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Effects of different structure-directing agents (SDA) in MCM-41 on the adsorption of CO<inf>2</inf>

Abstract:

CO2 capturing technologies have attracted significant attention in order to limit emissions and reduce their negative effect on the environment. Mesoporous silica materials (MCM-41) are easily recyclable, affordable, and thermally and mechanically stable, providing added benefits in CO2 capture. However, further studies are necessary to characterize the effects of MCM-41 pore size, adsorption temperature and surface silylation on CO2 adsorption efficiency. In this work, mesoporous silica is synthesized using alkyltrimethylammonium bromide with different chain lengths (CnH2n + 1 N(CH3)3Br, n = 14, 16 and 18) as structure-directing agents, and the adsorption capacity of CO2 on TTMCM-41 (C17H38NBr), CTMCM-41 (C19H42NBr), DTMCM-41(C21H46NBr) samples was measured gravimetrically at room temperature and pressure up to 40 bar. The silica structures were characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy (TEM). The XRD, N2 adsorption–desorption and TEM measurements indicated the presence of a well-ordered hexagonal array with uniform mesostructures. The mesoporous silica obtained, denoted as TTMCM-41, CTMCM-41 and DTMCM-41, had distinct physical properties, such as BET surface area, hexagonal unit cell, pore volume, pore diameter and pore wall thickness. CTMCM-41 exhibited an adsorption capacity (0.58 g CO2/g adsorbent) of more than DTMCM-41 (0.48 g CO2/g adsorbent) and TTMCM-41 (0.42 g CO2/g adsorbent). The results suggest that CTMCM-41 can be a better mesoporous adsorbent for CO2 adsorption.