Bismuth-Incorporated g -C 3 N 4 as an Efficient Catalyst for Light-Assisted CO 2 Fixation at Room Temperature under Atmospheric Pressure

The atom-efficient ring expansion of epoxides with carbon dioxide represents a key strategy for the sustainable synthesis of value-added cyclic carbonates from CO 2 . In this work, a bismuth nanoparticle-incorporated graphitic carbon nitride ( g -C 3 N 4 – x Bi) material is prepared by a facile two-step calcination and hydrothermal procedure. The integration of metallic bismuth NPs into the g -C 3 N 4 matrix narrows the material’s band gap, improves charge transfer migration, and extends the lifetime of exciton pairs, enhancing the overall catalytic efficiency. Incorporating Bi nanoparticles results in a 2.5-fold enhancement in catalytic activity compared with pure g -C 3 N 4 . Moreover, a combination of CN-1 Bi (6.1 wt % Bi NPs) and tetrabutylammonium iodide (TBAI) was found to be an efficient catalyst for converting different epoxides into corresponding cyclic carbonates under atmospheric pressure and room temperature conditions using a 230 mW/cm 2 xenon lamp. Furthermore, the catalyst retains its catalytic activity up to five cycles of catalysis, proving its chemical robustness under the experimental conditions. Several mechanistic investigations demonstrated the formation of CO 2 radical anions and epoxide radical cations, confirming that the reaction follows a photocatalytic pathway. The present study offers an ecofriendly approach toward sustainability and the synthesis of value-added chemicals under mild conditions.