Abstract
AbstractSurface functionalization is widely used to control the behavior of nanomaterials for a range of applications. However, methods to accurately quantify surface functional groups and coatings are not yet routinely applied to nanomaterial characterization. We have employed a combination of quantitative NMR (qNMR) and thermogravimetric analysis (TGA) to address this problem for commercial cerium, nickel, and iron oxide nanoparticles (NPs) that have been modified to add functional coatings with (3-aminopropyl)triethoxysilane (APTES), stearic acid, and polyvinylpyrrolidone (PVP). The qNMR method involves quantification of material that is released from the NPs and quantified in the supernatant after removal of NPs. Removal of aminopropylsilanes was accomplished by basic hydrolysis whereas PVP and stearic acid were removed by ligand exchange using sodium hexametaphosphate and pentadecafluorooctanoic acid, respectively. The method accuracy was confirmed by analysis of NPs with a known content of surface groups. Complementary TGA studies were carried out in both air and argon atmosphere with FT-IR of evolved gases in argon to confirm the identity of the functional groups. TGA measurements for some unfunctionalized samples show mass loss due to unidentified components which makes quantification of functional groups in surface-modified samples less reliable. XPS provides information on the presence of surface contaminants and the level of surface hydroxylation for selected samples. Despite the issues associated with accurate quantification using TGA, the TGA estimates agree reasonably well with the qNMR data for samples with high surface loading. This study highlights the issues in analysis of commercial nanomaterials and is an advance towards the development of generally applicable methods for quantifying surface functional groups.
Graphical abstract
Publisher
Springer Science and Business Media LLC
Subject
Biochemistry,Analytical Chemistry
Reference43 articles.
1. Baer DR. The chameleon effect: characterization challenges due to the variability of nanoparticles and their surfaces. Front Chem. 2018;6:145.
2. Clausen PA, Kofoed-Sørensen V, Nørgaard AW, Sahlgren NM, Jensen KA. Thermogravimetry and mass spectrometry of extractable organics from manufactured nanomaterials for identification of potential coating components. Materials. 2019;12:3657.
3. Hennig A, Dietrich PM, Hemmann F, Thiele T, Borcherding H, Hoffmann A, Schedler U, Jäger C, Resch-Genger U, Unger WES. En route to traceable reference standards for surface group quantifications by XPS. NMR and fluorescence spectroscopy Analyst. 2015;140:1804–8.
4. Radnik J, Kersting R, Hagenhoff B, Bennet F, Ciornii D, Nymark P, Grafström R, Hodoroaba V-D. Reliable surface analysis data of nanomaterials in support of risk assessment based on minimum information requirements. Nanomaterials. 2021;11:639.
5. Smith AM, Johnston KA, Crawford SE, Marbella LE, Millstone JE. Ligand density quantification on colloidal inorganic nanoparticles. Analyst. 2017;142:11–29.