Search results for "Absorption"
showing 10 items of 2701 documents
Direct determination of total mercury in phosphate rock using alkaline fusion digestion
2014
The aim of this work was to develop a new method to determine the mercury (Hg) concentrations in phosphate rock using a dedicated analytical instrument (the DMA80 Tricell by Milestone) that employs an integrated sequence of thermal decomposition followed by catalyst conversion, amalgamation and atomic absorption spectrophotometry. However, this instrument underestimates Hg concentrations when phosphorite and apatite rocks are investigated with a classic thermal decomposition treatment that complies with US EPA method 7473. Therefore, to improve the recovery of total Hg, we performed alkaline fusion digestion (AFD) directly inside the furnace of the instrument, using BCR(32) as a certified r…
Special needs and characteristic features of (photo)catalytic reactors with a review of the proposed Solutions
2019
Abstract In the present chapter, the analogies between photocatalytic systems and the systems where the more common thermally activated reactions take place are highlighted. The objective is to propose a unified approach for the analysis and the design, which, however, must take into account how and why photocatalytic reactors differ from reactors with thermal reactions. The necessity of absorbing photons to activate the photocatalytic process adds complexity to the system, but some approaches are presented to simplify the problems and make easier their solution.
Preparation of N-doped TiO2: characterization and photocatalytic performance under UV and visibile light
2009
Nanocrystalline N-doped TiO(2) samples were prepared by using TiCl(4) or TiOSO(4) as precursors. The powders were characterized by X-ray diffraction, BET specific surface area measurements, scanning electron microscopy, diffuse reflectance spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity was tested using the photodegradation of 4-nitrophenol under UV and visible light.Some samples were more active than commercial Degussa P25. A shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed in the samples obtained from TiCl(4). Two absorption edges were observed in the samples derived from T…
Optical suppression of ferroelectricity in polysiloxane copolymers with chiral and photochromic side groups
1998
The ferroelectricity of surface-stabilized aligned films of polysiloxane copolymers containing chiral esters and photochromic azobenzene moieties within the side groups is suppressed on UV irradiation and is rebuilt on visible irradiation. The liquid crystalline polymer (Sc* 64 SA 80 i) shows ferroelectric behavior below 64°C. The photoinduced modification of supramolecular order and the corresponding changes in its dynamics are studied by polarized UV/vis spectroscopy and broad band dielectric spectroscopy (10−2–105 Hz). The dielectric measurements show that UV irradiation causes a loss of ferroelectricity within an interval of 10 K below the phase transition temperature. The photochemical…
Structural Analysis and Photocurrent Spectroscopy of CCCs on 99.99% Aluminum
2003
A characterization of chromate conversion coatings (CCCs) formed in the presence and in the absence of accelerator (ferroferricyanide redox couple) has been performed by various techniques (transmission electron microscopy, TEM, glow discharge optical emission spectrometry, GDOES, X-ray absorption near-end structure, XANES, and photon correlation spectroscopy). The results of a detailed investigation on morphological, compositional, and solid-state properties of freshly converted aluminum samples at different immersion times (30 s-90 min) are reported. The TEM and GDOES data suggest the presence of iron-cyanide species only in the external layer of CCC of nearly constant thickness. The XANE…
Photoconductivity of Germanium Nanowire Arrays Incorporated in Anodic Aluminum Oxide
2007
Photoconductivity of germanium nanowire arrays of 50 and 100 nm diameter incorporated into Anodic Aluminum Oxide (AAO) membranes illuminated with visible light is investigated. Photocurrent response to excitation radiation with time constants faster than 10−4 s were governed by absorption of incident light by nanowires, while photokinetics with time constants of the order of 10−3 s originates from the photoluminescence of the AAO matrix. Possible applications of nanowire arrays inside AAO as photoresistors are discussed.
Photoelectrochemical investigation of passive layers formed on Fe in different electrolytic solutions
2004
Abstract The passive films formed on Fe in different electrolytic solutions, spanning almost the overall pH range, and with different growth procedures were investigated systematically by photocurrent spectroscopy. The potentiodynamic growth curves are compared both in aerated and de-aerated electrolytes and a potentiostatic growth procedure is also employed. For high positive formation potentials, similar anodic spectra are recorded in all solutions giving an optical gap very close to that expected for crystalline Fe2O3. The origin of photocurrent spikes is also investigated and the effect of the formation potential upon the measured absorption threshold is discussed taking into account th…
Impact of π-conjugation configurations on the photovoltaic performance of the quinoxaline-based organic dyes
2017
Abstract Three novel quinoxaline-based donor-π-acceptor type organic dyes were synthesized and explored as sensitizers in dye-sensitized solar cells (DSSCs). The impacts of various π-conjugation configurations which contain different quinoxaline derivatives on the absorption properties, electrochemical properties and photovoltaic performances, as well as theoretical calculations have been investigated systematically. The photovoltaic performances of these dyes were found to be highly relevant to the π-conjugated configurations. In particular, the DSSC based on the dye with 2,3-dioctylquinoxaline as the spacer exhibited the highest efficiency of 8.20% with a short-circuit photocurrent densit…
Direct measurement of optical losses in plasmon-enhanced thin silicon films (Conference Presentation)
2018
Plasmon-enhanced absorption, often considered as a promising solution for efficient light trapping in thin film silicon solar cells, suffers from pronounced optical losses i.e. parasitic absorption, which do not contribute to the obtainable photocurrent. Direct measurements of such losses are therefore essential to optimize the design of plasmonic nanostructures and supporting layers. Importantly, contributions of useful and parasitic absorption cannot be measured separately with commonly used optical spectrophotometry. In this study we apply a novel strategy consisting in a combination of photocurrent and photothermal spectroscopic techniques to experimentally quantify the trade-off betwee…
On the Semiconductor Spectroscopy for Identification of Emergent Contaminants in Transparent Mediums
2021
In this chapter, we present a theoretical study of photoelectronic processes in experimental silicon \({n}^{+}{\text{-}}p{\text{-}}{n}^{+}\) structures with applications in identifying emergent contaminants in aqueous medium. Contribution due to various mechanisms of photon absorption to the total photocurrent is calculated. Various mechanisms, such as the influence of tunneling on the spectral characteristic and selective spectral photosensitivity of samples under investigation were investigated. The nature of the relationship between energy parameters of the absorbed waves and the structural parameters is revealed. Expressions are obtained for photocurrent with and without external diffus…