Effect of Surfactant on CO2 Adsorption of APS-Grafted Silica Gel by One-Pot Process

Abstract

(3-Aminopropyl)trimethoxysilane (APS)-silica gels were prepared by a one-pot process using sodium silicate as a low-cost source of silica. XRD and SEM analyses revealed that the APS-silica gels were particles with diameters of around 100-200 nm. Furthermore, the introduction of amine groups was confirmed by FT-IR spectroscopy and CO2 uptake measurements. The adsorption properties of the gels were improved by addition of the surfactants hexadecyltrimethylammonium bromide (CTAB), Pluronic F127, and Pluronic P123, which acted as pore forming agents. Using Brunauer Emmett Teller (BET) analyses, we confirmed that both the surface area and pore volume were improved on addition of these surfactants. The larger surface area resulted in a greater number of amine groups being exposed on the outer surface of the APS-silica gels; therefore, CO2 uptake increased as the amount of surfactant used was increased. The APS-silica gels with F127 and P123 had pores from the porous particles with 5-11 nm diameters and gaps between particles, while the APS-silica gel with CTAB only had smaller pores from gaps between silica particles. These pore distribution differences resulted from the differences in the lengths of the surfactant hydrophobic chains, and the differences in pore sizes affected the CO2 uptake rates of the APS-silica gels. By comparison of the pore and CO2 uptake properties, we confirmed that P123 was a suitable surfactant for the preparation of APS-silica gel by a one-pot process using sodium silicate as the silica source.