Capturing Acidic CO₂ Using Surface-Active Difunctional Core-Shell Composite Polymer Particles via an Aqueous Medium

Multifunctional surface-active polymeric composites are attractive materials for the adsorption of various small molecules. Herein, dual-functionalized micron-sized surface-active composite polymer particles were prepared by a three-step process for CO₂ adsorption. First, polystyrene (PS) seed particles were prepared via the dispersion polymerization of styrene. PS/P(MMA-AAm-EGDMA) composite polymer particles were then synthesized by aqueous seeded copolymerization of methyl methacrylate (MMA) and acrylamide (AAm) in the presence of an ethylene glycol dimethacrylate (EGDMA) cross-linker. Finally, the amide moieties of PS/P(MMA-AAm-EGDMA) composite particles were converted into an amine-functionalized composite by using the Hofmann degradation reaction. The presence of primary amine groups on the surface of aminated composite particles was confirmed by some conventional chemical routes, such as diazotization and Schiff's base formation reactions. The formation and functionality of the PS seed, PS/P(MMA-AAm-EGDMA), and aminated PS/P(MMA-AAm-EGDMA) composite polymer particles were confirmed by Fourier transform infrared (FTIR) spectra analyses. Scanning electron microscopy (SEM) analysis revealed spherical shape, size, and surface morphologies of the PS seed, reference composite, and aminated composites. The elemental surface compositions, surface porosity, pore volume, pore diameter, and surface area of both composite particles were evaluated by energy-dispersive X-ray (EDX) mapping, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) analyses. Dynamic light scattering (DLS) and ζ-potential measurements confirmed the pH-dependent surface properties of the functionalized particles. The amount of the adsorbed anionic emulsifier, sodium dodecyl sulfate (SDS), on the surface of aminated PS/P(MMA-AAm-EGDMA) is higher at pH 4 than that at pH 10. A vice versa result was found in the case of cationic surfactant, hexadecyltrimethylammonium bromide (HTABr), adsorption. Synthesized aminated composite particles were used as an adsorbent for CO₂ adsorption via bubbling CO₂ in an aqueous medium. The changes in dispersion pH were monitored continuously during the adsorption of CO₂ under various conditions. The amount of CO₂ adsorption by aminated composite particles was found to be 209 mg/g, which is almost double that of reference composite particles.