Surface-modified nanomaterials have been commonly used in a number of research applications, and are increasingly used in commercial composite materials as well. Silica and other metal oxides nanoparticles can be purchased in large quantities from a number of suppliers, but the important information on the density of surface groups is typically not provided. This is surprising because it can directly impact parameters such as toxicity, biodegradability or reproducibility in manufacturing. Reliable surface-chemistry characterization methods are therefore necessary to establish adequate quality control and regulatory frameworks. In our work, we address this complex problem by the detailed study and the cross-validation of various methods for the quantification of functional groups and their stability. Two colorimetric approaches were used to assess the reactivity and accessibility of frequently used propylamine moitey. The first assay uses ninhydrin and the reporting dye is continuously generated. The other assay is a two-step reaction based on the conjugation and the subsequent release of 4-nitrobenzaldehyde as the reporting chromophore. In addition, fluorine-labeling reactions were used to probe the extent of surface groups coupling via ss 19F-NMR and XPS. These results are compared to the total amount of functional groups on the material determined by ‘dissolution’ 1H qNMR and TGA coupled with FTIR detection. These two methods can also inform about the chemical structure and allowed to quantify additional functional groups (C11COOH, stearate, methacryl, PEG). Further substrate materials (Fe2O3, TiO2, ZnO) were tested as well and the applicability/limitations of mentioned methods were critically assessed. Additionally, we are going to showcase that samples procured from various commercial suppliers can widely range in the functional group content, and can also contain impurities that interfere with some quantification methods. We believe that our findings can be highly relevant and practical for nanomaterials businesses as well as regulators and researchers from across many disciplines.

Multimethod quantification of nanomaterial surface functional groups

2019 Fall National Meeting

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