The potential use of two raw clays (Clay A: kaolin; Clay B: calcareous montmorillonite) as supplementary cementitious material (SCM) in blended cements was investigated. Cement replacement in mortars ...by 20% calcined Clay A and Clay B resulted in a considerable 28 day compressive strength improvement. The pozzolanic reactivity of Clay A and B is explained by characterisation of the structural changes upon calcination with XRD, ICP-MS, FT-IR, 27Al NMR, Mössbauer spectroscopy and SEM. At the temperature giving highest pozzolanic reactivity, kaolinite and montmorillonite were completely dehydroxylated, while calcite from Clay B was not completely decomposed. FT-IR, 27Al NMR and Mössbauer spectroscopy revealed considerable structural deformations of kaolinite in Clay A and montmorillonite in Clay B resulting in an amorphous, reactive state. Oxidation of iron in Clay B during calcination contributed to strong distortions of the octahedral sheet in the montmorillonite structure. Additionally, the formation of a glass phase due to reaction of coccoliths (CaCO3) and montmorillonite was observed.
•Calcination of raw calcerous montmorillonite can provide a pozzolanic source for environmentally friendly binders.•Oxidation of Fe2+ to Fe3+ in montmorillonite leads to structural disordering and thus to a higher pozzolanic reactivity.•Finely intermixed coccoliths in montmorillonite enable the formation of a reactive glass.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An in-depth understanding of the microstructural transformation that the matrix of clay undergoes prior to the complete dissolution of metal package container is crucial for predicting the ...effectiveness of the matrix of clay purposed as backfill material in the high-level radioactive waste (HLRW) disposal. Although irradiation can strongly influence microstructure its effect remains unclear. Herein, pure phlogopite single-crystal was chosen as a model material and irradiated in air by an electron beam (EB) at 0–1000 kGy. Variation in chemical/crystalline structure and microstructural transformation mechanism were explored by FT-ATR IR, XRD, TGA, CA and XPS. Key results reveal that irradiation caused extensive octahedral OH cleavage and lattice damage, marginal Si–OH formation and surface wettability elevation. With absorbed dose increases to 1000 kGy the majority of samples exhibited lattice plane expansion while the 200 kGy-irradiated sample exhibited shrinkage. 100 and 200 kGy-irradiated samples exhibited a variation level of ±2.5% (±0.3 Å) and a gap of 0.4 Å in (001) lattice plane. Concurrently, the amount of H2O and valance of metal element decreased while surface hydrophilicity increased slightly. 200 kGy-irradiated sample exhibited a CA of 7°, lower the pristine sample near 15°. Overall, phlogopite lattice appears to be unstable to EB irradiation at 0–1000 kGy. Transformation mechanism involves framework cleavage, H-atom migration, hydrogen-bond formation/destruction and reduction of electron. H-atom migration and hydrogen-bond variation played key roles. Normal silicate crystal appears to be unstable to medium-intensity β-ray irradiation. To enhance lattice stability, the number of OH and hydrogen bond should be reduced. This conclusion guides the design of radiation-resistant silicate material for use as backfill or curing material in HLRW disposal. For example, for curing material (e.g., glass), the concentration of OH in matrix base needs to be reduced. This cognization emphasises the role of OH in novel microstructural transformation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•The crystallinity of coal-series and water-washed kaolin are investigated.•The coal-series kaolin with poor crystallinity presents a lower pozzolanic activity.•The increase of amount of AlV and AlVI ...results in a higher pozzolanic activity.
In this paper, we investigated the pozzolanic activity of thermal-activated coal-series kaolin and two types of water-washed kaolin, which were calcined at temperatures ranging from 600 to 700 °C for 3 h. Chapelle test and strength activity index were used to evaluate the pozzolanic activity of thermal-treated kaolin. Results indicated that thermal-activated water-washed kaolin presented a higher pozzolanic activity when calcined at same temperature, which is due to its well-defined morphology, relatively high specific surface area, and high amounts of active aluminum. The incorporation of 10 wt% of calcined kaolin significantly increased the amount of hydrate water and promoted strength development at 7 and 28 days. Moreover, the crystallinity of kaolinite showed obvious impacts on the dehydroxylation temperature and aluminum structure. The optimum dehydroxylation temperature is mainly dependent on the crystallinity of the kaolinite; in addition, the aluminium structure is closely related to the kaolinite crystallinity. Well-crystallized kaolin showed higher pozzolanic activity than poorly crystallized kaolin at the same calcination condition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Porous dehydroxyl cobalt phytate displays superior OER stability with a V-t test for 80 h.•The role of dehydroxyl temperature in improving the OER performance is critical.•The OER ...activity and stability of cobalt phytate are even comparable to commercial RuO2.
