Effect of precursor concentration, surfactant and temperature on the size, morphology and nanostructure of zero-valent iron nanocrystals synthesised by a polyol route

Iron metal nanoparticles, due to their magnetic properties, reducing power and low toxicity, have numerous applications not only in groundwater and contaminated soil remediation but also in biomedicine as contrast agents in magnetic resonance imaging. However, obtaining this nanomaterial involves the use of strongly reducing, polluting and expensive reagents and high temperatures. Herein, the use of ethylene glycol and diethylene glycol in a strong alkaline medium that allows the direct reduction of iron(II) salts to iron(0) in the absence of any added reducer has been analysed for preparation of well-defined nanoparticles. The key roles of the polyhydroxylated surfactants (D-mannitol, D-mannose, polyvinyl alcohol and polyvinyl pyrrolidone) were identified, and their efficiencies were evaluated. In addition, conclusions have been drawn regarding the existence of a minimum temperature required for the reduction of the precursor, as well as the observation that the size of the nanoparticles increases with reaction temperature. The main result is that by combining surfactants and controlling the reaction temperature, pure cubic iron(0) nanoparticles smaller than 100 nm were obtained, thereby reducing the formation of hydroxylated by-products. The high reactivity, high magnetic response, long-term stability and small size of the iron nanoparticles produced in this work will allow their use in various applications.