The functionalization of silica-coated Fe₃O₄ magnetic nanoparticles (Fe₃O₄@SiO₂) using chlorosulfonic acid were afforded sulfonic acid-functionalized magnetic Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂–SO₃H) that can be applied as an organic–inorganic hybrid heterogeneous catalyst. The used Fe₃O₄ magnetic nanoparticles are 18–30 nm sized that was rapidly functionalized and can be used as catalyst in organic synthesis. The prepared nanoparticles were characterized by X-ray diffraction analysis, magnetization curve, scanning electron microscope, dynamic laser scattering, and FT-IR measurements. The resulting immobilized catalysts have been successfully used in the synthesis of 1,8‐dioxo-octahydroxanthene derivatives under solvent free condition. This procedure has many advantages such as; a much milder method, a shorter reaction time, a wide range of functional group tolerance, and absence of any tedious workup or purification. Other remarkable features include the catalyst can be reused at least five times without any obvious change in its catalytic activity. This procedure also avoids hazardous reagents/solvents, and thus can be an eco-friendly alternative to the existing methods. Graphical Abstract A highly efficient nano-Fe₃O₄ encapsulated-silica particles bearing sulfonic acid groups as a solid acid catalyst for synthesis of 1,8-dioxo-octahydroxanthene derivatives

Regarding green chemistry goals, silica-coated magnetite nanoparticles open up a new avenue to introduce a very useful and efficient system for facilitating catalyst recovery in different organic reactions. Therefore, in this paper the preparation of sulfonic acid-functionalized silica-coated magnetic nanoparticles with core–shell structure (Fe₃O₄@silica sulfonic acid) is presented by using Fe₃O₄ spheres as the core and silica sulfonic acid nanoparticles as the shell. The catalyst was characterized by infrared spectroscopy, scanning electron microscopy, X-ray diffraction analysis, dynamic light scattering, thermogravimetric analysis and vibrating sample magnetometry. Nanocatalyst can be recovered using an external magnet and reused for subsequent reactions 6 times without noticeable deterioration in catalytic activity.

CS/PVA/SA hydrogels modified with mesoporous Ag₂O/SiO₂ and curcumin nanoparticles for antibacterial biopolymer film.

Cu( i )@phosphorated SiO ₂ as novel, eco-friendly, easy to prepare, recyclable catalyst for the synthesis of β-hydroxy-1,2,3-triazoles in water is reported.