X-ray Photoelectron Spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Insight into the Pathways of Manganese Oxalate Thermal Decomposition to MnO and MnCO3.

X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were employed to study the isothermal decomposition of MnC2O4 under ultrahigh vacuum and N2 environmental conditions, respectively. High-resolution core-level XP spectra, X-ray-induced Auger spectra, and infrared spectra were obtained as a function of annealing time. In XPS studies, the time-dependent thermal decomposition characteristics were elucidated by analyzing surface composition, chemical shifts, satellites in the Mn 2p3/2 and Mn LMV bands, and Auger parameters for Mn and O. Functional groups developing during the ongoing reaction were identified by DRIFTS from characteristic vibrations. For the first time, the isothermal decomposition of manganese oxalate was shown to proceed via two pathways involving nucleation and accumulation of MnO and MnCO3. The kinetics of the decomposition in vacuum could be described by the Prout-Tompkins or/and by the Avrami-Erofeev models. The results obtained by XPS, DRIFTS, and ex situ XRD allowed concluding that the final product of oxalate decomposition was composed of MnO and MnCO3 or/and unidentate/polydentate carbonate structures populating the surface of the sample. A substantial formation of graphitic carbon was also observed and associated with interface chemical reactivities between the MnO particles and the supporting gold foil.

Impact of Carbon Fluoroxide Nanoparticles on Cell Proliferation.

Cytotoxicity of fluorescent carbon fluoroxide (CFO) nanoparticles (NPs) was studied in a label-free manner on several cancer and non-cancer cell lines. A direct cytotoxic effect of the CFO NPs was clearly observed by a suppression of cell proliferation. The real-time measurement of cell activities allowed to quantify the impact of the uptaken NPs on cell proliferation and after washout of the NPs from the cell culture medium. The results show more toxic effects of the CFO NPs on cancer than on non-cancer cell lines. The notion of NPs biocompatibility must be related to a maximum concentration value of the NPs acceptable for a given cell type. Furthermore, the cytotoxicity effects of NPs should be studied not only during their direct exposure to cells but also after their washout from the culture medium.

Kinetics of Hydrogen Generation from Oxidation of Hydrogenated Silicon Nanocrystals in Aqueous Solutions.

Hydrogen generation rate is one of the most important parameters which must be considered for the development of engineering solutions in the field of hydrogen energy applications. In this paper, the kinetics of hydrogen generation from oxidation of hydrogenated porous silicon nanopowders in water are analyzed in detail. The splitting of the Si-H bonds of the nanopowders and water molecules during the oxidation reaction results in powerful hydrogen generation. The described technology is shown to be perfectly tunable and allows us to manage the kinetics by: (i) varying size distribution and porosity of silicon nanoparticles; (ii) chemical composition of oxidizing solutions; (iii) ambient temperature. In particular, hydrogen release below 0 °C is one of the significant advantages of such a technological way of performing hydrogen generation.

Nanocrystallite-liquid phase transition in porous matrices with chemically functionalized surfaces.

Nanocrystallite-liquid phase transitions are studied for 1-octadecene confined in the pores of chemically functionalized silica gels. These silica gels possess similar fractal geometries of the pore system but differ in chemical termination of the surface, specific surface area (F) and pore volume (V). Linear dependencies of the melting temperature and specific melting heat on the F/V ratio are found for a series of silica gels with identical surface termination. A thermodynamic model based on experimental data is established, which explains the observed shift of the phase transition parameters for porous matrices with different surface chemistries. In addition, this model allows evaluation of actual changes in nanocrystallite density, surface tension and entropy upon melting.

Impact of Water Adsorption on Nonlinear Optical Properties of Functionalized Porous Silicon.

The porous silicon (PS) surface modification diagnostics due to functionalization and water adsorption/desorption processes were provided by the self-action effects of picosecond range pulsed laser radiation at 1064 nm. It was shown that the PS surface functionalization-oxide removal, alkylation, and oxidation-resulted in a refractive nonlinear optical (NLO) response sign turn to self-focusing (Δn>0) versus the self-defocusing (Δn<0) observed in the aged PS. The sensitivity of the proposed technique was revealed to water adsorption/desorption from the chemically oxidized PS interface. For the dried PS, the self-defocusing effect with corresponding NLO cubic susceptibility Re(χ (3))∼-4.7·10-9 esu was observed versus the self-focusing one (∼5·10-8 esu) for the PS positioned in saturated water vapor at room temperature. The obtained results demonstrate high sensitivity and wide versatility of the proposed readout technique based on pulsed laser radiation self-action at 1064 nm to the PS surface modification monitoring/diagnostics applications.

Luminescence behavior of silicon and carbon nanoparticles dispersed in low-polar liquids.

A comparative photoluminescence analysis of as-prepared and chemically modified (by alkyl chains -C18H37) silicon and carbon nanoparticles dispersed in low-polar liquids is reported. Influence of the low-polar liquid nature and ambient temperature on photoluminescence of the nanoparticles has been investigated from the point of view of their possible application as thermal nanoprobes.