Rapid synthesis of MCM-41 and SBA-15 by microwave irradiation: promising adsorbents for CO2 adsorption

Abstract

It is known that the world scenario is one of constant search for sustainable technologies that can reduce the emission of carbon dioxide (CO2) in the atmosphere. This is because CO2 is seen as the main responsible for the increase in the generation of greenhouse gases, which leads to global warming and climate change. The development of efficient adsorbents for CO2 capture is a current challenge. MCM-41 and SBA-15 were synthesized in a microwave reactor and used as adsorbents in this work. Microwave irradiation presents itself as an easy synthesis strategy with less preparation time and energy requirement. The silica synthesis period was extremely reduced (1 h) at a temperature of 60 and 80 °C in the microwave reactor, obtaining silica with good textural and chemical properties. The CO2 adsorption isotherms were performed at 0, 25, and 40 °C at 1 bar. The MCM-41 and SBA-15 present favorable results for CO2 capture processes, showing that pure silica synthesized by microwave already obtains promising results, reaching a maximum adsorption capacity of 2.16 mmol g−1 (1 bar—0 °C) and a good fit for the Langmuir, DsL and Toth models. Furthermore, to increase CO2 adsorption, the mesoporous silica was also modified via impregnation with branched polyethylene diamine (PEI) or tetraethylenepentamine (TEPA). It is worth mentioning that microwave irradiation reduced the synthesis steps and improved the properties and adsorption capacity of the silica. This work opens new opportunities in the efficient preparation of materials that require optimizing the adsorbent synthesis process. Graphical Abstract

Surface Heterogeneity Affects Adsorption Selectivity for CO2 Over CH4 in Bare Mesostructured Silica with 2D Hexagonal Symmetry and Different Pore Size

“…A linear trend was observed for the adsorbed amount vs. pressure (Figure 4a), which is in agreement with the literature at pressure larger or equal than 1 atm, [56][57][58] while marked curvature is observed at lower pressure, but especially at a lower temperature. [58,59] The obtained absorbed amounts are in good agreement with other reports, as summarized in Table 2.…”

Accelerating MCM-41 One-Pot Synthesis Through Microwave Irradiation

“…2 that the silicas exhibited a type IV(a) isotherm, sorption behavior typic of MCM-41 mesoporous materials, where the adsorption and desorption branches do not cross, which presents hysteresis of the H4 type. The presence of hysteresis H4 in the desorption branch suggests that mesopores are present, showing a sharp in ection at a relative pressure P/P0 of 0.5-0.9 [12,13] . The pore size distribution by BJH presents similar results between the two silicas, where a narrower pore distribution can be observed.…”

“…Both studies aimed to produce MCM-41, and showed similar surface areas, however demanding longer time for synthesis and removal of the surfactant. [13] It is worth mentioning that it would be possible to obtain even better textural and structural properties, since this decrease in surface area is related to the amount of surfactant still present on the silica surface, causing a blockage in the pores. This pore blockage can be associated with a decrease in micropore volume (V mp ) from 0.59 to 0.15 cm 3 g − 1 when comparing the removal of CTAB by calcination in a mu e furnace (MCM-41-M60-1) with the removal by microwave irradiation (MCM-41-OP-0.5), suggesting the presence of the surfactant in the silica micropores.…”

“…This statement is con rmed by the CHN elemental analysis, as the values obtained (14.1% and 15.2% -Table 1) show that the percentage of carbon is still expressive, which is not normal for pure silica. A pure silica MCM-41 synthesized in a microwave reactor at 60 ºC for 1h and calcined in a mu e at 550 ºC − 6h (MCM-41-M60-1) presents an average percentage of carbon of 0.22% [13] . This shows that CTAB is still present on the surface of the silica synthesized in this work.…”

Synthesis of Monodispersed Hollow Mesoporous Organosilica and Silica Nanoparticles with Controllable Shell Thickness Using Soft and Hard Templates

“…Mesoporous materials have garnered significant interest for various applications, such as catalyst support, , adsorbents, , optical materials, − and drug-delivery carriers , because of their unique properties, such as high surface areas, large pore volumes, high biocompatibility, and high biodegradability. − Hollow mesoporous organosilica (HMOS) nanoparticles are a class of mesoporous materials with organic groups between inorganic silica frameworks in the mesoporous shell and large internal cavities. , When HMOS is used as a drug-delivery carrier, large amounts of drug molecules can be incorporated into its cavity. − Therefore, considerable research has focused on various applications of HMOS.…”