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Methods of Investigating Structure and Chemical Composition
Published in Rishat G. Valeev, Alexander V. Vakhrushev, Aleksey Yu. Fedotov, Dmitrii I. Petukhov, A. N. Beltiukov, A. L. Trigub, A. V. Severyukhin, Nanostructured Semiconductors in Porous Alumina Matrices, 2019
Rishat G. Valeev, Alexander V. Vakhrushev, Aleksey Yu. Fedotov, Dmitrii I. Petukhov
X-ray absorption near-edge structure (XANES), less developed, or practiced than EXAFS, may provide valuable information about the oxidation state, coordination environment, and bonding characteristics of specific elements in a sample. The less common term near-edge X-ray absorption fine structure is used generally in the context of solid-state studies and is synonymous with XANES. The technique in practice requires a mix of qualitative and quantitative analysis to interpret the data and draw conclusions.
Tools and Techniques for Characterizing Nanomaterial Internalization/Uptake in Plants and its Importance in Agricultural Applications
Published in Ramesh Raliya, Nanoscale Engineering in Agricultural Management, 2019
The XAS spectrum has two parts, X-ray absorption near edge structure (XANES) and Extended X-ray absorption fine structure (EXAFS). Gui et al. reported the speciation analysis of Ce in lettuce plants by XANES (Gui et al. 2015). The oxidation state of cerium in butter head lettuce root was identified with XANES and it was found that Ce in the roots existed in a mixed oxidation state of Ce (IV) and Ce (III). μXANES studies on root samples of CeO2-treated corn plants revealed the speciation of Ce. The spectra obtained from epidermal and cortex spots were very similar to the spectra from CeO2 NPs and data analysis reported that Ce was mainly present as Ce (IV) (Zhao et al. 2012). Duran et al. exploited XANES for the Cu chemical speciation analysis in Phaseolus vulgaris (common Brazilian bean) seeds upon exposure to Cu-based nanoparticle solution. Cu accumulation spots were located and chemical speciation of the element was determined (Duran et al. 2017). In velvet mesquite plants, XANES spectra was used to confirm that Zn was found in the Zn (II) form and not as nanoparticles upon treatment with ZnO nanoparticles (Hernandez-Viezcas et al. 2011). Lopez Moreno et al. studied the biotransformation of ZnO and CeO2 nanoparticles in soybean seedlings and XAS spectra provided clear evidence of the presence of CeO2 nanoparticles in roots, but not ZnO nanoparticles (López-Moreno et al. 2010). XANES spectra from model compounds provided information about the speciation of Zn and Ce. The speciation of Ce in four different plant species upon treating their roots with nanoceria (4000 mg/L) was also determined based on XANES spectra for Ce from roots of treated plants on comparison with CeO2 nanoparticles as model compounds. Ce was found to be in the same oxidation state in roots and, thus, confirmed that no chemical transformation has happened in plant tissues after uptake of CeO2 nanoparticles (López-Moreno et al. 2010).
Non-Conventional Techniques for Characterization of Nanohybrid Materials Based on Clays
Published in Mahmood Aliofkhazraei, Advances in Nanostructured Composites, 2019
Denis T. Araújo, Breno F. Ferreira, Tiago H. da Silva, Maisa A. Moreira, Katia J. Ciuffi, Eduardo J. Nassar, Vicente Rives, Miguel A. Vicente, Katia J. Ciuffi, Eduardo J. Nassar, Vicente Rives, Raquel Trujillano, Antonio Gil, Sophia Korili, Emerson H. de Faria
The X-ray absorption spectrum can be divided into three regions, Figure 11 (Mazali 1998): Pre-edge region: This region is located between 2 and 10 eV below the absorption edge and refers to the electronic transitions from internal levels (1s, 2s, etc.) to partially occupied or unoccupied external levels with lower absorption energy than the bond energy. The measured absorption intensity can provide information about the oxidation state, bond nature, and symmetry site of the absorbing atom.XANES region: The region spanning from the absorption edge up to 50 eV above the absorption edge is known as XANES (X-ray Absorption Near-Edge Structure). Its theoretical analysis involves interaction of multiple photoelectron scattering and transitions to unoccupied levels (Figure 14). In this case, the scattering centers are located outside the first coordination sphere, which makes them sensitive to changes in the geometrical arrangement of the closest neighboring atoms. This may provide a large amount of information about site symmetry and crystallinity. EXAFS region: The region spanning from 50 to 1000 eV above the absorption edge is known as EXAFS (Extended X-Ray Absorption Fine Structure). This region presents oscillations originating mainly from simple diffusion processes (Figure 15). The oscillations are milder than those taking place in the XANES region. Only two atoms participate in the process, the absorbing atom and the backscattering atom of the first neighboring atoms. EXAFS analysis furnishes information about the interatomic distance (< 5Å) and the number and type of neighboring atoms located around the absorbing atom.
