Characterization of rigid and stable monolayers of a dibenzoic acid diamide bolaamphiphile on nanosized maghemite particles

The self-assembly of a dibenzoic acid diamide bolaamphiphile on the surface of nanosized maghemite (γ-Fe2O3) particles is described. The nature and structure of the prepared monolayers were characterized by X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the bolaamphiphile anchors to the surface through chemical bonding between one of the carboxylic head groups and the iron of the maghemite, leaving a pendant carboxylic moiety reactive. The coordination at the maghemite surface is of the unidentate type, as seen by a difference in wavelength between symmetric and asymmetric carboxylate bands of 249 cm−1. The amide linkages of the bolaamphiphile stitch the self-assembled molecules together by providing hydrogen bonding sites, thus forming a rigid monolayer. The structure of the bolaamphiphile is further confirmed by quantitative XPS analysis. Finally, rinsing the monolayer with HCl at pH 3 results in no significant IR spectral changes, thus confirming the stability of the monolayer in acidic conditions.