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"silicates"
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COsub.2 Sorption on Ti-, Zr-, and Ti,Zr-Pillared Montmorillonites
Montmorillonite is a layered clay mineral whose modification by pillaring, i.e., insertion of oxide nanoclusters between the layers, yields porous materials of great potential in sorption and catalysis. In the present study, an unrefined industrial bentonite from Kopernica (Slovakia), containing ca. 70% of montmorillonite, was used for the preparation of Ti-, Zr-, and mixed [Ti,Zr]-pillared clay sorbents. The pillared samples were characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and N[sub.2] adsorption at −196 °C and tested for the capacity of CO[sub.2] sorption at 0 °C and 1 bar pressure. The experiments revealed that pillared samples sorbed at least four times more CO[sub.2] than the parent bentonite. Of the materials tested, the sample pillared with mixed [Ti,Zr] oxide props showed the best performance, which was attributed to its superior microporosity. The results of CO[sub.2] adsorption demonstrated that the cost-effective use of crude industrial bentonite as the sorbent precursor is a viable synthesis option. In another experiment, all pillared montmorillonites were subjected to 24 h exposure at room temperature to a flow of dry CO[sub.2] and then tested using simultaneous thermal analysis (STA) and the mass spectrometry (MS) analysis of the evolving gases (STA/QMS). It was found that interaction with dry CO[sub.2] reduces the amount of bound carbon dioxide and affects the processes of dehydration, dehydroxylation, and the mode of CO[sub.2] binding in the pillared structure.
Journal Article
Some Novel Results Involving Prototypical Computation of Zagreb Polynomials and Indices for ISiO/Isub.4 Embedded in a Chain of Silicates
A topological index as a graph parameter was obtained mathematically from the graph’s topological structure. These indices are useful for measuring the various chemical characteristics of chemical compounds in the chemical graph theory. The number of atoms that surround an atom in the molecular structure of a chemical compound determines its valency. A significant number of valency-based molecular invariants have been proposed, which connect various physicochemical aspects of chemical compounds, such as vapour pressure, stability, elastic energy, and numerous others. Molecules are linked with numerical values in a molecular network, and topological indices are a term for these values. In theoretical chemistry, topological indices are frequently used to simulate the physicochemical characteristics of chemical molecules. Zagreb indices are commonly employed by mathematicians to determine the strain energy, melting point, boiling temperature, distortion, and stability of a chemical compound. The purpose of this study is to look at valency-based molecular invariants for SiO[sub.4] embedded in a silicate chain under various conditions. To obtain the outcomes, the approach of atom–bond partitioning according to atom valences was applied by using the application of spectral graph theory, and we obtained different tables of atom—bond partitions of SiO[sub.4]. We obtained exact values of valency-based molecular invariants, notably the first Zagreb, the second Zagreb, the hyper-Zagreb, the modified Zagreb, the enhanced Zagreb, and the redefined Zagreb (first, second, and third). We also provide a graphical depiction of the results that explains the reliance of topological indices on the specified polynomial structure parameters.
Journal Article
Connecting ISiO/Isub.4 in Silicate and Silicate Chain Networks to Compute Kulli Temperature Indices
A topological index is a numerical parameter that is derived mathematically from a graph structure. In chemical graph theory, these indices are used to quantify the chemical properties of chemical compounds. We compute the first and second temperature, hyper temperature indices, the sum connectivity temperature index, the product connectivity temperature index, the reciprocal product connectivity temperature index and the F temperature index of a molecular graph silicate network and silicate chain network. Furthermore, a QSPR study of the key topological indices is provided, and it is demonstrated that these topological indices are substantially linked with the physicochemical features of COVID-19 medicines. This theoretical method to find the temperature indices may help chemists and others in the pharmaceutical industry forecast the properties of silicate networks and silicate chain networks before trying.
