Tuneable Naphthalene-Based Microporous Polyimide Networks for CO₂ Capture and Conversion

Excessive emission of anthropogenic CO₂ in our atmosphere is a major cause of global warming and environmental issues. Climate change is a significant global challenge and causes a serious threat to the planet. Several strategies have been proposed to reduce the emission of anthropogenic CO₂, and to explore the use of CO₂ as an abundant feedstock for the production of sustainable fuels. Thus, capturing CO₂ using a porous polymer and the successful conversion into valuable chemical feedstocks is one of the vital solutions to mitigate this problem.<br/>Crosslinked porous polyimides (pPIs), a type of porous organic polymer (POP), offer a great potential for CO₂ capture and conversion, owing to their porous nature and excellent redox behaviour.^{1, 2} Generally, pPIs are synthesised by polycondensation of dianhydride with multi-amines. However, the incompatibility of solvents during the condensation yields lower surface area and limits total gas uptake. Here we describe in detail how we utilise the Bristol-Xian-Jiaotong (BXJ) approach,^{3, 4} using inorganic salts to tune the porosity and enhance the surface area by tuning the compatibility of the reaction solvent and the growing porous polymer. In this approach, we calculate the Hansen Solubility Parameters (HSPs) of our pPIs, and compare these with the HSPs of a wide range of common reaction solvents to find matching solvents for optimised synthesis conditions. Furthermore, HSPs can be tuned by inorganic salt additives (different ion sizes and concentrations), thus providing a useful method to fine-tune surface area and pore size distribution (PSD) of the polymers. The surface area and PSD of naphthalene-based pPIs acquired from non-BXJ polycondensation reactions have thus been optimised by calculating HSPs to find a suitable solvent for synthesis, and further optimised by salt additives. The surface area of BNPI-1 and BNPI-2 were enhanced from the published values of 16 and 15 m²g^-1 to 846 and 613 m²g^-1, respectively. The BXJ approach provides a simple route to tune the porosity properties in a controlled manner. Moreover, with the improved surface area and enhanced control over the PSD, CO₂ uptake of naphthalene-based pPIs were increased to 14 wt%. Currently we are exploring the use of these naphthalene-based pPIs in the electrocatalytic reduction of CO₂ into valuable chemical feedstock material.<br/><b>References</b><br/>1. B. B. Narzary, B. C. Baker, N. Yadav, V. D'Elia and C. F. J. Faul, <i>Polymer Chemistry</i>, 2021, DOI: 10.1039/d1py00997d.<br/>2. Y. Liao, J. Weber and C. F. J. Faul, <i>Macromolecules</i>, 2015, <b>48</b>, 2064-2073.<br/>3. J. Chen, W. Yan, E. J. Townsend, J. Feng, L. Pan, V. Del Angel Hernandez and C. F. J. Faul, <i>Angew Chem Int Ed Engl</i>, 2019, <b>58</b>, 11715-11719.<br/>4. J. Chen, T. Qiu, W. Yan and C. F. J. Faul, <i>Journal of Materials Chemistry A</i>, 2020, <b>8</b>, 22657-22665.