An overview of the methods for analyzing the chemical forms of metals in plants
Published in International Journal of Phytoremediation, 2022
Jiawei Yang, Lin Sun, Xing Shen, Min Dai, Imran Ali, Changsheng Peng, Iffat Naz
The method of direct detection of different forms of metals in plants is based on the X-ray absorption spectrum of Synchrotron radiation. Synchrotron radiation is the electromagnetic radiation emitted along the tangent direction of the orbit by charged particles traveling close to the speed of light. It was first discovered on the synchrotron in 1947. XAS is a material analysis technique based on synchrotron radiation using absorption spectrum. The principle is that, according to the different composition and structure of the sample and the difference in X-ray absorption intensity of the sample, the intensity of X-ray passing through the sample will attenuate to different degrees (Watson 1980). According to the different attenuation degrees, the X-ray absorption spectrum can analyze information such as material element composition, electron state and microstructure (Kroukamp et al. 2016). XAS spectrum can be divided into two parts: X-Ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure EXAFS (Bunker 2010; GAUR 2013). As shown in Figure 1, XANES was within 50 eV above the absorption edge, while EXAFS (50–1,000 eV) was above the absorption edge in the region above 50 eV (Zhao et al. 2019).
A review of biochar-based sorbents for separation of heavy metals from water
Published in International Journal of Phytoremediation, 2020
Muhammad Bilal Shakoor, Shafaqat Ali, Muhammad Rizwan, Farhat Abbas, Irshad Bibi, Muhammad Riaz, Usman Khalil, Nabeel Khan Niazi, Jörg Rinklebe
Sulfur containing materials such as low molecular weight organo-sulfur compounds or biochar are efficient in making complex with heavy metals therefore, biochar enriched with sulfur could be useful in removing heavy metals from contaminated water. Carbon-sulfur materials are sorption selective for heavy metals (Cd, Pb, Cu) which remove heavy metals by making strong binding of sparingly soluble metal sulfides on their surface (Wang et al.2015). Sorption of heavy metals onto biochar is highly dependent on S-containing thiol functional groups onto biochars. Thus, knowledge of S speciation on biochars is critical when potential heavy metals removal techniques are applied. The X-ray absorption near-edge structure (XANES) spectroscopy is an advanced technique which is commonly used to quantify and characterize S species present on different organic materials such as biochar (Wang et al.2013). The XANES analysis of oak and corn stover based biochar confirmed the occurrence of both types of S – Inorganic and organic (Cheah et al.2014). Previous data have shown that S containing thiol groups present in organic matter could make strong bond with Hg thus removing it from water(Blue et al.2010).
In situ characterizations for EPS-involved microprocesses in biological wastewater treatment systems
Published in Critical Reviews in Environmental Science and Technology, 2019
Peng Zhang, Bo Feng, You-Peng Chen, You-Zhi Dai, Jin-Song Guo
Based on the synchrotron radiation source, the photoelectrons excited by the X-ray passing through the sample are scattered by the surrounding coordination atoms. The intensity of X-ray absorption oscillates associates with the energy, and the electronic and geometric local structures of the sample can be obtained by studying these oscillatory signals. XAFS includes X-ray absorption near edge structure (XANES) (or near edge XAFS (NEXAFS)) and extended XAFS (EXAFS). The first 30–50 eV of XAFS from the X-ray absorption edge is called XANES, whereas the remainder of the spectrum corresponds to EXAFS. XANES reflects sensitively the chemical properties of the specific element, such as chemical bonding, charge state, and magnetic state, etc., and EXAFS can quantify the local coordination properties of the atom, including coordination number and bond length (Tanaka & Mizoguchi, 2009).