Tetrahedral charge and Fe content in dioctahedral smectites

AbstractNatural aluminosilicates can contain Fe in tetrahedral or octahedral coordination. Amongst smectites, tetrahedral iron is known to occur in Fe-rich nontronites but few indications exist for the presence of tetrahedral Fe in smectites of the montmorillonite–beidellite series. A set of 38 different bentonites showed a correlation of tetrahedral charge and Fe content in their smectites. All materials with large tetrahedral charge were rich in Fe. This could be explained by a general tendency of Fe to enter the tetrahedral sheet. To investigate this correlation, nine materials were selected and investigated by Mössbauer, UV-Vis, Fe K pre-edge and EXAFS spectroscopy with respect to tetrahedral Fe (Fe[IV]). The latter two methods were at the detection limit but Mössbauer and UV-Vis spectroscopy provided consistent results indicating the significance of both methods in spite of some scatter caused by the overall small amount of tetrahedral Fe. The results indicate the absence of any relation between Fe content and tetrahedral Fe. Tetrahedral Fe can be present in Fe-poor smectites and absent in the case of Fe-rich materials. This means that Fe-rich montmorillonites have a larger tetrahedral charge which is not caused by Fe[IV] but by Al[IV]. A possible explanation for this indirect relation is based on: the coordination of Al3+ in the weathering/smectite-forming solutions determines the coordination in the precipitates; and the Al[IV/VI] ratio increases with increasing pH. The correlation could thus be explained if the pH of weathering solutions generally was higher in Fe-rich parent smectite rocks than in more acidic smectite parent rocks. The relation between tetrahedral charge and Fe content can probably be explained by different geochemical contexts throughout the formation of smectites which affect the coordination of dissolved Al.

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Enhancement of the Peroxidase-Like Activity of Iodine-Capped Gold Nanoparticles for the Colorimetric Detection of Biothiols

Biosensors ◽

10.3390/bios10090113 ◽

2020 ◽

Vol 10 (9) ◽

pp. 113 ◽

Cited By ~ 1

Author(s):

Chia-Chen Chang ◽

Tsz-Lian Hsu ◽

Chie-Pein Chen ◽

Chen-Yu Chen

Keyword(s):

Gold Nanoparticles ◽

Catalytic Activity ◽

Detection Limit ◽

Enzymatic Activity ◽

Catalytic Properties ◽

Colorimetric Assay ◽

Colorimetric Detection ◽

Synergetic Effect ◽

Vis Spectroscopy ◽

Wide Range

A colorimetric assay was developed for the detection of biothiols, based on the peroxidase-like activity of iodine-capped gold nanoparticles (AuNPs). These AuNPs show a synergetic effect in the form of peroxidase-mimicking activity at the interface of AuNPs, while free AuNPs and iodine alone have weak catalytic properties. Thus, iodine-capped AuNPs possess good intrinsic enzymatic activity and trigger the oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB), leading to a change in color from colorless to yellow. When added to solution, biothiols, such as cysteine, strongly bind to the interface of AuNPs via gold-thiol bonds, inhibiting the catalytic activity of AuNPs, resulting in a decrease in oxidized TMB. Using this strategy, cysteine could be linearly determined, at a wide range of concentrations (0.5 to 20 μM), with a detection limit of 0.5 μM using UV-Vis spectroscopy. This method was applied for the detection of cysteine in diluted human urine.

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Mössbauer, XRD, and Complex Thermal Analysis of the Hydration of Cement with Fly Ash

Journal of Spectroscopy ◽

10.1155/2013/231843 ◽

2013 ◽

Vol 2013 ◽

pp. 1-9 ◽

Cited By ~ 2

Author(s):

Vili Lilkov ◽

Ognyan Petrov ◽

Yana Tzvetanova ◽

Plamen Savov ◽

Milen Kadiyski

Keyword(s):

