https://doi.org/10.3390/catal7040116
“Materials
Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, 99%), urea (CO(NH2)2, 99%), and sodium dodecyl sulfate (SDS) were purchased from Sinopharm Chemical Reagent Co Ltd (Shanghai, China). All chemicals were used as received without further purification. Deionized water was utilized in all the experimental processes.
Sample Preparation
Samples of SDS-assisted porous MgO were prepared by urea hydrolysis assisted precipitation of magnesium hydroxide from magnesium nitrate aqueous solution followed by thermal decomposition of the precipitated magnesium hydroxide. Typically, 3 g of urea (0.05 mol CO(NH2)2) and appropriate amounts of magnesium nitrate hexahydrate (2.56 g of Mg(NO3)2·6H2O for maintaining urea:Mg mole ratio of 5) were mixed in 50 mL of water with the addition of certain amounts of sodium dodecyl sulfate (0.1 g SDS) and stirred vigorously in a Teflon lined stainless steel autoclave at room temperature. The autoclave was then treated hydrothermally in a preheated oven at 120 °C for 12 h. The resulting precipitates were separated by filtration and repeatedly washed with DI water several times and dried at 70 °C overnight in the oven. Dried powders were next ground in a crucible, and calcined at 400 °C for 5 h in air. In all cases, the temperature of the furnace was increased at a very slow rate of 1 °C·min−1 until the desired temperatures were attained.”

“Figure 6. (a) Nitrogen adsorption-desorption isotherms and (b) pore size distributions of SDS-assisted MgO samples generated hydrothermally and calcined at 400 °C for 5 h.”
“The specific surface area of the SDS-assisted MgO was calculated using the Brunauer-Emmett-Teller (BET) method and the pore volume distribution was calculated by the Barrett-Joyner-Halenda (BJH) method. Figure 6a illustrates the N2 adsorption isotherms of the SDS-assisted samples. The isotherms were classified as type IV with a sharp H3 hysteresis loop, which reveals the existence of slit-type interparticle mesopores in the as-synthesized samples. This type of hysteresis loop is usually spotted on solids comprised of aggregates or agglomerates of particles forming slit shaped pores with a non-uniform size and/or shape [43]. The SDS-assisted MgO sample possesses a high specific surface area of 321.3 m2 g‒1, a high pore volume of 0.30 cm3 g−1, and a narrow micropore size distribution, with the majority centered at 1.88 nm (Figure 6b). It is obvious that the template SDS contributes tremendously to the fabrication of the porous structure in leaf-like MgO.”
“The morphological changes of SDS-assisted MgO materials during the thermal treatment were also examined using SEM analyses. Figure 7a,b indicates that a well-organized lamellate structure of the precursors crystallites is noticeable. The disordered thin-layer morphology of SDS-assisted MgO nanosheet is highly likely correlated with the considerable disorganization caused by the removal of interlayer water molecules after the calcination process, as shown in Figure 7c,d. Besides, well-developed hexagonal prisms crystallites of MgO-TD (Figure 7e,f) are observed, which provides a good explanation in the great variations of CO2 uptake between the SDS-assisted MgO nanosheet and the MgO-TD due to the significant differences in their morphology.”

“Figure 7. SEM images of (a,b) precursors; (c,d) MgO nanosheets after calcination at 400 °C for 5 h; (e,f) MgO-TC of different magnifications, respectively.”