Journal Article
Sol–Gel Synthesis of Translucent and Persistent Luminescent SiOsub.2@ SrAlsub.2Osub.4 Eu, Dy, B Materials
This publication offers an economically promising method of persistent luminescent silicate glass synthesis that does not involve high temperatures or ready-made (separately synthesized) PeL particles. In this study, we demonstrate the formation of SrAl[sub.2]O[sub.4] doped with Eu, Dy, and B in a SiO[sub.2] glass structure using the one-pot low-temperature sol–gel synthesis method. By varying the synthesis conditions, we can use water-soluble precursors (e.g., nitrates) and a dilute aqueous solution of rare-earth (RE) nitrates as starting materials for SrAl[sub.2]O[sub.4] synthesis, which can be formed during the sol–gel process at relatively low sintering temperatures (600 °C). As a result, translucent, persistently luminescent glass is obtained. The glass shows the typical Eu[sup.2+] luminescence and the characteristic afterglow. The afterglow duration is about 20 s. It is concluded that the slow drying procedure (2 weeks) is optimal for these samples to sufficiently get rid of the excess water (mainlyOH groups) and solvent molecules that can influence the strontium aluminate luminescence properties and have a pernicious effect on the afterglow. It can also be concluded that boron is playing a crucial role in the formation of trapping centers needed for PeL processes in the PeL silicate glass.
Journal Article
Carbonation behavior of hydraulic and non-hydraulic calcium silicates: potential of utilizing low-lime calcium silicates in cement-based materials
This paper presents a study on the carbonation behaviors of hydraulic and non-hydraulic calcium silicate phases, including tricalcium silicate (3CaO·SiO₂ or C₃S), γ-dicalcium silicate (γ-2CaO·SiO₂ or γ-C₂S), β-dicalcium silicate (β-2CaO·SiO₂ or β-C₂S), rankinite (3CaO·2SiO₂ or C₃S₂), and wollastonite (CaO·SiO₂ or CS). These calcium silicate phases were subjected to carbonation reaction at different CO₂ concentration and temperatures. Thermogravimetric analysis (TGA) tests were performed to quantify the amounts of carbonates formed during the carbonation reactions, which were eventually used to monitor the degree of reactions of the calcium silicate phases. Both hydraulic and non-hydraulic calcium silicates demonstrated higher reaction rate in case of carbonation reaction than that of the hydration reaction. Under specific carbonation scenario, non-hydraulic low-lime calcium silicates such as γ-C₂S, C₃S₂ and CS were found to achieve a reaction rate close to that of C₃S. Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscope (SEM) tests were performed to characterize the carbonation reaction products of the calcium silicate phases. The FTIR spectra during the early stage of carbonation reaction showed formation of calcium silicate hydrate (C–S–H) from C₃S, γ-C₂S, β-C₂S, and C₃S₂ phases with a similar degree of polymerization as that of the C–S–H that forms during the hydration reaction of C₃S. However, upon further exposure to CO₂, these C–S–H phases decompose and eventually converted to calcium-modified (Ca-modified) silica gel phase with higher degree of silicate polymerization. Contradictorily, CS phase started forming Ca-modified silica gel phase even at the early stage of carbonation reaction. This paper also revealed the stoichiometry of the Ca-modified silica gel that formed during the carbonation reaction of the calcium silicate phases using the SEM/energy dispersive spectroscopy (EDS) and TGA results.
Journal Article
Inoculation of Azospirillum brasilense associated with silicon as a liming source to improve nitrogen fertilization in wheat crops
This research was developed to investigate whether inoculation with
Azospirillum brasilense
in combination with silicon (Si) can enhance N use efficiency (NUE) in wheat and to evaluate and correlate nutritional and productive components and wheat grain yield. The study was carried out on a Rhodic Hapludox under a no-till system with a completely randomized block design with four replications in a 2 × 2 × 5 factorial scheme: two liming sources (with Ca and Mg silicate as the Si source and limestone); two inoculations (control - without inoculation and seed inoculation with
A
.
brasilense
) and five side-dress N rates (0, 50, 100, 150 and 200 kg ha
−1
). The results of this study showed positive improvements in wheat growth production parameters, NUE and grain yield as a function of inoculation associated with N rates. Inoculation can complement and optimize N fertilization, even with high N application rates. The potential benefits of Si use were less evident; however, the use of Si can favour N absorption, even when associated with
A
.
brasilense
. Therefore, studies conducted under tropical conditions with Ca and Mg silicate are necessary to better understand the role of Si applied alone or in combination with growth-promoting bacteria such as
A
.
brasilense
.
