Applied Clay Science最新文献

Clay minerals are used in a wide number of natural or artificial materials for municipal or nuclear waste management in which water diffusion is the principal transfer process. However, a quantitative assessment of the impact of the preferred orientation of lamellar clay particles on water diffusion is still lacking. Using 3D Brownian dynamics simulation on representative virtual clay porous media, a systematic study of water diffusion for single-porosity (illite or kaolinite) and dual-porosity (vermiculite) systems was conducted. The simulated water diffusion coefficients were validated through comparison with experiments and were used to build an Archie model including the degree of anisotropy in particle orientation. The results showed that water diffusion can be predicted based on a correct description of the solid phase organization and that clay particle orientation, such as interparticle porosity, is a primary parameter governing water mobility. Moreover, the anisotropy of water diffusion can be linked to the degree of particle preferred orientation, irrespective of the porosity value. The modified version of the Archie model for water diffusion in clay systems proposed here has many potential applications where decoupling of porosity and preferred orientation is needed, including better prediction of water transfers or improved designs of clay liners with sustainable use of natural mineral resources.

The chemical analysis of pure dioctahedral smectites exchanged by one of the typical CEC-index cations (e.g. Cu-trien) often shows significant Na-, Ca-, and K-contents which, in contrast to Mg, are not expected to occur in the octahedral sheet. They are supposed to occur in the interlayer but are not exchangeable - hence termed “fixed cations”. The aim of the study was to gain new evidence for the presence of naturally present fixed cations and find out if at least a part of these can be liberated by hydration after hydrothermal treatment.

The methodological approach for cation liberation tests included different treatments with water at 60 °C and 150 °C, partly using an ultrasonic bath, and different reaction times prior to addition of the Cu-trien index cation for CEC analysis.

The study proved that at least part of the naturally present fixed cations could be rendered exchangeable (liberated) by the hydrothermal treatment before an index cation is added. The differences were small but significant.

Liberation of fixed cations was thought to increase the CEC but the increased amount of exchangeable cations was accompanied by a decrease of the CEC, which can probably be explained by partial smectite dissolution. This hypothesis was supported by measurements conducted at higher solid to liquid ratio in order to suppress smectite dissolution. The CEC decrease was less pronounced but at the same time less cations were liberated. In conclusion, the naturally present fixed cations are strongly bound and, supposedly, can only be liberated if the smectite structure is affected.

Future work will be devoted to finding alternative methods which are suitable for quantification of naturally present fixed cations in bentonites/smectites.

Perfluorooctanesulfonate (PFOS) is a hazardous chemical, and its presence in surface and groundwater poses a risk to environmental quality and human health. Containment is often applied to immobilize PFOS to stop or minimize the exposure. Mineral-based materials became promising adsorbents. However, there is scope to develop adsorbents using locally available minerals and understand their adsorption mechanisms. Here, we developed oleylamine-modified composites using naturally occurring Iranian zeolite and diatomaceous earth (DE). The mineralogy and surface properties of materials were fully characterized, and the adsorption of PFOS from simulated wastewater was linked to it. Clinoptilolite in zeolite sample, calcite and kaolinite in DE were main mineral assemblages. The raw samples also contained silica as a main constituent of them. Thermogravimetric analysis suggested that the materials were successfully modified with the oleylamine molecules in the material's structure and surfaces. These were further supported by scanning electronic microscopy (SEM), Fourier transmission infrared spectroscopy (FTIR), and surface and pore size analysis. After adsorption at various pHs, the isotherm of adsorption was also performed at ambient temperature. Modified DE and zeolite tend to adsorb PFOS (14.1 and 25.5 mg/g, respectively) more than their raw counterparts (4.72 and 0.39 mg/g, respectively). Adsorption models suggest monolayer and, in rare cases multilayer binding capacities and affinities toward PFOS. We analyzed the post-adsorption materials and discovered that electrostatic and hydrophobic interaction was likely the main cause of PFOS adsorbed to the material. This research helps to improve our knowledge of how PFOS adheres to untreated and surfactant-altered zeolite and DE in aquatic environments.

