Applied Clay Science最新文献

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.

A green and universal synthesis strategy was demonstrated for preparation of bimetallic PdAg alloy nanoparticles supported on polydopamine-functionalized kaolin (kaolin-PDA-PdAg), where bimetallic PdAg alloy was synthesized by co-reduction of Na₂PdCl₄ and AgNO₃ with sodium citrate. Characterization results, including TEM results and XPS results, confirmed that bimetallic PdAg was alloying state and kaolin-PDA-PdAg was successfully synthesized through mussel-inspired chemistry. The kaolin-PDA-PdAg nanocomposite exhibited excellent catalytic activity and performance towards reduction of 4-nitrophenol, whose rate constant was found to be 3.46 min⁻¹ under condition of high concentration (10 mM) of 4-nitrophenol. Besides, kaolin-PDA-PdAg nanocomposite showed high catalytic performance for methyl orange and safranine-T as well. The high catalytic activity of kaolin-PDA-PdAg could be elucidated by electronic effect and synergistic effect of bimetallic PdAg alloy. These results suggest that kaolin-PDA-PdAg composites could be applied as high-efficiency catalysts for reduction of 4-nitrophenol and degradation of organic dyes. Furthermore, abundance and low-priced of raw materials kaolin, green and versatility of synthetic method endow kaolin-PDA-PdAg composites with broad application prospects. Strategy of bimetallic PdAg alloy anchored on kaolin in this text could provide an efficient platform for synthesis of bimetallic alloy nanoparticles loaded on various materials.

Halloysite with nanotube structure is a potential functional support to prepare high-performance catalysts for the oxidation of volatile organic compounds (VOCs) at low temperatures. In this work, rare earth metal ions promoted MnOx@halloysite system were synthesized and demonstrated improved toluene oxidation. The obtained catalyst exhibits excellent catalytic performance, including toluene conversion efficiency (T₉₀ = 232 °C), CO₂ selectivity (100%), super long-term stability and water resistance under the condition of toluene concentration with 1000 ppm. It has been demonstrated that the La-promoted halloysite-supported MnOx catalyst increased the ratio of Mn³⁺ and the number of surface oxygen vacancies, facilitating the formation of active oxygen species and enhancing low-temperature catalytic activity. Moreover, in situ diffuse reflectance infrared Fourier transform spectroscopy confirmed the intermediates generated during toluene oxidation. Toluene oxidation occurred via the benzyl alcohol → benzoate → anhydride reaction pathway over the obtained catalysts. This work provides a considerable experimental basis for understanding the catalytic performance and reaction mechanism of rare earth metal ions promoting the manganese oxides supported by clay minerals for toluene oxidation and paves the way for the development of high-performance catalysts toward toluene oxidation.

Compared with single photocatalytic reaction and single Fenton reaction, visible light assisted Fenton (photo-Fenton) reaction has higher degradation efficiency for environmental pollutants and great potential in the treatment of organic wastewater. Herein, a CoFe₂O₄/kaolinite (CFO/K) composite photocatalyst was synthesized by a simple sol-gel method, using kaolinite as a carrier. Such a composite was used to degrade tetracycline hydrochloride (TCH) through synergetic photo-Fenton reaction. Compared with pure CoFe₂O₄ (CFO), CFO/K containing 40 wt% of kaolinite (CFO/K-40%) had larger specific surface area, abundant surface active sites, and higher photogenic electron hole pairs separation efficiency. Hence, it exhibited a higher photocatalytic degradation efficiency than CFO, and the degradation efficiency was up to 84.82% within 30 min. After three cycles, the photocatalytic degradation efficiency could remain at 76.58%, exhibiting good catalyst stability. During the TCH degradation process, hydroxyl radical and superoxide radical were the dominant active species. In addition, the CFO/K-40% composite exhibited a good degradation performance for different organic pollutants. This study suggested that the CFO/K composite material, as an efficient photocatalyst, has promising applications in the field of kaolinite-based photocatalysts for the treatment of organic wastewater.

The diffusive flux of cations is enhanced and that of anions is decreased compared to that of water tracers in bentonite or other clays, as a result of electrostatic interactions between ions and the charged clay surfaces. Clays are often used or foreseen as barriers in waste disposal in order to protect the environment from hazardous materials. A consistent description of diffusion of various ions and uncharged species is important in this context, especially if long-term interactions between clays and other materials shall be predicted by reactive transport simulations. Here, diffusion of a suite of tracers (HTO, Cl, Na, Sr and Cs) in bentonite was investigated. Experimental through-diffusion data at different bentonite dry densities were described with models of increasing complexity. First, ‘standard’ empirical single ion transport models (uncoupled, simple Fickian diffusion) were applied for each density. These models served as reference cases for comparisons. For sorbing tracers (Na, Sr, Cs), surface diffusion models were used in a next step, where average surface mobilities for the cations were determined based on comparisons with transport parameters from HTO diffusion. Finally, a more complex model was developed in order to describe anion and cation diffusion in a coupled way. This model accounts for locally parallel diffusion in different environments, namely in ‘free’ water unaffected by surface charges, in diffuse (Donnan) layer water, within the Stern layer, and within interlayer water (D-S-I model). This coupled model requires additional parameters related to the bentonite microstructure as well as to cation mobilities in the Stern layer and in the interlayer. The latter were taken from literature. Microstructural parameters were constrained in a manner that overall anion exclusion matches anion accessible porosities found by the simple Fickian diffusion model. This was possible with a reasonable choice of microstructure parameters that are consistent with literature values. A good agreement between the experimental data and the simulated cation diffusion coefficients of the D-S-I model was found, using constraints by the HTO and Cl diffusion data. The interlayer pathway was found to be most important for diffusion of Na, Sr and Cs through bentonite. Stern layer diffusion was significant and more important than diffusion through the diffuse layer for Cs and Sr, while for Na the two pathways were of equal importance.