A comparative study is presented of the hydrolytic and thermal stability of 24 different kinds of monolayers on Si(111), Si(100), SiC, SiN, SiO2, CrN, ITO, PAO, Au, and stainless steel surfaces. These surfaces were modified utilizing appropriate organic compounds having a constant alkyl chain length (C18), but with different surface-reactive groups, such as 1-octadecene, 1-octadecyne, 1-octadecyltrichlorosilane, 1-octadecanethiol, 1-octadecylamine and 1-octadecylphosphonic acid. The hydrolytic stability of obtained monolayers was systematically investigated in triplicate in constantly flowing aqueous media at room temperature in acidic (pH 3), basic (pH 11), phosphate buffer saline (PBS) and deionized water (neutral conditions), for a period of 1 day, 7 days, and 30 days, yielding 1152 data points for the hydrolytic stability. The hydrolytic stability was monitored by static contact angle measurements and X-ray photoelectron spectroscopy (XPS). The covalently bound alkyne monolayers on Si(111), Si(100), and SiC were shown to be among the most stable monolayers under acidic and neutral conditions. Additionally, the thermal stability of 14 different monolayers was studied in vacuum using XPS at elevated temperatures (25-600 °C). Similar to the hydrolytic stability, the covalently bound both alkyne and alkene monolayers on Si(111), Si(100) and SiC started to degrade from temperatures above 260 °C, whereas on oxide surfaces (e.g., PAO) phosphonate monolayers even displayed thermal stability up to ∼500 °C.

Summary The addition of NaBH4 to Co–ethylenediaminetetraacetate (Co–EDTA) and Co–citrate solutions at 25 °C does not lead to generation of hydrogen. However, in the presence of Co‐based catalysts synthesized via chemical reduction of Co–EDTA and Co–citrate complexes with NaBH4 at elevated temperature, an intensive generation of H2 took place. In this study, the reduction mechanism of both complexes was elucidated by using various techniques. From the results of attenuated total reflection and mass spectrometry analysis, it was suggested that NaBH4 was oxidized to NaBO2 and that organic ligands of Co complexes were decomposed to gaseous hydrocarbons, such as C2H4, C3H4, and/or C2H3N. Structural characterizations of X‐ray diffraction, scanning transmission electron microscopy, transmission electron microscope, energy‐dispersive spectroscopy, and X‐ray photoelectron spectra on the catalysts revealed that Co(OH)2, metallic cobalt, and cobalt borate were obtained in both cases. The morphology of Co(OH)2 and the dispersion of metallic cobalt and cobalt borate nanoparticles were significantly different. In the case of the catalyst prepared from Co–EDTA, the nanoparticles of Co species aggregated with diameters from 100 to several hundred nanometers on Co(OH)2 slabs. On the catalyst prepared from Co–citrate, the Co(OH)2 formed sheets, and the nanoparticles of Co species formed clusters of 5–10 nm in diameter, which are dispersed well on the Co(OH)2 sheet. The catalyst obtained from Co–citrate showed higher catalytic activity on hydrolysis reaction of NaBH4 than that from Co–EDTA. Copyright © 2016 John Wiley & Sons, Ltd.