Polydopamine-modified mesoporous silica materials as a novel adsorbent for superior CO2 adsorption: Experimental and DFT study

Increasing environmental issues necessitate the development of new and well-designed adsorbents for separation and adsorption applications. We report a novel strategy to simultaneously improve the mesoporous silica materials (MCM-41) and CO2 adsorption performance by adding polydopamine (PDA) to the structure of MCM-41. Also, surface polymerization of MCM-41 with polydopamine increases functional groups. The presence of PDA can put spatial obstruction on the MCM-41 structure, lead to the formation of new porosity between the MCM-41 particles and increase the total pore volume. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDAX), N2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM) were utilized to study the properties of nanoadsorbents. The results demonstrated that PDA@MCM-10% had the maximum total pore volume (0.99 cm3/g) and pore diameter (7.1 nm) among all prepared samples, which are about 33.7% and 113.4% superior to those of MCM-41 (Vtotal: 0.74 cm3/g and Ave. pore diameter: 1.85 nm). The resulting PDA@MCM structure represented 5.12 mol/kg, 2.28 mol/kg and 1.54 mol/kg uptake capacities for CO2, CH4 and N2 respectively, which were 1.71, 2.59 and 3.27 times higher than pristine MCM-41 at 1 bar. Furthermore, the PDA@MCM exhibited excellent selectivity for CO2/CH4 and CO2/N2 samples. In addition to the different adsorption behaviors for CO2, CH4 and N2 removal, PDA@MCM-10% displayed better cyclic uptake capacity than those of the MCM-41 adsorbent after 10 consecutive cycles. The adsorption mechanisms in the uptake of CO2, CH4 and N2 were also studied by density functional theory (DFT) computations. Considering the inexpensive cost of synthesizing MCM-41 along with the favorable adsorption properties, the PDA@MCM can be a promising candidate for excellent gas adsorption.