Lignin-Engineered Metal Oxide Nanocatalysts for Sustainable CO₂ Fixation into Pharmaceutical Heterocycles

Lignin (a natural biopolymer present in agri-residue) is a versatile adsorbent and can serve as a promising platform to capture and fix CO₂, which is subsequently used for conversion to value-added chemicals. In this study, we engineered greener, economical, cost-effective, and sustainable lignin-derived metal oxide nanocatalysts (ZnOKL, ZnOAL, TiO₂AL, TiO₂KL, ZnOTiO₂@AL, and ZnOTiO₂@KL) for applications in CO₂ capture. The presence of transition metals in the lignin matrix offers an added advantage toward simultaneous CO₂ fixation and conversion. Such nanocatalysts were instrumental in the CO₂ fixation and further conversion into important active pharmaceutical ingredients (APIs), namely, cyclic carbonates and oxazolidinones. Such lignin derived sustainable nanocatalysts resulted in >99% cyclic carbonate and 5-19% oxazolidinone formation. The synthesized nanocatalyst exhibited efficient conversion and maintained its activity for up to five consecutive cycles. The incorporation of metal oxides into lignin enhanced the stability and adsorption capacity of the catalysts. This work offers a sustainable strategy to remove environmental CO₂, followed by the generation of APIs, thereby supporting climate change mitigation initiatives via a medicine-from-air approach.