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F. Horak, A. Nagl, K. Föttinger, A. Limbeck:
"Quantitative analysis of nano-particle catalyst surface modifications by Laser Ablation Inductive Plasma Mass Spectrometry";
Vortrag: ANAKON 2019, Münster, Germany; 25.03.2019 - 28.03.2019; in: "Programm", (2019), S. 63.

TiO2 nanoparticles (NP) can be used in a vast variety of areas ranging from conventional products such as paints, plastics and cosmetics to more high-tech applications like high temperature catalyst materials. The functional properties of the material are closely linked to the chemical/elemental composition and surface modifications. Especially surface modifications such as depositions of Au, Ag and other elements in varying amounts can significantly enhance or suppress catalytic properties of the regular TiO2 NP. Calculating reaction rates and turnover frequencies (TOFs)related to the catalytically active metal NP is crucial for the characterization of catalyst materials. Therefore, exact knowledge of the respective metal loading of the catalyst materials, which is otherwise usually unknown due to different synthesis techniques, is essential.
Due to the high thermal and chemical stability of TiO2 NP, conventional methods such as acid digestion, whilst being well established for many applications, are labor intensive, require a significant investment in laboratory equipment and there may not always be a suitable recipe at hand for specific compositions.
Here we propose a solid sampling approach based on Laser Ablation Inductive Plasma Mass Spectrometry (LA-ICP-MS), which enables a quantitative analysis of TiO2 NP without extensive sample pretreatment, use of concentrated acids or uniquely tailored digestion schemes. For this, the catalyst material was dispersed in volatile solvent and spread on polycarbonate disks. After the evaporation of the solvent individual clusters of NP material were ablated with a NWR213 laser-ablation system and analyzed with a Thermo Fisher iCap Q ICP-MS. Correction factors and calibration curves were determined from in-house reference material produced in a micro-dried-droplet (μDD) approach. These consist of defined mixtures of liquid reference material which are deposited in self-aliquoting wells to provide defined amounts of material with known composition. These μDDs were produced on the same substrate as used for the NPs to reduce potential matrix effects in the measurement. The results of the proposed laser ablation method, whilst not having the same precision of the liquid analysis, were in good agreement to those of the acid digestion. In addition to the bulk composition of the catalyst material, the significantly smaller sampling size of LA-ICP-MS, compared to a conventional digestion, enabled access to information on the homogeneity of custom materials. This information would usually been lost within the bulk concentration and is particularly useful for the evaluation of new material synthesis under development.

LA-ICP-MS, catalyst material, nanoparticle analysis, composition