The formation of metakaolinite during the thermal treatment of kaolinite consists of three processes which include the destruction of kaolinite sheet structure, the dehydroxylation and the ...recombination of silica and alumina into the structure of metakaolinite. The sequence of these steps is significantly affected by heating rate. The kinetics, mechanism and the influence of heating rate on the course of these processes were investigated by the methods of thermal analysis (DTG and TDA) and high-temperature X-ray diffraction analysis (HT-XRD) using the Kissinger kinetic equation. The activation energy required for the delamination, dehydroxylation and recombination of silica and alumina tetrahedron into metakaolinite is 538, 195 and 143kJmol−1, respectively. The thermodynamic data of the activated complex, calculated from the Wertera and Zenera law, enable to explain experimentally the observed influence of heating rate on the thermal transformation of kaolinite during heating.
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•The thermal transformation mechanism of kaolinite was described.•Ea of delamination, dehydroxylation and formation of metakaolinite was determined.•The high heating rate preferred the delamination process before the dehydroxylation.•The product of limited degree of dehydroxylation was formed under slow heating.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Common clay deposits contain a variety of minerals that provide low and unpredictable reactivity even after calcination. This study aims to enhance the reactivity of such low-grade clay via alkali ...thermal fusion, where clay was co-calcined with different dosages of NaOH to achieve superior reactivity. The effects of such co-calcination on the formation of reactive aluminosilicates were monitored using high-temperature in-situ X-ray Diffraction (XRD). Additionally, the role of different alkali dosages on the characteristics of the calcined clays was studied using ex-situ XRD, FTIR, ICP-OES, and 29Si NMR. The co-calcination process significantly enhanced the Al and Si dissolution from the calcined clays, which subsequently improved their pozzolanic properties. All of the alkali-fused SCMs satisfied the modified strength activity index (SAI) requirement and the lower dosages of alkali-containing samples (5 % NaOH) showed 50 % reduction in expansion due to alkali silica reaction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Animals exposure to polychlorinated biphenyls (PCBs) may result in retention of hydroxylated PCBs (OH-PCBs). OH-PCBs can be accumulated in animals, including humans, through the transmission of food ...chain. However, there are few studies on the accumulation and metabolism of OH-PCBs exposed to the body through daily diet. Therefore, this study was conducted to investigate the fate of OH-PCBs after being ingested through dietary intake. By adding 3-OH-PCB101 and 4-OH-PCB101 to the edible tissue of crucian carp, which were used as raw materials to prepare mouse feed, with an exposure concentration of 2.5 μg/kg ww. The exposure experiment lasted for a total of 80 days. The blood, feces and 11 tissues of mice at different times were analyzed qualitatively and quantitatively. It was found that major OH-PCB101 were accumulated in intestine or excreted with feces. A small part was accumulated in heart, lung and spleen. For the first time that the conversion from OH-PCB101 to PCB101 in mice was discovered, which shows from another perspective that persistent organic pollutants are difficult to be completely degraded in the environment. 4-MeO-PCB101, 3-MeSO2-PCB101, and 4-MeSO2-PCB101 were also found in various tissues. The results of this study show that after OH-PCBs accumulated in animals re-enter the organism through the food chain, they can be metabolized again and may be reversely transformed into the parent compounds. The present research shed new light on simulating the metabolic transformation process of OH-PCBs exposed to mammals through ingestion of fish. Available data show that second-generation persistent organic pollutants in the environment still need to be continuously concerned.
