Solvothermal Fabrication of NiO/Co3O4 Spherical Composites Modified with N-Doped Graphene Quantum Dots as a Catalyst in the Microwave-Assisted Synthesis of Spiro[diindenopyridine-indoline] Triones

N-Doped Graphene Quantum Dots (N-GQDs) have been extensively investigated owing to their interesting photochemical, and electrochemical properties. However, N-GQDs have rarely been introduced as catalyst in organic reactions. Herein, NiO/Co3O4 composites with diverse morphologies of hexagonal nanoplates, spherical, irregular nanocubics, and multishape are fabricated using different solvents and pH adjusters. In the following, the catalytic activity of engineered composites was screened, and it demonstrated to be in the order: spherical>hexagonal nanoplate>irregular solid nanocubic>multi-shape. The uniform spherical morphology makes exposure of a larger part of the reactive facets possible and provides accessible active sites. Next, novel NiO/Co3O4@N-GQDs spherical composites has been successfully fabricated by cost-effective, green and straightforward hydrothermal method. Proposed composite was applied as an efficient heterogeneous catalyst for the microwave-assisted synthesis of new and known indenospiro derivatives. The desired products were formed in excellent yields (88-97 %) within the short reaction time (6-14 min).