m² g⁻¹) and a larger pore volume (>0.30 cm⁻³ g⁻¹). The addition of surfactants gave rise to a significant increase in specific surface area from 194.3 to 341.4 m² g⁻¹ and pore volume from 0.30 to 0.49 cm⁻³ g⁻¹, respectively. Figure 1a shows the uptake of CO₂ by non-assisted MgO, MgO-TD, light MgO and MgO particles assisted with various surfactants when exposed at 300 °C to pure CO₂. Typically, the light-MgO was first calcined at 450 °C for 60 min under a flow of high purity N₂ (20 mL min^‒1) to avoid intrinsic adsorption of CO₂ on the surface of light-MgO. It is clear that SDS-assisted MgO exhibited the highest CO₂ uptake of 0.92 mmol g⁻¹, which is much higher than that of light MgO (0.05 mmol g⁻¹). For the SDS-added sample, although its CO₂ adsorption capacity per unit surface area (0.0028 mmol m⁻²) was lower than that for the surfactant-free sample (0.0044 mmol m⁻²), its specific surface area was higher, thus resulting in a much higher total CO₂ capture capacity. For the practical application, the total CO₂ capture capacity is more important. Besides, the MgO-TD with the highest specific surface area of 363.40 m² g⁻¹ yet displayed inferior CO₂ uptake of 0.29 mmol g⁻¹. The intrinsic reason for such phenomenon is still unclear to us. Although, the specific surface area and pore size are believed to be two of the parameters that influence the CO₂ capture capacity, some other parameters including chemical impurity, surface defects, etc. may have quite an influence [40].”

“Figure 1. (a) The influence of different types of surfactants on the CO₂ capture capacity; (b) XRD spectra of MgO compounds with different types of surfactants.”