4-Nitroaniline (4-NA) compounds are considered highly hazardous to the environment and can be found in various chemical products, including pigments, dyes, fungicides, and pesticides. The presence of 4-NA in water poses significant carcinogenic risks to humans. Therefore, there is an urgent need to monitor and detect the environmentally hazardous 4-NA, especially in water samples. In this study, we have developed a novel nanocomposite based on barium stannate/halloysite-based (BaSnO₃/HNTs) with a nanotube structure. The nanocomposite was synthesized using natural deep eutectic solvents (NADESs) and aimed at the selective electrochemical detection of 4-NA in water samples. Morphological studies clearly revealed the random incorporation of BaSnO₃ nanoparticles (NPs) with diameters ranging from ∼10–50 nm onto the surface of HNTs. The incorporation of BaSnO₃ NPs created more active sites and facilitated fast electron transport, as confirmed by EIS. Under a saturated N₂ condition and at pH 7.0, the BaSnO₃/HNT/SPCE exhibited excellent electrochemical performance with a very low limit of detection and a wide linear range of 2 nM and 0.009–1126 μM, respectively. Additionally, the proposed sensor for 4-NA demonstrated good anti-interference ability, repeatability (RSD ∼1.31%), and stability (RSD ∼1.09%). The obtained electrochemical analytical results of the synthesized composite validate its superior potential for real-time applications.

In this study, we synthesized intercalation compounds of 3,3′,5,5′-tetramethylbenzidine (TMB) and tetrasilicicfluormica (TSFM) via a commonly used cation exchange method with TMB²⁺/TSFM cation exchange capacity (CEC) ratios of 1.0, 2.0, 2.7, and 5.4. These materials were characterized using powder X-ray diffraction (XRD), X-ray fluorescence, thermogravimetric-differential thermal analysis, scanning electron microscopy, and visible absorption spectroscopy. The vapochromism of each sample was assessed directly from the exterior of the glass sample tube using diffuse reflectance spectroscopy. All specimens vacuum-dried at 50 °C appeared yellow but turned green under water vapor at TMB/CEC = 2.0, 2.7, and 5.4, and blue under acetonitrile vapor at all TMB/CEC ratios. The sample with TMB/CEC = 2.0, in particular, exhibited clear vapochromic effects towards water and acetonitrile. Methanol and formic acid induced color changes similar to that of water vapor but less intense, except at TMB/CEC = 2.0. The color of each sample faded upon exposure to gaseous ammonia, whereas ethanol, acetone, iodomethane, and nonpolar solvents did not induce any color changes. The powder XRD pattern suggested changes in the array structures of TMB in the interlayer spaces due to vapor exposure.

In the context of the radioactive waste management in deep geological formations, U(VI) retention by intact Callovo-Oxfordian claystone (COx) was studied by percolation-type experiments at 20 and 80 °C. The experimental results were confronted with modelling prediction based on a published adsorption model developed from dispersed media in the 20–80 °C temperature range. For the experiments at 20 °C, the adsorption model allowed to explain the results for the intact system; the retention was weak (R_d ∼ 10 L•kg⁻¹) and the analysis of the COx phases at the end of the experiment confirmed a retention of U by the clay fraction. The adsorption model in temperature also explained the observed trend of increasing retention with increasing temperature. However, it underestimated the temperature effect on the adsorption of U(VI) by the COx clay fraction, and other phases contributed to the retention. Solid-state analysis of the percolation-doped samples indicated a reactivity in the order pyrite>clay>calcite phases. The transposition of the knowledge at 20 °C from the dispersed system to the intact medium was therefore not possible at 80 °C for the studied U(VI)/COx system.

