Functionalization of multi-walled carbon nanotubes with phenylenediamine for enhanced CO2 adsorption

Abstract The adsorption performance of multi-walled carbon nanotubes (MWCNTs) towards CO 2 gas was enhanced by covalently grafting of phenylenediamine (PDA) via an activation-grafting process. Different loading amounts were achieved by changing the activation time and the dosage of activating agent. The so-synthesized adsorbents were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Thermogravimetry analysis, Transmission electron microscope, Raman spectroscopy and Nitrogen adsorption–desorption analysis. The CO 2 adsorption properties were studied via static volumetric method. The results indicated that the modification process did not alter the crystal structure, whilst the quantity of defect sites and amorphous structures increased greatly. Moreover, the average pore size after functionalization increased from 9.68 to 23.80 nm. 0.59 mmol·g −1 of CO 2 were captured by aminated MWCNTs at 303.15 K and 200 kPa, while the adsorption capacity of the raw materials was only 0.17 mmol·g −1 under the same conditions. Adsorption–regeneration cycles exhibited the stability of the PDA modified MWCNTs during the prolonged cyclic operations. We found that the adsorption of CO 2 on MWCNTs belonged to physical adsorption and the adsorption behavior of CO 2 on PDA modified MWCNTs was a chemical adsorption. The effective enhancement of the CO 2 capture ability was attributed to the increased number of active sites, which offered stronger interactions with CO 2 after PDA grafting.