Applied Clay Science最新文献

The In-situ Demonstration of Engineering Barrier System (In-DEBS), a field test in Korea, commenced operations in July 2016 to showcase the complex thermal-hydraulic-mechanical behavior of the engineering barrier in a high-level radioactive waste repository. To emulate the actual repository, the In-DEBS test utilized a heater and buffer material comprised of compacted bentonite blocks. From January to October 2022, the In-DEBS buffer was sequentially dismantled, and the buffer samples were collected and analyzed for physical properties such as dry density and water content based on the sample location. The findings indicated that the physical properties of the In-DEBS buffer material showed variations, which may have been caused by various factors such as technical gaps, the dismantling process, and temperature gradient caused by heaters. This study also presents several experiments conducted on the samples obtained from the In-DEBS field test and compared with laboratory experimental data of untreated samples. The thermal conductivity and the hydraulic conductivity of the field-collected samples were lower than those of the untreated samples and the swelling properties of the samples were found to be influenced by their respective locations within the buffer, Although the empirical correlation based on laboratory data on untreated samples demonstrated high accuracy, some discrepancies were observed between the properties of field samples and the predicted values, highlighting the importance of field tests.

A series of organoclays were synthesized by modifying bentonite with lecithin under two pH reaction solutions, one acid and one basic. The products prepared using various surfactant concentrations (0.2–5.0CEC) were characterized by multiple experimental techniques. The conformational arrangement of the loaded surfactant, as well as the fluctuation in lecithin molecular properties and interlayer cation content in the organoclay were evaluated. According to the experimental results, the conformation of lecithin in the organoclay interlayer space undergoes a transition from flat-lying layer to a tilted paraffin-type-bilayer. This phenomenon happens for both pH but, interestingly, follows two different mechanisms. It can be observed that the cations content decreased during the addition of lecithin at pH = 1.0, suggesting that the surfactant intercalated into the interlayer space through cation exchange. On the contrary at pH = 9.0, the zwitterionic nature of lecithin allowed its intercalation in the interlayer space via ion-dipole interactions with the cations. Compared with the organoclay prepared at pH = 1.0, the organoclay prepared at pH = 9.0 also exhibited weaker hydrophobicity, clearly reflecting the difference in the interlayer conformation.

In this study, solution casting was used to create hybrid biodegradable films that were made of Polycaprolactone (PCL) and Zn-Al layered double hydroxide (LDH) intercalated with salicylate (SA) (P-L-S nanocomposites). P-L-S (5%) nanocomposite film has a water vapor transmission rate of just 212.5 g/m²/day at 85% relative humidity, which is 55.5% less than that of pure PCL film. This outstanding performance of the water vapor barrier is mostly due to the convoluted action of 2D LDH nanohybrids. In addition, the hydroxyl groups of LDH create hydrogen bonds with the entering water molecules, further preventing the passage of water vapor. The aforementioned nanocomposite showed excellent biodegradability by decomposing by over 75% in just 90 days. More than 94% inhibition of E. coli and S. aureus in 30 min, which is a promising finding when compared to the existing literature, was demonstrated as a result of a controlled release of salicylate (intercalated between the inorganic lamella) to the medium. The P-L-S (5%) nanocomposite additionally showed the best radical scavenging ability against DPPH. (82%) in only 72 h. The aforementioned characteristics point to the possible uses for P-L-S nanocomposite films in the domain of biodegradable packaging.