The 2D/1D structure of ZnIn₂S₄/attapulgite was constructed by anchoring ZnIn₂S₄ nanosheets on the surface of attapulgite nanorods for the removal of tetracycline hydrochloride (TC) and rhodamine B (RhB). The 2D ZnIn₂S₄ was closely combined with the 1D attapulgite, and ZnIn₂S₄/attapulgite had a higher BET surface area (83.6 m²/g) than pure ZnIn₂S₄ (13.6 m²/g). The combination of ZnIn₂S₄ and attapulgite promoted pollutant adsorption by providing more exposed active sites and a larger contact area, which also contributed to enhanced photocatalytic performance. Under visible light irradiation, the as-prepared ZnIn₂S₄/attapulgite composites exhibited enhanced photocatalytic activity when compared with pure ZnIn₂S₄. After 9 min (50 min) of irradiation, the optimized ZnIn₂S₄/attapulgite photocatalyst removed about 99.9% RhB (82.1% TC). In addition, the ZnIn₂S₄/attapulgite photocatalyst demonstrated excellent photostability and availability. Compared with other photocatalysts, the samples in this work used natural minerals as the carrier, which significantly improved the dispersibility and adsorption performance of the catalyst, and was conducive to the improvement of catalytic performance. This work contributed to the development of photocatalysis for the removal of environmental liquid-phase pollutants.

This article investigates the intercalation of carbamide within globular glauconite involving the chemical activation of glauconite with carbamide solution-gel at varying concentrations of total nitrogen (N). Mineral nanocomposites were prepared with a multitude of novel functions. As the N concentration of the initial solution increased, the proportion of intercalated N enhanced to 8%. A 20% of N concentration in carbamide solution maximizes intercalation. Intercalation occurs in the interlayer of smectite layers (micropores) in glauconite. In nanocomposites, the decrease in specific surface space, total volume pores, and average pore size reflect the absorption of carbamide in meso- and macropores of glauconite globules. Glauconite nanocomposites retain a spherical particle morphology and a distinct microlayer close to the surface. The increased proportion of nitrogen in the microlayers close to the surface indicates a high filtration capacity of the globules. The near-surface microlayer serves as a diffusion channel for the glauconite interior, where new substances are absorbed in the micro- (interlayer) and macropores. The stepwise kinetics of nutrient release, which supports the various forms of carbamide absorption in glauconite, distinguishes the nanocomposites. In addition to N-compounds, glauconite nanocomposites are mineral sources of the available potassium (K) in soils. As a result, chemically manufactured glauconite nanocomposites have some following advantages: the micro-granular mineral form, a permeable inner near-surface microlayer, incubated in micro-, meso-, and macropores N-compounds, and the available K.

Adsorption technology has attracted increasing attention for the remediation of ammonia nitrogen pollutions from landfill leachate. However, developing effective adsorbing materials with low cost, outstanding activities and long-term stabilities in the aqueous environment remains a significant challenge. Zeolite with high ability of cation exchange is significantly preferable for the removal of ammonia nitrogen. Herein, a novel polyvinyl alcohol (PVA) thin membrane modified natural zeolite and Na-montmorillonite (NaMt) hybrid microspheres (denoted as PVA-(zeolite/Na-Mt)) adsorbent is successfully synthesized by a facile granulation and impregnation method. The adsorption experiments reveal that the multicomponent PVA-(zeolite/Na-Mt) microspheres show higher removal efficiency (98.16%) for ammonia nitrogen within 40 h even at a wide pH (3.0–11.0) and temperature (10–30 °C) range. Meanwhile, the spent PVA-(zeolite/Na-Mt) microspheres with high stability in aqueous environment for more than 20 days originates from the modification of the PVA molecule and enhanced adsorption performance that is beneficial for practical applications in the wastewater remediation field.

Machine learning was used to predict the effective diffusion coefficient of radionuclides in compacted bentonites to reduce the cost of experimental methods. Through-diffusion experiments were conducted to determine the effective diffusion coefficient of Re(VII), which was used as a surrogate for ⁹⁹Tc(VII), in compacted Anji bentonite. Five parameters (the external surface area, the ionic strength, the mass ratio of montmorillonite, the compacted dry density, and the accessible porosity) that affect the effective diffusion coefficient were calculated by a multi-porosity model to generate data for the analysis of the machine learning models to overcome the limited experimental data. The effective diffusion coefficient was predicted using two popular machine learning models, the Light Gradient Boosting Machine and Artificial Neural Network models, where the former exhibited higher sensitivity and accuracy in the prediction than the latter. The performance of the machine learning models was validated by comparing the experimental effective diffusion coefficients between this study and previous studies. The present work revealed that the machine learning method can be a powerful tool and may offer a new means of studying the effective diffusion coefficient.