Influence of aqueous environment on agglomeration and dissolution of thiol-functionalised mesoporous silica-coated magnetite nanoparticles.

The purpose of the present research work is to investigate the stability and dissolution of magnetite (Fe3O4) nanoparticles (NPs) and thiol-functionalised mesoporous silica-coated magnetite NPs (TF-SCMNPs). The state of NPs in an aqueous environment was investigated under different pH conditions. Changes in the NPs' mean diameter due to aggregation were measured over a specific time. The effects of contact time and pH on the dissolution of NPs were also investigated. In order to avoid possible aggregation, Fe3O4 NPs were coated with silica and functionalised further with thiol organic groups. These methods imparted excellent stability to magnetite NPs in an aqueous medium over a wide range of pH values with reasonable hydrodynamic size. The organic group bound magnetite NPs allowed these particles to circulate over a long time in the aqueous system, and particle aggregation and sedimentation did not occur. The trend of decreasing zeta potential was observed after grafting thiol onto the surface of the SCMNPs. The results also revealed that silica exhibited a noteworthy efficient in eliminating the pH dependence and enhancing the NP stability of SCMNPs and SH-SCMNPs in aqueous medium. On the other hand, the dissolution of Fe3O4 NPs was found to be detrimental at pH 2.0 and 4.0 or had a long contact time.