Topic
Raman spectroscopy
About: Raman spectroscopy is a research topic. Over the lifetime, 122605 publications have been published within this topic receiving 2891083 citations. The topic is also known as: Raman Spectrum Analysis & spectrum Analysis, Raman.
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TL;DR: A general model is developed that considers spinel defects and absorbed/adsorbed species as dominant controls on structural changes with particle size in hematite nanoparticles, including solid-state phase transitions, and supports the existence of intermediate phases during dehydration of goethite.
Abstract: Using Fourier Transform InfraRed (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM), we characterize the structure and/or morphology of hematite (α-Fe2O3) particles with sizes of 7, 18, 39 and 120 nm. It is found that these nanoparticles possess maghemite (γ-Fe2O3)-like defects in the near surface regions, to which a vibrational mode at 690 cm−1, active both in FTIR and Raman spectra, is assigned. The fraction of the maghemite-like defects and the net lattice disorder are inversely related to the particle size. However, the effect is opposite for nanoparticles grown by sintering of smaller hematite precursors under conditions when the formation of a uniform hematite-like structure throughout the aggregate is restricted by kinetic issues. This means that not only particle size but also the growth kinetics determines the structure of the nanoparticles. The observed structural changes are interpreted as size-induced α-Fe2O3
↔
γ-Fe2O3 phase transitions. We develop a general model that considers spinel defects and absorbed/adsorbed species (in our case, hydroxyls) as dominant controls on structural changes with particle size in hematite nanoparticles, including solid-state phase transitions. These changes are represented by trajectories in a phase diagram built in three phase coordinates—concentrations of spinel defects, absorbed impurities, and adsorbed species. The critical size for the onset of the α
→
γ phase transition depends on the particle environment, and for the dry particles used in this study is about 40 nm. The model supports the existence of intermediate phases (protohematite and hydrohematite) during dehydration of goethite. We also demonstrate that the hematite structure is significantly less defective when the nanoparticles are immersed in water or KBr matrix, which is explained by the effects of the electrochemical double layer and increased rigidity of the particle environment. Finally, we revise the problem of applicability of IR spectroscopy to the lattice vibrations of hematite nanoparticles, demonstrating that structural comparison of different samples is much more reliable if it is based on the Eu band at about 460 cm−1 and the spinel band at 690 cm−1, instead of the A2u/Eu band at about 550 cm−1 used in previous work. The new methodology is applied to analysis of the reported IR spectra of Martian hematite.
387 citations
TL;DR: Results clearly show that the BiVO4/CeO2 nanocomposite in a 0.6:0.4 mol ratio exhibited the highest photocatalytic activity in dye wastewater treatment.
Abstract: Preparation of bismuth vanadate and cerium dioxide (BiVO4/CeO2) nanocomposites as visible-light photocatalysts was successfully obtained by coupling a homogeneous precipitation method with hydrothermal techniques. The BiVO4/CeO2 nanocomposites with different mole ratios were synthesized and characterized by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). Absorption range and band gap energy, which are responsible for the observed photocatalyst behavior, were investigated by UV–vis diffuse reflectance (UV–vis DR) spectroscopy. Photocatalytic activities of the prepared samples were examined by studying the degradation of model dyes Methylene Blue, Methyl Orange, and a mixture of Methylene Blue and Methyl Orange solutions under visible-light irradiation (>400 nm). Results clearly show that the BiVO4/CeO2 nanocomposite in a 0.6:0.4 mol ratio exhibited the highest photocatalytic activity in dye wastewater treatment.
386 citations
TL;DR: In this article, the photoluminescence (PL) spectra at room temperature were measured and the strong UV excitonic emission indicates the good optical properties, and the weak deep-level emission reveals very limited structural defects in the crystals.
386 citations
Book•
01 Jan 1999
TL;DR: In this article, the Ligand Field Theory and the properties of transition metal complexes are discussed. But the authors do not discuss the applications of these properties in the field of molecular biology.
Abstract: Preface. Contributors, Volume I. Contents, Volume II. Contributors, Volume II. 1. Ligand Field Theory and the Properties of Transition Metal Complexes (A. Lever & E. Solomon). 2. Electron Paramagnetic Resonance Spectroscopy (A. Bencini & D. Gatteschi). 3. Mossbauer Spectroscopy (P. Gutlich & J. Ensling). 4. Polarized Absorption Spectroscopy (M. Hitchman & M. Riley). 5. Luminescence Spectroscopy (T. Brunold & H. Gudel). 6. Laser Spectroscopy (E. Krausz & H. Riesen). 7. IR, Raman, and Resonance Raman Spectroscopy (R. Czernuszewicz & T. Spiro). 8. Photoelectron Spectra of Inorganic and Organometallic Molecules in the Gas Phase using Synchrotron Radiation (G. Bancroft & Y. Hu). 9. X-Ray Absorption Spectroscopy and EXAFS Analysis: The Multiple-Scattering Method and Applications in Inorganic and Bioinorganic Chemistry (H. Zhang, et al.). 10. Electronic Structure Calculations on Transition Metal Complexes: Ab-Initio and Approximate Models (C. Martin & M. Zerner). 11. Electronic Structure Calculations: Density Functional Methods with Applications to Transition Metal Complexes (J. Noodleman & D. Case). Index.
385 citations
TL;DR: Recent approaches of utilizing the borrowing SERS activity strategy mainly through constructing two types of nanostructures are presented and the Raman spectra of surface water, having small Raman cross-section, on several transition metals for the first time are obtained.
384 citations