Assessment of Catalyst Selectivity in Carbon-Nanotube Silylesterification

The functionalization of carbon nanotubes (CNTs) plays a key role in their solubilization and compatibility for many applications. Among the many possible ways to functionalize CNTs, the creation of an Si–O–C bond is crucial for the formation of silicone composites. Catalyst-mediated silylesterification is useful in creating Si–O–C bonds because it is cost-effective and uses a hydrosilane precursor of lower reactivity than that of chlorosilane. However, it was previously demonstrated that two important silylesterification catalysts (zinc chloride and Karstedt’s catalyst) exhibit different selectivity for oxidized functional groups that are present on the surface of CNTs after oxidative acid treatment. This report details the selective modification of CNTs with various oxygenated functional groups (aromatic and nonaromatic alcohols, carboxylic acids, ethers, and ketones) using diazonium chemistry. Modified CNTs were used to assess the specifity of zinc chloride and Karstedt’s catalyst for oxygenated functional groups during a silylesterification reaction. Karstedt’s catalyst appeared to be widely applicable, allowing for the silylesterification of all of the aforementioned oxygenated functional groups. However, it showed lower efficacy for ethers and ketones. By contrast, zinc chloride was found to be very specific for nonaromatic carboxylic acids. This study also examined the Hansen solubility parameters of modified CNTs

XPS fast depth profile of the native oxide layers on AISI 304, 316 and 430 commercial stainless steels and their evolution with time

The thin oxide layers forming on the metal surfaces of metals determine their interactions with the environment and have a strong influence on the materials properties such as corrosion resistance. Such oxide layers typically have a thickness in the range of a few nanometres, which is a challenge for the analysis of their chemical nature and structure. To characterize such materials and surfaces, XPS using depth profile sputtering is a sensitive and powerful technique. However, it is rather elaborate and raises the risk of changing the nature of the surface layer during the analysis process. This work reports on a protocol for a faster approach to depth profile X-Ray photoelectron spectroscopy (XPS) analysis to obtain accurate and reproducible information on the oxide layer structure by using the snapshot mode of the XPS instrument. This protocol is applied to three stainless steels differing by their chemical composition: FeCr AISI 430, FeCrNi AISI 304 and the chemically more complex FeCrNiMo AISI 316. The respective oxide layer structures observed using this methodology are consistent with literature data. In addition, the structures have been confirmed using non-destructive techniques such as angle-resolved XPS (AR-XPS) and Hard XPS (HAXPES). Finally, the analysis protocol has been applied to obtain information on the evolution of the surface chemistry of those stainless steel grades resulting from mechanical polishing and subsequent aging in contact with atmosphere.The authors acknowledge SOLEIL for provision of synchrotron radiation facilities (proposal 20180830) and would like to thank D. Ceolin and J.-P. Rueff for assistance in using beamline "GALAXIES". The authors thanks the DGO6 for supporting this research in the field of AdEPT project (convention 1610449)Detriche, S (corresponding , author), Univ Namur, Namur Inst Struct Matter NISM, Lab Chem & Electrochem Surfaces CES, Rue Bruxelles 61, B-5000 Namur, Belgium. [email protected]