Fe3O4@RHA@TiO2: preparation, characterization, and application in the nanocatalytic synthesis of tetrahydrobenzo[b]pyrans†

Magnetic core–shell nanostructures (for example, magnetic nanoparticles with a silica shell) are suitable substrates for catalyst stabilization. In this study, silica nanoparticles were obtained from rice husk. Then titanium dioxide was embedded in Fe₃O₄@RHA and the Fe₃O₄@RHA@TiO₂ nanocatalyst was synthesized and identified using VSM, EDX, XRD, FE-SEM, and FT-IR techniques. This nanocatalyst had spherical particles with an average particle size of about 27 nm and good magnetic properties of about 23 emu g⁻¹. In this research, the optimization of the reaction parameters in the preparation of pyran derivatives was done through the multicomponent condensation of aromatic aldehyde, propanedinitrile (malononitrile), and dimedone by using the statistical technique of response surface methodology. Accordingly, the highest efficiency for the synthesis of pyran derivatives was obtained using 0.011 g of the Fe₃O₄@RHA@TiO₂ nanocatalyst at the temperature range of 118–119 degrees in 53 minutes under solvent-free conditions. Titanium dioxide (TiO₂) provides sufficient acidic sites to facilitate the synthesis of pyran derivatives. Due to its low cost, high chemical stability, and non-toxicity, it serves as an excellent component for the fabrication of the Fe₃O₄@RHA@TiO₂ nanocatalyst, making it highly efficient for organic synthesis. This method offers several advantages, including environmental friendliness, simplicity, green chemistry approach, cost-effectiveness, high yield, short reaction time, excellent recyclability, good physical and chemical stability, low catalyst loading requirement, and easy catalyst separation. These features make it a promising strategy for the preparation of pyran derivatives.