Facile fabrication of morphology-adjustable viologen-based ionic polymers for carbon dioxide immobilization and...

Viologens, also referred as 1,1'-disubstituted-4,4'-bipyridinium salts, exhibit exceptional redox properties, identifying them as building blocks for functional organic polymer materials with a wide range of potential applications, including carbon dioxide (CO₂) conversion and iodine capture. Herein, a series of viologen-derived ionic porous organic polymers (VIPOP-n), assembled from viologen derivatives, were designed and synthesized using a straightforward one-step strategy. The constructed polymer materials were subsequently characterized by Fourier Transform Infrared Spectroscopy (FT-IR), solid-state ¹³C nuclear magnetic resonance (¹³C NMR), X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM), and nitrogen adsorption-desorption isotherms, among other techniques. Notably, the variation of synthetic solvents significantly influences the construction of polymer materials, resulting in observable changes in morphology and structure, which in turn affect their potential applications in CO₂ cycloaddition reaction and iodine adsorption. The polymer VIPOP-3 exhibits superior catalytic performance under conditions of 80 °C and 1 atm CO₂, producing valuable cyclic carbonates with yields reaching 94%. Density Functional Theory (DFT) calculations indicate that inert-hydrogen bonding can effectively activate both the epoxide and CO₂, lowering the activation energy (E_a) of the cycloaddition reaction to 87.5 kJ mol^-1, as corroborated by kinetic evaluations. Additionally, all polymers exhibited effective iodine vapor adsorption capacities, with VIPOP-7 emerging as the most efficient material, displaying an adsorption capacity of 2.96 g g^-1. The adsorption process was investigated through various kinetic models, revealing that both physical and chemical adsorption were involved, with physical adsorption being the predominant process.