Applied Clay Science最新文献

As a nutrient partitioning agent and a growth stimulator, ractopamine (RCT) enhances the feed efficiency in animal-based food products and further it is employed clinically in certain pharmaceuticals. Subsequently, metabolites of RCT have long shelf life in animals associated with deleterious repercussions in humans. It is thus, vital to develop an effective design for screening method towards RCT detection to ensure human health, food and environmental safety. Thus, we present an integrate electrocatalyst hydrothermally designed by employing NiCo–LDH (NiCo- Layered Double Hydroxides) and F-HNT (functionalized- Halloysite nanotubes) and further utilized in the electrochemical sensing of RCT. The novelty of the present work shed light upon the unique assembly of the two individual NiCo–LDH and F-HNT components with superior structural features that resulted in a hybrid matrix. The outcomes of CV and i-t analysis under optimum conditions demonstrate outstanding electrochemical performance of the NiCo–LDH/F-HNT modified GCE sensor with a wide linear range 0.003–631 μM and low detection limit 1.1 nM, enhanced selectivity towards the detection of RCT. The uniquely engineered electrode material has therefore been applied to quantitate RCT levels in real-world samples in terms of practical applications.

The overuse or abuse of antibacterial drugs has led to serious health problems. At present, among various antimicrobial materials (natural, organic, inorganic, etc.), inorganic antimicrobial materials, especially ZnO, have received widespread attention. However, an important factor that influences the function of nanoparticles is agglomeration. The agglomeration-sensitive nature of ZnO compromises its antibacterial properties. Here, talc is used as a substrate to control the size and dispersion of ZnO, forming composite minerals with excellent antibacterial properties against both Escherichia coli and Staphylococcus aureus. According to transmission electron microscopy, ZnO/talc is easily adhered to bacterial cells, whereas atomic force microscopy reveals that antibacterial effects are caused by non-covalent interactions between ZnO/talc and bacterial membranes. The comprehensive investigation of antibacterial performance and interfacial interaction is conducive to our understanding of the antibacterial mechanism of inorganic compounds, and also provides new perspectives on the biological effects of inorganic nanomaterials.

Although clay minerals play fundamental roles in many environmental processes, especially in controlling the movement of various ions and molecules in soils, they are also useful precursors for a wide range of products that can be used to address other problems of environmental importance. This paper briefly reviews methods for activation and surface modification along with the preparation of pillared clays and clay complexes with organic molecules and polymers. After describing the application of natural clays to environmental problems, the remainder of the review is devoted to products that can improve environmental quality. These include adsorbents for the removal of various types of pollutant from waters, including heavy metals, organic and inorganic molecules. Clay-derived products also have roles in the destruction of organic waste, the production of environmental sensors, and combating various other environmental problems. Important roles exist for clay minerals in clean energy production, including light harvesting by hybrid materials based on complexes between porphyrins and clay minerals, and biofuel production where pillared clays have a role in the cracking of vegetable oils, and clay-based composites could act as storage media for H₂. The swelling properties of smectite clays form the basis for their use as environmental barriers, and these can be improved by composite materials based on clay-polymer complexes. Clays also have a role as lubricants in drilling fluids, and strategies for improving the efficiency of drilling muds are described. In addition, clay-derived products could have important uses in the control of atmospheric emissions, and the collection of CO₂ for use in the food and drinks industry. Finally, some other uses of clay-derived products are mentioned briefly, including complexes of clays with natural fibers as biodegradable food packaging materials, and as media for the slow release of fertilizers, pesticides and preservatives. Overall, clay minerals have several important roles in the production of cleaner sustainable environments, and these can be expected to increase in the future.

The relationship between the compressive strength of metakaolin-based geopolymer samples and different processing conditions has been investigated for both potassium and sodium based geopolymer systems. Cubic geopolymer samples were prepared by mixing the slurry for 1 h in a thermostatic bath at 0 °C. >1200 samples have been tested to gather enough data to carry out a meaningful statistical analysis. All the data evaluation and model development have been carried out extensively using R. The variation of curing and aging time, curing temperature, SiO₂/Al₂O₃ and H₂O/Al₂O₃ molar ratios has been accounted for via the application of statistical models whose reliability has been suitably checked. Curing has been performed in a sealed container at 100% relative humidity. Aging has been conducted in a climate chamber kept at 75% of relative humidity using an oversaturated solution of NaCl. Curing time has proved a positive relationship with compressive strength while aging time does not show evidence of any significant effect. Curing temperature negatively affects compressive strength. Increasing the SiO₂/Al₂O₃ molar ratio results in an increase of the compressive strength within a certain range of values for the ratio; however, above a threshold (3.8 for the potassium-based and 3.4 for the sodium-based geopolymer system) the mechanical properties decrease. The H₂O/Al₂O₃ molar ratio displayed an inverse proportionality with the compressive strength except for the sodium-based geopolymer, where the mechanical properties initially increased. A further comprehensive and statistically sound model has been proposed that allows us to predict the strength of geopolymer samples as a function of process variables and their composition, ranging in a rather wide set of values.

