Micro & Nano Technologies

Amphiphilic Magnetic Particle

Amphiphilic magnetic nanoparticles for hydrocarbons and metals removal
Davide Moscatelli - Department of Chemistry, Materials and Chemical Engineering

The amphiphilic magnetic particles are stable aggregates of magnetite which size ranges between 1 and 200 nm. An innovative synthesis process gives to the nanoparticles an amphiphilic nature, which means they are able to disperse in aqueous solutions while preserving a certain affinity with lipophilic substances (eg. : hydrocarbons, emulsions, oils and lubricants). Furthermore, unlike the common magnetic nanoparticles, they maintain their stability in water even at high temperatures.

This stability is achieved thanks to the coating treatment given to the nanoparticles ferromagnetic core material. The synthesis guarantees the simultaneous presence of both the lipophilic and hydrophilic compounds that will cover the nanoparticles during the reaction phase. The bond, created between the surface of the ferromagnetic material and the two compounds, is covalent. This bond ensures the appropriate stability between the coating and the nanoparticle. Unlike common nanoparticles, the surface is randomly functionalized by the two lipophilic-hydrophilic compounds and this leads to the creation of hydrophilic and lipophilic moieties on the same nanoparticle.

Depending on the amount of the hydrophilic compound, the nanoparticles are completely stabilized in water (when the quantities are above a certain threshold) or tend to precipitate and to aggregate (when the same are not sufficient) putting together the hydrophobic moieties and exposing the hydrophilic one to the water. The result is the formation of aggregates, in which the hydrophobic moieties are joined by van der Waals forces, the maximum size of 20 microns, characterized by a very high active surface area. This ensures the adsorption of high amounts of lipophilic phases thanks to the rearrangement of the structure of the compounds in the adsorption phase. Furthermore, given the small size, these compounds easier respond to the magnetic field and are therefore easier to divide from the reaction mixture or from any other matrix (liquid or solid) in which they are injected.

One of the main advantages about these nanoparticles is that they can be recycled and reused after washing with them with suitable solvents. The so “washed nanoparticles” may be used more than once to effectively remove hydrocarbons or any other hydrophobic or lipophilic compound from solid and liquid environments.

The invention, unique in its kind, has been patented by Politecnico di Milano with international patent and represents a breakthrough for the treatment of contaminated sites (soil and water). The NPs naturally adsorb the polluting compounds and are easily removed and recycled.  Another field of application is the recovery of high added value compounds (e.g., recovery of oil from tar sands).

The particles can also be functionalized to capture hydrophilic and metal compounds present, even in small amounts, in water and soil. This technology has been validated in the field thanks to the collaboration with a major industrial group. In 2016 the technology leads to the creation of spin-off company of the Politecnico di Milano: Captive Systems Srl. Research in the area continues not only on application and commercial aspects of the magnetic NPs but also on their optimization in order to make them effective in the recovery of various pollutants.