Phytic acid (PA) is a six-fold dihydrogenphosphate ester of inositol with cost-effective, environmentally friendly, and safe properties. Here, we successfully synthesize the dehydroxyl cobalt phytate (PA-Co-400) using PA as phosphorus sources by a one-pot wet-chemistry strategy to prepare the precursor PA-Co and then heat treatment at 400 °C under an N2 atmosphere for dehydroxylation. The average diameter, specific surface area, surface element distribution, and catalytic activity of the catalyst are significantly affected by dehydroxylation temperature. The specific surface area increasesfirstandthendecreases with the treatment temperature from 200 °C to 600 °C. The SEM results indicate that the average diameter of PA-Co-400 particle is 68.90 nm. The as-prepared samples are used as an anode catalyst for electrocatalytic oxygen evolution reaction (OER). The PA-Co-400 exhibits splendid OER performances with an overpotential of 310.31 mV at j10 (η50 = 349.35 mV, η100 = 367.20 mV), which are even comparable to commercial RuO2 (η10 = 310.54 mV, η50 = 389.80 mV, η100 = 450.60 mV). Moreover, the PA-Co-400 has a small Tafel slope of 53.27 mV dec−1, which is lower than commercial RuO2 (81.71 mV dec−1). The ultra-long durability of PA-Co-400 was tested for over 80 h at current densities of 10 mA cm−2 without a significant reduction in 1 M KOH.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Presents the fundamentals pertaining to the microwave treatment of ultramafic ores.•High temperature X-ray diffraction analysis showed the transition to heazlewoodite.•Conventional heating tests and ...thermodynamic modelling supported the microwave tests.
The mining of ultramafic ores is required to meet society’s continued demand for nickel. These deposits, however, are difficult to process due to their high serpentine content. Serpentine, a gangue mineral, increases slurry viscosity, slime-coats the valuable Ni-bearing mineral pentlandite, and reports to and dilutes the froth during flotation via the formation of bubble-fibre aggregates. Microwave pre-treatment can be used to convert the serpentine gangue to olivine, which should improve ore processing. However, the fundamental microwave properties and heating behaviour of ultramafic ores must be understood to develop a robust process. Microwave heating curves were developed for, and high temperature permittivity analysis was conducted on, two ultramafic nickel ores (Pipe and OK ore). Subsequently, TGA/DSC (thermogravimetric analysis/differential scanning calorimetry) and HTXRD (high-temperature x-ray diffraction) tests, along with a thermodynamic analysis using FactSage 7.3, were done to explain the heating behaviours and permittivity data. An unusual peak in the permittivity data was detected at 950 °C for the Pipe ore with both increasing and decreasing temperature; however, no phase transitions were detected in the TGA/DSC analysis. HTXRD of the Pipe ore revealed the presence of heazlewoodite at higher temperatures (950 to 1100 °C). Thermodynamic modeling of the Pipe ore system suggests that melting at higher temperatures is responsible for the decrease in the permittivities of this ore. To mitigate the melting and clumping of the ore particles, it is necessary to ensure that the processing temperature does not exceed 800 °C during microwave treatment. The OK ore, which contained less microwave response minerals than the Pipe ore, reached a maximum temperature of 500 °C after only 5 min of heating time, and therefore overheating was not an issue.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Different metals supported on SiO
2
were tested for the hydrodeoxygenation of phenol. For Pt/SiO
2
, Pd/SiO
2
and Rh/SiO
2
catalysts, phenol is mainly tautomerized, followed by hydrogenation of the ...aromatic ring. The direct dehydroxylation of phenol followed by hydrogenolysis is favored over more oxophilic metals (Ru, Co and Ni).