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•The fate of OH-PCB101 after being ingested through daily fish intake in mice was investigated.•OH-PCB101 can be reversely transformed into the parent compound PCB101.•PCB101 and metabolites of methylsulfonyl and methoxy were also detected in the tissues.•Most of 3-OH-PCB101 and 4-OH-PCB101 ingested through daily diet were excreted via feces.•It is important to study the further metabolism of OH-PCBs for evaluating the health risk of PCBs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High-pressure (700 MPa or ∼100 000 psi) compaction of dehydroxylated and hydroxylated UiO-66 for H
storage applications is reported. The dehydroxylation reaction was found to occur between 150 and ...300 °C. The H
uptake capacity of powdered hydroxylated UiO-66 reaches 4.6 wt % at 77 K and 100 bar, which is 21% higher than that of dehydroxylated UiO-66 (3.8 wt %). On compaction, the H
uptake capacity of dehydroxylated UiO-66 pellets reduces by 66% from 3.8 to 1.3 wt %, while for hydroxylated UiO-66 the pellets show only a 9% reduction in capacity from 4.6 to 4.2 wt %. This implies that the H
uptake capacity of compacted hydroxylated UiO-66 is at least three times higher than that of dehydroxylated UiO-66, and therefore, hydroxylated UiO-66 is more promising for hydrogen storage applications. The H
uptake capacity is closely related to compaction-induced changes in the porosity of UiO-66. The effect of compaction is greatest in partially dehydroxylated UiO-66 samples that are thermally treated at 200 and 290 °C. These compacted samples exhibit XRD patterns indicative of an amorphous material, low porosity (surface area reduces from between 700 and 1300 m
/g to ca. 200 m
/g and pore volume from between 0.4 and 0.6 cm
/g to 0.1 and 0.15 cm
/g), and very low hydrogen uptake (0.7-0.9 wt % at 77 K and 100 bar). The observed activation-temperature-induced dynamic behavior of UiO-66 is unusual for metal-organic frameworks (MOFs) and has previously only been reported in computational studies. After compaction at 700 MPa, the structural properties and H
uptake of hydroxylated UiO-66 remain relatively unchanged but are extremely compromised upon compaction of dehydroxylated UiO-66. Therefore, UiO-66 responds in a dynamic manner to changes in activation temperature within the range in which it has hitherto been considered stable.
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IJS, KILJ, NUK, PNG, UL, UM
Properties of metakaolins heated in a temperature range of 550–950°C for 6h are characterized by TGA and DSC for thermal analysis, NMR for Al coordination, and XRD for crystal structure. ...Dehydroxylation is the main reaction with heating temperature of 550–800°C, and then recrystallization becomes important. Although recrystallization affects greatly the beginning of geopolymerization reactions even at a moderate heating temperature like 800°C, a plateau of high compressive strength of geopolymers is obtained in the range of 650–850°C. It is found that optimal mechanical property of geopolymers can be obtained with metakaolins of sufficient dehydroxylation and low recrystallization. In zeolite synthesis using metakaolin, the reactivity of metakaolin was at a maximum when the content of AlVI was at a minimum. However, in the case of metakaolin geopolymer synthesis, joint effects of dehydroxylation and recrystallization determine the reactivity of metakaolin in geopolymerization reactions.
•Recrystallization is greatly detrimental to the dissolution in geopolymerization.•High compressive strength geopolymers are formed by heating kaolin in 650–850°C.•Effects of dehydroxylation and recrystallization determine geopolymerization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Aim
Bile acids are suggested to be involved in the antidiarrhetic effect of Goreisan (GRS). This study aimed to investigate the effect of GRS on fecal bile acid levels and composition of the gut ...microbiota in mice. Correlation analysis was employed to identify the potential gut microbiota associated with the alterations in fecal bile acid levels induced by GRS.
Methods
Male C57BL/6 mice were fed a diet supplemented with GRS water extract for 4 weeks. Feces and cecal contents were collected from the mice to determine bile acid levels and analyze bacterial composition.
Results
GRS administration significantly increased the levels of fecal secondary bile acids, including ω‐muricholic acid (MCA), hyodeoxycholic acid (HDCA), and lithocholic acid (LCA). In contrast, the levels of primary bile acids, such as β‐MCA, cholic acid (CA), and chenodeoxycholic acid (CDCA) showed a marked decrease. Further analysis revealed a positive correlation between the relative abundance of Alloprevotella, Dehalobacterium PAC001221, and Eubacterium g23 and fecal levels of ωMCA, HDCA, and LCA.