Thermal Analysis ◽

High Temperature ◽

Fly Ash ◽

Octahedral Coordination ◽

Tetrahedral Coordination ◽

Cement Pastes ◽

Pozzolanic Properties ◽

Tetrahedral Iron ◽

Complex Thermal Analysis ◽

Cement Mixtures

Hydration of cement with and without fly ash is studied with Mössbauer spectroscopy, XRD, and thermal analysis. Iron in cement is present as Fe3+-ions and occupies two octahedral positions, with close isomer shifts and quadrupole splittings. Iron in fly ash is present as Fe2+and Fe3+, and the Mössbauer spectra display three doublets—two for Fe3+in octahedral coordination and one for Fe2+. A third doublet was registered in the hydrating plain cement pastes after the 5th day, due to Fe3+in tetrahedral coordination in the structure of the newly formed monosulphate aluminate. In cement pastes with fly ash, the doublet of tetrahedral iron is formed earlier because the quantity of ettringite and portlandite is low and more monosulphate crystallizes. No Fe(OH)3phase forms during hydration of C4AF. The fly ash displays pozzolanic properties, which lead to lowering of the portlandite quantity in the cement mixtures and increasing of the high temperature products.

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Bioelectrocatalysis of Hemoglobin on Electrodeposited Ag Nanoflowers toward H2O2 Detection

Nanomaterials ◽

10.3390/nano10091628 ◽

2020 ◽

Vol 10 (9) ◽

pp. 1628

Author(s):

Ajay Kumar Yagati ◽

Hien T. Ngoc Le ◽

Sungbo Cho

Keyword(s):

Electron Transfer ◽

Detection Limit ◽

Indium Tin Oxide ◽

Direct Electron Transfer ◽

Electrochemical Measurement ◽

Clinical Diagnostics ◽

Detection Range ◽

H2o2 Detection ◽

Vis Spectroscopy ◽

Living Organisms

Hydrogen peroxide (H2O2) is a partially reduced metabolite of oxygen that exerts a diverse array of physiological and pathological activities in living organisms. Therefore, the accurate quantitative determination of H2O2 is crucial in clinical diagnostics, the food industry, and environmental monitoring. Herein we report the electrosynthesis of silver nanoflowers (AgNFs) on indium tin oxide (ITO) electrodes for direct electron transfer of hemoglobin (Hb) toward the selective quantification of H2O2. After well-ordered and fully-grown AgNFs were created on an ITO substrate by electrodeposition, their morphological and optical properties were analyzed with scanning electron microscopy and UV–Vis spectroscopy. Hb was immobilized on 3-mercaptopropionic acid-coated AgNFs through carbodiimide cross-linking to form an Hb/AgNF/ITO biosensor. Electrochemical measurement and analysis demonstrated that Hb retained its direct electron transfer and electrocatalytic properties and acted as a H2O2 sensor with a detection limit of 0.12 µM and a linear detection range of 0.2 to 3.4 mM in phosphate-buffered saline (PBS). The sensitivity, detection limit, and detection range of the Hb/AgNF/ITO biosensor toward detection H2O2 in human serum was also found to be 0.730 mA mM−1 cm−2, 90 µM, and 0.2 to 2.6 mM, indicating the clinical application for the H2O2 detection of the Hb/AgNF/ITO biosensor. Moreover, interference experiments revealed that the Hb/AgNF/ITO sensor displayed excellent selectivity for H2O2.

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Visible Light-Driven Photocatalytic Activity and Kinetics of Fe-Doped TiO2 Prepared by a Three-Block Copolymer Templating Approach

Materials ◽

10.3390/ma14113105 ◽

2021 ◽

Vol 14 (11) ◽

pp. 3105

Author(s):

Antonietta Mancuso ◽

Olga Sacco ◽

Vincenzo Vaiano ◽

Barbara Bonelli ◽

Serena Esposito ◽

...