Graphical Abstract
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The secondary bile acids deoxycholic acid (DCA) and lithocholic acid (LCA), formed by gut microbiota from primary bile acids via a multi-step 7α-dehydroxylation reaction, have wide-ranging effects on ...host metabolism and play an important role in health and disease. A few 7α-dehydroxylating strains have been isolated, where bile acid-inducible (bai) genes were organized in a gene cluster and encoded major enzymes involved. However, only little is known on diversity and abundance of intestinal bacteria catalysing DCA/LCA formation in the human gut in situ. In this study, we took the opportunity to screen metagenome-assembled genomes (MAGs) from sequence data of stool samples provided by two recent studies along with newly available gut-derived isolates for the presence of the bai gene cluster. We revealed in total 765 and 620 MAGs encoding the potential to form DCA/LCA that grouped into 21 and 26 metagenomic species, respectively. The majority of MAGs (92.4 and 90.3%) were associated with a Ruminococcaceae clade that still lacks an isolate, whereas less MAGs belonged to Lachnospiraceae along with eight new isolates (n total = 11) that contained the bai genes. Only a few MAGs were linked to Peptostreptococcaceae. Signatures for horizontal transfer of bai genes were observed. This study gives a comprehensive overview of the diversity of bai-exhibiting bacteria in the human gut highlighting the application of metagenomics to unravel potential functions hidden from current isolates. Eventually, isolates of the identified main MAG clade are required in order to prove their capability of 7α-dehydroxylating primary bile acids.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Bile acids, important mediators of lipid absorption, also act as hormone-like regulators and as antimicrobial molecules. In all these functions their potency is modulated by a variety of chemical ...modifications catalyzed by bacteria of the healthy gut microbiota, generating a complex variety of secondary bile acids. Intestinal commensal organisms are well-adapted to normal concentrations of bile acids in the gut. In contrast, physiological concentrations of the various intestinal bile acid species play an important role in the resistance to intestinal colonization by pathogens such as
. Antibiotic therapy can perturb the gut microbiota and thereby impair the production of protective secondary bile acids. The most important bile acid transformation is 7α-dehydroxylation, producing deoxycholic acid (DCA) and lithocholic acid (LCA). The enzymatic pathway carrying out 7α-dehydroxylation is restricted to a narrow phylogenetic group of commensal bacteria, the best-characterized of which is
. Like many other intestinal commensal species, 7-dehydroxylating bacteria are understudied
. Conventional animals contain variable and uncharacterized indigenous 7α-dehydroxylating organisms that cannot be selectively removed, making controlled colonization with a specific strain in the context of an undisturbed microbiota unfeasible. In the present study, we used a recently established, standardized gnotobiotic mouse model that is stably associated with a simplified murine 12-species "oligo-mouse microbiota" (Oligo-MM
). It is representative of the major murine intestinal bacterial phyla, but is deficient for 7α-dehydroxylation. We find that the Oligo-MM
consortium carries out bile acid deconjugation, a prerequisite for 7α-dehydroxylation, and confers no resistance to
infection (CDI). Amendment of Oligo-MM
with
normalized the large intestinal bile acid composition by reconstituting 7α-dehydroxylation. These changes had only minor effects on the composition of the native Oligo-MM
, but significantly decreased early large intestinal
colonization and pathogenesis. The delayed pathogenesis of
in
-colonized mice was associated with breakdown of cecal microbial bile acid transformation.
In this work, we have established a photoredox/Ti dual‐catalyzed dehydroxylation of cyclobutanone oximes. The resulting γ‐cyanoalkyl radicals undergo a cascade radical addition/cyclization with ...N‐acrylamides to afford cyanoalkyl substituted oxoindolines under mild conditions. This reaction also exhibits broad substrate scope and good functional group tolerance. Furthermore, it is applicable to late‐stage functionalization of complex molecules and gram‐scale synthesis, which illustrates its potential value in organic synthesis.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Optimisation of heat treatment of serpentine is critical for the development of large-scale CO2 sequestration by mineral carbonation.
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•Full amorphisation of antigorite cannot be ...achieved before the onset of forsterite formation.•Aluminium-rich antigorite shows significantly higher thermal stability than lizardite.•The activation energy for dehydroxylation of antigorite varies between 290 and 515 kJ mol−1.•Forsterite begins to form at 700 °C when only 49% antigorite converted to amorphous phase.•High Al2O3 antigorite is more suitable for mineral carbonation at high pressure conditions.
Heat-treatment of serpentine minerals generates structural amorphicity and increases reactivity during subsequent mineral carbonation, a strategy for large-scale sequestration of CO2. This study employs thermal analyses (TGA-DSC) in conjunction with in-situ synchrotron powder X-ray diffraction (PXRD) to record concurrent mass loss, heat flow, and mineralogical changes during thermal treatment of antigorite. Isoconversional kinetic modelling demonstrates that thermal decomposition of antigorite is a complex multi-step reaction, with activation energies (Eα) varying between 290 and 515 kJ mol−1. We identify three intermediate phases forming during antigorite dehydroxylation, a semi-crystalline chlorite-like phase (γ-metaserpentine) showing an additional reaction pathway for the decomposition of Al2O3-rich antigorite into pyrope, and two distinct amorphous components (α and β-metaserpentine) which convert into forsterite and enstatite at higher temperature, respectively. The combination of isoconversional kinetics with in-situ synchrotron PXRD illustrates, for the first time, that local crystal structure changes, related to intermediate phase and forsterite formation, are responsible for the steep increase in activation energy above 650 °C and only 49% dehydroxylation can be achieved prior to this increase. This suggests that the high thermal stability of Al2O3-rich antigorite would severely limit Mg extraction during application of mineral carbonation under flue gas conditions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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