Fabrication and CO2 adsorption performance of bimodal porous silica hollow spheres with amine-modified surfaces

Abstract

Carbon dioxide capture and storage (CCS) solutions have received enormous attention because CO₂ is a primary greenhouse gas and plays a key role in global warming and climate change. In this work, bimodal meso-/macroporous SiO₂ hollow sphere (BMSHS) samples with high specific surface areas were prepared by a hydrothermal method. Cetyltrimethylammonium bromide (CTAB) and perfluorododecanoic acid (PFDOA) were used as cotemplates and the CTAB/PFDOA weight ratio (R) was varied. The prepared samples were further modified with tetraethylenepentamine (TEPA), and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), and N₂ physisorption techniques. This was followed by CO₂ capture tests using a pure CO₂ stream in the temperature range of 35–130 °C. The results showed that all of the prepared samples contained small mesopores with a peak pore size of ca. 3–4 nm and larger mesopores or macropores with a peak pore diameter of ca. 103 to 117 nm. The mesopores and macropores are from the shell and the cavity of hollow spheres, respectively. The R exhibited a significant influence on the specific surface area, as the specific surface areas increased with increasing R. All of the TEPA-modified samples exhibited good CO₂ adsorption abilities, which were related to the amount of loaded TEPA, adsorption temperature, and the specific surface areas of the samples. A optimal amount of TEPA loading (about 50 wt%) and adsorption temperature (about 110 °C) were determined. The CO₂ adsorption amount increased proportionally with the specific surface area. The maximum CO₂ adsorption amount (4.41 mmol g⁻¹ adsorbent) was achieved on the BMSHS sample prepared at R = 40 and TEPA loading of 50 wt%. The present study provides new insight into the design and synthesis of novel porous materials for CO₂ capture.