In this review we explore the biotic transformations of nitrogenous compounds that occur during denitrification, and the factors that influence denitrifier populations and enzyme activities, and ...hence, affect the production of nitrous oxide (N2O) and dinitrogen (N2) in soils. Characteristics of the genes related to denitrification are also presented. Denitrification is discussed with particular emphasis on nitrogen (N) inputs and dynamics within grasslands, and their impacts on the key soil variables and processes regulating denitrification and related gaseous N2O and N2 emissions. Factors affecting denitrification include soil N, carbon (C), pH, temperature, oxygen supply and water content. We understand that the N2O:N2 production ratio responds to the changes in these factors. Increased soil N supply, decreased soil pH, C availability and water content generally increase N2O:N2 ratio. The review also covers approaches to identify and quantify denitrification, including acetylene inhibition, 15N tracer and direct N2 quantification techniques. We also outline the importance of emerging molecular techniques to assess gene diversity and reveal enzymes that consume N2O during denitrification and the factors affecting their activities and consider a process-based approach that can be used to quantify the N2O:N2 product ratio and N2O emissions with known levels of uncertainty in soils. Finally, we explore strategies to reduce the N2O:N2 product ratio during denitrification to mitigate N2O emissions. Future research needs to focus on evaluating the N2O-reducing ability of the denitrifiers to accelerate the conversion of N2O to N2 and the reduction of N2O:N2 ratio during denitrification.
► We review denitrification, denitrifier populations and enzyme activities, nitrous oxide and dinitrogen production in soils. ► We describe molecular techniques to assess gene diversity and reveal enzymes that consume nitrous oxide. ► We consider a process-based approach to quantify the nitrous oxide:dinitrogen ratio and nitrous oxide emissions. ► We discuss the management strategies to enhance nitrous oxide reduction during denitrification.
We report here the stabilization of the cubic phase under ambient conditions in the thin films of zirconia synthesized by electron beam evaporation. The cubic phase stabilization was achieved without ...the use of chemical stabilizers and/or concurrent ion beam bombardment. Films of two different thicknesses (660 nm and 140 nm) were deposited. While the 660 nm as-deposited films were in the cubic phase, as indicated by X-ray diffraction and Raman spectroscopy, the 140 nm as-deposited films were amorphous and the transformation to the cubic phase was obtained after thermal annealing. Extended X-ray absorption fine structure measurements revealed the existence of oxygen vacancies in the local structure surrounding zirconium for all films. However, the amount of these oxygen vacancies was found to be significantly higher for the amorphous films as compared to that for the films in the cubic phase (660 nm as-deposited and 140 nm annealed films). The stabilization of the cubic phase is attributed to the breaking of the oxygen-zirconium bonds due to the presence of the oxygen vacancies, which results in the suppression of the soft X
2
−
mode of vibration of the oxygen sub-lattice. Our first-principles modeling under the framework of density functional theory shows that the cubic structure with oxygen vacancies is indeed more stable under ambient conditions than its pristine (without vacancies) counterpart due to breaking of the oxygen bonds. The requirement of a critical amount of these vacancies for cubic phase stabilization is discussed.
Oxygen vacancy mediated cubic phase stabilization at ambient conditions in pure nano-crystalline zirconia films synthesized by electron beam evaporation.
Local and long-range structural properties, of sol-gel synthesized, Ce1-xNixO2 (0 ≤ x ≤ 0.1) nanopowders have been investigated. Substitution of Ce4+ by comparably smaller Ni2+/Ni3+ ions leads to ...decrement in lattice parameters. UV–visible spectra reveal decrease of bandgap with increase of disorder upon increasing Ni substitution. The photoluminescence (PL) spectra reveal five major peaks attributed to various defect states. Ni substitution results in the creation of oxygen vacancies (VO) which further leads to conversion of considerable amount of Ce4+ ions to larger size Ce3+. These changes notably, modify the structure of the host lattice. The defects created along with the structural modifications bring, changes in the PL emission. The disorder in the lattice results in increase of non-radiative decay which reduces the PL emission. An increasing VO and Ce3+ concentration at the surface acts as emission quenching centers. Lattice disorder and VO quantities were estimated using X-ray absorption (XAS), UV–vis and Raman spectroscopy.
•Single phase, nanocrystalline Ni substituted CeO2 were prepared by sol-gel method.•Ni substitution in CeO2, leads to reduction of Ce4+ → Ce3+ but does not alter its local structure.•Lattice strain and disorder (Urbach energy) increases with substitution.•Oxygen vacancies related defects cause redshift in band-gap and quenching of PL emission.
This article reports the detailed X-ray absorption spectroscopy (XAS) study of Al
1−
x
Cr
x
N (
x
= 4, 6, 11%) thin films synthesized by the reactive magnetron co-sputtering technique. All these ...films were crystallized with a hexagonal wurtzite structure with preferential orientation along the
a
-axis without the formation of any secondary phases. Surface chemical analysis to evaluate the Cr concentration was carried out using X-ray photoelectron spectroscopy. The study confirmed the presence of AlN and Cr in bonding with N. The local crystal structure around the Cr dopant in the as-synthesized and annealed thin films has been analyzed by both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques. From XAS, it was found that Cr replaced the Al atom in the AlN lattice and led to a localized CrN species with distorted tetrahedral AlN in the absence of Cr clustering. The bond lengths of (Cr-N)
ax
, (Cr-N)
bs
and Cr-Al, extracted from the EXAFS fitting, were found to decrease with the Cr concentration for both the as-synthesized and annealed thin films due to the enhancement of p-d hybridization between the dopant and the host atoms. However, in the annealed 11% Cr film, the bond lengths are larger than the other and tend to match the Cr-N geometry in CrN.