Conclusions
GRS was suggested to promote the formation of fecal secondary bile acids in mice, possibly through the enhancement of bacterial 7β‐dehydroxylation and 6β‐epimerization activities. These changes may be involved in the antidiarrhetic action of GRS. Concurrent evaluation of fecal bile acids and gut microbiota presents a promising approach for elucidating the novel mechanisms underlying the effects of kampo formulations, particularly in modulating the microbial metabolism of intestinal bile acids.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this study we report on the addition of a waste, a real spent corundum abrasive powder collected after testing, to a metakaolin-based alkali activated binder. The waste has been chosen as ...representative of spent grits produced by industrial blasting processes. In this model system based on metakaolin, the effect of corundum powder in the environment of high alkaline media was investigated in terms of 3D reticulation of the aluminosilicate amorphous structure of the consolidated geopolymeric mixes. A number of microstructural techniques (FT-IR, XRD, TGA/DTA) have been used in combination with less conventional one, such as the ionic conductivity measurements of the eluate produced after 24 h of immersion of the sample in water. The overall 3D aluminosilicate frame typical of MK-based geopolymer is retained also after 50 wt% addition of recycled corundum, as shown by FT-IR, XRD, and TGA/DTA. The traces of ceramic materials abrasion present in the waste showed good reactivity, as shown by the disappearance of their characteristic peaks in the XRD patterns. Ionic conductivity of the eluates evidenced the most extended reactivity of the alkaline activator solution in the case of 10 and 20 wt% addition of the waste. While the role of 20, 30 and 40 wt% addition of the waste to the MK-based matrix produced the highest compressive strength in the consolidated mortars after 28 days comparable to those of Ordinary Portland cement concretes. It was proved that, when produced using a partially reactive waste with well-formulated mix designs, metakaolin alkali-activated binders or mortars are an important aluminosilicate source for room temperature produced construction materials.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The human gut hosts trillions of microorganisms that exert a profound influence on human biology. Gut bacteria communicate with their host by secreting small molecules that can signal to distant ...organs in the body. Bile acids are one class of these signaling molecules, synthesized by the host and chemically transformed by the gut microbiota. Among bile acid metabolizers, bile acid 7-dehydroxylating bacteria are commensals of particular importance as they carry out the 7-dehydroxylation of liver-derived primary bile acids to 7-dehydroxylated bile acids. The latter represents a major fraction of the secondary bile acid pool. The microbiology of this group of gut microorganisms is understudied and warrants more attention. Here, we detail the bile acid transformations carried out by the 7-dehydroxylating bacterium Clostridium scindens in vitro and in vivo. In vitro, C. scindens exhibits not only 7α-dehydroxylating capabilities but also, the ability to oxidize other hydroxyl groups and reduce ketone groups in primary and secondary bile acids. This study revealed 12-oxolithocholic acid as a major transient product in the 7α-dehydroxylation of cholic acid. Furthermore, the in vivo study included complementing a gnotobiotic mouse line (devoid of the ability to 7-dehydroxylate bile acids) with C. scindens and investigating its colonization dynamics and bile acid transformations. Using NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry), we demonstrate that the large intestine constitutes a niche for C. scindens, where it efficiently 7-dehydroxylates cholic acid to deoxycholic acid. Overall, this work reveals a novel transient species during 7-dehydroxylation as well as provides direct evidence for the colonization and growth of 7-dehydroxylating bacteria in the large intestine.
Bile acids, the products of concerted host and gut bacterial metabolism, have important signaling functions within the mammalian metabolic system and a key role in digestion. Given the complexity of ...the mega-variate bacterial community residing in the gastrointestinal tract, studying associations between individual bacterial genera and bile acid processing remains a challenge. Here, we present a novel
approach to determine the bacterial genera associated with the metabolism of different primary bile acids and their potential to contribute to inter-individual variation in this processing. Anaerobic, pH-controlled batch cultures were inoculated with human fecal microbiota and treated with individual conjugated primary bile acids (500 μg/ml) to serve as the sole substrate for 24 h. Samples were collected throughout the experiment (0, 5, 10, and 24 h) and the bacterial composition was determined by 16S rRNA gene sequencing and the bile acid signatures were characterized using a targeted ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) approach. Data fusion techniques were used to identify statistical bacterial-metabolic linkages. An increase in gut bacteria associated bile acids was observed over 24 h with variation in the rate of bile acid metabolism across the volunteers (
= 7). Correlation analysis identified a significant association between the
genus and the deconjugation of glycine conjugated bile acids while the deconjugation of taurocholic acid was associated with bacteria from the
and
genera. A positive correlation between
and deoxycholic acid production suggest a potential role for this genus in cholic acid dehydroxylation. A slower deconjugation of taurocholic acid was observed in individuals with a greater abundance of
and
. This work demonstrates the utility of integrating compositional (metataxonomics) and functional (metabonomics) systems biology approaches, coupled to
model systems, to study the biochemical capabilities of bacteria within complex ecosystems. Characterizing the dynamic interactions between the gut microbiota and the bile acid pool enables a greater understanding of how variation in the gut microbiota influences host bile acid signatures, their associated functions and their implications for health.
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