Li, G.; Zakharov, D.N.; Sikder, S.; Xu, Y.; Tong, X.; Dimitrakellis, P.; Boscoboinik, J.A. In Situ Monitoring of Non-Thermal Plasma Cleaning of Surfactant Encapsulated Nanoparticles. Nanomaterials2024, 14, 290.
Li, G.; Zakharov, D.N.; Sikder, S.; Xu, Y.; Tong, X.; Dimitrakellis, P.; Boscoboinik, J.A. In Situ Monitoring of Non-Thermal Plasma Cleaning of Surfactant Encapsulated Nanoparticles. Nanomaterials 2024, 14, 290.
Li, G.; Zakharov, D.N.; Sikder, S.; Xu, Y.; Tong, X.; Dimitrakellis, P.; Boscoboinik, J.A. In Situ Monitoring of Non-Thermal Plasma Cleaning of Surfactant Encapsulated Nanoparticles. Nanomaterials2024, 14, 290.
Li, G.; Zakharov, D.N.; Sikder, S.; Xu, Y.; Tong, X.; Dimitrakellis, P.; Boscoboinik, J.A. In Situ Monitoring of Non-Thermal Plasma Cleaning of Surfactant Encapsulated Nanoparticles. Nanomaterials 2024, 14, 290.
Abstract
Surfactants are widely used in the synthesis of nanoparticles, as they have a remarkable ability to direct their growth to obtain well-defined shapes and sizes. However, their post-synthesis removal is a challenge, and the methods used often result in morphological changes that defeat the purpose of the initial controlled growth. The cleaning methods could be classified as thermal or non-thermal. In general, the structure of materials can be better preserved by non-thermal treatments. After the removal of surfactants, the highly active surfaces of nanomaterials may undergo structural reconstruction by exposure to a different environment. Thus, ex situ characterization after air exposure may not reflect the effect of the cleaning methods. In situ characterization is required to better understand the impact of various cleaning procedures. Combining X-ray photoelectron spectroscopy, in situ infrared reflection absorption spectroscopy, and environmental transmission electron microscopy measurements with CO probe experiments, we investigated different surfactant-removal methods to produce clean metallic Pt nanoparticles from surfactant-encapsulated ones. Non-thermal plasmas show the best results. It was demonstrated that both UV-ozone treatment and room temperature O2 plasma treatment lead to the formation of Pt oxides on the surface after the removal of the surfactant. These oxides are reduced to metallic Pt during in situ CO probe experiments. On the other hand, when H2 was used for plasma treatment, the Pt0 oxidation state and nanoparticle size distribution were preserved. In addition, H2 plasma treatment can reduce Pt oxides after O2-based treatments, resulting in metallic nanoparticles with clean surfaces. Thermal reduction in hydrogen leads to carbon species emerging onto nanoparticle surfaces after heating and agglomeration of Pt nanoparticles. Particularly, O2-based thermal treatments result in the formation of aggregates consisting of small nanoparticles. These findings provide a better understanding of the various options for surfactant removal from metal nanoparticles and point toward non-thermal plasmas as the best route if the integrity of the nanoparticle needs to be preserved.
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