Although silver nanoparticles are known for their antibacterial activity, little research has been carried out on what synthesis method provides the most effective particles. In this study, silver nanoparticles were synthesised via chemical reduction by using silver nitrate as the silver precursor, ascorbic acid as the reducing agent and sodium citrate as the stabilising agent. The solutions were adjusted to several pH values employing sodium hydroxide, citric acid or nitric acid. Dynamic light scattering and absorption spectra in the ultraviolet/visible region characterisation revealed that employing nitric acid to adjust the pH produced more varied and larger silver particle sizes. Then, silver nanoparticles were supported on montmorillonite and saponite through wet impregnation or ion exchange methods. Scanning electron microscopy, energy-dispersive X-ray spectroscopy and transmission electron microscopy characterisation confirmed that silver nanoparticles were successfully loaded onto the clay minerals. Next, the antibacterial activity of the samples was evaluated against Escherichia coli and Staphylococcus aureus by determining their minimum inhibitory concentrations and minimum bactericidal concentrations. The free silver nanoparticles did not show any antibacterial activity at 125 mg/L. In contrast, the silver-loaded samples obtained by wet impregnation and with a higher silver content displayed the strongest antibacterial effect. Finally, the cytotoxicity of the samples was determined in GM07492-A cell line by using an XTT colorimetric assay. The calculated IC₅₀ values revealed that the supported silver nanoparticles were barely toxic. Thus, the silver-loaded clay minerals obtained here are promising antibacterial materials with a high-grade safety profile.

A novel phase change capsule with layered double hydroxide (LDH) modified SiO₂ shell (named M-EPCM) was designed and prepared, which was used to improve the thermal regulation performance and flame retardancy of silicone rubber foam (SRF). The SRF-3 composite containing 18 wt% M-EPCM presented greatly improved thermoregulation ability, and excellent thermal reliability even after 100 cycles. Besides, SRF-3 also exhibited excellent flame retardancy, with the limiting oxygen index exceeding 31.0%, reduced peak heat release rate (36.4%) and low total smoke yield (13.8 m²). The flame retardant mechanism analysis revealed that barrier effect, catalytic crosslinking and polyaromatic reaction provided by LDH played an important role. Moreover, SRF composites have outstanding mechanical properties, especially SRF-3 which showed a 150% and 85% increase in tensile strength and compression strength compared with pure SRF, respectively. This article provides a new idea for further application of LDH in the field of thermal management.

Bentonites are used in deep geological disposal facilities as an engineered barrier to isolate high level radioactive waste, contained in metallic canisters. The present study, performed at laboratory scale, evaluated the behaviour of MX-80 (Na-bentonite) and FEBEX (Ca-Mg-Na-bentonite) in contact with carbon steel, subjected to a hydrothermal gradient. A dominant Na-Cl-SO₄ saline solution was injected towards the compacted bentonite from the top, while a heater, located at the bottom in contact with the steel disc, maintained a constant temperature of 100 °C. The cells were studied after one and six months of interaction. Changes in the physical (water content and specific surface area) and chemical (cation exchange capacity and element distribution) properties of the bentonite were observed, as well as the formation of a corrosion layer on the steel, at the interface with bentonite, mainly composed of magnetite, maghemite and hematite. The bentonites were mainly altered at the mm scale, being enriched in iron content, and changing their ion distribution to Ca-dominant smectite (in MX-80 bentonite).

Halloysite nanotubes (Hal) have been researched as carriers of various active compounds and polymer additives. Hal reinforced the polymers, while a designated trigger mechanism initiates the release of active compounds. Encapsulation of microbiological agents has been attempted to develop biological self-healing concrete, soil treatment, and environmental remediation, among others. Considering the lack of attention devoted to studying the encapsulation of the nutrients required for biological action and their release, this report presents the preparation and characterization of Hal loaded with the common microbiological nutrient yeast extract (YE) as a multifunctional nanocomposite carrier of microbiological nutrients. YE was loaded on the outer surface and inside the lumen of the Hal by using vacuum entrapment to prepare the YE-loaded Hal (HY) nanocomposites. Thermogravimetric analysis and UV–visible absorbance were used to quantify the loading and the release of YE from HY nanocomposites, showing increasing YE loading after the vacuum treatment and with higher Hal: YE ratios. Vacuumed 1:3 HY samples presented the best sustained-release profile. Field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FE-SEM-EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-Ray diffraction analysis (XRD) showed blocked lumens, and successful lumen loading of YE particles after the vacuum treatment and Hal-YE attachment by weak electrostatic bonding. Inter-particle YE-YE interactions were also evident. The YE loading procedure did not impact the interlayer space of Hal and lowered the crystallinity of the nanotubes. The HY nanocomposite effectively supported spore germination and bacterial growth, resulting in higher bacterial concentrations than conventional media after the expected bacterial death phase. The composition of the HY nanocomposite is easily adjustable, and the unloaded YE can be reused.

