Low-Cost Synthesis of Bimodal Mesoporous Silica-Based Materials by Pseudomorphic Transformation

Preparation of stable tetraethylenepentamine-modified ordered mesoporous silica sorbents by recycling natural Equisetum ramosissimum

It is well-known that global warming of the earth is caused by the progressive increase of CO₂ concentration in the environment due to the huge utilization of fossil fuels. As a result, the development of an efficient and economic method to capture CO₂ from large stationary sources, such as coal-fired power plants, cement and steel factories, and so on is urgent. In this study, ordered mesoporous silicas (E-SBA-15) have been prepared by using Equisetum ramosissimum plants as the silica sources and their subsequently incorporating with amino-containing compounds (tetraethylenepentamine, TEPA) and stabilizers (titanium isopropoxide, TIP). A variety of different spectroscopic and analytical techniques, such as nitrogen adsorption-desorption isotherms, low-angle X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transformed infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) are used to characterize the physicochemical properties of various materials. CO₂ adsorption capacities of prepared sorbents at 75 °C are obtained by TGA at atmospheric pressure. Among all sorbents, TEPA impregnated E-SBA-15 sorbents possess the highest CO₂ sorption capacity (1.60 mmol CO₂ g^-1_sorbent) under ambient pressure using dry 15% CO₂. However, TEPA/TIP incorporated E-SBA-15 sorbents exhibit enhanced durability during repeated sorption-desorption cycles compared to the above-mentioned sorbents. This significant enhancement in the stability of CO₂ sorption-desorption process is most likely due to the decreased decomposition/leaching of TEPA which is restricted via the steric effect of TIP. These synthesized sorbents from inexpensive resources (agricultural waste) exhibit good sorbent capacity and surpassing regenerability, revealing a promising CO₂ sorbent for the cost-effective applications in a cyclic adsorption process.