Direct air capture of CO2 using bi-amines-functionlized hierarchical mesoporous silica: Effects of organic amine loading, moisture and temperature

With the rapid increase of carbon dioxide (CO2) in the atmosphere, it has become urgent to reduce CO2 emissions. It is imperative to develop low-cost and high-efficiency CO2 direct air capture adsorbents. In this research, hierarchical mesoporous silica (HMS) was easily synthesized through a partitioned synergistic self-assembly method, and amine bi-functionalized HMS adsorbents were prepared using 3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane (DT) and tetraethylenepentamine (TEPA) employing various techniques. A high specific surface area (570 m(2)/g) and large pore volume (2.29 cm(3)/g) were obtained for the HMS with two types of pores (6.32 nm and 17.38 nm). The structural composition of amine-functionalized solid adsorbent affected the adsorption-desorption performance of CO2. Multi-stage pore structure with three-dimensional connection can effectively enhance the adsorption-desorption performance of adsorbent. The stable adsorption performance, the effects of organic amine loading, adsorption mechanism, relative humidity and adsorption temperature on the CO2 adsorption properties of D-HMS-T-50 were examined. The CO2 adsorption capacity of D-HMS-T-50 reached 4.99 mmol/g at 338 K, 1 bar and 30 % relative humidity. Additionally, a lower heat consumption of desorption (79.92 KJ/mol) is needed for D-HMS-T-50. The results proved that D-HMS-T-50 with high adsorption capacity and low regeneration energy can be provided as a solid amine adsorbent for direct air capture of CO2.