Applied Clay Science最新文献

Metal-organic frameworks with favorable adsorption performance have attracted increasing interesting in water treatment. However, the poor pH stability and tedious preparation processes are still the major disadvantages for practical application. To address these problems, novel palygorskite/MIL-88A(Fe) (PMFe-x) composites were prepared via a convenient in-situ growth strategy after incorporation of natural palygorskite into MIL-88A(Fe). The characterization results revealed that Pal was incorporated into the MIL-88A(Fe) crystal structure, and thus the as-prepared PMFe-x composites presented excellent adsorption performance and acid/alkali stability in the pH range of 2–12. The maximum adsorption capacity of composites to Congo red reached 1141.4 mg g⁻¹ within 3 h, which was much higher than that of pure MIL-88A(Fe). Moreover, the spent MOFs composites after adsorption of dye were facilely regenerated by calcination treatment at 300 °C under N₂ atmosphere, and the adsorption capacity of the regenerated composites to Congo red maintained more than 360 mg g^-1 after five cycles, Due to the excellent acid/alkali resistance and adsorption properties, the obtained MOFs composites presented good application prospects in water treatment.

Estimation of the swelling strain or swelling pressure is important for predicting the behavior of compacted bentonite barriers. In this study, the electrical conductivity of compacted bentonite was measured under free-swell and confined conditions to investigate the predictability of swelling strain or swelling pressure from the measured electrical conductivity. The evolution of electrical conductivity by water penetration was qualitatively consistent with that of swelling strain or swelling pressure, implying that monitoring electrical conductivity could be used to detect the initiation and termination of swelling process or any internal changes in compacted bentonite. The relationships between normalized swelling strain and normalized electrical conductivity, and between normalized swelling pressure and normalized electrical conductivity were developed based on the results of Ca-bentonite hydrated with NaCl solution, and those were verified using the results of Ca-bentonite hydrated with KCl and CaCl₂ solutions, and Na-bentonite hydrated with NaCl solution. Finally, the limitations and possibilities of using electrical conductivity in estimating swelling parameters and monitoring swelling process were discussed in this study.

The oxidation of 5-hydroxymethylfurfural (HMF) to 2, 5-diformylfuran (DFF) is an important reaction for the conversion of renewable biomass into feedstock chemicals. In this work, palygorskite (Pal)-supported ruthenium (Ru) catalysts were developed for the efficient selective oxidation of HMF to DFF. Using natural clay mineral palygorskite as the support enabled the immobilization and dispersion of Ru nanoparticles. A 100% HMF conversion, 98% DFF yield, and 98% DFF selectivity were obtained over Ru(III)/Pal catalyst after 4.5 h under the optimal reaction conditions at 110 °C and 10 bar of O₂ in toluene. Ru nanoparticles and palygorskite synergistically achieve the excellent catalytic performance of the catalyst. The Ru metal active sites facilitate the activation of the reactants or intermediates, accelerating the formation of DFF. Furthermore, due to their different particle sizes and Ru species, the Ru(III)/Pal catalyst exhibits higher catalytic activity than the Ru(0)/Pal catalyst for the oxidation of HMF to DFF. The palygorskite-enhanced dispersion effect on Ru nanoparticles augments the catalytic activity. Moreover, the palygorskite-supported Ru catalyst showed good stability and was reused for at least five times consecutive cycles without significant loss of its catalytic activity.

The Li-bearing claystone and carbonate are sedimentary rocks deposited in the lacustrine environment hosting the Bigadiç borate deposits in western Anatolia. The purpose of this paper is to explain the mineralogical, geochemical, stable isotope characterizations and formation of Li-rich claystone (hectorite, saponite), and have strategic, technological, and economic importance for the country's economy, which have not been sufficiently studied previously. In the rhyolitic and dacitic tuffs, sanidine and plagioclase crystals were altered, biotite and hornblende, Fe-oxidized, locally opaque, and chloritized in a sericitized, Fe-oxidized, argillized, calcified, and zeolitized glassy matrix. The claystone consists mainly of smectite and minor illite, volcanogenic quartz, feldspar, mica, hornblende, and occasionally calcite, aragonite, dolomite, and gypsum/anhydrite. Hectorite and saponite were determined based on the expansion of their basal peaks following heating at 500 °C and solvation with ethylen-glycol; additionally, hectorite expanded, and saponite was not affected after glycerine-saturated Cs-smectite and heating at 100 °C for 20 h. Smectite shows webby to crenulated forms, and coexist with feldspar, volcanic glass, rhomboidal calcite, blocky gypsum/anhydrite, and Fe-oxide phases. The Li values increase up to 2650 ppm in the smectite-rich claystone and marl, and up to 449 ppm in the volcanic rocks. The positive correlation of REE with each of SiO₂, Al₂O₃, and K₂O; positive correlation of MgO vs. Li, and increase of MgO + CaO, Sr, Li, LREE relative to MREE and HREE; negative Eu anomaly and high values of As and S suggest that the feldspar, mica, and hornblende alteration originating from the Miocene volcanic and pyroclastic materials and presence of gypsum/anhydrite during the hydrothermal alteration activities were the sources for the smectite formation. The high negative δ¹⁸O values of calcite, the δD and δ¹⁸O values of smectite and δ³⁴S‰ and δ¹⁸O‰ values of gypsum, and the ⁸⁷Sr/⁸⁶Sr isotope ratios range of calcite and gypsum suggest the contribution of mixing meteoric and hydrothermal environmental conditions during the depositional and diagenetic process(es) in the playa lake environment.