Journal Article
Sodium Zirconium Cyclosilicate in Hyperkalemia
Hyperkalemia is common in chronic kidney disease or heart failure, especially in patients receiving RAAS inhibitors. This study showed that sodium zirconium cyclosilicate (ZS-9), a highly selective cation exchanger, induces and maintains normokalemia.
Hyperkalemia (serum potassium level, >5.0 mmol per liter) is a common electrolyte disorder that is associated with serious cardiac dysrhythmias and increased mortality.
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–
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Patients with renal dysfunction and those with diabetes are at increased risk for hyperkalemia.
3
Therapies that inhibit the renin–angiotensin–aldosterone system (RAAS) are associated with hyperkalemia in patients with kidney disease or heart failure,
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,
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despite strong evidence that such therapy is beneficial in proteinuric chronic kidney disease,
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–
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diabetic nephropathy,
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and systolic heart failure.
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The use of existing polymer resins (e.g., sodium polystyrene sulfonate) has a poor side-effect profile and uncertain efficacy. Thus, there . . .
Journal Article
A phase 2 study on the treatment of hyperkalemia in patients with chronic kidney disease suggests that the selective potassium trap, ZS-9, is safe and efficient
Hyperkalemia contributes to significant mortality and limits the use of cardioprotective and renoprotective renin–angiotensin–aldosterone blockers. Current therapies are poorly tolerated and not always effective. Here we conducted a phase 2 randomized, double-blind, placebo-controlled dose-escalation study to assess safety and efficacy of ZS-9. This oral selective cation exchanger that preferentially entraps potassium in the gastrointestinal tract was given to patients with stable Stage 3 chronic kidney disease and hyperkalemia (5.0 to 6.0 mEq/l) during a 2-day period. Of 90 eligible patients with mean baseline serum potassium of 5.1 mEq/l, 30 were randomized to placebo, 12–0.3 g, 24–3 g, or 24 to 10 g of ZS-9 three times daily for 2 days with regular meals. None withdrew and ZS-9 dose-dependently reduced serum potassium. The primary efficacy end point (rate of serum potassium decline in the first 48 h) was met with significance in the 3- and 10-g cohorts. From baseline, mean serum potassium was significantly decreased by 0.92±0.52 mEq/l at 38 h. Urinary potassium excretion significantly decreased with 10-g ZS-9 as compared to placebo at day 2 (+15.8 +/- 21.8 vs. +8.9 +/- 22.9 mEq per 24h) from placebo at day 2. In this short-term study, no serious adverse events were reported; only mild constipation in the 3-g dose group was possibly related to treatment. Thus, ZS-9 was well-tolerated in patients with stable chronic kidney disease and hyperkalemia leading to a rapid, sustained reduction in serum potassium.
Journal Article
Phytoplankton spatial distribution on the continental shelf off Rio de Janeiro, from Paraiba do Sul River to Cabo Frio
Given the heterogeneous oceanographic conditions observed in the continental shelf and slope off Rio de Janeiro, the phytoplankton community is expected to adapt to the diverse trophic conditions using distinct strategies. Considering the C-S-R triangle, distinct phytoplankton taxa are expected to occur in Tropical Water (TW), in South Atlantic Central Water (SACW) and in Coastal Water (CW). The study area extends from Paralba do Sul River mouth to the region of Cabo Frio. Samples were collected on 28 stations, in 2011 austral summer. 209 phytoplankton taxa were observed, mainly dinoflagellates (93), diatoms (71), and coccolitophores (30). TW dominated the surface waters of the continental shelf and slope, 13 December 2013/Published online: 4 February 2014 and a typical tropical phytoplankton community, composed by stress-tolerant taxa, was observed. The rise in nitrate concentration caused by SACW uplift in the shelf and in the continental slope, at subsurface waters, and in silicate, associated with the Paraiba do Sul riverine plume, led to shifts in the phytoplankton community, increasing the contribution of ruderal taxa. The grouping of phytoplankton assemblages only in traditional groups would result in loss of information about the factors that determine community dynamics since the different species in each of these groups frequently share specific traits.
Journal Article