Two new types of catalyst were synthesized by the immobilization of H3PW12O40 (HPW12) on the surface of organic–inorganic polyoxometalate nanoparticles of H6Cu2[PPDA]6[SiW9Cu3O37]$12H2O (HybPOM) (PPDA ¼ p-phenylenediamine) and Go/Fe3O4/HybPOM nanoparticles. These catalysts were characterized by thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and alternating gradient force magnetometry (AGFM). The IR spectroscopy as well as XRPD reveal that HPW12 were immobilized on the support. The potentiometric titration with n-butylamine reveal that the catalysts can be classified as strong acids. The results show that the particles are mostly spherical in shape and have an average size in the range of 20–50 nm. The catalytic activities of the catalysts were probed through one-pot three-component Mannich-type reactions of aldehydes, amines and ketones in water at room temperature. The catalysts were re-used at least five times without any loss of their high catalytic activity.
