Evaluation of porous clay heterostructures modified with amine species as adsorbent for the CO2 capture

- Porous clay heterostructure were used as adsorbent for CO2 capture.
- Porous clay heterostructure displayed higher CO2 capture values than raw bentonite.
- CO2 adsorption capacity was increased by the incorporation of amine species.
- Dual-Site Langmuir model revealed physical and chemical adsorption sites.
- The addition of tetraethylenepentamine led to the highest CO2 adsorption at 1 bar.

Porous clay heterostructures (PCH) have been synthesized from raw bentonite, obtaining porous materials with high surface area and micro-, meso- and macroporosity. Both raw bentonite and PCH have been evaluated in CO2 adsorption processes at 1 bar and 25 °C. In both cases, adsorption isotherms were well fitted using the Langmuir model, obtaining an increase of the CO2 adsorption from 0.112 mmol CO2 g−1 for the raw bentonite to 0.640 mmol CO2 g−1 in the PCH. In order to improve the CO2 adsorption capacity, raw bentonite and PCH were functionalized with amine species, via grafting using 3-aminopropyltriethoxysilane (APTES) and via impregnation with polyethylenimine (PEI) or tetraethylenepentamine (TEPA). The isotherms of the amine-functionalized samples were adjusted to the Dual-Langmuir model, which assumes the coexistence of physical and chemical adsorption sites. From the profiles of the CO2 isotherms, it can been observed that grafted-PCH with APTES shows the coexistence of physical and chemical interactions, reaching 1.023 mmol CO2 g−1. The adsorption of CO2 on PCH impregnated with TEPA and mainly with PEI is governed by chemical interactions between the amine species located in the porous structure and/or on the surface of the adsorbent and the CO2 molecules, attaining maximum values of 1.644 and 1.465 mmol CO2 g−1 for TEPA and PEI, respectively.

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