Composite microspheres with PAM microgel core and polymerisable surfactant/polyoxometalate complexes shell

Abstract

The composite microspheres of poly(acrylamide) microgels (PAM) surfacely covered with [3-(acryloylamino)propyl]dodecyldimethyl ammonium-tungstophosphate complexes (APDDAB-PWA) were synthesized by using an ion-exchange reaction between APDDAB located within the porous PAM microgels and PWA in aqueous solution. The morphology and component of the composite microspheres were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis, respectively. The results indicated that PAM/APDDAB-PWA composite microsphere with different hierarchical surface structures could be obtained by controlling the weight ratio of APDDAB to PAM microgels, cross-linking degree of PAM microgels, the amount of PWA reacted with APDDAB in PAM/APDDAB, and solvent-washing process. Although the surface morphologies of the composite microspheres in detail were different, a general feature was of the core-shell structure and the wrinkly surface covered with APDDAB-PWA particles. The formation of the wrinkly surface is attributed to the difference in shrink between inside and outside of PAM microgel frameworks, and the formation of APDDAB-PWA small particles originates from the reaction between APDDAB aggregation and PWA. This composite microsphere with PAM hydrogel core is suitable to store water-soluble substances, and the shell composed of the surfactant/Keggin-type polyoxometalate complexes is not only amphiphilic but also catalytic. Additionally, PAM/APDDAB-PWA composite microspheres with big size and APDDAB-PWA particles with small size make the composite microspheres not only easy for separation but also beneficial for catalysis. These properties have been verified by the application of PAM/APDDAB-PWA composite microspheres to the deep desulfurization of fuel oil. This material provides an example to construct microreactors with new structure used in diphase catalytic reaction.