In any given matrix control over the final particle size distribution requires a constitutive understanding of the mechanisms and kinetics of the particle evolution. In this contribution we report on the formation mechanism of silver nanoparticles embedded in a soda-lime silicate glass matrix. For the silver ion-exchanged glass it is shown that at temperatures below 410 °C only molecular clusters (diameter 1 nm) by annealing above this threshold temperature of 410 °C. It is evidenced that the growth and thus the final silver nanoparticle size are determined by matrix- assisted reduction mechanisms. As a consequence, particle growth proceeds after the initial formation of stable clusters by addition of silver monomers which diffuse from the glass matrix. This is in contrast to the widely accepted concept of particle growth in metal−glass systems, in which it is assumed that the nanoparticle formation is predominantly governed by Ostwald ripening processes.

Formation mechanism of silver nanoparticles stabilized in glassy matrices.

Metal oxides are reviewed as catalysts to convert H2O and CO2 to fuels using solar energy. For photochemical conversion, TiO2 has been found to be the most stable and useful oxide material, but it is currently limited by its large bandgap and a mismatch between its conduction band and the redox couples for water splitting and CO2 reduction. A theoretical framework has been utilized to understand the basic thermodynamics and energetics in photochemical energy conversion systems. This is applied to model systems comprised of Ag2O and AgCl to examine why the former reacts thermochemically in air, while the latter reacts photochemically. For thermochemical conversion, zinc-, ceria-, and ferrite-based redox cycles are examined and examples of high-temperature solar reactors driven by concentrated solar radiation are presented. For CO2 splitting, theoretical solar-to-fuel energy conversion efficiencies can be up to 26.8% for photochemical systems, and can exceed 30% for thermochemical systems, provided that sen...

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Review: Photochemical and Thermochemical Production of Solar Fuels from H2O and CO2 Using Metal Oxide Catalysts

The ability of prokaryotic microorganisms to reduce the inorganic metals has opened up an exciting eco-friendly approach towards the development of natural 'nano-factories'. However, a number of issues have to be addressed from the nanotechnological and microbiological point of view before such a biosynthesis approach can compete with the existing physical and chemical methods. This report investigates the synthesis of silver oxide nanoparticles using Lactobacillus mindensis, isolated using fixer solution from an X-ray photographic laboratory. Nanoparticles obtained were characterized by means of UV-vis spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The UV-vis spectrum shows the absorbance maximum at 430 nm, which is a characteristic of surface plasmon resonance of silver. Further, the presence of stable nanoparticles in the range of 2-20 nm was determined using TEM analysis. Silver nanoparticles in the form of silver oxide were confirmed in the XRD study. In conclusion, Lactobacillus mindensis serves as a promising candidate in the quest to synthesize silver oxide nanoparticles through green chemistry.

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Lactobacillus Mediated Synthesis of Silver Oxide Nanoparticles

The formation of Cr3O8, Cr2O5, CrO2, and Cr2O3 by the decomposition of anhydrous CrO3 under a high oxygen pressure and their physical and chemical properties are presented. The crystal structure of CrO2 is a rutile type and its lattice constants do not vary with the ratio O/Cr. The specific gravity of CrO2 decreases with an increase in the ratio O/Cr. This is explained by assuming that the crystal structure of CrO2 contains an excess of Cr ions at interstitial sites. This crystal model is supported by the low electrical resistivity of CrO2. An electron microscopic examination showed an abnormal grain growth of CrO2 during the decomposition of Cr2O5 to CrO2. The activation energies of the decomposition of Cr2O5 and CrO2 to Cr2O3 in air are 61.7 and 48.2 kcal. per mole, respectively. The pressure-temperature diagram of various chromium oxides has been determined. From the pressure-temperature curve of CrO2-Cr2O3 the heat of decomposition is found to be 26.3 kcal. per mole.

Decomposition of Higher Oxides of Chromium Under Various Pressures of Oxygen

Silver oxide thin films have potential applications in ultra-high density optical non-volatile memories and in fluorescence imaging. In this paper, the physical properties of silver oxide thin films prepared at room temperature by the pulsed laser deposition (PLD) technique with varying oxygen pressure during growth are reported. The oxygen pressure in the growth chamber is varied between 9 and 50 Pa. The x-ray diffraction (XRD) analysis showed that all the films were polycrystalline. With increasing oxygen pressure in the growth chamber, it is observed that (i) the hexagonal Ag2O transforms to monoclinic AgO, (ii) the grain size in the film increases from 59 to 200 nm, (iii) the surface roughness of the film increases from 9 to 42 nm, (iv) the resistivity of the films increases from 1 to 4 × 104 Ω m, (v) the surface work function of the films increases from 5.47 to 5.61 eV and (vi) the optical band gap of AgO thin films decreases from 1.01 to 0.93 eV. Raman spectroscopy on AgO thin films shows low wave number peaks corresponding to the stretching vibration of Ag–O bonds. This study shows that single phase AgO thin films, a requirement for plasmonic devices, can be prepared at room temperature by the PLD technique with an oxygen pressure of 20 Pa.

https://iopscience.iop.org/article/10.1088/0022-3727/42/13/135411/pdf

L. W. Reeves

Papers

The thermal decomposition of silver oxide