Nano-SiO₂@MgAl-layered double hydroxides (NS@MgAl-LDH) core-shell nano-composites were successfully synthesized by a co-precipitation method. The as-synthesized NS@MgAl-LDH was characterized by SEM, TEM, EDX, TGA and BET. The equilibrium, thermodynamic and kinetic studies on the chloride sorption of NS@MgAl-LDH were performed in simulated concrete pore solution (SCPS). The results show that NS@MgAl-LDH exhibits a higher specific surface area (SSA) compared to MgAl-LDH. Besides, the chloride sorption capacity of NS@MgAl-LDH is significantly higher than that of pure MgAl-LDH, which is obviously influenced by initial pH-value and amount of adsorbents addition. Also, the chloride sorption process can be fitted by the Langmuir-model thermodynamically and the pseudo-second-order kinetics kinetically. The negative values of Gibbs-free energy (ΔG⁰) and standard enthalpy change (ΔH⁰) indicate that the chloride sorption is spontaneous and exothermic. Furthermore, the outstanding chloride sorption capacity of NS@MgAl-LDH is mainly contributed to the ion-exchange of chloride ions with interlayer ions in the highly dispersed MgAl-LDH.

Bentonite, a fine-grained geologic material rich in smectite clay, is considered for use in the isolation of high-level radioactive waste (HLRW) because of its low hydraulic permeability, high swelling pressure, and geochemical stability. A complicating factor in this application is that heat released by nuclear waste can trigger complex coupled thermal-hydraulic-mechanical-chemical (THMC) phenomena within the barrier. Prediction of these phenomena using large-scale simulators, which typically examine problems on scales of 10⁻² to 10⁴ m, is inhibited by insufficient knowledge of the material properties of bentonite and their dependence on temperature. Here, these properties were evaluated using replica-exchange molecular dynamics (REMD) simulations of a clay assemblage containing 27 Na-smectite nanoparticles with full atomistic-level resolution solvated using 187,131 water molecules. The simulations yielded predictions of heat capacity, thermal conductivity, thermal expansivity, hydraulic conductivity, and water and ion diffusivity at temperatures of 298 to 373 K. Results showed that temperature modulates the capacity of clay barriers to transfer heat, fluids, and chemical species to different degrees. Material properties of hydrated smectite predicted on scales of tens of nanometers and nanoseconds were consistent with the properties of bentonite measured on scales of centimeters and days.

Carbon steel and compacted bentonite have been proposed as candidate materials for the overpack and buffer, respectively, of the multi-barrier system of a geological high-level radioactive waste repository. Carbon steel corrosion may impair bentonite properties. The interactions of corrosion products and bentonite are analyzed with laboratory corrosion tests. Here coupled thermo-hydro-chemical-mechanical (THCM) models of two types of heating and hydration tests performed on compacted bentonite in contact with Fe powder are presented to study the iron-bentonite interactions at representative repository conditions. Tests on small cells (SC) were performed under unsaturated non-isothermal conditions in 25 mm long columns containing 21 mm of bentonite and 4 mm of Fe powder. Tests on medium-size cells (FB) were performed under unsaturated non-isothermal conditions in 99.8 mm long columns containing 86.8 mm of bentonite and 13 mm of Fe powder. Model results for the SC tests showed that magnetite and Fe(OH)₂(s) were the main corrosion products which compete for Fe²⁺ precipitation. Computed corrosion products precipitate mainly in the Fe powder, penetrate a few mm into the bentonite and reproduce the measured iron weight data. Model results of the FB tests showed that magnetite precipitates throughout the Fe powder interface and reproduce the main trends of the corrosion products. Model results of these corrosion tests will be of great relevance for the performance assessment of engineered barriers of radioactive waste repositories.