Synthesis of mesoporous silica nanoparticles from waste hexafluorosilicic acid of fertilizer industry

Hexafluorosilicic acid (H2SiF6) is one of the most harmful by-products of the agricultural industry and because of the enormous scale of the industry, disposal of the acid on such a large scale is a huge concern. H2SiF6 has adverse effects on both human physiology and the environment. Moreover, the acid is also corrosive to many common materials such as glass and metals. The method outlined in this paper aims to dispose of this corrosive and harmful by-product of the agricultural industry while also producing a very valuable product in the form of mesoporous silica nanoparticles (MSN's). Previous efforts to produce MSN's in bulk fell short as they were not sustainable, cyclic and/or required complex equipment. The current method aims at ammoniation of H2SiF6 with certain controllable parameters in order to obtain pure MSN's. The parameters used were rate of addition of ammonia and the rate of agitation post ammoniation. EDX and XRD confirmed that the synthesized particles were MSN's. Dynamic light scattering (DLS) of the various samples showed a good size distribution and confirmed that, by changing process parameters, we were able to control the particle size. BET confirmed a high surface area and an average pore size was also obtained. MSN's can be used for a variety of purposes, including formation of aerogels, bio-sensing, and particularly in targeted drug delivery where the properties of MSN's make it a very viable candidate. The process presented in this paper can be extended to make it a cyclic and sustainable process capable of producing two nanomaterials.