Search results for "Absorption"
showing 10 items of 2701 documents
Use of radiation sources with mercury isotopes for real-time highly sensitive and selective benzene determination in air and natural gas by different…
2015
A new analytical portable system is proposed for the direct determination of benzene vapor in the ambient air and natural gas, using differential absorption spectrometry with the direct Zeeman effect and innovative radiation sources: capillary mercury lamps with different isotopic compositions ((196)Hg, (198)Hg, (202)Hg, (204)Hg, and natural isotopic mixture). Resonance emission of mercury at a wavelength of 254 nm is used as probing radiation. The differential cross section of benzene absorption in dependence on wavelength is determined by scanning of magnetic field. It is found that the sensitivity of benzene detection is enhanced three times using lamp with the mercury isotope (204)Hg in…
Ultraviolet Filters in Cosmetics
2018
Abstract UV filters are used in sunscreen cosmetics to protect skin from the sunlight. Nowadays, they are also incorporated into other daily-use cosmetics. However, many concerns about their safety have been raised, because they can be absorbed through the skin, further metabolized and eventually bioaccumulated and/or excreted. These percutaneous absorption processes may result in various adverse health effects (i.e., allergic contact dermatitis) and other more serious systemic effects, such as carcinogenic and oestrogenic activity. For this reason, UV filters as well as their maximum allowed concentrations have been regulated by the legislations in force. In this sense, analytical control …
Photon absorption by aqueous TiO2 dispersion contained in a stirred photoreactor
1991
We present a simple experimental method which allows the evaluation of the absorbed photon flow. The method is based on measurements of transmitted photon rates (by means of standard actinometer solutions) for different reactor thicknesses and/or catalyst concentrations. The method was applied to phenol degradation reaction carried out in a stirred batch phtotoreactor containing aqueous TiO 2 (anatase) dispersion, directly irradied by a 1,500 W Xe lamp
Multichannel multiple scattering calculation ofL2,3-edge spectra ofTiO2andSrTiO3: Importance of multiplet coupling and band structure
2010
We report a theoretical study on x-ray absorption spectroscopy at the Ti-${L}_{2,3}$-edge of rutile and anatase ${\text{TiO}}_{2}$ as well as ${\text{SrTiO}}_{3}$. Using the first-principles multichannel multiple-scattering method, we obtain good agreement with experiment in all cases. We show that both multiplet-type electron correlation effects and the long-range band structure strongly influence the spectra. The differences in line shape between the three compounds are essentially a long-range effect which reflects the different crystal structures on a length scale of 1 nm.
Effect of titanium dioxide crystalline structure on the photocatalytic production of hydrogen
2011
The effect of the crystalline phase of TiO 2 (anatase, rutile and brookite) on its photocatalytic activity in hydrogen production from methanol-water vapours has been investigated by testing a series of both home-made and commercial TiO 2 photocatalysts, either bare or surface-modified by deposition of a fixed amount, i.e. 1 wt%, of platinum as co-catalyst. For all of the TiO 2 samples the rate of hydrogen production increased by one order of magnitude upon Pt deposition, because of the ability of Pt to enhance the separation of photoproduced electron-hole pairs. Under irradiation in the 350-450 nm wavelength range, brookite and anatase showed similar photoactivities, both superior to that …
Rate of photon absorption and turnover number: two parameters for the comparison of heterogeneous photocatalytic systems in a quantitative way
1993
Abstract In order to correctly compare the performance of different photocatalytic systems using polycrystalline semiconductor oxides, two parameters are proposed: the rate of photon absorption (rpa) and the turnover number (tn). From these quantities the quantum yield (qy), which indicates the efficiency of the absorbed photons for promoting a reaction event, can be determined. The phenol photodegradation reaction, carried out in aqueous dispersions of polycrystalline TiO2 (anatase) of different preparation methods and sources, has been used as “test reaction” in order to determine the tn, rpa and qy values.
ChemInform Abstract: Rate of Photon Absorption and Turnover Number: Two Parameters for the Comparison of Heterogeneous Photocatalytic Systems in a Qu…
2010
Abstract In order to correctly compare the performance of different photocatalytic systems using polycrystalline semiconductor oxides, two parameters are proposed: the rate of photon absorption (rpa) and the turnover number (tn). From these quantities the quantum yield (qy), which indicates the efficiency of the absorbed photons for promoting a reaction event, can be determined. The phenol photodegradation reaction, carried out in aqueous dispersions of polycrystalline TiO2 (anatase) of different preparation methods and sources, has been used as “test reaction” in order to determine the tn, rpa and qy values.
Photocatalytic activity of anatase-nickel ferrite heterostructures
2015
The simple co-precipitation route was used to couple commercial TiO2 anatase nanopowder with nickel ferrite (NiFe2O4). The morphology and the crystalline structure of composite nanoparticles were characterised by TEM, N2 adsorption-desorption, XRD and Rietveld refinement, XPS and XAS. The optical and magnetic properties were investigated. After co-precipitation NiFe2O4 nanoparticles, composed of spinel ferrite crystal phase, were formed on the surface of TiO2 anatase nanopowder. The TiO2/NiFe2O4 composite oxide demonstrated large specific surface area, high visible light absorption efficiency and efficient charge carrier separation, compared to pristine anatase TiO2 or pristine NiFe2O4, rep…
Physicochemical characterization of metal hexacyanometallate–TiO2composite materials
2015
The paper describes the synthesis and characterization of novel TiO2–metal hexacyanometallates (MHCMs) composite materials. The starting material, TiO2, was modified by addition of cobalt-hexacyanoferrate (CoHCF) or iron-hexacyanocobaltate (FeHCC) at various concentrations. The resulting composites were characterized as follows: cyclic voltammetry (CV) followed the formation of TiO2–MHCM clusters, TEM micrographs studied their morphology, XAS and XPS data indicated that MHCM bonds to TiO2 through the nitrogen atom of its –CN group and modifies the environment of Ti compared to that of pure anatase. As expected, and confirmed by UV-Vis and XP-valence band data, the electronic properties of T…
Brown Carbon Aerosol in Urban Xi'an, Northwest China: The Composition and Light Absorption Properties.
2018
Light-absorbing organic carbon (i.e., brown carbon or BrC) in the atmospheric aerosol has significant contribution to light absorption and radiative forcing. However, the link between BrC optical properties and chemical composition remains poorly constrained. In this study, we combine spectrophotometric measurements and chemical analyses of BrC samples collected from July 2008 to June 2009 in urban Xi'an, Northwest China. Elevated BrC was observed in winter (5 times higher than in summer), largely due to increased emissions from wintertime domestic biomass burning. The light absorption coefficient of methanol-soluble BrC at 365 nm (on average approximately twice that of water-soluble BrC) w…