Improved CO2 Sorption in Freeze-Dried Amine Functionalized Mesoporous Silica Sorbent

Preparation of Nitrogen-Doped Cellulose-Based Porous Carbon and Its Carbon Dioxide Adsorption Properties

Nitrogen-doped cellulose-based porous carbon materials were obtained by hydrothermal method and KOH chemical activation together with melamine as a nitrogen-doping precursor. The effects of hydrothermal temperature on the microstructure and surface morphology of the products were mainly studied. Also, the carbon dioxide adsorption capacity of the prepared porous carbon was investigated. It was found that when the hydrothermal carbonization temperature was 270 °C and the mass ratio of cellulose and melamine was 1:1, the largest micropore specific surface area of 1703 m²·g^-1 and micropore volume of 0.65 cm³·g^-1 were obtained, with a nitrogen-doping composition of 1.68 atom %. At the temperature of 25 °C and under the pressure of 0.1, 0.2, 0.3, and 0.4 MPa, the adsorption amount of CO₂ was 1.56, 3.79, 5.42, and 7.34 mmol·g^-1, respectively. Also, the adsorption process of CO₂ was in good accordance with the Freundlich isotherm model.

Investigation of CO2 Adsorption on Triethylenetetramine Modified Adsorbents of TETA(n)/Zr-TSCD

In the present study, a new type of material of Zr-TSCD was first synthesized and modified with different amounts of triethylenetetramine (TETA). The properties of the adsorbents were characterised with X-ray diffraction, UV-vis diffuse reflectance spectroscopy, FT-IR spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, N2 adsorption–desorption, energy dispersion spectrum, and thermogravimetric analysis. The results suggested that Zr-TSCD (TSCD=Na3C6H5O7·2H2O) was successfully synthesized through the coordination of Zr atoms from ZrOCl2·8H2O and O species in –COO– groups. After functionalization with TETA, the structure of Zr-TSCD was preserved and the adsorption capacity of CO2 was enhanced dramatically. At 75°C, TETA(30)/Zr-TSCD achieved a maximum absorption capacity of 175.1mg g−1 in a stream of 10mL min−1 CO2. The adsorption capacity ratio of CO2/N2, CO2/O2, and CO2/SO2 was 10.5, 7.4, and 1.2, respectively. In addition, the adsorption capacity of CO2 remained stable during 10 adsorption–desorption cycles.

2D/3D Assemblies of Amine-Functionalized Graphene Silica (Templated) Aerogel for Enhanced CO2 Sorption

This work investigates the one-pot facile synthesis of novel 2D/3D assemblies containing graphene silica (templated) aerogel sorbents for CO₂ capture, a greenhouse gas of major global concern. In this synthesis, 3D silica (templated) aerogels were formed along the planes of 2D graphene sheets, resulting in 2D/3D assemblies of flake-like shapes. The templates were burnt off from the 2D/3D assembly, leaving a mesoporous cavity which increased with the carbon chain length used in the synthesis method. As such, morphological features related to surface area and total pore volume increased significantly by over 80% as compared to blank (no template) samples and reached maximum values of 734 m² g^-1 and 0.42 cm³ g^-1, respectively. The increase in total pore volume allowed for higher content of impregnated amine into the 2D/3D assembly followed by a freeze-drying method. The CO₂ sorption capacity of the amine-functionalized 2D/3D assemblies reached high values at 4.9 mmol g^-1 (mass over weight ratio), equivalent to 11.67 mmol cm^-3 (mass over total pore volume ratio). The amine-functionalized 2D/3D assemblies were stable over 10 cycles of CO₂ sorption and desorption. Further, heat of sorption results were generally low, with the lowest value reaching 59 kJ mol^-1. These results are desirable for the deployment of 2D/3D assemblies as sorbents to capture CO₂.

Enhanced CO2 sorption efficiency in amine-functionalised 2D/3D graphene/silica hybrid sorbents

Owing to the geometrical features of 2D graphene intercalated into 3D mesoporous silica, CO₂ sorption increased by 51% and the heat of sorption reduced by up to 27% as compared to a pure 3D mesoporous silica sorbent without graphene.