Alkyl Phosphonate/Phosphate Coating on Magnetite Nanoparticles:  A Comparison with Fatty Acids

Abstract

Coated magnetite nanoparticles with a 6−8 nm average diameter were prepared. The surfactants used to stabilize the nanoparticles and disperse them in organic solvents were oleic acid (OA), lauric acid , dodecyl phosphonate, hexadecyl phosphonate, and dihexadecyl phosphate. Transmission electron microscopy analyses of the aggregation of the coated particles suggest that carboxylate surfactants provide the particles with better isolation and dispersibility as compared with phosphonate surfactants. However, Fourier transform infrared spectra of the phosphonate and phosphate coated particles suggest that these surfactants cover the surface of the nanoparticles in islands of high packing density. The thermogravimetric and differential scanning calorimetry measurements suggest that there is a quasi-bilayer of these surfactants covering the surface of the nanoparticles, with varying amounts of surfactant in the outer layer and with the second layer weakly bound to the primary layer through hydrophobic interactions between the alkyl chains. The desorption temperatures of the alkyl phosphonates and phosphate are higher than those of the carboxylate coated particles. The enthalpy of binding of the ligands suggests strong P−O−Fe bonding on the surface. Nevertheless, regardless of binding strength, the OA coated particles are better dispersed in organic solvents. Their higher hydrophobicity is likely due to different interactions among the oleyl chains and/or a smaller tendency to form bilayer structures.

Titania–silver and alumina–silver composite nanoparticles: Novel, versatile synthesis, reaction mechanism and potential antimicrobial application

“…Two degradation steps were observed for both TiO 2 -Ag and Al 2 O 3 -Ag, most readily seen from the derivative TG curves shown inset in Fig 7a and 7b. These double desorption steps are in agreement with studies of thermal stability of surfactants on nanoparticle surfaces conducted by Sahoo et al [51] and Perez-Diese et al [52]. Figure 7B), the derivative curve (inset, Figure 7B) shows that, unlike TiO 2 -Ag, the second mass-loss step -attributed to strongly bound surfactant -was dominant.…”

The design and utility of polymer-stabilized iron-oxide nanoparticles for nanomedicine applications

“…However, the -COOH/IONP coordination bond is labile and can be broken easily by increasing temperature or by exchange with another carboxylic acid compound. Phosphonic acid also shows a strong affinity for IONP surfaces through the formation of Fe-O-P-bonds [14]. Th ese bonds are more stable than the carboxylic acid bond and have shown stability for several weeks at neutral pH.…”

“…Th ese bonds are more stable than the carboxylic acid bond and have shown stability for several weeks at neutral pH. Phosphonic acid also shows a higher grafting density than the carboxylic acid group [14].…”

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

“…[313] They provide more stronger bonds compared to carboxylic acid molecules through creating FeOP bond, which equip iron oxide MNPs with coatings having good stability over several weeks at neutral pH. [314] …”