X-ray photoelectron spectroscopy (XPS) analysis of four Cu/SiO2 catalyst systems of different particle sizes of CuO on the surface showed variation in the relative peak area intensities of the shake-up lines to main core levels of the Cu 2p orbitals. These differences were attributed to various degrees of XPS-induced reduction of CuO initially formed on the surface by spin coating copper(II) acetate {Cu-(CH3CO2)2‚H2O, Cu(ac)2} solutions of varying concentration. Changes in Cu L3M4,5M4,5 X-ray excited Auger (XAES) line shapes under time-dependent exposure to the soft Mg KR X-rays revealed that smaller particle sizes were more susceptible to reduction to Cu(+1) than larger ones. The degree of reduction of Cu(+2) to Cu(+1) correlated with measured atomic force microscopic (AFM) particle heights of CuO on these substrates prior to XPS.

Functionalization of carbon nanotubes (CNTs) is important for enhancing deposition of metal nanoparticles in the fabrication of supported catalysts. A facile approach for oxidizing CNTs is presented using a sonochemical method to promote the density of surface functional groups. This was successfully employed in a previous study [J. Phys. Chem. B 2004, 108, 19255] to prepare highly dispersed, high-loading Pt nanoparticles on CNTs as fuel cell catalysts. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, cyclic voltammetry, and settling speeds were used to characterize the degree of surface functionalization and coverage. The sonochemical method effectively functionalized the CNTs. A mixture of -C-O-/-C=O and -COO- was observed along with evidence for weakly bound CO at longer treatment times. The integrated XPS C 1s core level peak area ratios of the oxidized-to-graphitic C oxidation states, as well as the atom % oxygen from the O 1s level, showed an increase in peak intensity (attributed to -CO(x)()) with increased sonication times from 1 to 8 h; the increase in C surface oxidation correlated well with the measured atom %. Most of the CNT surface oxidation occurred between 1 and 2 h. The sonochemically treated CNTs were also studied by cyclic voltammetry and settling experiments, and the results were consistent with the XPS observations.

To create new catalyst materials for fuel cell applications, multiwalled carbon nanotubes (CNTs) were functionalized with sCdO, sCsOsCs, sCOOs, and sCsOH groups using a sonochemical treatment method under acidic aqueous solution (HNO 3 /H 2 SO 4 ) conditions to make them amenable to deposition of highly dispersed, ∼4 nm diameter Pt nanoparticles. The Pt-CNT interface was probed with X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure spectroscopy (EXAFS), and Raman and attenuated total reflection infrared (ATR-IR) spectroscopies to elucidate the nature of the Pt cluster-CNT surface binding. The degree of disorder of the sp 3 -hybridized C from the CNTs, as measured by the Raman D-to-G integrated peak area ratios, increased with the degree of surface oxidation of the CNTs. EXAFS of the Pt L III edge showed Pt coordination with oxygen (in the form of PtO x ) at the outermost perimeter of the Pt clusters while the majority of the bulk, as shown by the XPS Pt 4f core level, was in the metallic form. Infrared measurements showed that the carbonyl CdO stretching at 1700 cm -1 red shifted to ∼1550 cm -1 following Pt cluster deposition. In addition, changes in the CsO structural features at ∼1030 and 1150 cm -1 were observed, indicative of Pt cluster binding with the ionic form of carboxylate, COO(Pt), or ester-like, C(dO)CO(Pt), O atoms.

One prevention and therapeutic strategy for diseases associated with peptide or protein fibrillation is to inhibit or delay the fibrillation process. Carbon dots (C–Dots) have recently emerged as benign nanoparticles to replace toxic quantum dots and have attracted great attention because of their unique optical properties and potential applications in biological systems. However, the effect of C-Dots on peptide or protein fibrillation has not been explored. In this in vitro study, human insulin was selected as a model to investigate the effect of C-Dots on insulin fibrillation. Water-soluble fluorescent C-Dots with sizes less than 6 nm were prepared from carbon powder and characterized by UV–vis spectroscopy, fluorescence, Fourier transform infrared spectrophotometry, X-ray photoelectron spectrometry, transmission electron microscopy, and atomic force microscopy. These C-Dots were able to efficiently inhibit insulin fibrillation in a concentration-dependent manner. The inhibiting effect of C-Dots was even observed at 0.2 μg/mL. Importantly, 40 μg/mL of C-Dots prevent 0.2 mg/mL of human insulin from fibrillation for 5 days under 65 °C, whereas insulin denatures in 3 h under the same conditions without C-Dots. The inhibiting effect is likely due to the interaction between C-Dots and insulin species before elongation. Cytotoxicity study shows that these C-Dots have very low cytotoxicity. Therefore, these C-Dots have the potential to inhibit insulin fibrillation in biological systems and in the pharmaceutical industry for the processing and formulation of insulin.

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