Functionalized biochar catalysts: Advancing green chemistry in synthesis of O- and N-heterocycles

The global shift toward sustainable chemistry has catalyzed the development of biochar as a versatile and eco-friendly catalyst in organic synthesis. Biochar, derived from biomass pyrolysis, offers tunable surface functionalities, high stability, and cost-effectiveness, establishing it as a viable alternative to conventional catalyst support. This review offers the first comprehensive overview of recent advancements in functionalized biochar-based catalysts for the synthesis of O and N-heterocycles. Particular focus is given to their applications in forming pharmaceutically and industrially important heterocycles, including chromenes, pyranopyrazoles, pyrazolopyridines, tetrazoles, oxindole dihydropyridines, benzylpyrazolyl coumarins, quinazolinones, spirochromenes, furoquinolines, and cyclic carbonates. This review explores the synthesis, functionalization, and catalytic performance of biochar, predominantly prepared via pyrolysis of diverse, renewable feedstocks such as chicken manure, neem bark, and wheat straw. These catalysts exhibit tailored properties, including large surface area, tunable porosity, and functional enhancements (e.g., by increasing reaction rates, selectivity, etc.) through the incorporation of magnetic, acidic, or metallic components. The review provides comparative insights into catalyst reusability, reaction efficiency, and mechanistic pathways, highlighting biochar's ability to replace hazardous reagents in heterocyclic synthesis. Additionally, examples are categorized by heterocycle type, offering detailed analyses of catalyst design, functionality, and advantages. The findings underscore the transformative potential of biochar-based catalysts in advancing green chemistry, while also pointing to opportunities for further innovation in this emerging field.