Keyword(s):

Photocatalytic Activity ◽

Visible Light ◽

Operating Conditions ◽

Soft Template ◽

Quantitative Phase Analysis ◽

Doped Tio2 ◽

X Ray ◽

Undoped Tio2 ◽

Fe Content ◽

Vis Spectroscopy

Fe-doped titania photocatalysts (with 1, 2.5, and 3.5 wt. % Fe nominal content), showing photocatalytic activity under visible light, were prepared by a soft-template assisted sol–gel approach in the presence of the triblock copolymer Pluronic P123. An undoped TiO2 photocatalyst was also prepared for comparison. The photocatalysts were characterized by means of X-ray powder Diffraction (XRPD), Quantitative Phase Analysis as obtained by Rietveld refinement, Diffuse Reflectance (DR) UV−Vis spectroscopy, N2 adsorption/desorption at −196 °C, electrophoretic mobility in water (ζ-potential), and X-ray photoelectron spectroscopy (XPS). The physico-chemical characterization showed that all the samples were 100% anatase phase and that iron was present both in the bulk and at the surface of the Fe-doped TiO2. Indeed, the band gap energy (Eg) decreases with the Fe content, with Tauc’s plot determined values ranging from 3.35 (undoped TiO2) to 2.70 eV (3.5 wt. % Fe). Notwithstanding the obtained Eg values, the photocatalytic activity results under visible light highlighted that the optimal Fe content was equal to 2.5 wt. % (Tauc’s plot determined Eg = 2.74 eV). With the optimized photocatalyst and in selected operating conditions, under visible light it was possible to achieve 90% AO7 discoloration together with a TOC removal of 40% after 180 min. The kinetic behavior of the photocatalyst was also analyzed. Moreover, the tests in the presence of three different scavengers revealed that the main reactive species are (positive) holes and superoxide species. Finally, the optimized photocatalyst was also able to degrade phenol under visible light.

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Comparative performances of phenolic sensors based on various CeO2-carbon material nanocomposites for environmental safety

Sensor Review ◽

10.1108/sr-11-2017-0235 ◽

2018 ◽

Vol 38 (4) ◽

pp. 467-477 ◽

Cited By ~ 1

Author(s):

Faisal K. Algethami ◽

Hadi M. Marwani ◽

Abdullah M. Asiri ◽

Mohammed M. Rahman

Keyword(s):

Detection Limit ◽

Carbon Material ◽

Chemical Sensor ◽

Ultra Violet ◽

Limit Of Quantification ◽

Content Type ◽

Electrochemical Approach ◽

Vis Spectroscopy ◽

Wet Chemical ◽

Sensor Probe

Purpose The purpose of this study is to prepare various CeO2-based carbon material (CNT, CB, GO) nanocomposites through a wet chemical process for the development of a sensor probe to detect various environmental toxins by using an electrochemical approach under room temperature conditions. A comparative study on sensitive and selective phenolic sensor (4-methoxyphenol; 4-MP) has been fabricated by modifying a glassy carbon electrode (GCE) with various nanocomposites (NCs) such as CeO2, CeO2–CNT (carbon nanotubes), CeO2–CB (carbon black) and CeO2–GO (graphene oxide) NCs. Design/methodology/approach The CeO2–CNT NCs were prepared by the wet chemical method at low temperature. NCs were characterized by various methods such as transmission electron microscopy (TEM), Fourier-transform infra-red (FTIR), ultra-violet/visible (UV-Vis) spectroscopy and XRD (X-ray diffraction). CeO2–CNT NCs were immobilized as a film on the flat surface of the GCE by using binders (5% Nafion). The electrochemical measurements of the 4-MP detection with the CeO2–CNT NCs/Nafion/GCE sensor were studied by the current-voltage method. Findings In the optimal conditions, the sensitivity, detection limit and limit of quantification of 4-MP sensor probe were found to be 47.56 µAcm-2 µM−1, 12.0 ± 0.2 nM and 40.0 ± 0.5 nM (S/N of 3), respectively. Research limitations/implications This electrochemical sensor showed an acceptable analytical performance in the detection of 4-MP with higher sensitivity, lower detection limit, large dynamic concentration range, good reproducibility and fast response time. Practical implications This electrochemical approach can be applied practically for the determination of selective 4-MP in real environmental and extracted samples. Social implications CeO2–CNT NCs/Nafion/GCE sensor probe was used for the safety of environmental and health-care fields at larger scales. Originality/value This electrochemical approach is a significant achievement on the development of sensor probe. The results are indicated as being technically detailed with an up-to-date account of recent chemical sensor research studies.

