New Green Adsorbent for Capturing Carbon Dioxide by Choline Chloride:Urea-Confined Nanoporous Silica

Green nanocomposite adsorbent based on nanoporous silica (NS) and deep eutectic solvent (DES) mixture of choline chloride–urea (ChCl:U) was synthesized as an alternative for carbon dioxide (CO2) adsorption. The nanocomposite adsorbent was prepared by sol–gel technique with the variations of ChCl:U (mole ratio 1:2) content in NS at 5–15% (w/w). Fourier transform infrared attenuated total reflectance (ATR-FTIR) results revealed the successful confinement of ChCl:U into NS from the presence of C=O carbonyl stretching, N–H scissoring bending, CH2 bending and C–N stretching peaks. The peaks intensity increased with increasing weight percentage of confined ChCl:U. In contrast, thermogravimetric analysis (TGA) showed decrement of thermal stability of the adsorbent when ChCl:U was confined into NS. The nitrogen physisorption demonstrated a decrease in specific surface areas of the sorbents with increasing ChCl:U weight percentage due to the transformation of micropores to mesopores. The CO2 adsorption capacity was found to be reduced when the weight percentage of ChCl:U was increased. The optimum adsorption capacity of 23.0 mg/g was achieved by 10% ChCl:U/NS sample. The mechanism of the adsorption was deduced from the ATR-FTIR and XPS spectra for 10%CuCl:U/NS showing that physisorption and chemisorption occurred during CO2 adsorption with the presence of carbamate ion.