Swelling capacity of smectite was studied over decades regarding its application as barrier in disposal of nuclear wastes in geological repositories as well as the induced volume change potential in soils according to moisture. In order to improve our knowledge in the swelling capacity of smectite, a miniaturized oedometer was developed to combine swelling pressure measurement with wide angle X-ray scattering (WAXS) characterization in real time during hydration of smectite. This coupled set up allowed studying hydration of smectite up to saturation under confined condions and linking crystalline swelling to pressure at various densities. The modeling of the WAXS patterns gave also quantitative information about the relative proportion of the different interlayer water types at saturation. In situ and operando data were acquired for homo-ionic Na⁺- and Ca²⁺-exchanged smectite at two different densities (1.5 and 1.8 g/cm³). The results showed that the swelling pressure rise was correlated to a sequence of water layer type with the transition from 0W to interstratification of 2W/3W layers, depending on the density. The cation valency controlled the rate of hydration with faster hydration in the case of divalent exchanged smectite. At saturation, with increasing density, the amount of 3W layers decreased to the gain of 1W and 0W layers. Results also confirmed that at saturation and a density of 1.8 g/cm³, the interlayer porosity represented the total one. Finally, this development provided opportunity to improve our knowledge in the swelling mechanism of compacted swelling clay materials upon hydration.

Morocco has significant phosphate reserves, but the extraction process generates a lot of waste rock. To tackle this problem, this study aims to make use of clay, a by-product of phosphate mining, to create acid-activated geopolymers. Four formulations of geopolymers were prepared by combining metakaolin (MK) and calcined clay (CC) in different proportions, which were then activated using phosphoric acid. Different techniques were performed for the characterization of raw and calcined clays as well as the elaborated geopolymers. Based on the XRD, FTIR, and SEM results, it was observed that an increase in the level of CC replacing MK led to the formation of new crystals like Monetite, Newberyite, and Brushite. The quantity of CC influenced the type of crystals formed. Moreover, the specific surface area analysis revealed that the geopolymer (GP2) containing 25% of CC exhibited the highest specific surface area. These materials were then tested for their ability to eliminate methylene blue (MB) from wastewater. The results indicated that GP2, a geopolymer made with 75% MK and 25% CC had the highest efficiency in removing MB with a rate of 98%. The material was highly reactive and achieved adsorption equilibrium in just 15 minutes. It was found to be effective in both acidic and alkaline environments. Furthermore, studies have shown that the Temkin isotherm model best explains how MB (a dye) is absorbed by GP2, with a high correlation coefficient. Additionally, the pseudo-second-order kinetic model was a better fit, suggesting that chemical interactions are more significant than physical interactions. Notably, the use of phosphoric acid to activate GP2 was found to selectively adsorb cationic dyes.

In this work, the effect of halloysite nanotubes alkali activation on its grafting efficiency with organosilanes was studied by Density Functional Theory and experimental investigations. In particular, computational analysis allowed to enlight the structural properties of the organic molecules attached to the silanol groups on halloysite outer surface. The energetics of the reactions showed that the pretreatment with a base is crucial for the modification of the surface due to the appearance of a high number of active sites which lead to thermodynamically favored exothermic processes. Experimental evidences are in good agreement with calculation hypothesis. For instance, the coating efficiency is higher after the alkali activation of the inorganic counterpart for both the investigated organosilanes. The findings here reported are important in order to improve any functionalization protocols for aluminosilicates without variations or loss of the hollow nanotubular morphological features and it paves the ground to halloysite based technological applications in many fields, from nanotechnology to catalysis.

Nanoparticles often-called proto-imogolites have been identified as an intermediate in the formation process of imogolite nanotubes as early as 1979. Their composition and structure are now well documented in the case of synthetic imogolite. One specific characteristic of proto-imogolite is that they have a curved shape with a local structure close to the one of imogolite. During a growth stage, they evolve toward nanocrystals (allophane, imogolite). Their thorough characterization has so far been difficult. Using synchrotron Small Angle X-ray Scattering coupled with Raman spectroscopy, we observe that proto-imogolites form during the initial stage of the co-precipitation of aluminum and silicon molecular precursors thanks to a reorganization process. The shape of the initial proto-imogolites, before the growth stage, depends on the synthesis conditions and controls the characteristics of the final product. We show using cryo-TEM images that, at the end of the growth stage, non-tubular nanostructures continue to coexist with nanotubes. Protocols to quantify remaining non-tubular nano-objects and purify the samples are discussed.

Active packaging aims to extend the shelf life of products and is normally obtained via direct incorporation of additives into the polymer matrices. However, this incorporation may cause some losses by volatilization during processing and rapid release during application. This study consisted of modifying clay minerals (halloysite (Hal) and kaolinite (Kaol)) with oregano essential oil (OEO) and incorporating them into a polymer matrix of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV). The modification method used – sonication followed by vacuum application – did not change the morphologies of the clay minerals and resulted in similar OEO incorporation efficiencies (43% and 45% for Kaol and Hal, respectively, using a 1:10 clay:oil ratio). However, Hal:10-OEO sample provided a slow OEO evaporation in temperatures suitable for microbial growth and was chosen for the preparation of PHBV nanocomposites. The PHBV/Hal:10-OEO/OEO composition presented the lowest oxygen permeability. The use of Hal:10-OEO modified clay also enabled a controlled release of OEO, resulting in an antimicrobial activity against E. coli close to the satisfactory value of 2 log units' reduction and 30% of antioxidant activity after 48 h of OEO release in food simulant medium, being promising for application in active packaging.