  Porous magnetic silica beads are promising materials for biological and
environmental applications due to their enhanced adsorption and ease of
recovery. This work aims to develop a new, inexpensive and environmentally
friendly approach based on agglomeration of nanoparticles in aqueous droplets.
The use of an emulsion as a geometrical constraint is expected to result in the
formation of spherical beads with tunable composition depending on the aqueous
phase content. Magnetic silica beads are produced at room temperature by
colloidal destabilization induced by addition of calcium chloride to a
water-in-oil emulsion containing silica and iron oxide nanoparticles. The
impact of the salt concentration, emulsification method, concentration of
hydrophobic surfactant as well as silica content is presented in this paper.
This method enables the production of spherical beads with diameters between 1
and 9 micrometers. The incorporation of magnetic nanoparticles inside the beads
structure is confirmed using Energy Dispersive X-ray spectrometry and Scanning
Transmission Electron Microscopy and results in the production of magnetic
responsive beads with a preparation yield up to 84 percent. By incorporating
the surfactant Span 80 in the oil phase it is possible to tune the roughness
and porosity of the beads.
