Nanoporous polystyrene–porphyrin nanoparticles for selective gas separation

Abstract

Highly cross-linked polystyrene–porphyrin nanoparticles were synthesized by a facile approach using emulsion free-radical copolymerization of styrene (St) with a tetra-functional cross-linker, 5,10,15,20-tetrakis(4-phenylmethacrylate)-21H,23H-porphine (PO), and a bifunctional cross-linker, divinylbenzene (DVB), in aqueous solution. Two samples were prepared, PO-St-DVB(1) and PO-St-DVB(2), with 0.7 and 2.6 mol% PO, respectively. The cross-link density of the particles increased with the increase of the PO content at a constant St/cross-linkers mol feed ratio. The morphology and the size of the polymer particles were studied by scanning and transmission electron microscopies. Gas adsorption measurements showed that the polystyrene–porphyrin nanoparticles possessed an inherently large surface area when dried by supercritical CO₂ from their dispersions in EtOH or DMF. In particular, the sample with the highest PO content (PO-St-DVB(2)) exhibited a Brunauer–Emmett–Teller (BET) surface area up to 334 m² g⁻¹ (282 m² g⁻¹ calculated from CO₂ adsorption) with a total pore volume of 0.37 cm³ g⁻¹ when dried from EtOH. Analysis of the CO₂ and CH₄ adsorption data using the ideal adsorption solution theory revealed that the PO-St-DVB(2) nanoparticles exhibited an adsorption selectivity for CO₂ over CH₄ of 25 at 263 K and 12 at 273 K, rendering them attractive candidates for use in CO₂/CH₄ separation and carbon dioxide sequestration processes.