Conformation-dependent Coordination of Carboxylic Acids with Fe 3 O 4 Nanoparticles Studied by ATR-FTIR Spectral Deconvolution.

The coordination of valeric acid (VA), glutaric acid (GA) and tricarballylic acid (TA) with Fe-OH on the Fe3 O4 nanoparticle surface has been systematically studied to elucidate the effect of COOH, molecular configuration and ligand concentration on the coordination by the combining use of attenuated total reflectance Fourier transform infrared (ATR-FTIR) and thermogravimetric analysis (TGA). The results show that the binding ability of the acids increases with the increase of the COOH number. Multiple conformations coexist for the dicarboxylic and tricarboxylic acid coordinated on the iron oxide NPs. Saturated coordination formed with only one-, two- or three-COOH conformation for VA, GA and TA, respectively, occurs under ligand-scarce conditions while unsaturated coordination formed with the mixture of uncoordinated, one- and/or two-COOH conformations for VA, GA and TA, respectively, exists under ligand-abundant conditions. The maximum coordination number for monolayer adsorption for VA, GA and TA on Fe3 O4 NPs is 9, 2.4 and 2.7 nm-2 , respectively. This study helps to understand the fine coordination mechanism caused by the acid molecules with different configuration and elucidate, for the first time, the fine conformation variance incurred by the surrounding ligand with different concentration and the way by which the ligand is added.