XANES reflects coordination change and underlying surface disorder of zinc adsorbed to silica

Zinc K-edge X-ray absorption near-edge structure (XANES) spectroscopy of Zn adsorbed to silica and Zn-bearing minerals, salts and solutions was conducted to explore how XANES spectra reflect coordination environment and disorder in the surface to which a metal ion is sorbed. Specifically, XANES spectra for five distinct Zn adsorption complexes (Znads) on quartz and amorphous silica [SiO2(am)] are presented from the Zn–water–silica surface system: outer-sphere octahedral Znads on quartz, inner-sphere octahedral Znads on quartz, inner-sphere tetrahedral Znads on quartz, inner-sphere octahedral Znads on SiO2(am) and inner-sphere tetrahedral Znads on SiO2(am). XANES spectral analysis of these complexes on quartz versus SiO2(am) reveals that normalized peak absorbance and K-edge energy position generally decrease with increasing surface disorder and decreasing Zn–O coordination. On quartz, the absorption-edge energy of Znads ranges from 9663.0 to 9664.1 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On SiO2(am), the absorption-edge energy of Znads ranges from 9662.3 to 9663.4 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On both silica substrates, octahedral Znads presents a single K-edge peak feature, whereas tetrahedral Znads presents two absorbance features. The energy space between the two absorbance peak features of the XANES K-edge of tetrahedral Znads is 2.4 eV for Zn on quartz and 3.2 eV for Zn on SiO2(am). Linear combination fitting of samples with a mixture of Znads complex types demonstrates that the XANES spectra of octahedral and tetrahedral Znads on silica are distinct enough for quantitative identification. These results suggest caution when deciphering Zn speciation in natural samples via linear combination approaches using a single Znads standard to represent sorption on a particular mineral surface. Correlation between XANES spectral features and prior extended X-ray absorption fine structure (EXAFS) derived coordination environments for these Znads on silica samples provides insight into Zn speciation in natural systems with XANES compatible Zn concentrations too low for EXAFS analysis.

Revealing differences in the chemical form of zinc in brain tissue using K-edge X-ray absorption near-edge structure spectroscopy

This study demonstrates the use of X-ray absorption near-edge structure (XANES) spectroscopy at the Zn K-edge to study the chemical form of Zn (Zn speciation) in situ within rodent brain tissue.

A first glance at the micro-ZnO coating of maize (Zea mays L.) seeds: a study of the elemental spatial distribution and Zn speciation analysis

Advanced microanalytical tools (micro-XRF and micro-XANES) were used to provide important information regarding potential nutrient bioavailability in ZnO-treated maize seeds, which is relevant to those interested in biofortification studies.

SPESIASI DAN BIOAVAILABILITAS LOGAM BERAT Cu DAN Zn DALAM TANAH PERTANIAN ORGANIK DAN ANORGANIK

Agriculture in Indonesia generaly applies agrochemical to improve the quality and quantity of the products, but the impact is, both lands and their products could be contaminated by pollutans especially heavy metals. This study aimed to determine the total metals, speciation, and bioavailability of Cu and Zn in organic and inorganic agricultural soils in Blahbatuh District, Gianyar Regency. The sequential extraction method was performed to release the bonds of heavy metals in each soil component and the determination of the metal concentration was carried out using AAS. The total metals of Cu and Zn in both organic and inorganic soils indicated that both type of soils were still classified as uncontaminated soils because the metal contents were below the maximum limit allowed. The total contents of Cu and Zn in the organic soil were of 45.3922 mg/kg and 47.7645 mg/kg, respectively, while Cu and Zn in the inorganic soil were 48.9121 mg/kg ??and 49.9474 mg/kg, respectively. Fractination in the organic and inorganic soil EFLE (easly, freely,leachable, and exchangeable), reducible, oxidisable, dan resistant including F4> F3> F2> F1 for Cu and F4> F3> F1> F2 for Zn. The bioavailability of Cu and Zn in the organic soils were 10.52-23.79% and 3.79-7.21% bioavailable, 10.03-25.50% and 14.99-32.68% potentially bioavailable, 38.64-63.19% and 41.20- 60.28% non bioavailable, while in the inorganic soil and were 18.31-32.63% and 4.54-7.85% bioavailable, 9.86-13.85% and 15.26-32.55% potentially bioavailable, and 40.20-59.14% and 42.84-58.26% non bioavailable. Consuquenthy, both types of the agricultural soils would be safe for planting various types of rice. Keywords: bioavailability, Cu and Zn, speciation, agricultural soil