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Fe-TiO2 Nanoparticles by Hydrothermal Treatment with Photocatalytic Activity Enhancement

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1024.39 ◽

2014 ◽

Vol 1024 ◽

pp. 39-43 ◽

Cited By ~ 4

Author(s):

Siti Aida Ibrahim ◽

Srimala Sreekantan

Keyword(s):

Photocatalytic Activity ◽

Hydrothermal Treatment ◽

Anatase Phase ◽

Sol Gel ◽

Xrd Analysis ◽

X Ray Diffraction ◽

Fe Content ◽

Vis Spectroscopy ◽

Activity Enhancement ◽

Brookite Phase

Fe-TiO2nanoparticles with 5-9 nm sizes were prepared by sol gel method subsequently subjected to hydrothermal treatment at 150°C for 6 h. Titanium (IV) isopropoxide and iron (III) nitrate nonahydrate were used as precursor. The morphology, structure and composition of the Fe-TiO2were investigated by X-ray diffraction (XRD), Transmission emission microscopy (TEM) and UV-vis spectroscopy (UV-vis). XRD analysis revealed the prepared samples was dominated with anatase phase and a trace of brookite phase. The TiO2crystallite size was reduced as Fe content was increased. Compared with the pure TiO2nanoparticles, the Fe-TiO2nanoparticles exhibited higher photocatalytic activity in decolorizing methyl orange into non-toxic inorganic products under UV irradiation.

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Modification of optical properties of PC-PBT/Cr2O3 and PC-PBT/CdS nanocomposites by gamma irradiation

The European Physical Journal Applied Physics ◽

10.1051/epjap/2020200201 ◽

2020 ◽

Vol 92 (2) ◽

pp. 20402

Author(s):

Kaoutar Benthami ◽

Mai ME. Barakat ◽

Samir A. Nouh

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Band Gap ◽

Color Difference ◽

Band Gap Energy ◽

Polybutylene Terephthalate ◽

Γ Irradiation ◽

Gap Energy ◽

Vis Spectroscopy ◽

Oxygen Atoms

Nanocomposite (NCP) films of polycarbonate-polybutylene terephthalate (PC-PBT) blend as a host material to Cr2O3 and CdS nanoparticles (NPs) were fabricated by both thermolysis and casting techniques. Samples from the PC-PBT/Cr2O3 and PC-PBT/CdS NCPs were irradiated using different doses (20–110 kGy) of γ radiation. The induced modifications in the optical properties of the γ irradiated NCPs have been studied as a function of γ dose using UV Vis spectroscopy and CIE color difference method. Optical dielectric loss and Tauc's model were used to estimate the optical band gaps of the NCP films and to identify the types of electronic transition. The value of optical band gap energy of PC-PBT/Cr2O3 NCP was reduced from 3.23 to 3.06 upon γ irradiation up to 110 kGy, while it decreased from 4.26 to 4.14 eV for PC-PBT/CdS NCP, indicating the growth of disordered phase in both NCPs. This was accompanied by a rise in the refractive index for both the PC-PBT/Cr2O3 and PC-PBT/CdS NCP films, leading to an enhancement in their isotropic nature. The Cr2O3 NPs were found to be more effective in changing the band gap energy and refractive index due to the presence of excess oxygen atoms that help with the oxygen atoms of the carbonyl group in increasing the chance of covalent bonds formation between the NPs and the PC-PBT blend. Moreover, the color intensity, ΔE has been computed; results show that both the two synthesized NCPs have a response to color alteration by γ irradiation, but the PC-PBT/Cr2O3 has a more response since the values of ΔE achieved a significant color difference >5 which is an acceptable match in commercial reproduction on printing presses. According to the resulting enhancement in the optical characteristics of the developed NCPs, they can be a suitable candidate as activate materials in optoelectronic devices, or shielding sheets for solar cells.

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