For the acid-leaching process of halloysite nanotubes (HNTs), the structure and energetic evolution is crucial for the basic understanding and further modification of HNTs. The specific surface area, pore volume, and bond distribution of HNTs at different Al leaching percentages were studied by molecular dynamics simulation. With the increase of the Al leaching percentage, the inner diameter of the halloysite nanotubes is gradually enlarged, forming some nanoporous (1–20 nm) interlayer spaces inside the tube wall of HNTs due to the strong bondings between the adjacent layers, and the specific surface area and pore volume of HNTs increased in a complex way at each transition stages. For the transition structures, the interlayer nanopores greatly increase the specific surface area and pore volume of HNTs, which is more obvious after 50% Al leaching. The free water molecules inside lumen structure of HNTs would have an impact on the thermodynamics and the structure evolution of HNTs. Although the transition structures with extremely large loading capacity may not be naturally most stable, they might be stabilized or achieved by some fast transient regulation methods.

Visualizing montmorillonite (MMT) platy particles dispersed in silica gel was firstly demonstrated by synchrotron X-ray multiscale tomography. The silica sol-gel reaction proceeded with the preservation of MMT dispersibility in water, MeOH, and DMF mixture. The 3D image reconstructed using high-resolution X-ray computed (CT) images (i.e., nano-CT) displayed platy particles in the range of 0.5—2.5 μm, which matched that observed in the field-emission microscope image of powder MMT. In addition, some platy particles are assembled by contacting their edge and layered surfaces, suggesting the presence of a house-of-cards structure. Given a decrease in the distance by 30% between platy particles roughly estimated using a decrease in volume by 65% before and after silica gelation, a dispersion state formed by micrometer-sized platy particles did not essentially differ after silica gelation. Therefore, these results indicated that the 3D image of MMT platy particles in silica gel reflected the dispersion state of MMT particles in the solvent.

This study investigated the main inorganic sinks of rare earth elements (REEs) in six peloid samples from four geological environments (hydrothermal, estuarine, coastal, and saline). We collected samples from each environment and determined pH, electrical conductivity, redox potential, temperature, elemental concentrations (major, minor, and REEs), mineralogy, and REE speciation. Additionally, principal component, hierarchical cluster, and multivariate analyses were used to investigate any relationship between REEs and phyllosilicates, iron, manganese, aluminum, and inorganic and organic carbon. Results showed that peloids from hydrothermal and estuarine environments presented the highest concentrations of minor elements and REEs (up to 109.78 mg/kg) with mineralogy dominated by quartz (31.6 to 92.4%) and phyllosilicates (49.3%). In contrast, coastal and saline peloids presented low concentrations of minor elements and REEs (up to 6.47 mg/kg) with mineralogy dominated by calcite (up to 74.6%), aragonite (up to 25.8%), and evaporitic minerals. Positive relationships were found between REE concentrations and the percentages of phyllosilicates (r = 0.978) and iron concentration (r = 0.986), which were supported by the operational speciation that showed that REEs were mainly associated with the residual and reducible fractions in hydrothermal and estuarine peloids. In coastal and saline peloids, the lower concentrations of REEs were attributed to their distribution on the reducible and oxidable fractions, from which they can mobilize. The results from this study revealed the inorganic sinks of REEs in peloids from hydrothermal, estuarine, coastal, and saline environments.

The mechanisms of unmodified, pure LDH and aqueous V(V) interaction have not been extensively studied yet, despite the important role of both layered material and element in the industry. The performed studies revealed that maximum capacity of LDH was heavily influenced by different layer and interlayer chemistry of the materials. Several possible mechanisms of V(V) removal from aqueous solutions were identified, depending on the chemical composition of LDH, V(V) initial concentration and background electrolyte concentration. Based on the Raman spectroscopy and application of 1-site 2-pK non-electrostatic model (herein reported for the first time for LDH-V), the formation of inner-sphere monodentate VO₃⁻ complexes at the surface of the LDH layers was confirmed at lower initial V(V) concentrations (0.05–1.0 mmol/L). At high initial V(V) concentration (5 mmol/L), the polymerized (V₁₀O₂₈)⁶⁻ form was identified and the precipitation of Mg and V-bearing phases was revealed by XRD. Additionally, the interlayer anion-exchange mechanism could not be explicitly excluded. The XPS method, however, excluded the reduction of V(V). The study clearly showed that V(V) bonding mechanism is affected by different reaction conditions which should always be considered during applications involving LDH and vanadium compounds.

In the present study, Ag nanoparticles modified Fe₃O₄ anchored on roughened halloysite nanotubes nanocomposites (Ag@Fe₃O₄/RHNT) with high peroxidase-like activity and good magnetism was fabricated, and accordingly, an efficient and sensitive colorimetric sensing platform was established for the detection of H₂O₂. Firstly, halloysite nanotubes was pre-treated and then Fe₃O₄ nanoparticles were uniformly deposited on the external surface of RHNTs. Finally, Ag nanoparticles were grown onto Fe₃O₄/RHNT by in-situ reduction method. All characterization results confirmed the successful synthesis of Ag@Fe₃O₄/RHNT. The resultant Ag-Fe₃O₄ RNHTs exhibited satisfied catalytic activity to the oxidation of TMB (4,4’-Diamino-3,3′, 5,5′-tetramethylbiphenyl) in the presence of H₂O₂, and the catalytic process is accompanied with the color changed from colorless to bule. Thus, a sensitive colorimetric sensor for detection of H₂O₂ was developed based on Ag@Fe₃O₄/RHNT nanocomposites. And the optimal reaction temperature and pH were determined to be 55 °C and 4, respectively. H₂O₂ can be detected in the range of 10–100 μM with the detection limit of 0.7 μM. In conclusion, we established an efficient colorimetric sensing system for H₂O₂, and applied it to detect H₂O₂ in milk and serum.

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.