This article reports the detailed X-ray absorption spectroscopy (XAS) study of Al
1−
x
Cr
x
N (
x
= 4, 6, 11%) thin films synthesized by the reactive magnetron co-sputtering technique.
Fourier transform infrared spectrometer equipped with attenuated total reflection and chemometrics were used to determine added sugar content (ASC), total soluble solids (TSS) and real juice content ...(RJC) in fresh and commercial mango juice. Sucrose solutions (0–27%), fresh mango juice adulterated with 0–27% sucrose, and two commercial brands were evaluated in wavenumber range of 4000–650
cm
−1. Partial least squares (PLS) discrimination and principal component analysis (PCA) were used to classify the samples with or without ASC. PLS and multiple linear regression (MLR) were carried out with and without data treatments. The detection limit for ASC was 3% for samples with low natural TSS, 5% for samples with natural TSS more than 10% and 3.6% for commercial samples. ASC, TSS, and RJC were predicted in the wavenumber range of 1476–912
cm
−1 using PLS (multiple correlation coefficient,
R
=
0.99) and three wavenumbers (1088, 1050, 991
cm
−1) using MLR (
R
=
0.98).
(Mn, Dy)-doped ZnO nanocrystals with Mn-concentrations of 0 and 2% and Dy-concentrations of 0, 0.5%, 1%, 2%, 4% and 6% have been prepared using a sol-gel technique. Preliminary structural ...characterisations of the samples have been carried out using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Fourier Transformed Infra-red (FTIR) spectroscopy. Changes in the luminescence characteristics of the samples due to rare earth doping have been investigated by Photoluminescence (PL) measurement and its effect on the magnetic properties of the samples has also been studied. The local structure at the host (Zn) and dopant (Mn and Dy) sites of the samples have been thoroughly investigated by synchrotron based X-ray absorption spectroscopy (XAS), which is an element specific microscopic technique comprising both X-ray near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements and the magnetic properties of the samples have been explained in light of the findings from XANES and EXAFS.
EXAFS measurements on sol gel derived (Mn, Dy) co-doped ZnO nanocrystals show that oxygen vacancies are created near the Dy sites into ZnO lattice. Thus, oxygen vacancy assisted bound magnetic polarons contribute to the RTFM in the Dy doped samples.
Fig. (a) The XPS spectra of the W 4f and Si 2p orbitals observed for WSe2 deposited on the SiO2 substrate, (b) the observed core-level spectrum of the Si 2p orbital and the valence-band spectrum of ...the bare SiO2 substrate, (c) the observed core-level spectrum of the W 4f orbital and the valence-band spectrum of WSe2, and (d) schematic diagram of the energy band alignment at the few-layer and bulk WSe2/SiO2 interfaces.
Display omitted
•We report the simple liquid exfoliation method to synthesize WSe2 nanosheets.•It acts as a substitute for the chemical vapor deposition growth mechanism.•The band offset investigations are carried out using XPS and VBPES measurements.•Type-I band alignment at the WSe2/SiO2 heterointerface is observed.
In this work, we study the band alignment of few-layer thick WSe2/SiO2 heterointerface. The few monolayer thick WSe2 nanosheets are synthesized on 300 nm SiO2/Si substrate by employing liquid exfoliation method. Structural and optical investigations of fabricated WSe2 nanosheets were investigated using X-ray diffraction (XRD), Raman, valence band photoemission spectroscopy, and atomic force microscopy (AFM). By resorting to X-ray photoelectron spectroscopy (XPS) and valence band photoemission spectroscopy (VBPES) measurements, we found that WSe2/SiO2heterointerface Type-I band alignment. Moreover, our calculations reveal that values of valence band offset and conduction band offset at the WSe2/SiO2 interface were found to be 3.79 ± 0.05 and 3.21 ± 0.05 eV, respectively.
Compression-induced (≤1.01 GPa) phase transformation, local deformations, and pore architecture modifications in zeolitic-imidazole framework (ZIF-8) powder have been investigated, ex situ, using ...X-ray diffraction, extended X-ray absorption fine structure, Fourier transform infrared, and positron annihilation lifetime spectroscopy. Compression-induced reduction in crystallinity leading to partial amorphization of ZIF-8 is observed to be an irreversible phenomenon. The amorphization of ZIF-8 was accompanied by local deformations in imidazolate ring bonding. The study has confirmed the retention of Zn–N tetrahedral arrangement in the amorphous state of the framework through X-ray absorption measurements. The phase transformation and local deformations lead to modifications in powder morphology as well as reduction in internal porosity of the framework. The triplet state of positronium (o-Ps) has been used to investigate the pressure-induced pore architecture modifications. At the lowest applied pressure (0.20 GPa), partial collapse of open free volume inside the crystalline ZIF-8 leading to reduction in internal porosity has been observed, while the crystal structure is maintained. On further increasing the pressure, amorphization of ZIF-8 is observed leading to cataclysmic modifications in the pore architecture. The amorphous phase of the framework possesses a continuous random network of open volumes having a broader size distribution with fewer interconnections as compared to the crystalline counterpart. The present study also indicates the evolution of a new crystalline topology of ZIF-8 at applied pressure of 1.01 GPa through complementary techniques.
PDF
