Ionic interfacial engineering of chitosan–Fe3O4@mesoporous silica hybrids for CO2 adsorption and epoxide cycloaddition

Chitosan is an attractive renewable platform for CO₂ capture and utilization, but its practical use is limited by low accessible surface area and poorly defined adsorption-active interfacial environments. Here, sulfonated Fe₃O₄@mesoporous silica was integrated into chitosan through an aqueous assembly route to create magnetically recoverable bio-inorganic hybrids with mesoporosity and SO₃⁻/NH₃⁺-rich ionic interfacial domains. Hybridization increased the accessible surface area from 0.039 m² g⁻¹ for pristine chitosan to 92.48 and 23.68 m² g⁻¹ for CSFmS1 and CSFmS5, respectively, and improved CO₂ uptake to 0.66 and 0.40 mmol g⁻¹ at 278 K and 1 atm. Isotherm fitting, kinetic analysis, apparent thermodynamic descriptors, and isosteric heat trends collectively indicate heterogeneous and reversible CO₂ adsorption, with CSFmS1 showing consistently stronger affinity than CSFmS5 over the investigated temperature range. Screening-level CO₂/N₂ selectivity estimated from Henry’s law and IAST at 298 K indicates CO₂-preferential adsorption based on single-component isotherms. Molecular simulations provide mechanistic support for preferential CO₂ association near SO₃⁻/NH₃⁺ ionic domains and diffusion through connected free-volume regions via a bind-and-release mechanism. As a downstream utilization demonstration, the CSFmS1/TBAB system promoted epoxide/CO₂ cycloaddition under a CO₂ balloon, reaching 99.2% conversion of styrene oxide and 95.4% conversion of epichlorohydrin while retaining the practical advantage of magnetic recovery. These results indicate that accessible mesoporosity and ionic interfacial domains are the principal design features governing CO₂ uptake in chitosan-based hybrids and provide a mechanistically informed strategy for bio-inorganic materials that couple CO₂ adsorption with downstream conversion.