The novel waste-based eggshell/Fe(OH) 3 plate-like nanocomposites were synthesized using the mild co-precipitation method, and their catalytic properties were investigated. These nanocomposites demonstrated high catalytic activity, stability, and reusability as multifunctional and heterogeneous catalysts for the green multi-component synthesis of 2 H-indazolo[2,1- b]-phthalazine-trione derivatives under solvent-free and thermal conditions. The synthesized nanocomposites’ morphology, nanoparticle size, structure, crystalline nature, and thermal stability were characterized using FESEM, TEM, FT-IR, XRD, and TGA analyses. The results indicate that these nanocomposites are efficient, cost-effective, and environmentally friendly catalysts, highlighting their potential for sustainable chemical and industrial processes.