2.1.2. Silica coating on magnetic nanoparticles

An ethanolic solution comprising of 25% water is taken in a 1L container and pH is changed to 12 using 10 N Sodium hydroxide solution. Fe₃O₄ nanoparticles are added to the above basic ethanolic solution and sonicated for about an hour. About 12.5 mL of TEOS (0.033 mol) is added above sonicated solution slowly at 1 mL/min and stirred for an hour. The Fe₃O₄ particles coated with silica layer are separated using external barium ferrite magnet, washing with distilled water for further use. The removal of ionic impurities is performed by heating to 90 °C at 30 using 0.3 M trisodium citrate and then ageing with 0.5 M tris. The former solution is at pH 6 and later solution is at pH of 8 and ideally remove both iron impurities and unreacted components. The overall synthesis of silica functionalized magnetic nanoparticles is given in Fig. 1 . The overall yield of SMNP in this method vary from batch to batch, overall yield is 4 to 5 g.

Diagrammatic representation of Fe₃O₄@SiO₂ Synthesis: Synthesis of nanoparticles using ferrous sulphate heptahydrate, NaNO₃ as starting materials and sodium hydroxide as reducing agent. The NaNO₃ in equilibrium with FeSO₄ generates in situ which allows nanoparticle formation.